Induction length

[cpr1]

Are there any fluidynamics experts on this forum? https://www.youtube.com/watch?v=hHjf9zhQIRk if you have a look on this video from about 1.11 I guess more fuel is wasted to atmosphere than going in the engine on WOT , does this happen because the induction is not of the correct tuned length to the cam timings ?

What are your thoughts?

[Richspec]

probably, you can work out the correct induction length BUT its a compromise because we are space limited in the minis usually. Like the 8 port pictured, you can have x amount of room inside the bonnet for your air filter, then x amount air gap to your throttle bodies, then throttle bodies of a,b or c which leaves y amount of space for your inlets to the head face.
I cant recall which way round it is, longer inlet gives more torque at high rpm or vice versa.

[cpr1]

probably, you can work out the correct induction length BUT its a compromise because we are space limited in the minis usually. Like the 8 port pictured, you can have x amount of room inside the bonnet for your air filter, then x amount air gap to your throttle bodies, then throttle bodies of a,b or c which leaves y amount of space for your inlets to the head face.
I cant recall which way round it is, longer inlet gives more torque at high rpm or vice versa.

I know that you can calculate the tuned induction length (that is from the valve seat to air horn end) , but on that video on WOT I do not expect all that loss, seems like air flow is not quite good! is it the positive and negative pressure waves restricting flow ?

[MiNiKiN]

Whilst I would not consider myself a 'fluiddynamics expert' I have some knowledge about the matter from tuning 2-strokes.
It needs to be said, that in this video the induction waves are heavily disturbed by the headwind.
Ideally you would have a reflection of the pressure waves at the open pipe end, and hence some 'charging effect'. If you manage to tune the pipe length wrong, such that you have your longitudinal pressure waves' peak at the 'open end' rather than its node you get a lot of sprayback and losses, like in the video.

The tendency is the longer the intake the more torque at low revs, BUT still you have to get your tuned length exactly right or you loose the positive effects. And your exhaust manifold and cam duration also also plays a role once the whole system gets in resonance.
Tuned length pipes in an ICE are rocket-science. There are computer calculation models out there, which are complex and usually still can only narrow your trial spectrum.

So far my 2p on a tiny glimpse at this very comprehensive topic that has delivered the substance of many Phd's already.


https://en.wikipedia.org/wiki/Longitudinal_wave

[Hipwell]

The Lucas injection is like using a calendar to tell the time. Its adjusted at wide open throttle at peak power and not much else matters. Fueling is fixed for any throttle opening in a very 2d fashion. The injector technology is more akin to a hose pipe than what you expect of a fuel injector, this can be seen as the fuel is squirted on the closed throttle slide, atomisation is very poor. Saying that it did win 200+ GP's

This is typical of long duration cams and less than ideal inlet lengths, as for fuel been wasted not a chance, each cylinder fill is 325cc(ideally) that's a lot of air at 8000rpm and the fuel will be going back in even on another cylinders induction cycle depending on valve overlap.

[850man]

There is a photo of 2 guys, one being Jon Scott from memory here in Aus holding up a Weber connected to 2 clear plastic lengths of hose attached to a engine on a dyno. They were determining the optimum length for an inlet manifold by simply starting at a measurement and then shorten the hoses, take another dyno run, repeat.
David Vizard did similar testing and from memory a 7inch manifold was found to work the best.