Twin weber manifolds

[Painter an]

Hi are there any advantages between short or long twin side draught inlet manifolds?
Cheers

[Erikmex]

Longer the better, usually inner wing clearance is what limits things

[Painter an]

Longer the better, usually inner wing clearance is what limits things

Thanks m8 was not sure if people had short because of like you said iner wing clearance in mk 2 escort.why is longer better? Cheers

[katana]

Longer inlet runners generally improve torque - sometimes significantly in injected set-ups!

[Erikmex]

It’s all to do with pressure waves, if you imagine the inlet flow on an induction stroke flowing through an open inlet valve, when that valve closes the flow through the runner dead heads sending a pressure wave in the opposite direction, when the cylinder then comes onto its next induction stroke that pressure wave inside the runner has more energy and a higher gas speed in a longer inlet tract vs a shorter , so when the valve opens again it assists cylinder filling, there’s more to it than that but in short.

[Painter an]

It’s all to do with pressure waves, if you imagine the inlet flow on an induction stroke flowing through an open inlet valve, when that valve closes the flow through the runner dead heads sending a pressure wave in the opposite direction, when the cylinder then comes onto its next induction stroke that pressure wave inside the runner has more energy and a higher gas speed in a longer inlet tract vs a shorter , so when the valve opens again it assists cylinder filling, there’s more to it than that but in short.

Thanks guys v informative

[Graham]

there is also a ram air effect, air has interia like everything else, so once you have a long column of air moving it doesnt want to stop so tends to carry on filling the cylinder even when the engine is actually pushing the air back out again or even sometimes a slight supercharging effect

[Painter an]

Does that mean longer trumpets are better as well

[Graham]

yes, as far as the engine is concerned it just sees length of inlet, long manifold short trumpet, short trumpet long manifold will perform the same, there is always the odd exception, but in the vast majority of cases long is good, and on older 2 valve per cylinder engines ive never seen an instance where you can go too long and still fit the induction system to the car. i say that as i did once try some 1 metre long trumpets they were too long for the very top of the rev range, but the midrange was something else altogether

[katana]

i did once try some 1 metre long trumpets they were too long for the very top of the rev range, but the midrange was something else altogether

That I would have liked to see LOL!

[Colr6]

What would a 90 degree bend in the trumpet effect have to get more length ?

[Graham]

Problem with a 90 bend is air doesnt like going round corners, so you'd probably be worse off

[Painter an]

So the longer trumpet is benefitial so what about longer filters does this have same effect

[Erikmex]

I learned the lesson when I was 8 on my first bike, a 2Stroke 50cc Italjet. When we got it it was flat as a pancake until high revs. My dad made around 5 different length trumpets for various conditions ie. deep mud, hardpack etc. The smaller dia longer ones had best low end to mid. And the shorter larger dia ones have more top end

[Erikmex]

No because filter are open, they don’t increase gas speed

[Graham]

So the longer trumpet is benefitial so what about longer filters does this have same effect

no, because the filter doesnt form part of the actual inlet tract

[katana]

Problem with a 90 bend is air doesnt like going round corners, so you'd probably be worse off

Depends on how you bend them - VW have some interesting,curved inlet tracts and plenums - not sharp 90's but long sweeping 180 turns that I believe are over 300mm long

[Graham]

Depends on how you bend them - VW have some interesting,curved inlet tracts and plenums - not sharp 90's but long sweeping 180 turns that I believe are over 300mm long

i agree, but your not going to get anything like that fitted to and x/f in an escort