I'm still getting familiarized with how it works but my impression so far is that I can just use stock injectors and stock fpr with it (for 7-8psi boost), is that right?

I did search a lot but everyone seems to run bigger injectors.

Originally posted by T_K
I'm still getting familiarized with how it works but my impression so far is that I can just use stock injectors and stock fpr with it (for 7-8psi boost), is that right? I did search a lot but everyone seems to run bigger injectors.

No.

how about bigger injectors, stock fpr, shorter pulse off boost?

Whatever gave you the idea you could use a stock pressure regulator?

ok ok I'll just go read more :+




...
and so I found I need a 1:1 FPR.

you need a 1:1 fpr. otherwise when you're at 8psi of boost your fuel rail pressure has been effectively LOWERED by 8psi (due to the pressure difference) and you will thus be getting less fuel. pressure is a relative measurement - normally taken in reference to atmospheric pressure (gauge pressure) rather than absolute pressure. if your fuel rail had a pressure of 40psi (gauge) and you were also boosting 40psi (gauge) then the effective pressure difference between the rail and intake manifold would be 0 psi. you would simply be dripping fuel into the mani.

ok

now again about the stock fpr, couldn't I just use a rising rate addon fpr like the basic vortech fmu with 1:1 setting?

the thing is I got a '95 and I just don't want to cut the fuel rail :)

Originally posted by T_K
ok now again about the stock fpr, couldn't I just use a rising rate addon fpr like the basic vortech fmu with 1:1 setting? the thing is I got a '95 and I just don't want to cut the fuel rail :)

hmmm, you don't cut the fuel rail(I'm not sure who has cut thier fuel rail, think about it)...I think your confused about cutting the fuel pressure regulator to allow you to lower the fuel pressure and you typically only need to do this if you have oversized injectors and are NOT using the MS. I can't remember what the factory fuel pressure is, but you might as well just hack your regulator anyway. I set my static pressure @ about 45 psi. Buy the areomotive regulator that everyone uses. Proven and pretty cheap.

I got a SFMU very cheap so I'll just use that for the time being till I get a better idea how the whole thing works.

did you read my explanation of why you're supposed to use a 1:1 fpr? the idea is to take the pressure differential out of the equation and focus fuel adjmustment on using pulsewidth ONLY. the MS does not use rising fuel pressure to increase fuel. it uses pulsewidth. if you use your SFMU while the MS is assuming static pressure you're going to be running very rich. if you want to use your SFMU don't use the MS. if you want to use the MS get a 1:1 fpr. AFAIK the MS is not made to compensate for changes in fuel pressure. this is why you use a 1:1 FPR to keep the pressure difference between the rail and the manifold contstant.

here's an example:

0vac/boost and fuel pressure at 45psi.

pressure difference is 45psi.

10psi boost using a 1:1 fpr and fuel pressure is at 55psi (relative to the atmosphere).

pressure difference is still 45psi.

this makes things much simpler.

if you want to use your SFMU you're going to need to have the MS monitor fuel pressure as well and come up with your own fuel tables which compensate for the changing fuel pressure.

the whole point of the MS was so we could ditch less accurate means of fuel management such as rising rate FPR's.

I will use the SFMU for now and when I get more familiar with engine management I'll get a MS and 1:1 fpr. Thanks for the advices :)