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The Single Plane/Carbureted LS Engine Camshaft Thread

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Old 08-04-2014, 12:59 PM   #1
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Default The Single Plane/Carbureted LS Engine Camshaft Thread

This thread is a work in progress. The list items below will become links as I complete the corresponding materials.

The Single Plane/Carbureted LS Engine Camshaft Thread

In choosing a performance camshaft for any engine, there are many things that must be taken into consideration in order to select the right cam for optimal performance for your unique application. Choosing a camshaft for a carbureted, single plane or short runner equipped LS based engine has some additional considerations to achieve optimal performance. This thread is intended to be resource for anyone building a carbureted LS engine or LS engines equipped with single plane style/short runner type intake manifolds.

Here is an outline of material to be included in this thread:

Last edited by speedtigger; 12-07-2015 at 07:42 PM.
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Old 08-04-2014, 02:18 PM   #2
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Default General Camshaft Selection Guidelines

General Camshaft Selection Guidelines -This section is for people who are new to the cams selection process. These guidelines are intended to be specific to single plane equipped or carbureted LS engine applications.

Find A Cam That Fits Your Desired Characteristics:
I have defined 4 common categories that aftermarket camshaft buyers typically fit into as a guide and framework for discussion. The guidelines are formulated to be relevant for 5.3-6.2 liter naturally aspirated LS engines. Smaller or larger “stroker” type engines or engines utilizing forced induction may fall outside these parameters. Use these guidelines to get you “in the ball park” of that camshaft type that might suit your project best:
NOTE: These are general guidelines for discussion purposes and are not intended to be “rules”. It is the individual builder’s responsibility to assure all research and final details of their project are correct and fit their purpose.

Group 1 Factory Upgrade, Mild Performance, RV (recreational vehicle) / 4x4 vehicles, Towing, Performance/Mileage

Idle Characteristics: Smooth “factory” type idle

Typical Operation RPM Ranges: idle-5800

Typical Camshaft Intake Valve Durations at .050”: 190-210

Typical Compression Ratios: Stock

Typical Optimal Torque Converter Stall RPM: Factory to 2500

Typical Optimal Gear Ratios with a 26”-28” Tall Tire: Stock

Intake Manifold Style Compatibility: Dual Plane Style

Typical Carburetor Type and Size: Most any type factory or replacement style carburetors 450-750 CFM

Typical Exhaust Configuration: Factory style exhaust or small to medium tube headers with free flowing exhaust

Powerband and Driving Characteristics by Group: Group 1 cams typically have power right off idle, good low end torque, smooth operation, good for towing and very heavy vehicles and completely stock vehicles with no other required modifications.

Durability and Accompanying Valve-Train Components & Considerations: Group 1 cams typically require no special components, however it is common for matching valve springs to be highly recommended. No other valve train modification is typically necessary. These cams are typically capable of going tens of thousands of miles or more maintenance free.
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Group 2 Street Performance, Hot Rod, Muscle Car, Mild Competition, Off-Road performance 4x4

Idle Characteristics: Noticeable to Choppy “hot-rod” or “performance” type idle - often described as having “slight lope”

Typical Operation RPM Ranges: 1200-6500

Typical Camshaft Intake Valve Durations at .050”: 210-225

Typical Compression Ratios: 9:4-11:1

Typical Optimal Torque Converter Stall RPM: 2500-3500

Typical Optimal Gear Ratios with a 26”-28” Tall Tire: 3.42-4.10

Intake Manifold Style Compatibility: Dual Plane or Single Plane

Typical Carburetor Type and Size: Performance tuned factory carburetor or performance aftermarket 650-750 CFM

Typical Exhaust Configuration: 1 3/4” headers and increased diameter high flow exhaust

Powerband and Driving Characteristics by Group: Group 2 cams typically have emphasis on mid-range torque and upper RPM power output. Expect strong increases in power, extended RPM range and good to fair drive-ability. In order to obtain maximum acceleration, vehicles using these cams will require increase torque converter stall speed or a manual transmission. In addition, a higher numerical ratio final drive ratio (rear end gearing) will be necessary to allow the engine to operate in its ideal RPM range. These cams will benefit from headers and larger free flowing exhaust.

Durability and Accompanying Valve-Train Components & Considerations: Group 2 cams will always require matching, higher pressure and often higher lift capable valve springs. In addition, hardened pushrods are recommended in many cases. Other valve-train item upgrades may also be recommended by the camshaft supplier for cams in this category. Most cams in this group are typically capable of going tens of thousands of miles maintenance free. However, some specialty cams in this category may use more aggressive designs that could require more frequent valve spring replacement.
.

