Cam Gurus....
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 3,399
Likes: 278
From: Olmsted Falls, Ohio
Cam Gurus....
Assuming the cam is factory installed "straight up", what changes in performance could I expect to see if I advanced the cam 4 deg?
Stock L82 cam: .450"I/.460"E lift, 222I/222E deg duration, 114 degrees lobe separation. 205hp@4800rpm and 255tq@3600rpm
Thanks,
Stock L82 cam: .450"I/.460"E lift, 222I/222E deg duration, 114 degrees lobe separation. 205hp@4800rpm and 255tq@3600rpm
Thanks,
Pro
Joined: Aug 2001
Posts: 605
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From: hamilton square NJ
Re: Cam Gurus.... (KenSny)
I remember reading something about that. I believe that you gain more on the top end of the engine and lose some of your bottom. I'm not too sure on that one though :chevy
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 3,399
Likes: 278
From: Olmsted Falls, Ohio
Re: Cam Gurus.... (Ganey)
Ganey, that's what I was thinking. Does it mean that advancing 4 deg means that the intake opens 4 deg sooner and the exhaust closes 4 deg sooner during overlap? If so, does it follow that the effective LCA is now 110?
Would it follow that retarding 4 deg would "help" high end?
[Modified by KenSny, 9:58 AM 8/7/2001]
Would it follow that retarding 4 deg would "help" high end?
[Modified by KenSny, 9:58 AM 8/7/2001]
Melting Slicks
Joined: Mar 2000
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From: WANTED: '68 rear valance with b/u light assemblies IM, e-mail, or PM me here. Thanks!
Re: Cam Gurus.... (KenSny)
Assuming the cam is factory installed "straight up", what changes in performance could I expect to see if I advanced the cam 4 deg?
Stock L82 cam: .450"I/.460"E lift, 222I/222E deg duration, 114 degrees lobe separation. 205hp@4800rpm and 255tq@3600rpm
Thanks,
Stock L82 cam: .450"I/.460"E lift, 222I/222E deg duration, 114 degrees lobe separation. 205hp@4800rpm and 255tq@3600rpm
Thanks,
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 3,399
Likes: 278
From: Olmsted Falls, Ohio
Re: Cam Gurus.... (63Banshee)
63Banshee - Good suggestion for all of us. That's exactly what I've been doing, reading some books by David Vizard. Sometimes he gets carried away in providing a lot of test results to state the answer in just a few sentences. But I tried to glean enough to ask the question for clarification since I was not talking about an aftermarket performance cam.
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
Re: Cam Gurus.... (KenSny)
Ken, factory as well as aftermarket grinds have the LCA selected to provide a good balance between low end torque and top end power. Most of the time this means they are ground with 4 dgr advance (i.e. using a straight up chain/sprocket will yield 4 dgr advance).
Advancing the cam beyond with the cam grinder has done with an offset sprocket will give you slightly better low end, but it will take more of fthe top end than you gain down low. Think of it as a bell curve.
In some rare cases advancing or retarding a cam makes sense, but this is probably because the wrong cam was chosen in the first place.
One case I can think off would be a drag car that because of gearing hits the traps at too high rpms, and also has traction problems. In this case retarding the cam makes sense to kill some low end (regain traction) and give a few hundred more useable rpm up top for the traps.
Advancing the cam beyond with the cam grinder has done with an offset sprocket will give you slightly better low end, but it will take more of fthe top end than you gain down low. Think of it as a bell curve.
In some rare cases advancing or retarding a cam makes sense, but this is probably because the wrong cam was chosen in the first place.
One case I can think off would be a drag car that because of gearing hits the traps at too high rpms, and also has traction problems. In this case retarding the cam makes sense to kill some low end (regain traction) and give a few hundred more useable rpm up top for the traps.
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Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 3,399
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From: Olmsted Falls, Ohio
Re: Cam Gurus.... (zwede)
zwede: What I was thinking tho was that the '75 was truely de-tuned for smog reasons (down from ~250 hp to 205 hp). Other than the cat exhaust restricting the engine, and some leaning out of the carb, everything else "seems" to be the same as a '74 L82. Now if the '74 cam grind was totaly different than that's where the major loss occurs, but I actually don't see that much difference in the specs.
Yes, yes, I know, stop all this guessing and just go ahead and install a new cam. Well, maybe late next year (probably a Comp Cams XE262), but this year is new heads (World S/R Torquers). So I was thinking of pulling the water pump and timing chain cover to try a few things first. I need to install a new oil pan gasket and probably a timing chain gasket because of leaks.
Maybe I'll just "bite the bullet" and do it all this winter. Geez, the wife will rant and rave, but maybe I can live in the garage most of the day....
Yes, yes, I know, stop all this guessing and just go ahead and install a new cam. Well, maybe late next year (probably a Comp Cams XE262), but this year is new heads (World S/R Torquers). So I was thinking of pulling the water pump and timing chain cover to try a few things first. I need to install a new oil pan gasket and probably a timing chain gasket because of leaks.
Maybe I'll just "bite the bullet" and do it all this winter. Geez, the wife will rant and rave, but maybe I can live in the garage most of the day....
Race Director
Joined: Sep 1999
Posts: 11,361
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From: Plano TX
Re: Cam Gurus.... (KenSny)
Ken,
The drop from 74 to 75 is almost entirely because of the cat. The early monolithic cats easily cut 40-50 hp. Replacing that piece of junk with a modern cat will free up almost all of the loss. That change alone (with re-jetting of the Q-jet) should put you on par with the 74 at 250 hp. For good cats, look at random tech and dynomax.
The drop from 74 to 75 is almost entirely because of the cat. The early monolithic cats easily cut 40-50 hp. Replacing that piece of junk with a modern cat will free up almost all of the loss. That change alone (with re-jetting of the Q-jet) should put you on par with the 74 at 250 hp. For good cats, look at random tech and dynomax.
Thread Starter
Melting Slicks
Joined: Apr 2001
Posts: 3,399
Likes: 278
From: Olmsted Falls, Ohio
Re: Cam Gurus.... (zwede)
zwede - Thanks, I'm currently running with no cat, 2-1/2 duals all the way back, no other smog stuff is on the engine anymore. I had Lars rebuild/rejet the carb. I also rebuilt the distributor and changed the advance to 36deg in by 2800rpm and about 16 deg at idle now. Just looking to see what else I can squeeze out of it this year.
Race Director
Joined: Apr 1999
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From: CORVETTE 77 385 C.I. TEXAS
Re: Cam Gurus.... (KenSny)
L-82 cam is same. Exhaust & tuning gets 250+. http://www.corvetteforum.cc/ubb/Foru...ML/008082.html
Heads are a good idea. Large valves & cam 335+.
:cheers:
Heads are a good idea. Large valves & cam 335+.
:cheers: