Vacuum regulated fuel pressure
Turbo Mini Forums

Hi,

I am using two 1100 cc injectors on a n.a. 1380 with a 286 cam. I am just starting to tune the engine and I am afraid that idle may be a problem due to the large injectors. I was thinking that vacuum regulated fuel pressure would improve this a little bit has anybody experience with this?

Kind Regards Will van Gemert

You should be OK with those injectors. I use a total of 960cc per port on the 998Turbo.

Connecting the vacuum to the fuel pressure regulator will reduce the fuel pressure at idle and part load. This will then require a higher pulse width which should help.

We use boost/vacuum regulated fuel pressure.

The problem with very low pulse widths is that the injector flow is no longer linear, as assumed by the ECU fueling calcs. You can overcome this to some extent with fine adjustment of the VE table.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

And if you reduce the fuel pressure....the injector will no longer spray, just dribble.

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

Paul,

What is the pressure difference that you use between full boost and max vacuum?

I just got the engine to idle quit good. The engine does have the tendency to galop (rpm rising falling about 400 rpm at idle).

Will

most people set the fuel pressure to 3 bar, mine include, and the fuel pressure track the manifold pressue pretty closley

at cruise i see fuel pressures of about 40psi at idle about 37psi, and max decel maybe 33-35 psi, full boost (20 psi) i see around 65 psi fuel press

Edited by Joe C on 26th Mar, 2011.

If you connect the vacuum hose to the regulator, you should see a steady differential presure between rail and manifold, presumably 3 bar.

Measured pressure in the fuel rail will be around 2.5 bar if you have a good idle. The injectors will work fine at this.

If the rpm is wandering about, check that you have a flat VE map in the idle area. A bumpy map can often cause wandering.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Will,

Are you running the siamese options under MS2/Extra v3.1 ??

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Yes I am running the siamese option. I posted last on this forum early last year. At that moment I was waiting for bigger injectors and had some sync problems but due to a personal accident I had to abandon the project for about a year. Perhaps you rember me. I have solved the sync problem by using high quality shielded cable for crank and cam sensors annd rerouting them away from the high tension leads. My engine specs in random order are 1380CC 1.5 roller rockers stage 4 cylinderhead with rimflow valves carbon fiber pushrods ultra light flywheel and backplate cr 12.5 megadyne 286 camshaft. home made inlet manifold with portinjection and single 52 mm Nissan throttlebody.

Yes, I remember your original post. I wondered what had happened to your project.

Welcome back.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

As I did not completely do nothing last year the car is now completely ready so I am hoping to take her out on the road next week to start setting up everything correctly. I will start a seperate thread for this. How did you connect your vacuum tube to the fuel regulator? Mine only has fuel line connections and a pressure setting bolt.

You will need a new regulator then.

Something like this:

http://www.merlinmotorsport.co.uk/p1989/RA...oduct_info.html

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."