Group 3 Street/Strip, Off-Road Performance, Mild Race / Bracket Race, Moderate Competition

Idle Characteristics: Aggressive “chop” to rough “race-style” idle

Typical Operation RPM Ranges: 1800-7200

Typical Camshaft Intake Valve Durations at .050”: 225-240

Typical Compression Ratios: 10.5:1-12.5:1

Typical Optimal Torque Converter Stall RPM: 3500-5000

Typical Optimal Gear Ratios with a 26”-28” Tall Tire: 3.73-4.56

Intake Manifold Style Compatibility: Single Plane and Dual Plane-(Square Port)

Typical Carburetor Type and Size: Performance aftermarket or specialty racing carburetor 750-1050 CFM

Typical Exhaust Configuration: 1 3/4” - 1 7/8” header with large diameter high flow race-style exhaust

Powerband and Driving Characteristics by Group: Group 3 cams typically emphasize upper mid-range torque and high RPM horsepower. These cams deliver substantial power increase and extended RPM range with little consideration given for drive-ability or street manners. For optimal performance, vehicles equipped with cams in this group will require high stall torque converters or manual transmission. In addition, these cams require a properly matched final drive ratio (rear end gearing) to allow the engine to operate at its ideal target RPM range. These cams require large tube exhaust headers and high flow race style exhaust.

Durability and Accompanying Valve-Train Components & Considerations: Group 3 cams will always require matching valve springs and hardened and/or larger diameter pushrods and may require special valve spring retainers and locks. These camshafts can often require special rocker arms and high performance valve lifters. These camshafts will require occasional to frequent valve spring replacement depending on design.
.

Group 4 Race, Off-Road/Dirt Race, Circle Track, Competition

Idle Characteristics: Rough or Radical, “race-car” type idle

Typical Operation RPM Ranges: 2500-8000+

Typical Camshaft Intake Valve Durations at .050”: 235-270+

Typical Compression Ratios: 12.5-15:1+

Typical Optimal Torque Converter Stall RPM: 5000+

Typical Optimal Gear Ratios with a 26”-28” Tall Tire: 4.10+

Intake Manifold Style Compatibility: Single Plane or Custom Built Race/Tunnel Ram Manifolds

Typical Carburetor Type and Size: Specialty racing carburetor 850-1150+ CFM

Typical Exhaust Configuration: 1 7/8” - 2+” header with open exhaust or racing exhaust

Powerband and Driving Characteristics by Group: Group 4 cams emphasize high RPM torque and horsepower. These camshaft are chosen by users who desire maximum horsepower and a winning edge in competition with no consideration given to street use. Camshafts in this group require either a race style high stall torque converter or a manual transmission. In addition, these cams require a properly matched final drive ratio (rear end gearing) to allow the engine to operate at its ideal target RPM range. These cams require large tube headers and open exhaust or special maximum flow racing exhaust systems.

Durability and Accompanying Valve-Train Components & Considerations: Group 4 cams often require substantial valve train modification. While some camshafts in this category may only require matching valve spring and hardened pushrods, more often cams in this group will require complete upgrade of the entire valve train system including everything from lifters, pushrods, rocker arms, special valve springs, retainers, valve locks and in some cases, rev-kits and even auxiliary valve spring oilers. Careful planning and detailed discussion with your camshaft/valve train supplier/manufacturer should be observed when purchasing a camshaft in this category.

Last edited by speedtigger; 08-16-2014 at 06:29 PM.
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Old 08-04-2014, 02:23 PM   #3
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Default Carbureted and Single Plane Cam Consideration / The Camshaft and Manifold Relationshi

Carbureted and Single Plane Cam Consideration / The Camshaft and Manifold Relationship

Why Single Plane Manifold Equipped LS Engines Require Additional Consideration When Selecting a Camshaft

Single plane equipped and carbureted LS engines need different camshafts than your typical, traditional factory style, plastic EFI intake equipped LS engine. To understand why, you must look no further than the intake manifold design. Every naturally aspirated LS style engine ever produced came from the factory with a plastic, equal length, tuned, long runner intake manifold design. Conversely, your carbureted LS will likely be equipped with a shorter runnered, cast aluminum manifold design that will be either a single plane style intake manifold like the Edelbrock Victor (Jr.), Holley 300-131/132 and GMPP LSX Single Plane or a dual plane style intake manifold like the Edelbrock Performer RPM, Holley 300-129/130 and GMPP LSX Dual Plane.

In looking at the different intake manifolds designs, you will note that they have different port lengths, port cross sectional measurements and port volumes as well as layouts and configurations. Because of these differences, the air and/or air-fuel mixture behaves differently in a running engine. While there are many considerations, the two most often mentioned by top engine builders are: intake port length and intake port cross sectional area. The cross sectional area, shape and consistency of an intake port determines how much air can physically travel through it at a given pressure. The length of the port determines how much mass the air and fuel will have between the intake valve and the intake manifold's plenum and distance the air/fuel must travel to the cylinder from the plenum. These two key characteristics determine the performance characteristics that your choice of intake manifold will impart on your engine.

What we know about the manifold runner's relationship to power is that the longer the intake runner, the lower the RPM range the engine will typically be tuned for. The shorter the intake runner, the higher a given engine will typically be tuned for. We also know that the smaller the intake runner in cross sectional area, the better the low RPM torque and response might be at the expense of high RPM and maximum power. The larger the effective cross sectional area of the runner, the greater the higher RPM horsepower capabilities might be at the expense of lower RPM torque.

So, if you look at a short runner, single plane intake manifold like the Edelbrock Victor, you will quickly conclude that this intake manifold will deliver it's best performance at a higher RPM than the dual plane or factory EFI intake manifold. This is an accurate conclusion. When looking at the dual plane intake manifolds, their longer runner design and often smaller port cross section would lead you to conclude this manifold will deliver it's optimum performance and a lower RPM than the single plane or factory EFI intake manifold. This also typically proves true.

