Am I Going To Be Happy With This Camshaft?
These days though, a lot of them have more lift and duration on the intake side. I've never been convinced that works as well and Doug Dutra proved it did not with the slant 6.
Here's what I know from the math I use.
That as the bore to stroke ratio gets closer to 1.0 (the bore and stroke are the same) the more exhaust timing it will want.
As the rod to stroke ratio gets lower, it will want more exhaust timing.
Running the math for my 340 my math calls out a single pattern cam.
If I run the math for a 4.1 bore, 3.79 stroke it calls for a 14 degree split.
I know the math is very close because I had an engine on the dyno that used it and the torque and power peaks were exactly where the math said they would be.
I used to be pretty much opposed to a split like that. I'm still against buying a shelf cam with the de facto 4 degree split.
That's some marketing ****. I've run the numbers on lot cams and I've never seen this math call for a 4 degree split.
The least I've seen is 6 degrees and that was a Pontiac I ran the numbers on.
The other exception may be high RPM stuff that may be way over square and with a reasonable R/S ratio. They look like they want a bunch of split.
I also think that valve size plays a big roll in duration splits.
The smaller the exhaust valve the more split it will want.
I remember when I started building engines a 1.94 exhaust valve for a BBC was standard. By the mid 1990's I was going no bigger than a 1.88 and later on I tried to stay around 1.84.
That big exhaust valve takes up space that's better used for intake valve diameter.
Of course all this is NA stuff.