2 fuel pressure regulators
Turbo Mini Forums

My SPI manifold has a 15 psi regulator. The top part of the diaphragm is vented and situated inside the plenum so the fuel pressure should rise and track 15psi above boost.

I also have a Malpassi regualtor intended for non turbo carb use...

Can I splice this into my current fuel return pipe so that I get 15psi + 1-5psi (depending on what the Malpassi is set to) ?

From the picture I would say no.

Well not unless you put the whole regulator in the plenum.

Its reference pressure looks like it comes from that small hole in the top of the body (top right of picture).

So it should do 1-5psi above the reference pressure whether you feed it with 15 psi or 150psi just so long as you feed it with something above the 1-5psi range.

The only way you could get it to "add" pressure is if the reference port (the little hole) was at the pressure you wanted to add to.


EDIT, and I don't think this kind of regulator is meant to go into the return line anyway, they are usually in the supply line feeding the carb at 1-5psi above atmospheric. Put it in the return line, it would probably just open fully to try and achieve some pressure in the return line (which is doomed to fail).

Edited by Rod S on 24th Oct, 2015.

Schrödinger's cat - so which one am I ???

You're right, I was thinking the 'out' pipe was a return pipe, but, of course it isn't - it just goes off to the carb.

Could you drill and tap a take-off on the reference hole and connect to the plenum?

http://www.turbominis.co.uk/forums/index.p...tid=469104&fr=0

The spi regulator is referenced to the pre throttle pressure. If you are intending to use the spi set up in a boosted application, it should still work since the regulator will be inside the plenum. There are larger injectors available.

You can also modify the top of the regulator to make it adjustable

Adding in tg e second regulator on the return will only create a restriction and make tg e return 5 psi, it will not add to the 15psi.

Edited by Sprocket on 24th Oct, 2015.

Good good, thats how I thought the SPI regulator one worked.

It was originally going to be a 998 turbo so the original injector would have been ok (just). But now it's a 1275 turbo I need to rethink it.

The last time I used the SPI manifold was on an almost identical spec 1275 NA. At peak power, the injector was pinned open (112% duty cycle in the logs) so I'm guessing I'll want around 50% more fuel on the turbo. I looked for the injectors you documented on TMF some years back, but it wasn't looking hopeful that I'd get one. If I make the SPI reg adjustable, could I get 50% more fuel through the standard injector or is that unrealistic?

Schrödinger's cat - so which one am I ???

I wanted to try and rig something up to measure dead-time anyway, so I think I'll get measuring today.

Its looking more likely that I'll need a different injector. If anyone has anything suitable stashed away, let me know.