Intake tuning for Cam duration

[CJROTHY]

Tried a few searches, did not see anything like this question:

Trying to calculate proper intake runner length for Cam duration. Looking at specs, I see ADV duration at 265, and .050 duration at 204. Which do I use to calculate the pulse from - or is there a different method used to figure this out?

At .050 the valve is mostly closed, and I assume that the valve closes at the same rate it opens (never NOTICED any assymetrical flat-backed lobes), so the valve is certanly decellerating by .050, but does anyone know exactly when to count the closing outbound wave as 'created'?

Also, in complete ignorance, I was thinking of using a Stage II cam for a daily driver that needs to smog. Is this a good choice, and are headers matched to a particular cam?

[torq455]

stage II? cam from Milzy? so assuming a 3400?

[CJROTHY]

'86 Firebird, 2.8 MFI, was looking at crane for now.

[Guest]

Since when does Crane have a "stage II" cam?

I really hate the way these internet kids have latched on to this idea that everything comes in "stages" for upgrades.

I also don't understand why you say "at .050" the valve is mostly closed, but when is it closed at .050"", Umm at .050" the valve is going to be .050" open or away from being closed. This term is used because for years industry 'experts' aggreed that there really was no appreciable flow under .050".

Don't worry about matching the intake to the cam, unless you're going to be running Le Mans, or competing top fuel. An off the shelf cam, especially from Crane will work fine with your stock intake.

[bszopi]

IIRC, he is designing his own intake, so that is probably why it matters to him.

[CJROTHY]

Raven, I was using the Crane POWERMAX 2030, (which was formerly advertized as the Compucam 'Stage II'), out of sheer ignorance, as mentioned earlier, to begin benchmarking my own intake. And thanks for the note on flow at .050, I had never heard about flow ceasing there, only that .050 was a reliable way to describe the duration from intake to exhaust.

What I am trying to do is going to involve really a LOT of effort to look and work well, and I am trying to cut down on the 'million monkeys' hit-and-miss development method. Designing this intake is going to heavily depend on cam selection, and I am trying to avoid tapping and instrumenting an intake - instead initially I'd rather have the thing sized in the rough range so that I can adjust the length at the dyno for 'fine-tuning'.

Rather than bagging on my confessed-up-front lack of in-depth understanding of the mysteries of cam grinds, can I instead ask this site's collective vast knowledge of cams to answer the earlier question "Is this a good choice"? I am trying to get get more power out of a daily driver that will pass emissions, staying below 6,000 rpm. So far I have only aftermarket manufacturer's descriptions of different cams, which without dyno sheets, is naked marketing: I.E. Lying.

I could really use some help here. I'd rather not spend the time and money to build up an engine, then buy several cams and learn first-hand at the dyno which I want. I understand duration, lobe profiling, what it is doing with the valves and timing, but only generally how those relate to the power band and emissions. I have assembled many V-8 engines, but mostly stock parts. Every time I step off the reservation, it's usually a long and hard learning process. New to this town, I don't know of an engine shop that I can trust to know what it's doing and take advice from.

[geoffinbc]

Did you buy the cam yet? If you have not installed it then return it and get the 260 or 272 cam. The 2030 cam is a joke. Mine also made excessive noise. It sounded like a diesel. Dont tell me I didn't adjust my valves right. I did. So I tossed it and went back to the stock Camaro cam which is a better cam than the 2030. The only thing the 2030 had over the Camaro cam was torque. But the Camaro cam climbs to 5500 no sweat. The 2030 cam had a hard time getting to 5000.

I dont know why they advertise it as computer compatible. Its LSA is too narrow and and the IC event happens too early.

http://members.shaw.ca/betterthanyoutoo/camshaft_guide.htm

To help you view a powerban get a dyno sim and make up an engine. Then enter cam data for every cam. You dont have look at the power numbers that not important but look at the curve each cam makes. Also remember in your own head that intake and exhaust systems will affect it. But the cam is still the overall deciding factor on where power is built.

[CJROTHY]

Didn't buy the cam yet, I'm doing the math now. It's gonna take me all summer to build the test rig with ECU and harness.

I'll take all the recommendations i can get

Thanks a ton for the link.

Still left with the question When (in degrees referenced to intake cam lobe) is the pressure pulse formed?

[geoffinbc]

Use an engine simulation program. The pressure wave is not a constant rise and fall. It rises and falls as the crank goes through its stroke and the valve opens and closes. These 2 events and how they relate to each other dictate the wave.

We cannot give you a number. You need several very advanced mathimatical calculations to create the theoretical wave for you.

Think of it visually the same as you would a sound wave.

[SappySE107]

I can use dynomation to give theoretical wave patterns at RPM but I need a ton of information and have to use at least 20" primaries on headers to do the wave analysis. Still would be decent for coming up with an intake based on it but I don't have the program at the moment nor the time at the moment to be messing with it. I would have to have a cam to base it on first though, and could then tweak between intakes and cams but to have the program do it takes away the wave analysis between each test. I would have to take their final results and then put the wave testing back in.

Other than the program, id have no idea what so ever on how to even comprehend it. I suck at the math.

[Guest]

Have you read about intake design at www.grapeaperacing.com ?

[torq455]

from the sounds of it, you may like the 260.