Camshaft ideas/theories

[houser45]

Ok i am wanting you cam experts to explain what these different cams will “act” like in the same exact engine. 360 cu inch injected alcohol sprint car engines. 14 to 1 compression, solid rollers. The first is a 264/268 @.050 106 lsa. The second is a 259/272 @.050 106 lsa. Same engine, how will the engines act?

[408 Nova]

About the same. There is not enough of a difference in them to make any noticeable difference in the way the engine idles, comes up on the cam, or performs on the track at your cubes and compression. That's assuming the lobe profiles are very nearly the same on both cams.

[Geoff2]

Bigger cam might raise TQ & HP by 100-300 rpm.

[CamKing]

Assuming the lobes all come from the same lobe family, with the same lash settings, the smaller cam will move the power curve down about 200rpm.

[houser45]

And we are calling the bigger of the two cams the 264/268? Correct? Will the peak torque be higher and narrower on the 264/268?

[CamKing]

And we are calling the bigger of the two cams the 264/268? Correct? Will the peak torque be higher and narrower on the 264/268?

Yes, the 264/268 is the "bigger" cam.
The Peak torque would be higher, but so would peak HP, so the torque curve would not be narrower, unless the ports don't allow the bigger cam to move peak torque up.

[houser45]

Thank you, so if the engine was “acceptable “ as far as drive ability was concerned, what would be the advantage of using the smaller of the two?

[CamKing]

Thank you, so if the engine was “acceptable “ as far as drive ability was concerned, what would be the advantage of using the smaller of the two?

With the same gear, it would come off the corner harder, and be faster on re-starts.
If you can change gears, so the engine is coming off the turns 300rpm higher, and the heads allow the larger cam to make power 200rpm's higher then the smaller cam, then the larger cam would come off the corner just as hard, and pull harder past the flag stand.

[houser45]

Thank you, so if the engine was “acceptable “ as far as drive ability was concerned, what would be the advantage of using the smaller of the two?

With the same gear, it would come off the corner harder, and be faster on re-starts.
If you can change gears, so the engine is coming off the turns 300rpm higher, and the heads allow the larger cam to make power 200rpm's higher then the smaller cam, then the larger cam would come off the corner just as hard, and pull harder past the flag stand.

Ok, now add mufflers to the equation? Does this change anything? The added duration exhaust of the smaller cam help ?

[CamKing]

adding exhaust duration with mufflers does not help, and can actually hurt the top-end power. There's nothing you can do with the cam, to make a muffler less restrictive. The only thing you can do with the cam to help, is to widen the LSA, but keep the ICL the same. This will open the exhaust valve earlier, and close it earlier. The earlier closing reduces the amount of time the exhaust pressure can contaminate the intake charge, during overlap.

[houser45]

Ok. Thanks for the responses.

[cjperformance]

adding exhaust duration with mufflers does not help, and can actually hurt the top-end power. There's nothing you can do with the cam, to make a muffler less restrictive. The only thing you can do with the cam to help, is to widen the LSA, but keep the ICL the same. This will open the exhaust valve earlier, and close it earlier. The earlier closing reduces the amount of time the exhaust pressure can contaminate the intake charge, during overlap.

Amazing how many dont get this, and want more duration to 'make up for' muffler restrictions

[F-BIRD'88]

Is tge valve lash the same on bo?h cams? If its a bigg difference the effective net running duration could be a wash. The net effective valve open AREA could also be pretty much a wash, depending...

In other words not enough info on these two similar cams ...

[houser45]

.008” lash on both.