Ok, i'm in the process of choosing parts for my 383.


i have a one question.

ok
AFR heads flow 275cfm on the intake side, and 195cfm on the exhaust side. (thats at .500 lift) (AFR 195's)
so the intake flows much better than th exhaust.

now can someone explain a what it takes to match a cam to heads cause from what i understand. a good motor must have the heads and cam work together.

is it best to have a custom ground cam?

what kind of cam should i be looking for or how do i find the right cam.

 

IMO, a custom ground cam will always be the best for performance...but not the wallet.

I've read great things about the LPE 219/Superram. Also, an XR276 seems to work well with a Stealthram, what kind of intake will you be running?

-Rippin

 

A custom ground cam is only better if the designer came closer in his design to what your other components will work best with than an off-the-shelf cam comes.

Definitely not always the case.

A custom ground cam costs $25 more than an off-the-shelf one. If you think you can do better than professional cam designers with engine dynos and lots of experience with motors alot like yours, try your hand at it.

As far as matching the cam to the heads, look at your engine's intended RPM range, and its exhaust-to-intake flow ratio, and the lift at which "port stall" occurs. Ideally you'd want a cam that has the correct intake duration for the RPM band you want; a split pattern higher on the exhaust side if the E/I ratio is less than about .72, a single pattern if it's between .7 and .8, or a pattern split toward the intake if it's higher than .8 (obviously the ranges overlap somewhat); and peak lift such that the port approaches or just barely reaches "stall" for a few degrees at the very peak of its lift so that it flows as much as possible of the valve cycle. Then tune the "sharpness" of the torque peak and the RPM it occurs at with the lobe separation and intake centerline.

If you don't have to ask what all of those things are or how they work, you might be able to specify a custom cam that will out-perform an off-the-shelf one.

 

ok,
its off the shelve cam then.

now i just don't know what cam to pick then.

its going in a 383, AFR195's(CNC) and miniram.
10.5:1 compression
motor will be NA

car will have a 2800 stall
and i would like her to have power from 2500-6000rpm

Good idle but i want it to really wake up after 3500rpm, and pull like a raped ape after that. Any suggestions for a cam are greatly welcomed.

I wasn't asking if i should get a custom cam. more or less i was asking is it better to get a custom cam, and have someone do the motor tan get an off shelve cam?

 

A custom cam is better, if and only if: your engine combination is sufficiently unusual for its intended purpose that there are no off-the-shelf grinds that are appropriate; and you, or your cam designer, can characterize the motor's needs sufficiently accurately to produce a better match for what the motor wants than you can go out and buy.

It's not like the act of some person other than a cam compnay grinding a cam, or specifying the grind, is some kind of magic guarantee of a more perfect cam than a "mass-produced" one, as if every "mass-produced" one is somehow fundamentally flawed and every "custom" one is somehow superior. That notion is ludicrous.

There's more to specfying a cam than just the head flow; although the head properties are certainly one very important part of the process. The other main piece of the puzzle is the torque vs. RPM curve that the engine needs for its intended application. That's determined by what it's being used for (street, oval track, drag racing, etc.); the car's weight; and its gearing. All of those things have to work together to get the best possible match.

 

ok i am getting it kinda.

somebody told me that AFR heads are great heads. but they flow alittle to well on the exhaust side and there for choosing a cam would be very important.

 

I didn't know that it was possible for a head to flow too well on either side. I'm such an idiot. I guess I just learned something.

Seriously, that just means that an engine with AFR heads doesn't benefit as much (if at all) from a cam profile that has a larger exhaust lobe. Typically an AFR-headed motor will run its best with a more nearly symmetrical cam. Go back to my comment about the exhaust/intake flow ratio, that's what I was talking about.

But there are ALOT of AFR-headed engines in the world, and all 3 models or whatever of their heads are very familiar to professional engine builders and cam grinders. You might want to look around at what cams the people that are going fast with those heads are running; I'd bet there are quite a few of them with either off-the-shelf cams, or at least cams with off-the-shelf lobes, that you can just buy or have ground for $25.

Look at Comp's lobe selection for example. They're all right there in their catalog (well maybe not all their lobes, but at least the series that are the most common) and you can pick lobes that suit your application and create your own cam that way for just $25 more than a typical box-stock one. That way you get the benefits both of their R&D on lobe design and of the oportunity to tailor a cam to your motor. All you have to do is to learn how each of the various cam design features applies to you and your motor and its use so that you can make an intelligent selection. The other major cam mfrs have similar programs and procedures and pricing.