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Manifold length for twin 40s
paulf - 22/5/03 at 08:05 PM

I have been offered a manifold to fit webers to a crossflow.I am told it is a short version which is what is required to fit a seven type car.Can anyone who has one fitted tell me the actual length required so as i can measure it before buying it.
I know this has been discussed recently but cant find the actual size required.
Paul.

Viper - 22/5/03 at 09:29 PM

the shorter the manifold the higher the torque the longer the manifold the higher the revs....

Stu16v - 22/5/03 at 10:24 PM

quote:

the shorter the manifold the higher the torque the longer the manifold the higher the revs....


Wrong way round m8

The THEORY behind tuned lengths is that the longer the inlet tract (i.e manifold, intake trumpets etc) the torque the engine will pick up at lower revs, but at the expense of power at the top end of the range. But in practise, very often it turns out to be b*ll*x anyway, changes in inlet AND exhaust lengths depend on the whole package of engine tune. The only way to find out is experimentation on a rolling road/dyno.
Paul, are you talking about power, or merely trying to get a manifold that fits? IIRC Scutter has had similar troubles recently, I beleive that depending on how engine sits in relation to chassis, a manifold with a slight 'swan neck' may be required.

HTH Stu.

kingr - 23/5/03 at 08:19 AM

Yup, seconded, longer manifold = greater volume of air = greater mass of air = greater inertia (given that it's travelling at the same speed as it would with a shorter manifold) which means more air/fuel mix is forced into the cylinder (or not blown back out as the case may be) at lower RPMS.

Kingr

Peteff - 23/5/03 at 08:50 AM

I think he just wants it to fit under the bonnet.

yours, Pete.

kingr - 23/5/03 at 09:05 AM

Short as possible probably then!

Kingr

paulf - 23/5/03 at 08:19 PM

Thats correct I have been told it is a straight manifold without swan neck and about 3 inches between faces, will this fit a book dimension car when fitted with twin dellortos and air filters?.I wanted to know before I pay for it as I wont be trying it on the car for a while as it is presently set up with a downdraught carb.

quote:
Originally posted by Peteff
I think he just wants it to fit under the bonnet.

yours, Pete.

Viper - 25/5/03 at 06:34 PM



Wrong way round m8

HTH Stu.


yep your right............must put my cock up to either to drunk or to tired...