J-Rod

Well, folks had been asking that we start a new thread, as the other thread had gotten quite long. So, for refernece, here are the threads in question.

The original cam thread which got locked.
https://ls1tech.com/forums/generation-iii-internal-engine/99118-difference-between-tr224-comp224.html

The Camshaft Discussion Part II thread which had lots of good info, and had a lot of views.
https://ls1tech.com/forums/generation-iii-internal-engine/101100-camshaft-discussion-part-ii.html

So, now we are on part III.

For those of you who may have missed out, I encourage you to go read the other threads to get an idea of what folks are talking about here. If you have concrete info about the "how and why" of cams, or cam dynamics, then please post. The purpose of this thread is not "What cam should I put in my car with xxx combo". That is what the search feature is for. If you look, most likely your question has been answered about 20 times today alone. Now, if its not, and you have something specific to ask, feel free to post up. I just don't want this thread to turn into the cam recommendation thread. Read up, get educated, and then you can decide for yourself what cam to buy...

With that in mind, let the ideas flow....

J-Rod

Ok, lets have a quick discussion on one of the thing that folks seem to overlook. Folks get hung up on solely the duration @ .050 to spec a cam. Quite honestly there are tons more to consider than lift @ .050. Sure, its important, but so is the rest of the range.

So, I am going to build three hypothetical cams and show you what I mean.

Here are 3 ls1 cam lobes from comp that are the same using the .050 specs (228 degrees). But then look at gross, and .200 you will see that all cams are not the same... Notice how gross lift .006 goes down while .050 stay the same, and .200 get larger, thats means the last lobe is more agressive than the first lobe. Anyhow, look at it and see if this makes sense to you.

Comp lobe 3755

.006 282
.050 228
.200 141

Lift with 1.7 rockers is .539

Comp Lobe 3717

.006 281
.050 228
.200 145

Lift with 1.7 Rockers is .571

Comp Lobe 3724

.006 277
.050 228
.200 149

Lift with 1.7 Rockers is .588

These are all Ls1 lobes. When you get into grinding a BBC lobe on an Ls1 core, or a Ford hydraulic roller lobe on an ls1 lobe, then you have even more choices. The point I am making is that even within Comp you can't just look at .050 as your determining factor. There is a lot more to lobes than just duration @ .050 You must look at the whole cam, and the whole package. You need to look at:

N/A or P/A
Intake tract length
header / Exhaust length
I/E ratio
and about 50 pages more, in short there is plenty to consider, and all of it matters to one extent or another. Yes you might get "close" with a off the shelf cam, but if the rest of the motor is custom, shouldn't your cam be too. Or if not, at least tailor your selection to your application...

Ok, so lets look at those specs again...
.006|282|281|277
.050|228|228|228
.200|141|145|149

So, as you can see, the first lobe is a "slower" lobe this means it initially opens sooner, at .050 the cams are all the same, and @ .200 duration is less than the other cams, meaning the cam is "smaller". What does this mean?

Well, its a balancing act really. You want to get that valve open as quickly as possible. But, the valvetrain of a hyd. roller is HEAVY. Even with Ti parts it heavy. And to keep it under control means mean springs. On top of that, mean springs mean collapsed lifters. So, that means going to Comp-Rs.

In talking with a tuner recently he did a test with the XE-R lobes, versus some of the stuff he doing which came from other lobes like BBC, or Ford. In his case, he was takign the slower lobes as he was able to keep the wear and tear on the valvetrain down, and had no issues with spring replacement or spring breakage even with bigger cams.

I am going to illustrate two big cams I am going to make them symetrical to make the math a bit easier for folks, so bear with me. Ok, if we look at two larger cams. Lets look at a 248/248 106. Yes, I know it is a big cam, but it helps illustrate my point.

Lobe #1 is the XE-R lobe (3734) Lobe #2 is a BBC Hyd Roller on an Ls1 (3357)

(EDIT) I Editied the format of my cam spreadsheet to make it easier to read on the forum.