The reason for this is all about mass, velocity and restriction. Understanding the relationship between intake manifold design and its effect on mass, velocity and restriction is the cornerstone of making horsepower in your LS engine or any naturally aspirated piston engine for that matter. And, in that understanding, you must recognize that the goal for any intake manifold design is to balance between maximum mass and velocity and flow restriction to achieve optimal performance for a given application.

The Cam/Manifold Tuning Relationship

For the sake of brevity in this conversation, I will have to assume that the reader understand the basic dynamics of a 4 cycle piston internal combustion engine. If the reader is not clear on this, here is a nice resource:

http://en.wikipedia.org/wiki/Four-stroke_engine


The cam/manifold relationship is all about timing. In viewing the above illustration, one unfamiliar with performance camshaft design might conclude that intake valve opens at exactly top dead center (TDC) and closes at exactly bottom dead center (BDC). However, as you likely know they do not. The reason for this is because air has mass and can be compressed and expanded. Being able to understand and visualize this dynamic is key to comprehending optimal valve timing and hence performance camshaft design.

Intake Runner, Valve Timing and Pressure Waves

Imagine you are at the beach. You see a wave come in and it washes ashore. The wave crashes onto the beach and travels as far inland as its inertia will carry it, then it recedes back to the ocean. Now imagine you and a friend are on the shore, just at the edge of where the waves can reach, each with a big bucket. You have a contest to see who can capture the most water from each wave as it rolls in. The trick to getting the most water in your bucket will be to time when the peak of the wave is closest to you. Too soon, nothing but sand. Too late and most of the water has receded away again. Just right and you get the most water. This is what the camshaft and intake valve conspire to do. Only instead of water at the beach, it is the air and fuel filling your piston's cylinder.

Now imagine you are in a room at the end of a long hallway and there is a door at the other end of the hallway. Behind that door is a room filled to the top with water. Then, that door opens releasing a wave that travels down the hallway. You know that this wave will wash into your room filling it until the waves energy is expended, then it will flow back out of the room into the hallway until the water level equalizes. In this scenario, your job is to trap as much water from that wave in your room as possible. So, you open the door to your room as the wave approaches and let the wave of water in and then try close your door just as the water level in your room peaks and before it can flow back out of your room and into the hallway. This example illustrates the pressure waves in your intake manifolds runners in a running engine. As your intake valve opens and the piston moves down, the air and fuel rush though your intake system to fill that low pressure void in your piston's cylinder. In this example, the initial room full of water represents your intake plenum, the hallway your intake runner and your room at the end of the hallway and it's door represent your piston's cylinder and intake valve.

Now, imagine a shorter hallway between the rooms that is half as long. Because this hallway is shorter, the wave will be much shorter and more intense. And, since the hallway is shorter, the wave will get to your room much quicker. So, you better be ready with that door! You have to get the door open quicker and be ready to close it sooner as the wave will be shorter and more intense. This visualization is the illustration for why short runner intake manifolds need different cam timing. The pulse of air and fuel coming down the intake runner is shorter in more intense because it is closer to the plenum. So you have to open the intake valve quicker to let it in and close it sooner to trap the air fuel mixture before the piston, that has passed bottom dead center (BDC), starts raising to push it back out.

Camshaft Overlap And Its Effect On Volumetric Efficiency

Overlap is the time when the exhaust valve and the intake valve are both open at the same time between the exhaust cycle and the intake cycle while the piston is at or near top dead center (TDC). Overlap imparts both benefits and detriments depending on the application of a particular engine.

The benefit is that the spent exhaust gases rushing out of the piston's cylinder into the exhaust port creates a low pressure area behind it. This low pressure wave creates low pressure in the piston's cylinder and since the intake valve has already started to open, that low pressure starts to pull air and fuel into the piston's cylinder before piston itself even starts its own signal by moving down the cylinder for its intake stroke. In effect, overlap can help create a sooner and stronger overall low pressure signal to the intake tract than the cylinders displacement could create on its own. This increased "pull" on the intake charge creates a higher velocity and longer duration intake pulse wave. This stronger longer wave can be capitalized on more by a short runner, single plane intake because the cylinder is closer to the plenum where the air and fuel is stored whereas a long runner intake is farther from the plenum and cannot capitalize on the stronger pulse as much. This increased pulse wave intensity improves volumetric efficiency in the midrange and helps to broaden the power curve of an otherwise high strung short runner, single plane intake manifold.

The detriment is that, as overlap increases, so does the roughness of the idle and in addition, the manifold vacuum, drivability and low speed torque diminishes. So, if you have power brakes, vacuum operated accessories or have a tight stall converter, you might not have any fun driving a car equipped with a camshaft with a lot of overlap.

Summary

So, from a performance standpoint, no problem right? Just open the intake valve quicker and close it sooner while adding a healthy dose of overlap when running a short runner intake. Well, maybe, but that imparts some practical challenges with piston to valve clearance problems, but that is the topic of the next post.

