Possible insight into the TDB "cam wars"

[Joe R.]

Re: Possible insight into the TDB "cam wars"

Joe, I think the Comp Cam number you are pertaining to is 270H with a 270/270 overall duration and 224/224 @.050" with .470"/.470" lift, 110 lobe centers. This is a fast rise cam with only 46 degrees to split between rise and fall ramps below .050" lift. Understand this cam will greatly increase cylinder pressure due to shorter overall duration compared to an L79 (222/222) with 290 degrees. The lazy ramps of an L79 yields 68 degrees to split between rise and fall ramps below .050" lift.

Now on your "cam game boy" try the L79 specs with the fast rise/fall rates of the Comp 270H at 268 overall duration. I think you will find performance improvements.

Hi Gene:

I started the EA simulation process by simulating my engine with a variety of OEM hydraulic cams, and the L79 cam quickly rose to the top. It's actually quite hard to beat the L79 cam in this particular engine. The pocket ported heads with the higher E/I ratio favor a single-pattern cam like the L79, and the larger 383 cubic inch displacement is more tolerant of the 222 degree duration than a 327 would be.

No matter what I do, the fattest torque curve keeps coming back to a cam with durations of about 220 degrees. That leaves me with just the lobe centerlines to play with. With the stock exhaust system, an LSA that is larger than the 110 degrees of most aftermarket cams and larger than the 114 of the L79 looks best in the EA simulations. I'm tempted to try this with a custom cam.

I have decided to use a roller cam in this engine because I'm tired of worrying about ZDDP in the oil and cam break-in (been-there-done-that with my current engine). I also like the benefits of the faster ramp times that roller cams can provide. The Comp Cams 280HR comes close to being a roller version of the L79 cam, so this is where I ended up with in my EA simulations.

By the way, my "cam game boy" EA simulator bears out your view that the Edelbrock 2102 offers an improvement over the OEM 929 cam. The EA simulations show a very slight reduction in low end torque, but significant imcreases in high rpm torque and power. And these simulations assume a stock Corvette exhaust system.

So, maybe my "cam game boy" isn't so bad after all.......

[Duke W.]

Re: Possible insight into the TDB "cam wars"

Engine simulation programs are tools and guys misuse tools all the time. I've pointed out in the past that the value of simulations is the relative results, not the absolute results.

I've established baselines for various OE engines by tweaking the models to correlate as best as possible to chassis dyno test results. Then you make changes from there, and if a change like massaged heads yields 7-10 percent more power in the upper rev range that will usually show in the real world regardless of the absolute error.

Everything is relative!

As I pointed out in the Tale of Two Camshafts article, modern LS-X valve timing is very different than vintage Corvette engines and currently available aftermarket designs. Durations and overlap are modest, but the lobes are phased much later, and the same design philosophy works as well on vintage as modern Corvette engines. GM clearly figured something out here, but aftermarket designs haven't changed in 50 years. You look at various product lines from Comp Cams for instance, and almost all are ground on a 110 degree LSA with early lobe phasing. The only thing that changes is lift and duration. In fact, I'm convinced they are all ground from the same lobe master, and the designs are clearly not very creative. They are all "old school".

Everyone seems to have a favorite cam - probably the one that they bought for their engine. The Edelbrock 2102 has been mentioned before. The trouble with that cam and virtually every other aftermarket design is that they have more overlap than the 300 HP cam, so the idle behavior won't match the OE engine. When I went about improving the upper rev range power of the 300 HP engine, the boundary conditions were to maintain OE idle behavior with minimal loss of low end torque and pass a PV. I don't know of any aftermarket cams that will pass a PV in a base engine. They all have too much overlap that will roughen up the idle.

The people that really count in my book are those who modified and assembled their engines to my specifications whether using an OE cam of one of my designs. All the engines produced equal or better low end torque, significantly more top end power with the useable power rev range extended 500-1000 revs. They all idled just like the OE engine and used all the major OE components that can be identified in Flight Judging. One passed a PV and the others would have no problem in a PV as far as meeting overall OE engine behavior. In short, they met all design objectives and the owners are very pleased with the results.

