quote:Originally posted by George P:quote:
Originally posted by Jake:
... Said we were giving up some low end power with the 114 deg lobe separation angle ...
I strongly disagree with him because your motor is a Big Valve motor. I'll guarantee you he's wrong. With the big intake valve, and canted valve geometry the effects of overlap are amplified. You want to minimize overlap to optimize low rpm power, improve drivability, improve vacuum at idle. The lobes were chosen based on 114 degree LSA, and the way they interact at top dead center, in the overlap period. The lobes are pushing the limits for the boundaries I established. As far as I'm concerned, 112 degree LSA screws that up a bit. It will still work, but not the way he's telling you it will work. Expect drivability and low rpm power to be worse, not better.
Wider LSA results in opening the exhaust valve earlier which also improves high rpm over-rev when mufflers are involved. This is why they say narrow LSA cams put more demand on the exhaust system, i.e. the system must be better designed and have low back pressure.
There is a lesson here for the unwary.
Many many mechanics, cam grinders, engine tuners, exhaust specialists, carb specialists ect have small block Chevy indelibly etched into their minds, Even if they are aware of the differences it seems hard for them to eradicate the Chev influences. So the 351C gets treated as if it was a 350 Chev.
This is a Catastrophic Error.
The 351C is a completely different beast to all other comparable engines and must be treated as such.
Make sure any experts you speak to truly understand the difference or performance will suffer.
I have come across this phenomenon often and seen the results as being a very "average performing" 351C and upon conversing with those involved discovered the build been viewed through the 350 Chev prism, this then led to the engine as being christened a "dud" because it did not perform to expectation when really the "duds" were those that did not understand the 351C.