540 RAT

Here is a reply from Joe Sherman, responding to this discussion on another Forum:

"Here is a cute little story. Years ago, I tested a 280 Comp magnum against a 280 Isky Mega hyd--- The Isky beat the Comp every where by up to 18 to 20 HP, and 18 to 20 ft lbs-- I am sure it was the Isky was on a 108 and the Comp was on a110-- Some trhings just dont change."

JOE SHERMAN RACING


Joe also said:
"Its always been this way, and probably always will."

63mako

No they didn't use a thumper cam but:

Yet Comps Technical FAQ page clearly states "Wider LSA = wider powerband.
Comps "Thumper" line with it's narrow LSA is only mass produced by them. They have a "Market nitch" and this article is attempting to exploit that. These are built to sound like a performance build without the performance, not to produce the most street power.

Almost every cam manufacturer uses a 110 or 112 LSA in their full line of street performance cams. Why would they do this if that is not the best street performance option? The street performance, 4x4, marine, nitrous, turbo, are all 110 or higher. Marine cams are a great example. You want them to pull hard from the bottom end all the way to top RPM, kind of like a true street performance engine. Most are ground on a 112 LSA. The new Corvette ZR1's are ground on a 118 LSA. Think they do this to lower power output?
The only aftermarket factory grind 107 or lower LSA cams are circle track or pro stock, drag race cams which operate in a limited RPM range and bottom end power is no concern.

rham

I am not trying to say this is not a Comp add, I was referencing the fact that the icl's were not constant as mentioned by gskull. If you change the lca and don't change the icl then that is not a true apples to apples comparison either as most performance cams are ground with 4 or more degrees advance, Comp uses 4 on most of their cams.

I agree the cr needs to change to make things even.

It is just ironic because Vizard who has no cam allegiance has been pushing this for years and when a cam company who grinds most of their cams on a 110 lca grinds one on 107 everyone is quick to cry wolf.

rham

Each cam has 6 degrees difference from ex open to int close which indicates the lca is being spread. I dont understand your point.

63mako

David Vizard is right. 108 will make more peak power in this application due to higher DCR and higher cylinder pressures among other things. His chart calls for 108 on my 383 build for best power and torque. No arguement, he is probably right.

Problem is with all things equal the DCR with 108 goes past the point I can use pump gas. Detonation becomes an issue. Also the bottom end is soft, and idle quality sucks. I would have to rev it and slip the clutch to take off, and the vacumn drops to the point power brakes, headlight operation and wiper operation would be an issue. That is where streetability and intended use comes into the equation.

Basicly, if we all built for maximum power with that the only consideration, all our cars would suck to drive on the street. The dyno charts starting @ 2500 never account for this. They need to chart from off idle to maximum HP to get a true picture on a street build. I see both sides with many years of racing and many years of street car building experience. Others with similar experience have reached the same conclusions as evidenced in their builds.

DRIVESHAFT

On the 107 lsa cam, the intake opened at 21° BTDC and the exhaust closes 16° ATDC. They were opened at the same time for 37°.

On the 110 lsa cam, the intake opened at 18° BTDC and the exhaust closes 13° ATDC. They were opened at the same time for 31°.

On the 113 lsa cam, the intake opened at 15° BTDC and the exhaust closes 10° ATDC. They were opened at the same time for 25°.

The overlap for the three differnt profiles was 37°, 31°, & 25°. It was definitely three different cams.

rham

I agree with that, but Vizard talks of making max power in the rpm band you are using- not just peak power. He recommends lower overlap values for street driven cars to keep vacuum up. But his point is that the lca should be constant so if you have to decrease duration to make it work with the lca then that is what you do. I dont know if he is right but he makes a good argument.

63mako

With a given compression you have 2 options. With a build if you start at 110 LSA and are on the verge of detonation and you increase to 112 you can decrease your duration to maintain DCR.
The 112 with less duration will lose some peak HP and torque but maintain streetability with a flatter torque band and better vacumn pulling better off idle.
If you go to 108 you have to increase duration to maintain DCR. The 108 with more duration will make more power and torque with the tradeoff being less streetability, vacumn and a narrower but higher powerband. All depends on your intended use.
You can't go off a dyno chart that starts at 2500 RPM to see this difference! That chart will show the 108 is the cam to use in most instances.

rham

I am not trying to ruffle feathers I am just trying to learn. I have raced dirt track cars in the past but I am building a mild 355 in a 78 and just want the most bang for the buck out of the cam. Using Vizards book I have come to a cam spec of 262/262 at 108 lca ground at 4 degrees advanced which gives an overlap of 46. I also looked at Lunati's VooDoo 262/268 and was wondering if it would work better. I know dyno graphs dont show under 2500 but does the power drop off that sharply? Here is a graph from a Vizard engine, also a link to the article.


