d_roedel

--I AM NOT TALKING ABOUT CONE FILTERS, or gaining 80hp with a bolt on, AND DO NOT WANT A DEBATE ABOUT THEM TO START, ---

This is for a complete motor build of a 2.7.
I am about to dive into my intake manifold project and looking for some flow #'s

any body have flow #'s of a stock NA manifold?

throttle body?

or an equation to determine aproximate cfm for the throttle body by diamter?

the plan is to cut and shorten runners on a stock manifold and create a larger plenum above it to optimize it for higher rpm, and blend the tops of the runners to imitate velocity stacks.

thanks!
derek

bleucamaro

As for stock numbers, I'm unsure, but there are flow calculators and intake plenum design calculations online if you google search "intake manifold design" or "plenum design" and I have found that the factory runner length for an S2 is optimized at about 4400RPM.

What RPM are you trying to set the peak torque at? What are you trying to achieve by running a larger plenum?

SoCal Driver

Changing the diameter of the runners works as well as changing their length.

Does not take into consideration the resonance or pulsing of the intake. The reason for a plenum to absorb the shock wave.

Skunk Workz

Stock NA 2.5 TB flows 410 CFM @ 20.4"... stock intake anything between 233 to 251 CFM @ 28" depending on which runner you flow...

d_roedel

awsome, thanks skunk. looks like bored or custom throttle body is not necesary

i am trying to optimize between 4-7k rpm, and have read articles all with the info that plenum volume should be about 1.5 to 2 times the engine displacement, to answer your q.

d_roedel

also, does anyone have a specific runner length to recomend? i have been searching google and not comming up with credible sources.

nine-44

I ran the #s for the NA and turbo intakes, as far as I can tell, they are like spot on for performance. The plenum size I beleive, is supposed to be based on the volume of one cylinder's displacement, not the total. And yes, I have read the 1.5 to 2 times the displacement as well. If you want some good reading material... Forced Induction Performance Tuning by A.Grahm Bell. I was looking into design. When tuning, you can do a loop runner off the back of the plenum around to the bottom intersecting at 90 degrees, to even air flow. I'll be damned if Porsche didn't do this with the 968 intake. I can't say that they missed much of anything, I can say that they withheld some tech on the 944 series. The diameter, the length and the plenum sized all checked out when I ran the #s. If you want to move the power band up sacrificing down low, pull about 2" off the length. That would put the length at the low side of suggested and moving power to the upper part of the revs. If you don't have it, get the book, about 40 bucks and priceless on the info man. Prolly my best book find yet! Good luck

Skunk Workz

If you are aiming for high rpm hp like you said,then I'd get a bigger TB...of at the least port the one you have. The number looks high,but it's still slightly a restriction. Even on a 2.5. But to really gain some,you'll need a slightly more aggressive cam with a bit of overlap to let the engine breathe at the far end of the rpm range.

d_roedel

already got that under control,, milledge cam. I was actually lookin at using an elderbrock or ricer supply company throttle body somewhere in the 65-70mm range.,

nine-44 i have also heard the 2" shortening form another source, so this looks like what i might do. the turbo manifold looks easier to shorten but has a smaller plenum, so i might go this way and make sure the runners come out at 2" shorter than the NA.

Serge944

I second Bell's book. I bought it a few weeks back and its much better than Corky's.

Calculation based, the maximum our engines will flow is about 270 CFM at 1 BAR. Something to keep in mind.

d_roedel

i will, but is that for a 2.7 or 2.5?

Serge944

oops, 2.5!. Just multiply 270 by (2.7/2.5)

Geo

Based upon what?

I know from a recent conversation with Jon Milledge that the 2.7 head does not flow as well as the 2.5 head.

Serge944

These are ideal figures based on physics. They do not pertain specifically to the 944 line. Displacement is proportional to potential flow rate.

d_roedel

geo -oh really, seems odd since the intake is much larger, maybe the port is too big. does the intake or exhaust suffer on the 2.7 head? and by how much?