The story continues with a '64 300HP being assembled with massaged heads and the McCagh Special camshaft, and I hope to see dyno test results this year. I think Crane has how made four or five McCagh Special cams, so other projects are in work.

Duke

[Gene M.]

Re: Possible insight into the TDB "cam wars"

[QUOTE=Duke Williams (22045);

..........Everyone seems to have a favorite cam - probably the one that they bought for their engine. The Edelbrock 2102 has been mentioned before. The trouble with that cam and virtually every other aftermarket design is that they have more overlap than the 300 HP cam, so the idle behavior won't match the OE engine....


Duke[/QUOTE]

OH, this is where you are WRONG. In actual real life I have done this and the difference can't be noticed at all.

Aftermarket cam went thru a pv no problem. It is best to verify a statement in actual practice and not just on a computer or on paper.

[Gene M.]

Re: Possible insight into the TDB "cam wars"

Hi Gene:.......

So, maybe my "cam game boy" isn't so bad after all.......

Joe,
First I hope you understand "cam game boy" is in humor, no insult intended.

Can you model modified faster rise and fall ramps with flat tappet cams? I think you will find the L79 fashioned this way would increase cylinder pressure a bunch by redesign of the lazy ramps to something like the Comp 270H.

See ya at Carlisle same spot.

[Duke W.]

Re: Possible insight into the TDB "cam wars"

OH, this is where you are WRONG. In actual real life I have done this and the difference can't be noticed at all.

Aftermarket cam went thru a pv no problem. It is best to verify a statement in actual practice and not just on a computer or on paper.

Okay, how about getting a Dynojet chassis dyno test and comparing it to John McRae's Special 300 HP configuration dyno test published in the Fall 2010 Corvette Restorer.

Get the digital files on a disk and we can plot the results for both engine on the same chart and post them here.

Duke

[Joe R.]

Re: Possible insight into the TDB "cam wars"

Joe,

Building a similar engine and will try the roller version of the L79. Going to use AFR 220 heads on it. Been shaved but using BRC flat tops.

Have never used the "high tech" charts etc. etc. Just ran the L79 up and down the street and kicked dirt in the face of all the LT-1 drivers. Can't hate that cam enough! Always liked the L79 for that reason.

Looking forward to seeing you in Carlisle. Come on by!

JR

[Clem Z.]

Re: Possible insight into the TDB "cam wars"

people who bought corvettes back in the day if they were interested in performance ordered at least 4:11 rear gears and the factory cams worked great with those gears. i even ordered my 454 450 HP 70 chevelle with 4:11 gears. i never worried about cruising down the highway turning 4000/5000 RPMs.

[Joe R.]

Re: Possible insight into the TDB "cam wars"

Joe,

Building a similar engine and will try the roller version of the L79. Going to use AFR 220 heads on it. Been shaved but using BRC flat tops.

Have never used the "high tech" charts etc. etc. Just ran the L79 up and down the street and kicked dirt in the face of all the LT-1 drivers. Can't hate that cam enough! Always liked the L79 for that reason.

Looking forward to seeing you in Carlisle. Come on by!

JR

Hi Joe:

Hey, that's great that you are working on a similar engine. Will it be a 383? Maybe we can talk engines at Carlisle.

[Joe R.]

Re: Possible insight into the TDB "cam wars"

Joe, I think the Comp Cam number you are pertaining to is 270H with a 270/270 overall duration and 224/224 @.050" with .470"/.470" lift, 110 lobe centers. This is a fast rise cam with only 46 degrees to split between rise and fall ramps below .050" lift. Understand this cam will greatly increase cylinder pressure due to shorter overall duration compared to an L79 (222/222) with 290 degrees. The lazy ramps of an L79 yields 68 degrees to split between rise and fall ramps below .050" lift.

Now on your "cam game boy" try the L79 specs with the fast rise/fall rates of the Comp 270H at 268 overall duration. I think you will find performance improvements.

