Exhaust manifold pressure reading
Turbo Mini Forums

Mountune acheived 1:1 on the Works group A Escort Cosworths, but you do have to look at how big the turbo was and how much boost they were running with that little restrictor. The cam timing is apparently the key but no one will tell you where to start other than testing on the dyno.

Vizard allures to it in one of his books, but again doesnt give away any real data.

Edited by Sprocket on 1st Mar, 2015.

Does it matter that much? I butchered a metro turbo manifold and a tired gt17 together & that drove well and made more power than you could ever need in a road car.

Since you can get the same power with less pressure and heat, you will have less strain on the engine and a more reliable setup that will need fewer rebuilds. But that's your decision if that matters much.

As for the 1:1 ratio, the issue is not the average but when you get it in the engine cycle. Look at Paul's simulation data and you'll see that you if you can get a better ratio at the right time, you get the most out of it.

http://www.jbperf.com/

I made the manifold as long as I could with it at the back of the engine,without major subframe modification at least. I'd be interested to see a back to back Dyno test between a manifold like mine and a remote mani.

The 140bhp/160lbs my car made was with a modified na 1 3/4" exhaust it now has a full 2.5" turbo back system so wil be going back in the Dyno soon to see if there's any difference

Cheers

Dave the Cake

In many cases getting near 1:1 isnt that difficult.

But generally if it's a smaller unit that spools early, then it will tend to see a higher pressure ratio.

IMO 1:3 is mental though, and really I can see no excuse for seeing above 1:2 boost/EGBP

Even 6-700hp engines I've worked on that still have good spool I'm still seeing around 1:1.3 at max boost

Til the pressure sensor took a dump ( crappy egay purchase ) on my own car up to around 17psi I was pretty much bang on 1:1
That's with a factory log style cast manifold with turbo mounted onto it and from a single point of view approx 3.1 litre engine.

@ Custard, looking at headline numbers wont tell the full story. Spool, spread of torque etc etc is where you'll likely see the differences.
Cant imagine a 2.5" system making much difference. Even changing from 2.5" to 3" on cars making close to 500hp I've worked on hasnt made any noticable difference
So 1 3/4" would have been quite adequate and no restriction anyway at the 140hp range

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will