Quick and Dirty Cam Calculator Spreadsheet
___________________________________________ 0.006 __ 0.050 __ 0.200
Intake Duration - ID_______________________ 297 __ 248 __ 168
Exhaust Duration - ED______________________ 297 __ 248 __ 168
Lobe Center Angle - LCA (also known as LSA) 106 __ 106 __ 106
Intake Centerline - ICL____________________ 106 __ 106 __ 106


Intake Valve opens - IVO___________________ 42.5 __ 18 __ -22 BTDC (- indicates ATDC)
Intake Valve closes - IVC__________________ 74.5 __ 50 __ 10 ABDC
Exhaust Valve Opens - EVO__________________ 74.5 __ 50 __ 10 BBDC
Exhaust Valve Closes - EVC_________________ 42.5 __ 18 __ -22 ATDC (- indicates BTDC)
Exhaust Centerline - ECL___________________ 106 __ 106 __ 106
Overlap____________________________________ 85 __ 36 __ -44 degrees

___________________________________________ 0.006 __ 0.050 __ 0.200

Intake Duration - ID_______________________ 304 __ 248 __ 159
Exhaust Duration - ED______________________ 304 __ 248 __ 159
Lobe Center Angle - LCA (also known as LSA) 113 __ 113 __ 113
Intake Centerline - ICL____________________ 113 __ 113 __ 113


Intake Valve opens - IVO___________________ 39 __ 11 __ -33.5 BTDC (- indicates ATDC)
Intake Valve closes - IVC__________________ 85 __ 57 __ 12.5 ABDC
Exhaust Valve Opens - EVO__________________ 85 __ 57 __ 12.5 BBDC
Exhaust Valve Closes - EVC_________________ 39 __ 11 __ -33.5 ATDC (- indicates BTDC)
Exhaust Centerline - ECL___________________ 113 __ 113 __ 113
Overlap____________________________________ 78 __ 22 __ -67 degrees

___________________________________________ 0.006 __ 0.050 __ 0.200

IVO delta__________________________________ 3.5 __ 7 __ 11.5
IVC delta__________________________________ -10.5 __ -7 __ -2.5
EVO delta__________________________________ -10.5 __ -7 __ -2.5
EVC delta__________________________________ 3.5 __ 7 __ 11.5
ECL delta__________________________________ -7 __ -7 __ -7
Overlap____________________________________ 7 __ 14 __ 23



The XE-R lobe is a .615 lift, and the BBC is a .566 lift. But, if you look at the .200 specs, you could do a XE-R lobe on a #3729 lobe which is
.006 - 287
.050 - 238
.200 - 159

Lift is .605 on the 3729 lobe. So imagine using the 3729 on the intake side, and the 3356 on the exhaust side. So, if you look at the specs on the cam, its a 238/248 .615/.566 it looks to be a standard split, in reality its a reverse split or almost symetrical cam when you look @ .200.

So, lets discuss this. In talking with a certain tuner, he saw no gains going to the more agressive lobes, and has stepped away from those cams, and is concentrating more on slower lobes and more valvetrain control.

VINCE

iTrader: (1)

Sounds like that tuner is just playing it safe. Solid Roller cams require much stronger springs and they last. Just a little more maintenance. I see no reason why we cant use HUGE cams if the heads support the cam specs. I have always wondered why we keep going bigger with cams on stock heads though? There has to be a point of no return..

J-Rod

Yes and no. Yes they are playing it safer by using a cam with less agressive lobes, but they did testing with XE-R lobes and saw no power gains in the particular designs they were testing. That to me is interesting, as if it pans out you could in theory save a lot of valvetrain wear and tear.

Depending on the application solid rollers can kill springs in a very, very short period of time. I have been over to a shop where they had a 55 gallon drum of used VascoJet triples because of the frequency of the spring changes required. Keep in mind a spring is a wear item. It has X number of cycles in it. The replacement frequency is based on heat, number of cycles, etc... One of the issues with agressive XE-R lobes is that you are accelerating a relatively heavy valvetrain mass (Hydr. roller lifters are HEAVY). To keep that mass under control you need a strong spring. The problem with a strong spring is that you collapse the stock lifter. Now, if you go over to a solid roller, you can do a tight lash roller, get a slightly more agressive lobe going, but be easier on springs. So you ask, HOW. The simple answer is when you go over to a solid roller lifter you can drop weight. Lower the valvetrain mass, and spring load decreases.