Hi Gene:

I don't think the ramp rates make a big difference in performance, but for a given duration at .050, faster ramp rates yield a slightly larger "area under the curve."

The EA simulator allows you to specify a duration at .050, and then select from a list of ramp types such as "mild hydraulic flat tappet" or "aggressive hydraulic roller." When I make just this one change on the L79 cam, the difference for the aggressive roller ramp is small but positive across the rpm band, amounting to roughly 10 HP and 10 foot-pounds at the peaks.

From a performance perspective, I don't think there are any down sides to the faster ramps, but as Duke has often pointed out, the entire valve train takes more of a beating with the fast ramps. The spring rates have to be higher to control the valve closing, which leads to the need for screwed-in rocker studs and stiffer push rods. If the cam is a flat tappet cam, the risk of wiping a cam lobe increases too.

So, the fast ramp rates set off a domino effect that has to be carefully considered. I think the effects are manageable if the entire valve train is engineered as a system, but failing to do this can lead to problems.

[Joe R.]

Re: Possible insight into the TDB "cam wars"

Hi Joe:

Hey, that's great that you are working on a similar engine. Will it be a 383? Maybe we can talk engines at Carlisle.

Joe,

It's a 010 block 4 bolt. Kryptonite crank and rods for a 383 and bored 70 over. Had BRC's 60 over but the block was bored to TRW and Bow-tie rods. BRC's a little small for those TRW holes. Just enough to run a little oil thru. Boring to 70 will fix that. Had this combo in a 91 Corvette L-98 with an Ultradyne 276/284 R12 roller and 1.6 rockers on the intakes. Used a Lingenfelter Box, headers and a tuner down in Florida that took time to customize a chip to make it run.
Gonna put this in a 63 Roadster with a tube frame C-4 Suspension!
See you in Carlisle. Need all the suggestions I can gather.

JR

[Joe R.]

Re: Possible insight into the TDB "cam wars"

Joe,

It's a 010 block 4 bolt. Kryptonite crank and rods for a 383 and bored 70 over. Had BRC's 60 over but the block was bored to TRW and Bow-tie rods. BRC's a little small for those TRW holes. Just enough to run a little oil thru. Boring to 70 will fix that. Had this combo in a 91 Corvette L-98 with an Ultradyne 276/284 R12 roller and 1.6 rockers on the intakes. Used a Lingenfelter Box, headers and a tuner down in Florida that took time to customize a chip to make it run.
Gonna put this in a 63 Roadster with a tube frame C-4 Suspension!
See you in Carlisle. Need all the suggestions I can gather.

JR

Hi Joe:

Well, your 383 setup is going to be more extreme than mine. Since I am now thoroughly infected with "NCRS disease," I have decided to make my 383 look like a bone-stock L79. That way my Top Flight 67 can continue to resemble a stock, NCRS-correct car.

I even went to the trouble of finding a suitable 657 block so that I could keep the stock PCV system and the stock 67 valve covers. The only concession on the external appearance will be the use of the very similar looking Z28 intake instead of the L79 intake. Most people would never notice the difference.

If I didn't have these constraints on my build, I would probably have gone completely out of control and used a Dart block and AFR heads. I think it would be really fun to build a 427 small block using a Dart block. Maybe that will be what I do after the 383!

[Joe C.]

Re: Possible insight into the TDB "cam wars"

Hi Gene:

I don't think the ramp rates make a big difference in performance, but for a given duration at .050, faster ramp rates yield a slightly larger "area under the curve."

The EA simulator allows you to specify a duration at .050, and then select from a list of ramp types such as "mild hydraulic flat tappet" or "aggressive hydraulic roller." When I make just this one change on the L79 cam, the difference for the aggressive roller ramp is small but positive across the rpm band, amounting to roughly 10 HP and 10 foot-pounds at the peaks.

From a performance perspective, I don't think there are any down sides to the faster ramps, but as Duke has often pointed out, the entire valve train takes more of a beating with the fast ramps. The spring rates have to be higher to control the valve closing, which leads to the need for screwed-in rocker studs and stiffer push rods. If the cam is a flat tappet cam, the risk of wiping a cam lobe increases too.

