Short trumpets, Rover V8...

[wedg1e]

Hmmm. As I have my induction plumbing in bits, I find myself contemplating the length of my tracts (oo-er) and wondering what benefit may be had from shortening them? My engine is in a mild state of 4-litreiness, fast road cam, manifold/ heads have had some porting work, uprated FPR, short valve guides/ double springs, flap-type injection. Any advantage to short trumpets on such an engine, if so (and ignoring the technicalities of how to extract them ;-) ) how much would be a reasonable amount to lop off?

Expecting a slating...

Ian

Edited for the hell of it... ;-)

>>> Edited by wedg1e on Friday 18th July 22:50

[HarryW]

Wedgie speak to Tim Lamont (he at ACT), he'll have the data on trumpet sizes versus engine tune.
I would have thought that if it is a proper 'gas flowed' set up then shorter and wider may be the way to go (IMHO).

harry

[jmorgan]

Mine were just shortend rather than changed. It was explained and made sense, better flow or sommit (given that the motor was already in bits it cost an extra 20 quid). With the rest of things going on I wanted to keep some costs down. I assumed the lathe was used?

[joospeed]

generally speaking, shortening the intake will move torque up the rev range, however you might be able to fil in a hole in the torque cruve, but you wouldn't know unless you did repeated rolling road tests, costly.
also be very careful if you just lop off the top without putting a large radius on the end .. a straight ended pipe costs serious airflow (there's some figures in vizard's A series book ) .. seems that with a generous radius you can pick up alot of extra airflow over a straight ended pipe. Why not just fit some of Tim's carbon pipes into your plenum (suspect you'll have to open out the manifold to get them ni maybe?).

[2 sheds]

Joolz is correct about torque curves, you could remove the standard trumpets and cut around 15mm off then re-fit, this would give you a tad more at the top end, it shouldn't change the torque curve that much either, this task is a pain in the arse, heat the trumpet base in an oven first then it should be possible to extract the trumpets,
Alternative plan, if you have bonnet clearance, fit a spacer between plenum and trumpet base, i think 8mm would produce an improvement, the later (gems type plenum) is better certainly worth a few BHP , this is slightly taller and has a flat top.
Or you could just take joolz' advice
Tim

[wedg1e]

Thanks for that, chaps: I was thinking more along the lines of pulling them out and cutting the bottoms off, rather than Joolz barbaric chainsaw-massacre solution ;-) I do have SOME engineering sympathies, you know!
How about short trumpets AND a plenum spacer, then? At what stage do you have to go for big airflow meter, throttle body and space shuttle fuel injectors?
I was thinking more torque rather than more power, incidentally.

Tim, what £££ for some carboniferous trombones?

Ian

[2 sheds]

Ian
The Airflow meter and injectors (Jaguar) are a good idea, offering more torque if you can't find any i probably have some tucked away somewhere that you can have cheap,
Larger throttle probably not worth the expense,
My Superflare trumpets ( which come fitted in base on exchange basis) are £250,
A 390 would respond well to these upgrades.
Tim

[wedg1e]

2 sheds said:

Ian The Airflow meter and injectors (Jaguar) are a good idea, offering more torque if you can't find any i probably have some tucked away somewhere that you can have cheap, Larger throttle probably not worth the expense, My Superflare trumpets ( which come fitted in base on exchange basis) are £250, A 390 would respond well to these upgrades. Tim

Mwuahahahahahahahahahahahahaaaaaaaaaaaaaa.........


...but define cheap? (Off-line if you prefer)


Ian

[2 sheds]

Mwuahahahahahahahahahahahahaaaaaaaaaaaaaa.........


...but define cheap? (Off-line if you prefer)


Ian
[/quote]


Done..

[marcus]

Anyone do anything for the blimmin' 2.9 V6, I'm running out of things to chop off / grind out and want to get some air into the beast!
Mr ACT, surely you want to use my car as a development mule

Marcus