tech question re injectors

[za - sti]

when matching injectors to your power requirements how important is it if the injectors are oversived ie 850cc ones for below 400bhp engine

does this create an overfuelling issue or do they just operate well below capacity

cheers

za

[AlanG]

One of the problems with too big a size injector is atomisation at low revs.

You could probably get away with on 850's but why bother. You will have better control over the whole rpm range if you size injectors to suit your application.

In your case 550's.

If you're buying 850's cause they are cheap, i'd advise to run a higher fuel pressure than what you run just now, just to get good atomisation (in other words not the std FPR) You may find you can't get the fuelling just perfect at low rpm but a best as can do, cause there isn't enough flexibility in the GEMS to do so.

e.g.  at low rpm you might have a lean mixture at for example 1300rpm. If you increase fuelling by even one point, you may then have a rich mixture at that point and that's because the injectors are too big and you can't get fine enough tuning at these zones.

Talk to Steve Simpson as he has been mapping your car and will be better placed to advise, though i think he'll recommend running injectors to suit the spec.

[za - sti]

Cheers Alan, no its just thinking about future plans

the car is running the standard 440cc injectors but with the 2.5 this will be a limiting factor, along with the turbo, TMIC, 2.5inch exhaust.

was  just wondering if it was worth fitting the biggest ones now rather than changing them when things get out of control as they usually do

cheers