ITB and adj runner lengths

whipped · Post by **whipped** » Sun Jan 27, 2008 12:29 am

Since the butterfly valve is "non existant" when at WOT, it makes sense that you could swap different length velocity stacks on after the throttle bodies and find the perfect length for your engine....

Tuned runners if you will.

You could probably go to a dyno with a handfull of exhaust bits and have a good idea on what works best on a particular engine.

Now would this translate over to a conventional manifold if you added a plenum?

Series8217 · Post by **Series8217** » Sun Jan 27, 2008 3:44 am

People with ITB setups do that all the time to tune for their cams and specific motor.

What do you mean by translating over to a conventional manifold? Do you mean you would be varying plenum size? Not sure what you mean about the plenum..

p8ntman442 · Post by **p8ntman442** » Sun Jan 27, 2008 8:13 am

Are your trying to design an intake (Plenum and runners), based on data collected from an ITB test session with different length runners?

There should be some correlation, depending on the plenum volume. Obviously the bigger the plenum the more similar to no plenum it is. also the larger the TB opening and closer to each runner the more similar it will be.

Draw it out on paper, and estimate your pressures at any given time with a runner intake and plenum setup. Use the Ideal gass law to determine the conditions of the air in the plenum. Now do the same with the Runners only and see how much of a difference there is with out the plenum. You should be negligable at or near WOT because the velocity pressure of the incoming air, overcomes the resistance of the single TB.

Pyrthian · Post by **Pyrthian** » Tue Jan 29, 2008 9:21 am

find a way to make a "chinese finger trap" work. with a throttle body on top.

The Dark Side of Will · Tue Jan 29, 2008 9:30 am

I have wondered about using telescoping velocity stacks and ball screw or similar actuators controlled by the ECM. The computer would adjust velocity stack length based on RPM. The telescoping stacks would even have taper built in.

Pyrthian · Post by **Pyrthian** » Tue Jan 29, 2008 9:42 am

chinese fingers traps not only get longer & shorter - they get also get wider when shorter, and narrower when longer - just gotta find a way to seal them.....

Kohburn · Post by **Kohburn** » Tue Jan 29, 2008 10:20 am

Pyrthian wrote:chinese fingers traps not only get longer & shorter - they get also get wider when shorter, and narrower when longer - just gotta find a way to seal them.....

latex

whipped · Post by **whipped** » Tue Jan 29, 2008 11:00 am

Not a bad idea... I don't think it even has to be perfectly sealed. Think "trombone"... Just have a large overlap between the slides.

Fastback86 · Post by **Fastback86** » Tue Jan 29, 2008 2:36 pm

Take a cue from Yamaha:

http://www.motorcycle-usa.com/Article_P ... 819&Page=1

There's even an animated picture halfway down to show how it works.

Series8217 · Post by **Series8217** » Tue Jan 29, 2008 3:41 pm

Isn't that just a dual runner length intake that works by seperating the upper runners from the lower ones instead of having a flapper valve?
I think Will and Ryan are talking about a continuously variable telescoping intake..
Though maybe that pic is misleading.

whipped · Post by **whipped** » Tue Jan 29, 2008 4:34 pm

I was thinking temporary for dyno testing. I don't think it would offer much torque advantage, but I could be wrong.

A design cue from a telescope R&P focuser:

p8ntman442 · Post by **p8ntman442** » Tue Jan 29, 2008 5:31 pm

The chinesse finger trap idea is the ideal solution, Think of the Boxing glove that comes out of the wall and reaches across the room. The arm gets thinner and longer. Now take that square peg and make it a round one. The solution (variable length) is easy enough, the ideal solution (variable length and diameter) is very complex.

S8n · Post by **S8n** » Tue Jan 29, 2008 6:09 pm

BMW used a step-less variable intake on the 745i motor. it used a motor on the back of the manifold to rotate a runner-in-a-runner to make it longer or shorter, depending on RPM and load. This was not ITB though, but Valvetronic, so no throttle body anyways.

p8ntman442 · Post by **p8ntman442** » Tue Jan 29, 2008 6:42 pm

Does the TB need to be before the runner, or can it be like trumpets on an ITB?

Blue Shift · Post by **Blue Shift** » Tue Jan 29, 2008 6:48 pm

That braided wire tube they use to cover cables or hose works just like those chinese finger traps if the weave is right. The stuff I played with was. If you could impregnate it with some sorta elastomer to seal it, you could probably make VGI runner out of it?

nfswift · Post by **nfswift** » Tue Jan 29, 2008 8:57 pm

Hahah, as cool as a VGI would be imagine those Yamaha style ITBs adapted to a V6... it would be like the new air grabber/shaker hood, they "pop up" when you get on the gas :love10: I'd rock that...

Kohburn · Post by **Kohburn** » Wed Jan 30, 2008 10:58 am

Blue Shift wrote:That braided wire tube they use to cover cables or hose works just like those chinese finger traps if the weave is right. The stuff I played with was. If you could impregnate it with some sorta elastomer to seal it, you could probably make VGI runner out of it?

specificly expandable braided sleeving - there is a lot of braided sleeving that is not expandable.

http://cableorganizer.com/braided-sleeving/

or $$$$ for the high temp stuff good to 200C

http://cableorganizer.com/Bentley-Harri ... -686dm.htm

Pyrthian · Post by **Pyrthian** » Wed Jan 30, 2008 4:06 pm

nfswift wrote:Hahah, as cool as a VGI would be imagine those Yamaha style ITBs adapted to a V6... it would be like the new air grabber/shaker hood, they "pop up" when you get on the gas :love10: I'd rock that...

yes - BUT - they actually go DOWN as the RPM's shoot up

crzyone · Post by **crzyone** » Wed Jan 30, 2008 5:18 pm

Well, I understand why would would want a variable length trumpet but its just not needed.

With a good exhaust, cams and ITBs you are looking to make 400+hp and 330+ torque. Why does a fiero need any more power down low to begin with? 1st gear is going to be traction limited and everything after that is going to be in the power band anyways.

Why not make a good set of trumpets that are tuned for upper rpm power and leave it at that.

I agree you will need a variety of trumpet lengths for tuning purposes to see how much power they make but a variable length trumpet would be hell to tune.

whipped · Post by **whipped** » Wed Jan 30, 2008 5:26 pm

crzyone wrote:Why not make a good set of trumpets that are tuned for upper rpm power and leave it at that.

I agree you will need a variety of trumpet lengths for tuning purposes to see how much power they make but a variable length trumpet would be hell to tune.

If I were to go to the dyno, I would want to test everything from 0" to 20" of runner length.

I forget the kind of dyno, I think it's a mustang, but one of them lets you set the load speed. Imagine being able to hold the RPM @ 3000 and varying the intake runner length for the best torque. Hold it at 3500, etc etc.... Now I don't think they'll let you stand behind a car on a dyno (nor would you want to) so some kind of automatic dial-a-matic deal would be necessary.

But I can settle for random lengths of exhaust tubing and an hour of dyno runs... *shrug*