Last edited by speedtigger; 08-16-2014 at 06:32 PM.
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Old 08-04-2014, 02:24 PM   #4
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Default Why Single Plane Equipped LS Builds Have More Piston to Valve Clearance Limitations

Why Single Plane Equipped LS Builds Have More Piston to Valve Clearance Limitations

In the previous post we talked about how a single plane intake manifold will need a sooner intake valve close than a traditional EFI, long runner, factory style intake equipped LS engine. Because of this, to get enough intake duration for a given RPM range, we must open the intake valve sooner as well. In addition, we know that a single plane equipped LS engine will also improve midrange and upper RPM range power with more valve overlap. This means that not only do we have to open the intake valve earlier to achieve this, but we also have to hold the exhaust valve open longer.

The problem with this is that the overlap cycle happens when the piston is at or near top dead center (TDC). Open the intake valve too soon or leave the exhaust valve open too late while the piston is near top dead center and they will collide. The damage that this can cause can often destroy more than just the piston or valve, but the resulting carnage can take out the cylinder head, block and more. So, we want to be very careful to do our homework and check our piston to valve clearances carefully when creating and installing large camshafts created for single plane equipped LS engines.

What If I Don't Have Or Don't Want to Cut Valve Reliefs In My Pistons?

For people who are building engine combinations based on stock shortblocks, there are limitations on the cam duration they can use if they are not willing to fly-cut valve reliefs into their pistons for additional clearance. For people who are running the big valve LS3/L92/LY6 square port heads, this is even more limited as the increased head diameter of the large intake valve reduces piston to valve clearance further.

For people who's intended RPM range is below 7000 RPM, this may not be a problem if they have not milled their heads to increase compression as camshafts of relatively modest intake durations of 230 degrees and less can make great power at speeds up to 7000 RPM in a single plane equipped LS engine. Unfortunately, for people building budget combos, head milling is often a part of the formula. So, it is very important that the engine builder considers this correlation before the milling begins.

Piston To Valve Clearance Practical Limits and Calculations

So, now that we know the reasons why there are extra piston to valve clearance considerations in creating an proper camshaft for a single plain equipped LS engine with stock pistons, lets look at how we measure and estimate piston to valve clearances.

Valve Drop
The object of measuring valve drop is to determine how far a valve can open before it touches the piston while that piston is at top dead center in the cylinder. Knowing this figure is the only way one can estimate piston-to-valve clearance without actually measuring an assembled engine. Furthermore, knowing this allows engine builders to determine which camshafts might fit in a given engine without further modification. There are two ways to measure valve drop. Actual valve drop (assembled) and estimated valve drop (not assembled).
Actual (assembled) Valve Drop
The most fool proof way is to measure valve drop in an assembled engine. Just rotate the crank until the the piston is at top dead center and then lower the valve until it touches the piston. Whatever that distance is, that is your valve drop. Do this for both intake and exhaust valves as they are most often different.

Estimated (unassembled) Valve Drop
You can also estimate valve drop while the cylinder head is not on the engine. For this start by placing the cylinder head on a flat surface and lower the valve until it touches the surface in which the head rests. This measurement of how far the valve "drops" is your cylinder head valve drop. Next measure your piston to deck height relationship. Most LS engines have a positive deck(between .005" to .008" is most often reported by builders). Next measure the thickness of your head gasket. The formula looks something like this: Cylinder head valve drop + head gasket thickness - positive deck height = valve drop. this is very accurate for an engine equipped with flat top pistons. Here is an example:
.155" + .051" - .007" = .199"
Again, do this for both intake and exhaust valves as they are most often different. Also, engines with dome pistons or dished pistons might better be done assembled as it is difficult to account for the different piston surface shapes using this method.
Cam Lobe Profiles, Ramp Rates and Lift
Another consideration in piston-to-valve clearance is lobe profiles and lift. One misconception that a lot of new builders have is that camshaft lift determines piston to valve clearance. While it is a factor, it is much less of a factor than the timing of the valve events. Consider this: A 5.7 liter LS1 has a stroke of 3.622". Your typical camshaft has a valve lift of .600". So, if the piston is at bottom dead center, the valve is still a full 3 inches way from the piston even and full open lift. However, when at top dead center, the piston is only .200" away from a fully closed valve. So, if that valve were to open full at top dead center, they would collide when the valve had merely reached 1/3 of its full lift. As you can see, valve timing is the main factor in piston to valve clearance in your LS.

With the above said, total lift is part of the equation in how fast a camshaft will open the engines valves. So, if the piston is leaving top dead center on the intake stroke and the intake valve is accelerating faster than the piston as it departs top dead center, as it often does at around 10 degrees ATDC, then the aggressiveness of the lobe can reduce piston-to-valve clearance. So, don't assume a different lobe profile will clear just because it has the same duration and lobe center angle.