One of the big issues that affects as spring is fatigue. This is sometimes called "work hardening". You can visulaize this by taking a piece of metal and bending it back and forth. At the point where you bend it, it will get hot, the metal will "work harden" become brittle and break.A spring is no different. That is why keeping a spring which is under a lot of stress cool is very important.

Again, its all about how that lobe works with the spring. Keep in mind, if you had the valvetrain to take it, you could spin a stock cam to 7500-8000 rpms you wouldn't make any power, but the car would rpm.

Keep in mind that a bigger lobe keeps a valve open longer. So, on stock head the thing most people aren't keeping in mind is keeping lift under control. Open the valve too far and the port is going to be so turbulent its pointless. But, with a restrictive stock port, you prop tha valve open for as long as you can, and you will make power thats what duration is for. As rpm increases, time decreases, so to offset that duration off the seat must increase for the motor to have time to breathe.

The difference between ported heads and stock heads is that a ported head can move more air more efficently, so the valve doesn't need to be open as long to get the same aircharge in. You could make the same power with a stock head as a ported head provided you can keep the valve open long enough on the stock head to allow the same ammount of air and fuel in and out as you do with a ported head. This is the key to your stock classes, and some of the classes we compete in which are lift limited, and restricted to unported heads.

Magred2001vette

iTrader: (2)

So j-rod, what are your thoughts on the aggressive XE-R lobe design on the G5X-2 cam used with stock heads. Do you feel the duration and lift at 240/.609 is asking too much of the stock head flow capabilities?

...and yes, great #'s have been achieved w/ this cam on stock heads, but some seem to think its too much for the marginal gains.

Cstraub

iTrader: (1)

Speaking as someone who does concentrate on lobe lift numbers past .050", I will have to support J-rod on their importance. When designing an engine specific stick, I look at the airflow of the heads, I prefer in .025" increments. This gives you a look at the "Air Enviroment" how it is flowing, where the surges are and where "dirty air" may come into play. By studying the air movement, you can take advange of air in areas of the flow range with the lobe selection, and you can also crutch areas with lobe for poor flowing ranges of the head. You can have the trickest set of heads in world, but if that cam doesn't open and close the valves to take advantage of it, then all you have is a waste of money.

Agressive and mild lobes. Again they are used to work with the airflow. A killer set of heads on a NA car that will see mostly street use. . .mild lobes. If the head is flowing good air, then you can easily open the valve and give the engine a smooth broad power band. Take a good set of heads, mismatched runner volume...undersized for the CID of the engine, you need an agressive lobe to pack that cylinder. Positive manifold pressure cars need mild lobes.

Vince to address your statement about huge cams.. . .If you have a good set of heads and they are matched to the combo and the RPM level is not drastic. . say 6500 and above for these cars with ported heads and 347 CID, you don't need a large cam. The heads, if moving air effiecentlly, only need to open a relative amount to the flow of the heads because the heads' velocity will easily fill the cylinder. Hence the head is doing the work. Now back up to a NHRA Super Stocker, CC volume maintained on runner, $500 valve job, and a size 16 foot on the gas. This engine will need a huge cam due to the fact the engine will see an RPM range way out of the intended range of the engine and cylinder head. This being the case a huge cam is needed because the cam now has to do most of the work to crutch the heads to make power in the desired range.
So, it is my "gospel" that for those of you that have stock heads and limited mods and want to run at the big end of the RPM scale, you need bigger cams. For those of you that have high dollar heads from the Forum Vendors and such, and are staying in a relative mid range rpm, you can use a smaller cam and have a broader more usable power band.

Lets address these lifers while I am here. Hyd. rollers were designed to run at low to mid range rpm and give pushrod engines more power under the 6K RPM range. That was the intended use. Now we have pushed them into RPM that they were never intended to be used. Merc. Marine used these things in both SBC and BBC. I won't go into detail but Merc's warranty rate went way up, these marine engines running 4K and 5K all day long experienced valvetrain problems. It is now common to replace springs on the Merc. BBC engines at 200 Hours, thats 20K miles. The hyd roller in these engines is in the .560" range and 220 duration. The point I am trying to make is the hyd. roller, although a wonderful part, is a maintenance nightmare when taking them out of their intended power range for a short time or running them at the upper end of the scale for long periods of time.

