NZ951

Thats mate! Looking good...

Ok, now back to intake pressure waves / ST's johnson.

DanG

I'll chime in, for once I actually know something about a topic. Believe it or not, I work on this stuff all day. Engine induction systems product development engineer.

The shape/angle of the wall opposite the runner opening are not whats critical for these pressure waves. The critical dimension for runner tuning is length, and this length is simply from the intake valve to the opening at the plenum. The opposite wall on the plenum has no real effects here, although its certainly still important, mainly its contribution to consistent flow through each runner on an asymmetric manifold.

I could try to explain the whole wave phenomenon it a little more detail, but howstuffworks probably does it better...

http://auto.howstuffworks.com/question517.htm

However, on a turbo car, our efforts are better spent elsewhere. Decreasing restriction/increasing flow and dropping charged air temps is the thing to work on.

NZ951

Cool, so I can make my triangular plenum and keep the orientation of the IC / IC pipes! yay.

J Chen

Whatever you do NZ, try to maximise runner lenght.
That way you wound'nt kill the torque.

NZ951

I am trying to "tune" the runner lengths, not just make the as long as possible. It will either be 9 inches or 11 inches, hopefully 11 as that means 4 reflective waves. If I can fit 10 inches, I will be making it 9 for example. Unless I change the tune target!

DanG

The engineer in me wants to say you should at least try to run some tests on a flowbench if you're going to start buildin your own manifold. If things conspire against you, you could see 5-10% differences between runners, most likely makeing some run too rich, while others run too lean. (Unless you've got four WBO2s and stand-alone EMS with individual cylinder control).

Here's some links to get you started...

http://www.speakeasy.org/~synchris/e...flowbench.html
http://tractorsport.com/flowbenchparts.htm

I'm lucky, I've got a few flowbenches at work that I can use whenever. I just don't have the desire to uild my own manifold just yet. Maybe once I start running out of things to tweak on my new car.

J Chen

Is there space for 11 inch runners. A friend of mine did
some calculation sometime back & it seems that the ideal
would be 15-16 inches measured from the valve seat but
where to find the space.

NZ951

Funny you should say, it will be flow tested by runner, unlike some, and it will be used in conjunction with individual WBO2 and EGT

Are you sure there is 11 inches space there including the required distance from the velocity stack to the pelnum face? I am thinking AOS would be in the way...

Dan, velocity stacks in a turbo application or not?

J Chen

Hey NZ,
Re-read my post.

NZ951

Yeah I got it, I meant 11, You need 11 plus twice the diameter of the runner (2 inches for me), in distance from the end of the stack to the plenum...

special tool

Well, you are limted to 4 EGT's NZ because wideband o2 will give you nothing good being placed between head and turbocharger.

fortysixandtwo

Why would getting 11" of runner be difficult? The factory ones are about 15".

DanG

DEFINITELY. If you're going through the efforts of building your own manifold, this part is a no brainer. It should also help you with packaging, since your runner lengths extend into the plenum a bit.

This is a pretty good discussion about it, except his design for the "180 deg." bellmouth is flawed, the bell radius should be about half the tube radius, his looks to be closer to 1/4 or so. If he bumped that bell radius up to around 1/2 tube radius, the CFD results should show it flows the best.

http://www.gt40s.com/ubbthreads/show...p?Number=29735

NZ951

I already posted this earlier in the thread, but its because of velocity stacks and the requirement to have twice the diameter of the tube in distance from the end of the stack and the plenum, also, the stock runners have a lot of form cast in them, I wont be casting the intake, it will be a one bend runner hopefully.

NZ951

The runner dia will be 2 inch looking at my calculations. I think Corky Bell suggests a whole diameter radius in the stack... hmmm maybe I read it wrong.