Anyone know where I can get one made south of Bristol. Just fitted an ST170 engine and the exh ports look like they need 1.75" primaries. The old
zetec manifold I have used for the last two years is 1.5" and leaves a step which will give impede flow.
There was reference to exhaust design theory on the board a while ago but I can't find it. Tied in primary and secondary lengths, diameters,
engine HP and capacity etc. Anyone help by pointing the way?
[Edited on 20/5/09 by Dusty]
go for as big a primary as you can get away with!
Surely thats not the case is it? I realise you want low restriction but the scavenge effect of a 12" pipe is going to be negligible - sapping
power?
I may be completely wrong, I'm just thinking of the induction side of things where bigger throttle bodies do not always give better performance
above a certain size.
My four stroke tuning book has a formula and explanation - will look it out if you want.
Mark
quote:
Originally posted by cd.thomson
I may be completely wrong, I'm just thinking of the induction side of things where bigger throttle bodies do not always give better performance above a certain size.
dave ashurst made the spreadsheet you're talking about.
It was based on the formulas from something or other.
Does this mean you have a Zetec manifold to dispose of?
Having said all that, having too big an exhaust is nowhere near such a problem as too big on the induction side.
If the inlets are too big the gas speed is too low and cylinder filling, especially at lower rpm, is poor (low torque). But the exhaust gases come out
under pressure, and gas speed is not so much of an issue
John
quote:
Does this mean you have a Zetec manifold to dispose of?