Variable Length Velocity Stacks

Postby **mrpham** » Mon Feb 13, 2012 3:25 pm

I found something cool while I was on YouTube, was watching videos on the Mazda 787B LeMans race car.

It you watch from 40seconds onwards, you can see they have a system that changes the length of the velocity stacks. It's amazing! Don't think it's practical to build it for our cars, but thought it was very interesting

http://youtu.be/0qPHsk0t1uo?t=40s

Postby **NitroDann** » Mon Feb 13, 2012 3:27 pm

They did it in F1 as well. Also there are a vouple of production cars that did it by memory BMWs.

Dann

Postby **mrpham** » Mon Feb 13, 2012 3:33 pm

NitroDann wrote:They did it in F1 as well. Also there are a vouple of production cars that did it by memory BMWs.

Dann

Pretty cool stuff

When I was trying to google it, I think some road bikes have it too?

Curious as to how it's setup... based on throttle position, RPM, or just a combination of everything.

Apu · Postby **Apu** » Mon Feb 13, 2012 3:36 pm

NitroDann wrote:They did it in F1 as well. Also there are a vouple of production cars that did it by memory BMWs.

Dann

Yup, Bimmers have variable intake as do/did some Alfas - obviously not exactly the same as this, but similar principles I believe.

hks_kansei · Postby **hks_kansei** » Mon Feb 13, 2012 3:54 pm

Even the NB8A has an extremely simplifoed version of this.

http://en.wikipedia.org/wiki/Variable_l ... e_manifold

wozzah1975 · Postby **wozzah1975** » Mon Feb 13, 2012 4:14 pm

hks_kansei wrote:Even the NB8A has an extremely simplifoed version of this.

http://en.wikipedia.org/wiki/Variable_l ... e_manifold

Similar theory, but inferior to the one in the first post. The Ford Falcon 6 usues this style of set up too, From 1994 on. The butterflys open up at higher RPM an effectively shorten the runner length. The trouble is with all the bends and butterflies etc it creates turbulence in the manifold and huge variations in air speed. Some are better than others, but I know the Mazda FWD BP version doesn't flow very well.

Cheers
Woz

Jeo · Postby **Jeo** » Mon Feb 13, 2012 4:53 pm

Toyota's 4AGE has a version of this as of 83.

Well cool video though.

Postby **mrpham** » Mon Feb 13, 2012 5:06 pm

Yeah definitely a lot of engines that use a variable inlet length, but use of it with ITBs is something I've only known about since today. Just something I found while reading up about ITBs. Would be nice ot have for our cars, but not enough space in our engine bays.

Also found this a good read too, link was posted on another forum.

http://forums.neons.org/viewtopic.php?t=294784
http://www.superbikeplanet.com/2006/Oct ... 0clock.htm

http://youtu.be/Wy7hysrKfoY

Postby **NitroDann** » Mon Feb 13, 2012 5:24 pm

There isnt enough room in an MX5 engine bay for useful sized ITBs at all if they are straight. And Ive never seen curved ones in an MX5 bay.

Dann

Postby **mrpham** » Mon Feb 13, 2012 5:37 pm

NitroDann wrote:There isnt enough room in an MX5 engine bay for useful sized ITBs at all if they are straight. And Ive never seen curved ones in an MX5 bay.

Dann

lol

I borrowed the runners (curved) from my friend's M3, initial measurements say that they will fit. So I'll be playing around with them when the time comes, my super accurate ass-dyno should be able to give some numbers about extra length but curved runners.

Mr nanotech · Postby **Mr nanotech** » Mon Feb 13, 2012 5:46 pm

My brothers 2011 R1 has this. I was astounded when he mentioned it lol

wozzah1975 · Postby **wozzah1975** » Mon Feb 13, 2012 6:25 pm

mrpham wrote:
NitroDann wrote:There isnt enough room in an MX5 engine bay for useful sized ITBs at all if they are straight. And Ive never seen curved ones in an MX5 bay.

Dann

lol

I borrowed the runners (curved) from my friend's M3, initial measurements say that they will fit. So I'll be playing around with them when the time comes, my super accurate ass-dyno should be able to give some numbers about extra length but curved runners.

As with any ram tube, regardless of length, the most important thing is that the air around the entry be as undisturbed as possible. On most cars the length of the tubes is limited by the room you have to fit them, so in most cases it's a compromise. You are far better off with a ram tube thats slightly shorter than in needs to be to get undisturbed air than you are finding the optimum length and having the entry of the ram tube compromised.

Angled runners are not ideal, and in most cases you're better off with the angle of the runners correct in relation to the port, rather than finding an ideal length with an angled runner. You'll find that more than likely the M3 runners are designed to work with the M3 inlet port and will be angled to suit. They may not work on your engine as well.

The shape of the entry of the ram tube is also super important, there are some shockers out there.

As long as you're dynoing it in the engine bay, or simulating it fitted thats fine. I love mucking around with this sort of stuff

Cheers
Woz

Duane · Postby **Duane** » Tue Feb 14, 2012 6:47 pm

nanotech wrote:My brothers 2011 R1 has this. I was astounded when he mentioned it lol

They have more of a 2 stage system. At a change over rpm point the longer tube lifts out of the short one allowing the air to bypass and take the shorter path. Not really a true variable but effective any way.