jasono718

iTrader: (-1)

im at 25psi and running lean with 550s.. what should i upgrade to now???
thx

Ben

iTrader: (33)

more fuel pressure

Lex

or larger injectors ?

PAT!

iTrader: (1)

What are you running for a pump?

jwarriner

25psi on a Big 16G is going to be close to the limits of 550s assuming you're at 75psi of fuel pressure (50 base + 25psi of boost). Are you measuring pressure? Does it peg at 75psi or drop off? Are you running an FMU than puts the pressure higher that 75psi? On my Small 16G DSM I ran 660cc injectors and a Walboro 255 HP, it was happy, had plenty of fuel and enough pump. I also had an aftermarket FPR that could handle the Walboro 255.

As others have stated, it's your injectors or you fuel pump. Knowing which, or if it's both, is a matter of measuring pressure and logging duty cycle.

magnamx-5

iTrader: (7)

850's Or just get a 255 and run abit more pressure you are most likely outflowing the stock rail at those pressures though you need a dual feed or **** vood fuel rail for that much power. I thought you wanted 22 psi why the jump? Or add some Water methanol injection and the bsfc will go down and the power will come up.

magnamx-5

iTrader: (7)

his factory pressure at 25 psi would be akin to 75 psi of fuel pressure even the 255 doesnt flow enough fuel past 90 psi to support more than 300 or so hp check out the specs and flow rates for your self. http://www.autoperformanceengineerin...l/fpspecs.html to be conservative you want 1 gallon of fuel flow per 100 hp or so.

jwarriner

Well then I'd advise him to get some larger injectors and an aftermarket FPR that'll handle the Walboro 255 HP and run no more than 50psi base pressure. DSMs have made 500hp on a Walboro 255 HP running 43.5psi base pressure and 30psi on large turbos. The secret is in the injector, 850cc/min injectors, and you don't need to run insane fuel pressure that'll cause a dramatic drop off in the Walboro.

magnamx-5

iTrader: (7)

his stock FPR and most other oe FPRs are 1-1 while in boost. His fuel rail is realy limiting him in my opinion more so than the 550's even.

jwarriner

Possibly so, the Miata rails, and all the lines for that matter, are tiny. If I wanted to make 300+ hp I'd run at least an -8 AN line from the tank to an aftermarket rail and then something like an Aeromotive FPR, and maybe run a larger return as well. The 550s should be good for 300 or more HP with 50psi base pressure. If he's not making that kind of power then it's time to look elsewhere besides the injectors.

magnamx-5

iTrader: (7)

I agree

jwarriner

I had been assuming that at 25psi he was making 300+ hp AND running lean. But if not then I totally agree the injectors are fine.

magnamx-5

iTrader: (7)

by 25 psi if the turbo is doing as it should at that pressure he should be able to hit 550 cfm on the big 16g should be enough for 350 easy if his tune is anywhere near right he should hit 320 but like you said before it is all in the tune.

Braineack

iTrader: (62)

when does more boost pressure increase the pressure in your rail?

magnamx-5

iTrader: (7)

becouse his stock fpr raises 1-1 ratio, with boost. duh :gay:

jwarriner

???

As magna said, stock FPR raises your fuel pressure 1:1 with boost. If it were not this way your injectors would spray less fuel as the pressure differential across them decreased.

Ben

iTrader: (33)

you're both right. and both wrong.

to get differential pressure you have to subtract manifold pressure from fuel pressure. base + boost - boost = base

magnamx-5

iTrader: (7)

Actualy i am right and warriner is just explaining it to generically/ If i am not right then all our 12-1 fprs are realy 11-1 think about it.

jwarriner

That's the way I see it. The first 1:1 is just to overcome the extra pressure in the manifold, the other 11:1 is more fuel.

jasono718

iTrader: (-1)

im running a vortec fmu and a walbro 190lph hp pump.. i feel that the only thing limiting me is the rail and maybe the line to the rail... was gonna switch to a -8 or -6 line from the tank to the rail... but i havent had a chance to measure or find out what type of fitting ill need to attach the line to the pump/tank...also wanted to switch to an aftermarket dual feed rail but cant seem to find any on the market right now.. and dont want to make my rail dual feed....