Lifter Mfg. As some of you know we lost the largest hyd. roller retro mfg. about 2 years ago now. They also made flats and along with this lifters went out of the roof on price. I was part of "venture" . . .it was an adventure. . .to produce a replacement. Where I am going is if you are running your engine to the extreme you want a fully machined part with Eaton type valving. This valving is the preferred type and will make more power.

It all comes down to a matched combination designed to do what you want. All aspects are important. If your like me, get some good shelf parts/mods and drive ( I have a K&N filter only on my M) and if you want a serious piece, get good parts and designed to work for your intended power range.

I hoped I haven't bored anyone.

Chris

CHRISPY

Great post!!!

J-Rod how was driveability with the "softer" lobe. Were there noticeable differences in idle, low rpm driveability?

lsx24

iTrader: (45)

I don't know if this is the time or place to ask this, but here goes. I am curious about valvetrain reliability, at high RPMs yes, but more importantly with faster ramp rates of the lobe. In analyzing the 3 cams posted above, they have the same lift at 0.050, but their different ramp rates theoretically contribute to spring wear. I plan to assemble the cam/valve components only once (yea right) so I probably won't swap it out if I find a sweet spot in wear and profile.

What I fail to see is why a less aggressive lobe prolongs spring wear, when total lift is held constant. I see the lobe profile accelerating the spring at one rate, and the spring has to be able to oscillate within control at that rate of acceleration. Add another cam with a different profile (but same total lift), and the spring still supports the same distance, but gets there at a different speed.

Does the spring perform the same amount of work for both profiles? If wear is a tangible factor, maybe not. Again when lift goals are the same. Now if you add RPM to the equation, it might increase wear exponentially because that is another relevant factor in spring movement. Therefore choosing a spring for the intended RPM range and intended ramp rate becomes even more crucial. Is it a case of diminishing returns when 'aggressifying' the lobe profile, when you can increase RPM (and corresponding support components) to leverage the horsepower equation?

DenzSS

Net lift is the same, but the way the work is done is significantly different. Imagine compressing a spring with your hands slowly. Now imagine putting that spring on a bench and smacking it hard with a hammer. That is the difference between "soft" and "aggressive" lobes.

VINCE

iTrader: (1)

Very good points here. Thanks guys..

AINT SKEERED

iTrader: (2)

If a head flow peaks at .600, will going with a .610 lift be best or stay just below the peak ? Reason I ask is my brother has Trick flow heads that are out of the box stock on his Mustang and he has a stg 2 trickflow cam with .563 lift and is running 1.7 rockers(now .598). I have seen where stock TRICK FLOW heads peak at like .550 or so and he is over his peak, will this actually hurt performance or will it stay in the peak flow #'s longer and work better?

Cstraub

iTrader: (1)

Ain't,
It is better to go over. Now we are off in the area of pushrod defection. Years ago we put 3/8" pushrods on SBC for strength. Then someone decided that was to much weight and we went to 5/16" in performance applications. We'll now we have come full circle. Due to testing fixtures like spintrons and advances in filming technology we have seen that pushrod defection in higher rpm is a problem. Pushrods have been recorded to bend/defect as much as .100". This reduces lift and worst of all has a rebound affect on the closing side of the lobe. Pushrod defection can be read on a dyno sheet in the SCFM column. Telltale sign is increase and decrease spikes.
The fix has been to go to larger diameter pushrods with heavier wall, say around .113 to .120" wall. Diameter ranges anywhere from 3/8" to 1/2" stuff depending on application. Tapered pushrods, both single and double, are preferred in the professional ranks.
What kind of power loss can defection have. We went from 9.500" long 5/16" in a 410 Sprint engine to 9.500" single taper 7/16" to 3/8" and picked up 40HP. This was a 790HP engine. So defection was costing him about 5%.
So, going over won't hurt, but if the pushrods in the engine are defecting, then you aren't going to gain anything.

Chris

SStrokerAce

iTrader: (2)

Yep it's the fact that the coils smack against each other harder. The distance between the coils on a spring doesn't compress equally but it acts more like a sliky with one coil smacking into the one below it and so on. The harder you hit it the less life it will have.