Estimating Valve Clearance
Knowing your valve drop as measured by the 2 methods above is a key first step in estimating if a cam you wish to purchase will fit in your engine. The next part of the process is figuring your likely piston to valve clearance. There are two methods for this below: estimated TDC valve clearance and estimated actual valve clearance. Estimating your actual valve clearance is the most accurate way of predicting if a particular camshaft profile will fit or need additional piston flycutting.
How To Estimate Valve Clearance At TDC For A Given Camshaft
This is the process of estimating your valve clearance while the pistons is at top dead center. This is a great method for quickly estimating if your acceptable valve clearance is "in the neighborhood". This practice is an easy and great place to start because the cam suppliers can tell you the lobe lift of their profiles at various points. Comp Cams has these figure listed in their catalog. Here is an example of an LSL cam lobe:
Advertised Duration: 281
.050" Duration: 231
.200" Duration: 154
Total Lobe Lift: .363"
Lobe Lift @ TDC with 106 degree centerline: .081"
Lobe Lift @ TDC with 110 degree centerline: .067"

Lift with 1.7 Ratio Rocker: .617"
In this example, you can see that if your intake lobe is on a 106 degree centerline, your intake lobe lift will be .081" at that point. So .081" x 1.7:1 rocker ratio yields .1377" or rounded to .138" valve lift. If your intake valve drop is .199" then your piston to valve clearance at TDC would be: .061". But, that is probably not your ACTUAL piston-to-valve clearance.
Your actual piston to valve clearance will likely not be at top dead center, but closer to 7-10 degrees ATDC for the intake and 7-10 degrees BTDC for the exhaust. So, be ready for your actual piston to valve clearance to be less.
How To Estimate Your Actual Valve Clearance With A Given Camshaft
As you read above, your actual closest piston-to-valve clearance is not at top dead center. It might be between 5 and 15 degrees before or after top dead center. This is caused by the differences in speed between the valves open and close rates vs. the piston speed as it approaches and departs from top dead center. This complex relationship is difficult to visualize and even more complicated to plot easily. Fortunately, computers can do this job for us.
I have been trying out this great Excel based Piston to Valve clearance calculator. It appears to work properly. Give it a try and tell us what you think:
Piston To Valve Clearance Calculator
In the example above where the piston-to-valve clearance was .061" at TDC, the piston-to-valve clearance calculator predicts the actual estimated valve clearance to be .038" at 9 degrees after top dead center. So, you can see how if you only do the TDC calculations, you will likely be underestimating your clearance by a significant amount. In this case .023". While some might feel comfortable with .061" intake piston-to-valve clearance, not many are willing to brave .038" clearance.

How much is enough? Ultimately, that is up to you. The oft quoted old standard is .080" for the intake valve and .100" for the exhaust, but that does not seem to be the norm in the performance LS world. Several LS performance builders and cam vendors that I talk to more often quote between .040" - .060" intake and .060" - .090" exhaust in a well set up valve train system. Others push this even further. With that said, the ultimate responsibility is the vehicle owner's as he is the one who will be cleaning up the carnage and paying for the repairs.

Last edited by speedtigger; 08-17-2014 at 10:51 AM.
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Old 08-04-2014, 02:28 PM   #5
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Default Some Wisdom From The Top LS Cam Gurus - Geoff Skinner

Q & A with Geoff Skinner of Engine Power Systems (EPS)
Question: Were you the first to offer a cataloged cam specifically for single plane equipped LS engines?
Geoff: As far as I know, that might be true.

Question: How did that come about?
Geoff: People were asking me for it.

Question: One of the big concerns with budget racers who don't want to fly-cut is how big can they go. I understand this is limited by piston to valve clearance.
Geoff: Yes. With a single plane you want to open the intake valve as early as possible and that is limited.

Question: What is the safe IVO with your proprietary EPS camshaft lobes on a LS1 or LS2 engine without valve reliefs if the heads are not milled?
Geoff: Maybe up to 9 to 10 degrees. I would like to see people have a minimum of .060" piston to valve clearance.

Question: What is the safe EVC in the same scenario with EPS lobes?
Geoff: Maybe up to 9 - 10 degrees. I want to see .090" on the exhaust as it needs to have more clearance in case of valve float.

Question: Is overlap more than just the result of your chosen IVO and EVC? Do you ever look at a particular project and think that it needs 'X" amount of overlap?
Geoff: Yes. In fact, I will often adjust the EVC where it needs to be to achieve what I think is optimal total overlap.

Question:How does overlap from earlier IVO affect powerband compared to overlap from later EVC?
Geoff: IVO is crucial on a single plane combo. The single plane needs to get things going earlier. So, for me, the IVO is the primary consideration. The EVC can add needed overlap for a given combos needs, such as a situation where you have a runner with a large effective cross sectional area. Comparatively speaking, an engine with a larger induction system might need more overlap. For example, square port stuff vs cathedral port packages. Getting the overlap where it needs to be will help tune that induction system for maximum power. In a scenario where you have no good comparative data and are not sure where to put the EVC, you might just make it equal to the IVO.

Question: How does the EVO event affect power?
Geoff: Earlier EVO makes more power on a dyno and for a drag racer, earlier will likely be better. But, earlier EVO will affect transition, throttle response and drivability. Road racers and street cars will want a more conservative EVO than drag racers for these reasons.

Question:Same question for duration. Is it just result of chosen valve events, or do you know to feed an engine of a certain size that you need "x" amount of duration?
Geoff:No, not on duration. When I design a camshaft I start with the IVC and move on from there. Durations are a product of the chosen valve events for the combination.