So, the fast ramp rates set off a domino effect that has to be carefully considered. I think the effects are manageable if the entire valve train is engineered as a system, but failing to do this can lead to problems.

EA Pro (v 3.5) allows much more accurate modeling of camshaft ramp rates. The user specifies duration @ 0.050 and then one more duration........your choice either @ J604d ("seat-to-seat") or @ 0.200. Seat-to-seat is more meaningful, IMHO, because it is the so called "advertised" duration. Once these two parameters are calculated, the algorithm calculates a ramp rate which is based on the delta between these two parameters. The tighter the "delta" the more aggressive the lobe, the faster the ramp rate, the more "area under the curve". Consider the 30-30 cam has a "delta" of 56/56 int/exh, the LT1 a "delta" of 53/56 int/exh, and an aggressive solid roller such as mine, a "delta" of 38/38 int/exh. Full race circle track solid rollers have "deltas" closer to 30 degrees!

Does a faster ramp make a difference in power output? You bet it does! As you remember, when roller cams first became popular in the aftermarket in the late sixties, they were responsible or large power gains. That was no mere hype, as you know. My modeling of over 100 configs and using over 50 different vintage, and aftermarket cams, as well as custom designs shows the advantage of a roller setup over a comparable flat tappet cam. In all cases, two otherwise similar specification cams, one flat and the other roller show that the roller consistently delivers a much broader torque curve, with the power starting to come on earlier, and being sustained higher in the rev range than the flat tappet. You are making a wise decision by going with a hydraulic roller in your build!

To those skeptics who have little faith in the power of desktop dyno simulators, it must be pointed out thatthese programs are only as good as the people who use them. Bullshlt in........bullshlt out. One must be accurate in one's specifications when inputting information into these programs. The EA 3.0 is not a good predictor of engine output because of the importance of accurate input of camshaft parameters. The weak choices per ramp rates (i.e.: "mild" "moderate", "aggressive") do not go far enough and are a ballpark estimate, at best.

I eventually designed a 331 inch engine based on a solid roller version of the "30-30" cam. The program predicted the following SAE corrected (GROSS.........open headers, no accessories except water pump, 93 PON octane) values where the iterations were at 500 RPM intervals starting at 1500 and ending at 7000 RPM:

Peak flywheel power: 463 HP @ 6350 RPM
Peak flywheel torque: 433 ft-lbs @ 5200 RPM
Avg flywheel power: 303 HP
Avg flywheel torque: 359 ft-lbs
Torque comes on early. It develops 238 ft-lbs @ 1500 RPM.
Power is sustained well past the peak. 442 HP @ 7000 RPM.

Dyno test results bear this out.

[Joe R.]

Re: Possible insight into the TDB "cam wars"

Everyone seems to have a favorite cam - probably the one that they bought for their engine. The Edelbrock 2102 has been mentioned before. The trouble with that cam and virtually every other aftermarket design is that they have more overlap than the 300 HP cam, so the idle behavior won't match the OE engine. When I went about improving the upper rev range power of the 300 HP engine, the boundary conditions were to maintain OE idle behavior with minimal loss of low end torque and pass a PV. I don't know of any aftermarket cams that will pass a PV in a base engine. They all have too much overlap that will roughen up the idle.
Duke

Hi Duke:

I think the term "more overlap than the 300 HP cam" needs to be quantified and put into perspective.

As I understand it, the calculation that takes into account both the duration of the overlap and the lift profile results in a quantity called "overlap area". The EA simulator can calculate the overlap area for any specified cam, so I tried it out on several cams in their library. Following are the results:


Comparison of Overlap Area in sq. inch * deg:

Stock 327-300 (929) cam: 0.3

Crane 113941: 1.4

Edelbrock 2102: 1.5

Stock L79: 3.2

Com Cams 280HR: 5.5

Duntov: 6.0

Stock LT1: 8.1

Stock 30-30: 11.7



I have the Crane 113941 in my 327-300 engine, and Gene Mano has the Edelbrock 2102 in his. Both of us are very pleased with the idle characteristics and low end torque of these cams.