Cstraub, great post! Pushrods are all to often left out, 40hp gain on anything is a huge increase in HP!

Bret

J-Rod

Ok, so lets look at something else. Lets look at a softer lobe vs a faster XE-R lobe, and try to get the camshafts "more similar". Again, for this exercise I am going to use a fairly large lobe, and I am going to do it symetrically to make it easier to follow. Ok, we're going to do a 3731 XE-R lobe vs a 3356 XE Marine lobe for a BBC. The XE Marine has the following caveat beside it

Ok so lets look at those two cams.


Quick and Dirty Cam Calculator Spreadsheet
___________________________________________ 0.006 __ 0.050 __ 0.200
Intake Duration - ID_______________________ 291 __ 242 __ 163 3731 Lobe
Exhaust Duration - ED______________________ 291 __ 242 __ 163 3731 Lobe
Lobe Center Angle - LCA (also known as LSA) 106 __ 106 __ 106
Intake Centerline - ICL____________________ 106 __ 106 __ 106


Intake Valve opens - IVO___________________ 39.5 __ 15 __ -24.5 BTDC (- indicates ATDC)
Intake Valve closes - IVC__________________ 71.5 __ 47 __ 7.5 ABDC
Exhaust Valve Opens - EVO__________________ 71.5 __ 47 __ 7.5 BBDC
Exhaust Valve Closes - EVC_________________ 39.5 __ 15 __ -24.5 ATDC (- indicates BTDC)
Exhaust Centerline - ECL___________________ 106 __ 106 __ 106
Overlap____________________________________ 79 __ 30 __ -49 degrees

___________________________________________ 0.006 __ 0.050 __ 0.200

Intake Duration - ID_______________________ 298 __ 242 __ 153 3356 Lobe
Exhaust Duration - ED______________________ 298 __ 242 __ 153 3356 Lobe
Lobe Center Angle - LCA (also known as LSA) 106 __ 106 __ 106
Intake Centerline - ICL____________________ 106 __ 106 __ 106


Intake Valve opens - IVO___________________ 43 __ 15 __ -29.5 BTDC (- indicates ATDC)
Intake Valve closes - IVC__________________ 75 __ 47 __ 2.5 ABDC
Exhaust Valve Opens - EVO__________________ 75 __ 47 __ 2.5 BBDC
Exhaust Valve Closes - EVC_________________ 43 __ 15 __ -29.5 ATDC (- indicates BTDC)
Exhaust Centerline - ECL___________________ 106 __ 106 __ 106
Overlap____________________________________ 86 __ 30 __ -59 degrees

___________________________________________ 0.006 __ 0.050 __ 0.200

IVO delta__________________________________ -3.5 __ 0 __ 5
IVC delta__________________________________ -3.5 __ 0 __ 5
EVO delta__________________________________ -3.5 __ 0 __ 5
EVC delta__________________________________ -3.5 __ 0 __ 5
ECL delta__________________________________ 0 __ 0 __ 0
Overlap____________________________________ -7 __ 0 __ 10



Ok, so as you can see, the XE is 3.5 degrees larger at .006. As we have talked about before .006 is what you call gross lift. Thats where most cam mfg's used to rate cams, its nice to know, but not critical, because there is so little airflow at this lift.

Now, we move up to .050 as we can see, both cams are equal which was of course the point of this.

Ok, last, we move on to .200 at this point you can see that the XE-R lobe is bigger from here on its got 5 degrees more duration at .200 and if you plot that out you will most likely see that it is slightly bigger both in lift and duration all the way through the lift range.

Ok, so lets go back to both lift and valve events. Here is why I selected the lobe that I did. Lets say that you look at those two cams I just created. Now, you ask yourself, what if I throw out .006 and .050 and look more at the .200 what do I need to do to get there. Well, you open the comp lobe catalog and you look at down the page till you get to a lobe with 153 degrees of duration @ .200 and you find that sure enough, the #3726 lobe (232 @ .050) fits the bill. It was no coincidence BTW, that I selected the 242, I wanted to use something as an example that had an easy match @ .200.

