speedtigger

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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:

• General Camshaft Selection Guidelines
  This section is for people who are new to the cams selection process. In this section you will see how camshaft selection relates to intake manifold design, torque converter stall speed, rear end gearing, exhaust selection, carburetor sizing and more. These guidelines are intended to be specific to single plane or carbureted LS engine applications.
• Carbureted and Single Plane Cam Consideration / The Camshaft and Manifold Relationship
  This section is for those who want to understand why their single plane equipped and/or carbureted LS engine needs a specially designed camshaft to realize it's full potential.
• Why Single Plane Equipped LS Builds Can Have More Piston to Valve Clearance Limitations
  This section explains piston to valve clearance considerations and measurements and why that "ideal" custom camshaft for your carbureted LS engine may require piston flycutting or aftermarket pistons with valve reliefs. In this section, you will also find resources for estimating your piston to valve clearance.
• Some Wisdom From The Top LS Cam Gurus
  Q & A's Questions and answers with top LS cam experts on the topic of camming your single plane or carbureted LS engine.

  • Geoff Skinner of EPS
    
  • Kip Fabre of Cam Motion
    
  • Brian Tooley of Brian Tooley Racing
    
  • Martin Smallwood of Tick Performance
    
• Example Drag Race Combination from LS1Tech members
  This section will have details from some top performing carbureted LS combos from those who are willing to share their success.

speedtigger

iTrader: (16)

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.

speedtigger

iTrader: (16)

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.

speedtigger

iTrader: (16)

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).
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.

speedtigger

iTrader: (16)

Q & A with Geoff Skinner of Engine Power Systems (EPS)
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: geoff@engpwrsys.com

speedtigger

iTrader: (16)

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.

speedtigger

iTrader: (16)

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!

Sales@Tick

iTrader: (3)

Great information here Steve, you've spent a lot of time on this I can tell. Your visualizations are perfect.

speedtigger

iTrader: (16)

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.

dogsballs

good work mate.

speedtigger

iTrader: (16)

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.

VLS1

Only just seen this now, top effort putting all that information together.

speedtigger

iTrader: (16)

Q and A with Kip Fabre of Cam Motion
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: info@cammotion.com

speedtigger

iTrader: (16)

Q & A with Bran Tooley of Brian Tooley Racing
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
briantooleyracing@gmail.com

JakeFusion

iTrader: (7)

Good stuff, Steve!

dogsballs

Worthwhile mentioning static and dynamic compression up the top?!?

speedtigger

iTrader: (16)

Stayed tuned DB. Jason Mangum of Texas Speed talks a bit about that in his Q & A; coming soon.

Zmg00camaross

iTrader: (11)

Probably the best post in YEARS here on tech! Can't wait to go super Vic.

mOtOrHeAd MiKe

iTrader: (8)

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?

My6speedZ

iTrader: (18)

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.