Question: In starting with the IVC, what are your primary considerations?
Geoff: I am looking at size of engine, effective cross section of the total inductions system. This means carburetor, intake manifold and cylinder heads together and the desired RPM/power range.
About Geoff Skinner: Geoff was co-founder of Thunder Racing and was the man behind their hugely successful line of custom camshafts including the TR224 and the T-Rex. Geoff is now the owner/operator of Engine Power Systems where he is not only renowned for his advanced valve train development program and custom camshaft service, but also for cutting edge EFI tuning services. Geoff is well know throughout the community for his proprietary EPS camshaft lobes. These cam lobes set a new standard for performance and stability. Throughout Geoff's career he has likely sold over 10,000 camshafts.

Geoff Skinner
Engine Power Systems
1116 Executive Park Ave
Baton Rouge, LA 70806
Phone: (225) 751-8500
E-Mail: [email protected]

Last edited by speedtigger; 08-20-2014 at 02:44 PM.
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Old 08-04-2014, 02:30 PM   #6
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Default Example Drag Race Combination from LS1Tech members

Example Drag Race Combination from LS1Tech members

Coming Soon!

In this post you will see the details of some top performing carbureted LS combos from those who are willing to share.
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Old 08-04-2014, 02:38 PM   #7
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I hope this thread becomes useful to answer most general carbureted LS questions and is a springboard for some great conversation.

If you see any errors or have any contributions to this topic, let's hear it!
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Old 08-04-2014, 10:57 PM   #8
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Great information here Steve, you've spent a lot of time on this I can tell. Your visualizations are perfect.
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Old 08-05-2014, 02:37 PM   #9
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Thank you Martin. I really wanted to get all this stuff into a single resource that we could share. I look forward to interviewing you some more so that I can share your insight and experience on this important topic.
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Old 08-06-2014, 05:07 AM   #10
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good work mate.
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Old 08-10-2014, 05:29 PM   #11
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Thanks. I am finishing up the interview with Kip Fabre from Cam Motion for the interview section. He was really amazing to talk to. 50 years grinding cams. Countless major championships. A living legend. It really was a privilege.
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Old 08-11-2014, 04:14 AM   #12
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Only just seen this now, top effort putting all that information together.
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Old 08-15-2014, 02:37 PM   #13
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Default Some Wisdom From The Top LS Cam Gurus - Kip Fabre

Q and A with Kip Fabre of Cam Motion
Question: How long have you been in the Cam business?
Kip: I started grinding camshafts in 1965. I started my company in 1978.

Question: How did you get started?
Kip: My uncle and dad had an engine shop back in the 60s, so I grew up around it. I started out at Custom Engines in Baton Rouge. At first it was just regrinding stock cams, and then I started grinding hot rod cams for local guys.

Question: What made you start your own cam company?
Kip: I was grinding stock and industrial cams in the beginning. During that period, I saw some motorcycle racing cams that guys were using; they were junk. So, I started making some that were much more accurate which improved performance. After looking at automotive cams during that time I saw the same thing; mostly junk. So I thought that I needed to learn how to design cams; that was in about 1980.

Question: What is the most important recent development in performance camshaft manufacturing?
Kip: Because of the advance of computerized machining, we have the ability to give somebody exactly what they want. Back in the day, making a master lobe took 8 hours. Now, I can do it on the computer in 3 minutes to one hour; most in 3 minutes. As far as lobe development goes, some lobes that I made over 30 years ago still cannot be beat for some applications. Today we design lobes for many different applications. They are not any new magic lobe designs out there. Some may call them magic but they are not. Lobes should be designed for a given valve train, rpm, hyd., solid, intake side, exhaust side, supercharged, nitrous etc.; many different factors.

Question: Your website has only LS specific content. Why is that?
Kip: Because that is the only ones we want to do now. We decided to specialize. The LS engines are a lot of fun and I like the customers. Also, the LS cam market is the largest cam market out there right now. So, why mess with anything else?

Question: How do you spec cams differently for carbureted LS engines?
Kip: Each engine is different. I look at the whole picture. If you look at my website, my custom grind questionnaire asks for a lot of information. Even with that, I still want to talk to the customer to make sure I have all of the information I need to get it right.

Question: I have seen you say, that a lot of people use cam lobes that are too aggressive. Tell us about that.
Kip: What I mean by too aggressive is: you can be aggressive, but not be violent. You have to have a lobe that is controllable. You can only be so aggressive for a certain duration and lift. Going too aggressive is not needed. The difference in power is not worth it to tear up your valve train. Think of it like this: When you walk out to your car, you can walk regular or you can stomp your feet. Your still getting to the car the same way, but you won't be killing your feet.

Most might not know, but hydraulic lifters were not designed for violent lobes. They were designed so that production vehicles would not need periodic valve lash adjustments. They just aren't capable of handling a violent lobe. An aggressive lobe is okay. When you put a violent lobe on a hydraulic, you get some radial expansion in the lifter which opens up the tolerances; then they bleed down and you have the lovely noise of valves tapping.