Ok, so now lets concentrate on those valve events, forget about LSA, I mean it, toss it out the window. Look at when the valves open and close, thats all. Now, as I said lets look at trying to use a smaller faster opening lobe to match that bigger slower opening lobe.


Quick and Dirty Cam Calculator Spreadsheet
___________________________________________ 0.006 __ 0.050 __ 0.200
Intake Duration - ID_______________________ 281 __ 232 __ 153 3726 Lobe
Exhaust Duration - ED______________________ 281 __ 232 __ 153 3726 Lobe
Lobe Center Angle - LCA (also known as LSA) 106 __ 106 __ 106
Intake Centerline - ICL____________________ 106 __ 106 __ 106


Intake Valve opens - IVO___________________ 34.5 __ 10 __ -29.5 BTDC (- indicates ATDC)
Intake Valve closes - IVC__________________ 66.5 __ 42 __ 2.5 ABDC
Exhaust Valve Opens - EVO__________________ 66.5 __ 42 __ 2.5 BBDC
Exhaust Valve Closes - EVC_________________ 34.5 __ 10 __ -29.5 ATDC (- indicates BTDC)
Exhaust Centerline - ECL___________________ 106 __ 106 __ 106
Overlap____________________________________ 69 __ 20 __ -59 degrees

___________________________________________ 0.006 __ 0.050 __ 0.200

Intake Duration - ID_______________________ 298 __ 242 __ 153 3356 Lobe
Exhaust Duration - ED______________________ 298 __ 242 __ 153 3356 Lobe
Lobe Center Angle - LCA (also known as LSA) 106 __ 106 __ 106
Intake Centerline - ICL____________________ 106 __ 106 __ 106


Intake Valve opens - IVO___________________ 43 __ 15 __ -29.5 BTDC (- indicates ATDC)
Intake Valve closes - IVC__________________ 75 __ 47 __ 2.5 ABDC
Exhaust Valve Opens - EVO__________________ 75 __ 47 __ 2.5 BBDC
Exhaust Valve Closes - EVC_________________ 43 __ 15 __ -29.5 ATDC (- indicates BTDC)
Exhaust Centerline - ECL___________________ 106 __ 106 __ 106
Overlap____________________________________ 86 __ 30 __ -59 degrees

___________________________________________ 0.006 __ 0.050 __ 0.200

IVO delta__________________________________ -8.5 __ -5 __ 0
IVC delta__________________________________ -8.5 __ -5 __ 0
EVO delta__________________________________ -8.5 __ -5 __ 0
EVC delta__________________________________ -8.5 __ -5 __ 0
ECL delta__________________________________ 0 __ 0 __ 0
Overlap____________________________________ -17 __ -10 __ 0



Ok, now as you can see, @ .006, the cam is 8.5 degrees smaller.

At .050 the cam is 5 degrees smaller, and it has 10 degrees less overlap. Valve timing has changed dramatically @ .050 also. As you can see, that 5 degrees made a difference. Valve events for the XE-R lobe are at 42 and 42, and for the XE are at 47 and 47. As we said before, the XE-R is more extreme, so lets look at what happens when we move the .050 events to 47 on the XE-R lobes.


Quick and Dirty Cam Calculator Spreadsheet
___________________________________________ 0.006 __ 0.050 __ 0.200
Intake Duration - ID_______________________ 281 __ 232 __ 153 3726 Lobe
Exhaust Duration - ED______________________ 281 __ 232 __ 153 3726 Lobe
Lobe Center Angle - LCA (also known as LSA) 111 __ 111 __ 111
Intake Centerline - ICL____________________ 111 __ 111 __ 111


Intake Valve opens - IVO___________________ 29.5 __ 5 __ -34.5 BTDC (- indicates ATDC)
Intake Valve closes - IVC__________________ 71.5 __ 47 __ 7.5 ABDC
Exhaust Valve Opens - EVO__________________ 71.5 __ 47 __ 7.5 BBDC
Exhaust Valve Closes - EVC_________________ 29.5 __ 5 __ -34.5 ATDC (- indicates BTDC)
Exhaust Centerline - ECL___________________ 111 __ 111 __ 111
Overlap____________________________________ 59 __ 10 __ -69 degrees

