RevTheory wrote: ↑Sat May 19, 2018 11:26 am
What some of these usual characters refuse to acknowledge is that what Vizard did was compile over 10,000 dyno tests and do his best to make one part of cam selection as easy as possible for an engine platform that's still wildly popular. He's not talking about bandaids for intake-limited class racing or NASCAR or sled pulling and he's said as much. You only have to read what he has written.
His whole premise was to get you close enough to optimum that you could either go to the dyno with it, run an ICL sweep, rocker sweep and lash sweep (if solid) and nail it down flat (as opposed to showing up with a wheelbarrow full of cams that are all over the place) or if that isn't possible, and it so-often isn't, just install the damn thing and know that you're pretty damn close. And way closer than if you'd spent a half-hour reading the descriptions from 5 different cam companies. "Noticable idle, strong torque, 1,800 to 6,200 rpm, 283 to 400 cid."
I don't know why (actually I do) these same guys won't just see it for what it is. The argument that it doesn't work for 4-valve, 15,000 rpm Jap bikes or diesel container ships is horribly dishonest. A wise man would know what it's for and where to use it. Why the desperate attempt to "prove" your intellectual superiority? It seems you're doing the opposite.
If I was building my first 383 and following David's lead, it would be 10.5:1 compression, Air-Gap intake, 195cc heads with a 2.05 intake valve and cammed 274 at .006 on a 107 based on his overlap charts and 128. Right out of the gate. Now tell me how "wrong" that is.
Sure, if you want to get into the hows and whys, you can start digging deep into things. None of us have ever argued against that. Some of you just go out of your way to take what David has taught in a 124 page book and try to just crush it with things it was never intended to do.
Exercise a little common sense and some wisdom. If you scroll down to the bottom of the page and choose a cam for a restricted, dirt track class to throw in your boat, it's on you. Use the information as intended.
I would have to know where you'd want the horsepower to peak, how much vacuum you needed, what the heads flowed, what it's going in, the vehicle weight, the transmission, the rearend ratio, what you're doing with it, and a million other things.
No one here can tell you where that cam will peak without the .050" duration, how the heads flow, what the lift is, etc....and for crying out loud, whether or not it's a hydraulic roller or a hydraulic flat tappet.
Your 274 @ .006" cam could be a 218 @ .050" quiet lobe that's easy on the valvetrain, or it could be a 226 @ .050" spring eater.
That's the issue with formulas. There's too many variables to come to any conclusion.
I had a very high-reputation cam grinder make a camshaft for a SBF build that I was doing, based on some "software". It was 28 peak hp down to a cam that I had spec'd and down over 10 average hp, with the same torque, and within 200 rpm of the same hp peaks.
A piece of software may get you close, but without experience on a certain engine family, or trying a hand-full cams, IMO, you're gonna miss the boat.
One of my pet peeves is hearing someone say, "I have a cam ground by so-and-so and it's perfect!" How do you know? How many different cams did you try?
