4 replies to this topic

[warning634]

Hi all

Can someone please explain what effect different length trumpets have on engines response/performance?

Many thanks

Kevin

[nicklouse]

Hi all

Can someone please explain what effect different length trumpets have on engines response/performance?

Many thanks

Kevin

loads if info in Visards big book but to sum up in a very general way.
 

 Generally speaking, the shorter the inlet trumpet the higher the engine speed at which optimum cylinder filing occurs, meaning the peak torque point occurs at higher revs. This is due to the length of standing pressure waves in the inlet tract. Shorter trumpets lead to shorter standing waves and therefore higher frequencies at which the standing waves optimize cylinder filling.

 

 

and this can also change depending on the inlet manifold design.

 

Visard does list some "total" lengths IIRC

[warning634]

Cool thanks for that.

I'm running split 45 fitted with the MED DCR stub stack kit (ment for a single 45) having some issues with a flat spot, and was thinking of fitting some different trumpets, but was unsure what length to fit.

Also the car is a Tarmac rally car, and I have a itg filter fitted, just wondering if I should run it without a this air filter. As I see lots of other rally cars with no filters, what do u think??

[nicklouse]

personally get some ITG trumpet filters and a selection of trumpets and play.

 

or rolling road session. with some different trumpets.

 

as to what size. there are so many variables it does really need to be done empirically.

 

so people might have as good guessing point if they ran the same spec. build but.....

Edited by nicklouse, 16 September 2015 - 09:45 AM.

[matty...]

Have you check what your AFR readings are?

Where about in the revs is the flat spot, and where is you peak torque at the moment? What do you rev it to?

Cam timing can be advanced for better low/mid or retarded for top end.

We found on the se7ens running a split weber, that inlet runner length had more of an effect on the torque curve than different length\design of trumpets, these had little effect in comparison. As did the design of the restrictor rings they use, which they actually made more power with the rings fitted, which suggests that the air speed is a little low in the lower rev range on the 45 split weber system.

A longer inlet runner will give you better low to mid range, but you'll lose a bit at the top end.