___________________________________________ 0.006 __ 0.050 __ 0.200

Intake Duration - ID_______________________ 298 __ 242 __ 153 3356 Lobe
Exhaust Duration - ED______________________ 298 __ 242 __ 153 3356 Lobe
Lobe Center Angle - LCA (also known as LSA) 106 __ 106 __ 106
Intake Centerline - ICL____________________ 106 __ 106 __ 106


Intake Valve opens - IVO___________________ 43 __ 15 __ -29.5 BTDC (- indicates ATDC)
Intake Valve closes - IVC__________________ 75 __ 47 __ 2.5 ABDC
Exhaust Valve Opens - EVO__________________ 75 __ 47 __ 2.5 BBDC
Exhaust Valve Closes - EVC_________________ 43 __ 15 __ -29.5 ATDC (- indicates BTDC)
Exhaust Centerline - ECL___________________ 106 __ 106 __ 106
Overlap____________________________________ 86 __ 30 __ -59 degrees

___________________________________________ 0.006 __ 0.050 __ 0.200

IVO delta__________________________________ -13.5 __ -10 __ -5
IVC delta__________________________________ -3.5 __ 0 __ 5
EVO delta__________________________________ -3.5 __ 0 __ 5
EVC delta__________________________________ -13.5 __ -10 __ -5
ECL delta__________________________________ 5 __ 5 __ 5
Overlap____________________________________ -27 __ -20 __ -10



Well, as you see, when we move the .050 valve evetns to 47, the LSA moves to 111.

The delta @ .006 is now 13.5 and 3.5.

The delta is 0 @ .050.

As you can also see, by looking at the .200 we have moved those valve events around also. There is now a 5 degree delta @ .200.

I guess what I am trying to show is there is so much more to a cam than just .050, and just because its big @ .050 doesn't mean its big all the way through.

SilverGhost

iTrader: (53)

Nice info. I am most interested in the talk about stock vs ported heads and their relationship to duration/"big" vs "small" cams.

Everything makes clear sense about airflow and how long you want to hang the valves open, what this is making me wonder is the advantages and disadvantages then of big cams that were primarily designed to work with stock heads when they are used with a nice set of ported heads.

Based on the comments so far..it seems possible then that you could have a cam that is "too big" with ported heads because if you are hanging the valve open too long the port can become turbulant and reach the old point of diminishing returns so to speak?

So then is it safe to say that with ported heads, a larger lift rather than a larger duration becomes the more important aspect?

How about LSA when dealing with ported vs stock heads?

J-Rod

Glad you are enjoying it.

Remember duration is basically there to allow you to leave the valve open longer. The main gain to this is to allow the valve to be open long enough at higher RPM for the motor to get enough air and fuel to make power at X rpm. Well, a cam should be designed around the heads. But most cams out these days are "designed" to be used with ported heads. Folks are using tham with stock heads and seeing decent results, but I don't know of any cam specifically designed for stock unported heads.

You can overcam an engine there is no doubt. Its all about what you want the motor to do. But, a port becomes turbulent when the air comes "unstuck" from the wall of the port. The is a byproduct of port design. One of the things you will find is the stock port goes turbulent well before most ported heads. So, the big concern on a stock head is not having too much lift, as performance will drop if most of the time the port is open is in a turbulent region

Yes, and no. Provided you have enough clearance, you can offset lift with duration or vice versa, but most folks feel duration is a bit more important than lift. Air takes time to get moving. Think of it like liquid.. When you turn on the fauct a the house it take a fraction of a second to get to the bottom of the sink. Think of a cam the same way. Once its moving you want to use that moving column of air it as long as you can. Now, this doesn't take into consideration reversion, etc... I'm just simplifying it as best I can...

LSA is not what you worry about. Its about when to open and close the valves. You're heads are part of that equation. Look at what Chris said above about looking at what a head does and match cam profile to the head...

Jammer

iTrader: (1)

[LSA is not what you worry about. Its about when to open and close the valves. You're heads are part of that equation. Look at what Chris said above about looking at what a head does and match cam profile to the head...]

On the LSA subject.. (assume very good flowing ported heads)
Lets say we have 2 cams, both have same duration specs..for argument well say its a 244 XE intake Lobe and 248 XE-R Exhaust lobe. One runs a 108 and the other a 112.