While both cams have slightly more overlap area than the stock 327-300 cam, they have a lot less overlap than the stock L79 cam, and WAY less than the stock Duntov, LT1, and 30-30 cams. By any accounting, the Crane 113941 and Edelbrock 2102 cams are fairly mild cams.

There might be a PV judge somewhere who could reliably detect the difference in how the idle characterics of these cams compare to the stock 327-300 cam, but I sure can't.

My guess is that either of these cams would make it through the PV process, although I have no plans to attempt a PV with my car. From a remark made by Gene Mano in an earlier post, it sounds like he has in fact passed a PV with the Edelbrock 2102 cam.

I think it is possible to increase the overlap slightly without it being detectable, but if you want to pass PV with an aftermarket cam, you just have to make sure you don't get too greedy in trading off overlap for higher top end power.

As I noted in my original posting, though, it does appear that *IF* the engine is running through a stock exhaust system, a custom cam can provide tangible benefits over a catalog aftermarket cam. With a custom cam that has a later intake closing and a larger LSA, you can manage to have your cake and eat it too. To me, this is the key contribution you have made to this debate, and it needs to be fully understood in its proper context.

So far, I'm leaning toward such a cam for my 383 project. Not because all the aftermarket cams are junk (because they aren't), but because most of them are not optimized for running through a stock exhaust system.

[Joe C.]

Re: Possible insight into the TDB "cam wars"

Hi Duke:

I think the term "more overlap than the 300 HP cam" needs to be quantified and put into perspective.

As I understand it, the calculation that takes into account both the duration of the overlap and the lift profile results in a quantity called "overlap area". The EA simulator can calculate the overlap area for any specified cam, so I tried it out on several cams in their library. Following are the results:


Comparison of Overlap Area in sq. inch * deg:

Stock 327-300 (929) cam: 0.3

Crane 113941: 1.4

Edelbrock 2102: 1.5

Stock L79: 3.2

Com Cams 280HR: 5.5

Duntov: 6.0

Stock LT1: 8.1

Stock 30-30: 11.7



I have the Crane 113941 in my 327-300 engine, and Gene Mano has the Edelbrock 2102 in his. Both of us are very pleased with the idle characteristics and low end torque of these cams.

While both cams have slightly more overlap area than the stock 327-300 cam, they have a lot less overlap than the stock L79 cam, and WAY less than the stock Duntov, LT1, and 30-30 cams. By any accounting, the Crane 113941 and Edelbrock 2102 cams are fairly mild cams.

There might be a PV judge somewhere who could reliably detect the difference in how the idle characterics of these cams compare to the stock 327-300 cam, but I sure can't.

My guess is that either of these cams would make it through the PV process, although I have no plans to attempt a PV with my car. From a remark made by Gene Mano in an earlier post, it sounds like he has in fact passed a PV with the Edelbrock 2102 cam.

I think it is possible to increase the overlap slightly without it being detectable, but if you want to pass PV with an aftermarket cam, you just have to make sure you don't get too greedy in trading off overlap for higher top end power.

As I noted in my original posting, though, it does appear that *IF* the engine is running through a stock exhaust system, a custom cam can provide tangible benefits over a catalog aftermarket cam. With a custom cam that has a later intake closing and a larger LSA, you can manage to have your cake and eat it too. To me, this is the key contribution you have made to this debate, and it needs to be fully understood in its proper context.

So far, I'm leaning toward such a cam for my 383 project. Not because all the aftermarket cams are junk (because they aren't), but because most of them are not optimized for running through a stock exhaust system.

Joe,

Very well written commentary!

Remember that the cam lift areas (units: "inch-degrees") that you specified above were derived using the guesstimates that are plugged into EA3.0's algorithm as "mild", "moderate" and "aggressive" "flat tappet" or "roller" lobes. Those lift areas, figured using more accurate ramp acceleration rates (based on actual rated durations @ specified lobe lifts) as is done with EA Pro will be different. Comparing lift areas that are within a 2 inch-degree variation based on those "guesstimates" is like adding .51 + .52 and then giving the answer as 1.030.