Dyno Results

TESTED AT SPEED-O-MOTIVE
DTS ENGINE DYNO

RPM TQ HP
2,600 389 193
2,800 401 214
3,000 401 229
3,200 406 247
3,400 414 268
3,600 425 291
3,800 433 313
4,000 439 334
4,200 443 354
4,400 445 373
4,600 445 390
4,800 443 405
5,000 438 417
5,200 431 427
5,400 423 435
5,600 414 441
5,800 403 445
6,000 391 447
6,200 379 447

http://www.popularhotrodding.com/eng...ock/index.html

63mako

Read the article. Looks good on paper. With 10 to 1 compression, iron heads and a 224 duration cam with 108 LSA I am very suprised it has no issues running on pump gas. Being able to dial the timing back to 34 helps. The factory roller cam vortec truck block is a great starting point. The 224 cam won't give up much bottom end either, even with a narrower LSA but they did mention the torque started pulling well @ 3000 RPM. Gearing can really make a difference in your bottom end performance on a stock stroke build like this. With 3.70 gears it will perform much better than a 3.08 which could be a slug until you get the rpm up. Build it. Let us know how it runs.

540 RAT

Dude, you are WAY too cynical for your own good. Jeez, lighten up. Nationally known Pro Engine Builder and winner of the first Popular Hotrodding Engine Masters Challenge said this:


"Years ago, I tested a 280 Comp magnum against a 280 Isky Mega hyd--- The Isky beat the Comp every where by up to 18 to 20 HP, and 18 to 20 ft lbs-- I am sure it was the Isky was on a 108 and the Comp was on a110-- Some trhings just dont change."

JOE SHERMAN RACING


So, I suppose you are going to say that Isky sponsored that test, right? Get a life. I'm guessing you must be running a wide LSA cam in your motor and are feeling insecure about it. There is no other reason for you to be making such a big stink about this. If you know so much, then explain why the Godfather of Engine Building, Joe Sherman above, has seen this same thing throughout his entire career, if it isn't valid. And why the same thing turned up with the winner of the Big Block Engine Masters Challenge a couple of years ago, if it isn't valid.

540 RAT

You are absolutely correct, they are for sure 3 different cams. What's so hard to see about that? Maybe gkull's calculator had dead batteries.

gkull

I see now where i was wrong. A fair test would have open all intakes at the same time

MotorHead

I heard you were supposed to lose torque when going from a dual plane to a single plane, someone told me this at a car show a while back

63mako

I never said it wasn't valid. On the contrary. Reread post # 27. Joe Sherman is a race engine builder. The Engine Masters competition is also only about building for absolute maximum HP. Neither really gives a crap about street manners and for their intended purpose they are correct as is David Vizard when he says you will pull the most power out of a 383 with 2.02 valves with a 108 LSA. If you read my posts carefully I do say you will give up a little maximum HP and torque for street manners by going with a wider LSA in all my posts. This is a fact and I don't dispute this in anything I have posted. You will also have a smoother idle, better vacumn and a wider powerband with a wider LSA. This is also a fact that you can't dispute. I have a wider lsa cam for the reasons I mentioned and because I have a 150 nitrous shot on top of a cam and compression that is at the limits of safe DCR even with the wider LSA. Engine built as a matched unit for my intended purpose. It won't be the fastest down the quarter mile. Is yours? Gkull runs a dyno for a living and road races his car competatively. He is running a 112 LSA. I have seen and owned cars that are overcammed and have had to change more than a few out because of it. I have had to change gearing to more closly match my engine build as well. Cam selection is not a one size fits all. Do what you want, even if you want to insult me, I really don't care. Just trying to contribute.

TheSkunkWorks

I believe it has been well established that the subsequent effects of having not kept the intake valve closing (IVC) events constant somewhat skews the test results within the article, making them difficult to quantify objectively; the fly in the ointment being that CR's were not adjusted appropriately in compensation for that variance (read, "too expensive to have been practical"). For those who don't understand the role IVC timing plays in DCR, VE%, cylinder pressures and such (which significantly influence the size and shape of an engine's power curve), it might be easy to miss that point. What I have a problem with is that there was evidently no mention of this "little" detail in the article.