Question: What are the best cam lobe measurements which a builder might look at to determine its intensity and stability?
Kip: I would say the .000 to .01 to .050 to .200. I like them to start off soft. When this area is too aggressive it shocks the valve train and lifter; kind of like being rear ended in a car. If you use a solid lifter you can be much more aggressive and pick up power because the solid lifter can take it.

Question: Have you done Spintron testing of your lobe designs?
Kip I have done many test on a Spintron in the past. The first was at McLaren. We made some cams for the Buick V6 when they were running at Indy. Now, I use computer simulation. These simulations can tell me when the acceleration rates and jerk get out of control and when the valves will start to float.

Question: Do you use different lobe profiles for intake and exhaust?
Kip: The lobes we make are different on the intake and the exhaust. The exhaust opens under pressure the intake does not. We learned many years ago that using excess lift on the exhaust is not the way to go. When I see bigger exhaust lift than intake lift on cam specs, I recognize that as something that is left over from the old flat tappet days.

Question: What changes do you make to cam designs in regards to compression?
Kip: An 11:1 compression engine will usually make more power than a 9:1 engine. But where this really shows up is at idle and lower RPM. If you put a cam with a lot of overlap on a low compression engine, it will idle like crap and be a pig down low. We saw a lot of this in the 80s. Fortunately, most of the LS engines we work with will have some good compression. Now, in a race only application where the RPMs are kept up, I might cam the 9:1 and 11:1 engine about the same, but in a street application I will reduce the overlap and duration to get some more cylinder pressure which improves the street manners and torque. There is a lot more to this, but that is the short answer.

Question: What are some of your greatest achievements?
Kip: We have helped win a lot of races. I can't remember them all right now, but if you look on our website you will see that we helped teams win 6 NHRA Pro Stock Championships, 6 NHRA Motorcycle Pro Stock Championships and 2 NHRA Top Fuel Championships. There have been a lot more over the years; offshore boats, tractor pulls etc.
BIO:
Kip Fabre is the owner of Cam Motion. He has been grinding cams for 50 years. Kip started Cam Motion in 1978. He has ground cams from everything from championship Top Fuel race cars and Pro Stock motorcycles to airplanes and industrial equipment. Kip has helped numerous notable top level racing teams win championships and his contributions to the accomplishments of top racing teams have made him a legend in the camshaft industry. Kip now primarily focuses on LS and new LT custom camshafts.

Kip Fabre
Cam Motion
2157 Beaumont Drive
Baton Rouge, LA 70806
Phone: 866-461-9536
Email: [email protected]

Last edited by speedtigger; 08-20-2014 at 02:45 PM.
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Old 08-15-2014, 07:17 PM   #14
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Default Some Wisdom From The Top LS Cam Gurus - Brian Tooley

Q & A with Bran Tooley of Brian Tooley Racing
Question: How did you get started in the Performance and Racing Industry?
Brian: My first passion was actually computers. I joined the Navy in 1983 to be a computer technician working in missile control center on a ballistic missile submarine. That same year I bought a brand new Z-28 off the showroom floor, and that started my love for automotive performance.

Question:You have a lot of knowledge about high performance cylinder head development. How did that come to be?
Brian: By the mid 80's me and a buddy of mine were porting our heads on our kitchen tables. By the late 80's I was porting heads and intakes for all of my buddies cars. In 1989 me and a buddy won King of the Hill at the Corvette Homecoming with a 1988 TPI Corvette, even beating the "big name" guys setups and the new 32 valve ZR1 Corvettes. When we told our competitors at the race what the combination was we were called liars, that left a definite impression on me. By 1993 I bought a flow bench and started porting heads full time. I had no one to help me, and no one to teach me. That made for a long, slow learning curve, but it did keep my mind open to all theory's rather than being strapped to someone else's theory's that might be wrong.

Question:How has your extraordinary knowledge about cylinder head development and testing influenced your opinion on camshaft design?
Brian: As I gained knowledge of head design, I realized that big valves can act like cam overlap, chamber shape can act like cam overlap, overly large exhaust ports can reduce top end horsepower, etc. So I feel that my knowledge of heads has certainly helped me with cam design. When I specify the cam open and close events, I'm always crutching at least one of those events based on the cylinder head design.

Question:You have done some interesting back to back camshaft testing that is unique. How did that come about?
Brian: Cam and head testing started when I was running the engine dynos at Holley Performance in the mid 90's where I had to test the SysteMax head/cam/intake packages among other things. I had my own chassis dyno by 2001 which was acquired by Summit Racing/Trickflow Specialties when they bought Total Engine Airflow in 2004. TFS has 2 engine dynos so there was a fair amount of testing performed there. Most recently I've paid Richard Holdener to do cam testing at Westech which has really helped us prove or disprove a lot of theory's. Working with Richard has been one of the best things that I've ever done, he's a super nice guy with a open mind.

Question:Some of what you learned in your LS cam testing goes against conventional thinking. Can you tell us about that?
Brian: The way people "think" something works frequently comes from bench racing sessions or numerous books and magazines. Unfortunately most books and magazines are written by guys with journalism degrees who know little about engines. Also, what works in one engine may not work in another, so without testing that exact combination you really don't know what the engine "likes" or "dislikes". With hydraulic roller cams, more times than not, less lift and less lobe intensity has actually made more power everywhere. However, very few people actually have the resources to do that type of testing. And since they "think" they know what makes for a better cam, if the specs aren't like what they "think" works, then they disregard it as a poor design.