All else being equal, would the 108 bleed off a little more from clutch dump off the line, allowing for perhaps less power to the ground than the 112? But then do better from say the top of 1st through the rest of the run at WOT.
Overall...On the other hand it would seem the 108 would do better NA and the 112 better on say a 250 shot? Any if any of this is correct, ..why?
Trying to understand one small aspect at a time.

SStrokerAce

iTrader: (2)

As J-Rod said LSA is a byproduct of the proper valve events. Usually the ICL will dicatate the LSA, but it's not a definate. Proper cam designs do not plan the LSA, that is just a byproduct of ICL, ECL, duration, valve events, desired overlap area. Overlap area is one of the reasons that we all talk about what LSA should I do this cam etc.... More overlap the less driveable the motor is at low RPM and low throttle settings, so to simplify we want more LSA to get less overlap. LSA is one of two things when determining overlap duration being the biggie. Less duration means less overlap for a given LSA. So that means that if you want to keep the same idle and increase duration you need to increase LSA, or if you want to decrease duration you need to decrease LSA.

Now the old wives tale of more LSA means a flatter TQ curve is not true. It's not the LSA's fault but the fact that most likely you are moving the ICL up so that is changing the intake closing event. I have yet to see a scientific dyno test (engine dyno not chassis dyno) that proves the wider LSA means flatter TQ curve. If it flattens out it means that you changed the events enough to negate some tuning effects at certain RPM.

Now J-Rods lobe comparison is interesting, very long and hard to follow. One thing you need to look at here is not just the similar duration numbers and compare other specs, but lobe/valve area numbers.

The lobe area is the key here, and with the 3731 and 3356 there is a big difference that is much easier to see in a graph than in a bunch of numbers but the area number still shows how much more is actually there.

3731 = 30.26 inch deg
3356 = 27.90 inch deg

Which means that the 3731 lobe has 8.46% more area. That means the lobe is open 8.5% longer letting in more air = more power.

Now the 3726 vs. 3356 comparison is interesting too....

3356 = 27.90 inch deg
3726 = 28.25 inch deg

So now the same .200 duration, 10 degs less .050 duration and still more area. 1.25% more.

If you want to get back down to the same lobe area then you have to go down to the 3725 lobe with 27.88 inch deg of area. That's a 230 duration @ .050 with 151 @ .200, looks like the extra lift helps that one out.

Now we have to remember that these lobes are also designed for different size base cirlces, a lobe on a BBC has a smaller base circle than it would on a LS1 with the same lobe. Cam bearing journal diameter is why. One of the good things of the LS1 is that the lobes can be aggressive since the base circle is so dam big.

So when all these guys wonder why LS1's are so quick part of it is the camshaft journal size. It allows us to run aggressive lobes which produce more lobe area in less duration so we can make tons of HP and TQ.

BTW I e-mailed J-Rod two graphs of these lobes being compared with one another so maybe he can post them.

Bret

Jammer

iTrader: (1)

I guess the question I'm trying to ask is, with regards to my above statement, will the 108 cause more reversion and bleed of too much cylinder pressure. The whole premise I'm trying to understand is what effects does a 108 have vs. a 112 all other things being equal? On the surface I would think the 108 would simply move the TQ up, producing more at higher rpms...cause the more overlap down low means less up top, when compard to the 112 . Am I way off base on this?
Is the 108 more likely to allow for a dirty intake charge and provide poorer cylinder pressure, and therefor poorer Torque for a large portion of the powerband?

And, am I off in my generic thinking that more overlap bleeds off compression/cylinder pressure...because I also understand that increasing overlap can, at times increase cylinder pressure...and bleding off pressure is actually due to the intake closing and exhaust opening events...not overlap at all which seems to be more convential thinking.

A lil' clarification over here!

For memorys sake, the 3720-3734 are XE-R, only correct me if I'm wrong.
SStroker- thanks!

99 Black Bird T/A

iTrader: (4)

Seems like that pretty much should destory the argument one should use stock pushrods with good sized aftermarket cams because the stock pushrod can act as a easy to replace "fuse" when P to V occures.

Katech basically said the samething a few years ago. That pushrod flex/deflection was a bad thing because it resulted in less valve train control.