# Cam info



## Topkat (Sep 9, 2010)

I have a 67 GTO with the "S" cam 288/302 duration,
lift with 1.5" rockers .408/.407
LSA= 116 degrees.
Ive never drove the car and dont know what to expect performance wise.
I read Mr. Hands "How to build max perf. V-8's"
He says that wide LSA (Lobe seperastion angle) lowers compression and makes it run better on lamer gas. He also says they did this so the motors would last longer.
As well as shifting the power curve to the high end. (And this cam is the highest seperation the Pontiac put in the GTO)
He implies that Pontiac " dumbed down the motor"
Will a tighter LSA increase lower end torque?
I want the mighty beast to melt the tires from a dead stop. and into lower mid range
Is it that simple?
Thanks as always


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## jetstang (Nov 5, 2008)

This is a odd cam, short lift, long duration. They are compensating for lift with duration to make the cam thinks it's bigger than it is. The LSA of 116 is really high, and will kill top end power. This should be a great torque cam that is all in by 4000 RPMs.
What is the HP rating on this cam?
Personally, I would get a bigger cam. Unless the lift specs are at .050, then it's a different animal..
If that's at .050, then it's a big cam and they used the long lsa to get it to idle and have vacuum. A .500 lift with 288/302 with a 110 lsa will have a pretty aggressive idle and not make power til around 3000 rpms. While the 116 lsa will allow idle and pull the power band down.


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## 05GTO (Oct 6, 2004)

Lowering the lsa will decrease the fuel economy and the engine vacuum, if you go too low and have power brakes they will feel like manual brakes while idling thru parking lots, if your transmission is an automatic it may change the shift points and also require a stall torque converter.

As you decrease the LSA you will increase the overlap degrees that both valves will be open and if the exhaust is too restrictive the performance may be worst or stay the same. 

Just my humble opinion,


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## BearGFR (Aug 25, 2008)

Topkat said:


> He says that wide LSA (Lobe seperastion angle) lowers compression and makes it run better on lamer gas. He also says they did this so the motors would last longer.


Well.... sort of. But LSA -by itself- is not the whole story. In fact, it's sort of an indirect in the way it affects compression. What really matters when it comes to compression is the point at which the intake valve closes in relationship to crank degrees. That rising piston can't compress anything in the cylinder until that intake valve shuts, right?, and the later in the stroke that intake closing event happens (the piston is farther up the cylinder) then the less pressure you're going to get. If you've got two cams, one with an LSA of 110 and another with an LSA of 116, and they are installed "straight up", then the wider LSA will indeed have a later intake closing event and will make less cylinder pressure. However, if you install both cams with the same intake centerline (say at 106 degrees ABDC) then both cams will make exactly the same cylinder pressure because that intake closing event is happening at the same time with both of them. 
Most aftermarket cam suppliers provide a spec card that states how their cam should be installed in the engine "for best results", and almost without fail that installation spec will be in terms of where you should place the intake centerline. Doing that is what's called "degreeing the cam". 

Can you "play" with the spec? Sure. "Advancing" the cam (moving the intake closing event earlier) will result in more cylinder pressure and will tend to move the torque/power curves lower in the rpm range and sacrifice torque/power at high rpm. "Retarding" the cam (moving the intake closing event later) has the opposite effect. Don't expect to use cam timing alone though to control compression and resulting detonation. On my engine, retarding the cam a full 8 degrees (that's a TON) from the cam manufacturer's specs would only drop peak cylinder pressure by about 18 psi, but the resulting "hit" on the torque curve would cost me about 2-3 tenths in e.t.

Bear


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