The rate at which the valve is lifted off of its seat during the early part of the lift cycle will also affect the exhaust note. A fast initial lift will impart a more "crisp" sound while a slow initial rise will not. I like to use the word "cadence" when describing how overlap affects idle characteristic.

[Duke W.]

Re: Possible insight into the TDB "cam wars"

Hi Duke:

With a custom cam that has a later intake closing and a larger LSA, you can manage to have your cake and eat it too. To me, this is the key contribution you have made to this debate, and it needs to be fully understood in its proper context.

That's something I stumbled across while playing around with different valve timing to maximize broad range torque/power. Then when I compared my designs to modern LSx designs I realized that GM had already discovered this, and it works as well on vintage small blocks as on modern LSx engines, the only difference being that massaged vintage heads yield a higher E/I ratio than LSx heads, so less exhaust duration is optimal rather than more. I discussed all this in the Tale of Two Camshafts article.

In one design I attempted to optimize a mechanical lifter cam for the OE manifolds/exhaust system and pocket ported heads with an E/I flow ratio of 0.80 using the three vintage small block OE mechanical lifter lobes without regard for idle behavior. The best average torque/power from off idle to 7000 occured at about 1.5 sq-in-deg overlap, but the long durations and wide LSA could not be ground on the available cam blank without reducing the base circle. The other issue was that the idle would be too smooth - not as smooth as the 300 HP cam, but noticeably smoother than any OE mechanical lifter cam.

It may depend on the PV judge as to whether the referenced Crane and Edelbrock cams would be detectable in a 327/300. A 327/300 should idle butter smooth at no more than 500 RPM, and I believe that increasing the overlap from no more than 0.5 sq-in-degree to 1.5 would be detectable. One poster in this thread made an implied claim that the Edelbrock 2102 passed a PV in a 250 or 300 HP engine, but his profile does not indicate this despite stating Duntov awards for two 350 HP Corvettes. The 2102 could probably pass a PV in a 350 HP engine.

The other issue is relative inlet/exhaust duration. Massaged heads need less exhaust than inlet duration, so the referenced cams would very likely work better if the lobes were swapped and the inlet phasing delayed, which is what I effectively did with the 300 HP cam to create the McCagh Special camshaft.

I have complete dynamic analyses of all the OE lobes, but nothing on aftermarket lobes despite trying to obtain some data. One vendor I visited had absolutely no written documentation on the lobes - just ancient lobe masters hanging on the wall.

Being as how the OE lobes and valvetrain have proven reliability, I wanted to retain it and not take any chances. More aggressive lobes that require greater spring force benefit engine performance, but can reduce valvetrain reliability and durability if taken too far.

Your summary of EA's effective overlap area seems to mostly jibe with what I have, but remember that it also takes into account valve size, so the Duntov cam has less effective overlap with the 1.72/1.50" valves used on most 283s, than the 1.94/1.5" used on 327s with the Duntov cam.

The value is also sensitive to rocker ratio and lash on mechanical lifter cams. As I've discussed before, actual small block rocker ratio varies from about 1.37:1 at the lash point to 1.44:1 at peak lift with an approximate 0.3" lobe, but EA doesn't allow variable rocker ratio, so I specify a fixed 1.44:1 rocker ratio and specify lash at 1.44 times clearance ramp height. Using suitable valve sizes for the engines, I think my models for mechanical lifter cams have somewhat less effective overlap than what you quoted, but they are still quite high - more than the OE engine configuration can effectively use - and cost considerable low end torque compared to similar durations with about 1.5 sq-in-deg effective overlap.

Nevertheless, as I've stated so many times before, the value of these simulations is in the relative results, not the absolute results as long as you input reasonable configuration data that represents as accurately as possible the complete engine from air inlet to exhaust tail pipe.

Duke