Had CR's been duly adjusted in the name of pure science, we would nevertheless be viewing the combined effects of more overlap w/earlier IVC's vs. those of less overlap w/later IVC's. However, while the former would most probably still have had higher peak power, it's not likely it would have had much, if any, more average power under the curve. Had IVC's been kept constant, which wouldn't have warranted CR adjustments, we would have been looking at the combined effects of more overlap w/later exhaust timing vs. less overlap w/earlier exhaust timing. IMHO, this would have been a more fair comparison, but at the end of the day one simply cannot completely isolate the effects of changing LSA from secondary consequences resulting in the process, and I'm a bit disappointed that the published results evidently weren't better qualified with explanations of such subtleties.

63mako

Exactly my point. That keeps peak cylinder pressures equal in all tests. That would be a much more fair test.
And for 540 RAT, Here is some corespondence I had with Rich Lear when designing my build. The -4 numbers are retarding the cam for optimum cylinder pressures. This build is a crappy 114 LSA HR cam in a 383 with tiny AFR 195 competition ported heads.
I installed mine straight up and sacrificed 16HP of peak power to live in the RPM range I want to use, keep cylinder pressures at or under 100% VE to avoid detonation issues and be able to use the nitrous safely. Should still be pushing 700 HP with a little 150 shot of nitrous. Looking for streetable power not maximum possible. If you notice 4 degrees change of the intake valve closing makes 16 peak HP difference. This wasn't even mentioned in your "head to head" test. Yet they moved that closing point 3 degrees then 3 degrees again. Good guess. Would you feel "insecure" about the choice if you were me?

63mako

Well, I obviously know more than you so I will take a shot at explaining it to you.
Both cams are single profile, Both cams have 280 advertised duration.
The Isky cam has .485 lift and 232 duration @ .050.
The Comp cam has .480 lift and 230 duration @ .050.
Faster ramp rate = more power.
Keeping the valve open longer at a higher lift allows more cylinder filling = more power.
I would bet the intake closing point might well be a couple degrees later on the isky cam also due to comp grinding their cams 4 degrees advanced and the Isky having a tighter LSA.
This would allow better cylinder filling and VE = more power
I would also bet the Comp cam has better street manners.
Is that another "apples to apples test".

I try not to resort to personal battles on here but explain the whole picture if I have a valid point. It is a forum and others who are looking for something other than absolute maximum power need to be made aware of some of the consequences of their choices.
You have chosen on numerous occasions to personally attack mine and others viewpoints if they are not the same as yours. It is usually by quoting a magazine article or someone elses opinion taken out of context. If you chose to make personal attacks or insult someone elses intelligence you should take it to PM and or be prepared to back up what you say with real facts, your own knowledge, or experience not something you read or a quote taken out of context.

cardo0

This 18-20hp is more of what i expect than the <10hp difference found in the Chevy HP mag test. For less than 5hp its not worth the effects of greater overlap. But for 20 ponies or 20 ft-lbs it is.

There is a limit for each engine/head/vlv size combination. It has to do with exh scavenging and maximizing cyl filling. Yes Vizard says 108 is best for 350" sb with the stock type head and 2.02 vlvs. But other things like bigger vlv heads, roller cam, rod length and diffinatly cubic inches all have an effect. For ex 383" with 2.02 vlvs in a stock head - 106 is optimum.
But hey lets look at short circle track 350" racers. Try like 105 LSA for their cams. They need max mid range torgue out of the corners and may never see 5,500 rpms before the end of the tiny straight.
Everyone has to evaluate there eng combo for what is optimum.

Glad to see others here understand what Vizard has provided for very little cost in his books. Read more, send less, go faster.

cardo0

63mako

OK Last post. Read the graph on post # 1
With the DP the 107 cam has 4 peak HP more and 14 ft. lbs more peak torque than the 113 LSA cam.
With the SP the 107 cam has 1 peak HP less and 12 ft. lbs more peak torque than the 113 LSA cam.
The average HP drops 17 and the average torque drops 14 going from the 107 to 113 cam. This is less than 3% on this motor. Trust me you won't feel a seat of the pants difference with a 3% drop in power. Most of this difference due to decreased cylinder pressures with the 113 cam due to a 6 degree earlier intake closing point! Retard the 113 LSA cam a couple degrees or increase static compression a little to maintain comparable DCR and you will make this difference up. (See what 4 degrees retard does to peak power with a wide LSA in post #37) If any of you have ever driven a 600 HP, 11 to 1 small block the biggest issue is making it streetable. The streetability difference (idle quality, vacuum, Low RPM manners) between a 107 LSA cam and a 113 LSA in this build would be night and day. Done argueing with everybody on this. Do what you want.