Question: I see a lot of the big "pet name" max effort cams push piston-to-valve clearance to extremely tight numbers.
What do you think the safe limit is for piston-to-valve in a well set up valve train?
Brian: I like to see a minimum of .040" on intake and .060" on exhaust.

Question: You sell a lot of valve springs to LS enthusiast and shops, how did you become "the valve spring guy"?
Brian: The credit for a lot of what I know about valve springs goes to the testing I was involved in while I was at Trickflow Specialties. The Spintron testing combined with durability testing was really an eye opener. The springs we tested with the most open pressure didn't have as good of a trace on the spintron as the Platinum springs we sell. Springs with too much open pressure are certainly hard on valve tips when using stock rockers so they hurt durability. Springs with less pressure had really poor control. So it's a fine line between sufficient pressure to control the valve train, but not so much to cause durability issues. My competitors having spring failures combined with another competitor going out of business certainly helped the popularity of our springs.

Question: With your knowledge of cylinder heads and valve springs, you must have some opinions on the aggressive new cam lobes that are on the market. What do we need to know about choosing the right lobe for a custom camshaft?
Brian: In 2001 I tested two cams back to back in a 8000 rpm hydraulic roller Ford engine on our chassis dyno. The cams were almost identical with identical lift except for a big difference in ramp speed. The faster ramp speed cam made less power everywhere and floated the valves 1000 rpm sooner than the "slow" ramp speed cam we were running. This was the first time that I had seen a slower ramp speed cam make more power everywhere with my own eyes. Just this spring we tested two cams back to back in a 7500 rpm 408 engine with identical exhaust lobes, centerlines and intake duration. The "slower" ramp speed cam made 15 rwhp more power. That's why it's so important to actually do the testing to find out what works, rather than "speculating" that the faster ramp speed/higher lift cam will make more power. If a slower ramp speed cam makes more power, it will have much better durability, and that makes it the obvious choice for a street driven car. We've seen cams with .030" more intake lift make 3 more hp, that's not a good trade off in terms of power gained versus durability lost, at least for us. One of the most obvious things is, if the catalog says "These lobes are VERY hard on parts and are not generally recommended for street use" then maybe they shouldn't be used on a street car that is going to have miles put on it.

Question:What parameters should an engine builder look for to determining whether they should use a beehive or a double spring for their application?
Brian: You have to look at ramp speed, lift and valve weight. I had a guy with a LS9 cam and a aftermarket beehive spring call me who broke one of the springs in 1500 miles. He was in complete disbelief that he broke a .625" lift beehive spring with a .562" lift cam. However he didn't realize that a LS9 intake lobe has the same opening ramp intensity as a Comp XE-R lobe, and his L92 intake valve weighed over 110 grams. The LS9 cam was designed for a titanium intake valve that weighs less than 80 grams.

Question: In your opinion, are titanium retainers worth the expense?
Brian: In my opinion yes they are. Anytime that I can save weight in the valve train I do. I spent a great deal of time designing my retainers to be light, even at the risk of people "thinking" they were too thin. However I had our retainers stress tested and the stock locks will fail and pull through the center before the retainer will fail.
Bio:
Brian Tooley is the owner of Brian Tooley Racing. Previously, Brian worked at Holley Performance where he helped develop the SysteMax head, intake and camshaft packages. Brian also founded the renowned Total Engine Airflow which he turned into one of the most successful CNC cylinder head porting shops in the country. In addition he worked with Summit Racing Equipment and Trickflow Specialties developing CNC programs for existing heads, as well as developing all new cylinder heads. Brian is also known throughout the performance community for his line of quality, affordable spring kits

Brain Tooley
Brian Tooley Racing
888-959-8865
[email protected]

Last edited by speedtigger; 08-20-2014 at 02:45 PM.
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Old 08-15-2014, 07:59 PM   #15
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Good stuff, Steve!
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Old 08-17-2014, 12:26 AM   #16
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Worthwhile mentioning static and dynamic compression up the top?!?
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Old 08-17-2014, 07:38 AM   #17
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Stayed tuned DB. Jason Mangum of Texas Speed talks a bit about that in his Q & A; coming soon.
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Old 08-17-2014, 09:58 AM   #18
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Probably the best post in YEARS here on tech! Can't wait to go super Vic.
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Old 08-18-2014, 02:43 PM   #19
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Thanks to all involved for taking the time to put some actual tech back into this site!

It was great to read about cam and intake theory without "pet name" cams or eleventybillion millimeter multi-piece composite intakes (and the associated heat soak debate).

Is there any consideration going to be given to the differences in cylinder filling as it relates to a wet manifold vs. a port injected version, and cam design/characteristics?
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Old 08-18-2014, 06:33 PM   #20
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Fantastic thread Tigger. Great job on collecting and organizing this information. It will help many people, get a better grasp on what these numbers and figures mean when rattling them off in a tech thread, plus it is always good to throw some love in the carb intake direction for the single plane guys.
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