Variable Inlet Length

[Doof 11]

Just been pondering variable inlet manifolds. Anyone know what sort of gains they can produce? or know anything about them at all?

 

Doesn't the GTi-6 have some sort of fancy inlet manifold gubbins?

 

I know Sean was looking to do some RR tests with different length trumpets on his new engine, i'd be interested to see what difference in top end there is between really short and really long trumpets.

 

I'm just wondering whether it might be worth having a go at making one, can't imagine it'd be that difficult and with mappable ECU's you could easily vary the length linearly with the revs.

 

Thoughts anyone?

 

Lewis

[Ahl 4]

Its a nice idea, but perhaps a lot more hassle than its worth?

[smckeown 1]

hassle ? nah!. I'll have something to show you lot next w/e hopefully to show how easy it is to vary the inlet tract during mapping.

 

There was a post recently i commented on that showed the diff. between short and medium trumpets; it showed clearly the dsiff; very interesting too it was.

 

I'd predict my car is about 4 weeks away from mapping, and there will be a lot opf experimentation

 

Sean

[Doof 11]

Yea i agree it's probably loads of work for not a huge gain but if you're bored and like building things, why not?

 

If anyone knows of results using different trumpets I might get an idea of the sort of gain that could be had in terms of torque low down from long runners and top end from really short runners.

 

EDIT:

 

Sean, keep us posted on that, i'll be really interested to see how it goes. Any idea what that other thread was called?

Edited February 11, 2007 by Doof

[boombang 2]

If you surmise that low down you need long runners, and at top end you need short, surely you could make up a sliding tube affair where oil pressure works against springs to slide a larger tube over a smaller one?

 

Say for example you decided 100mm best at 2k RPM, 80mm at 4k, 60 at 6k - one tube inside, shaped edge to smooth airflow in. Another tube fitted outside which is spring loaded to hold outer tube in extended position.

 

Oil feed goes into a frame around external tube with piston that pushes tube inwards with increased pressure - get the piston size and spring rates correct and you'd have an incredibly over-complicated variable length inlet.

 

Other way is if the ECU can control aux functions, have two stage style inlet like 2.0 Mi16/s!6 and use an RPM function as a switch with some sort of actuator to switch, again like the S16 system (which IIRC uses vaccuum via RPM?)

 

Either way it is remarkably over-complicated and sure results from testing like Sean might be doing would show if it is worthwhile.

 

Use of engine would also play a big part in if it was even worth looking at.