Here's my setup:
93 miata
15g Greddy turbo and manifold
2.5" TurboTony DP
Flyin Miata dual-feed fuelrail
305 Supra injectors (green tops)
Megasquirt PnP

I'm looking to turn up the boost to 10psi from its current 5 psi. I also have an inline fuel pump, but I don't want to put that on unless it's absolutely necessary.

So, possible or not with my current setup? Or should I put the Pierburg pump on there for a little more security?

 

The Pierburg fuel pump is absolutely unnecessary unless you're running an AFPR. My setup uses 440cc injectors at 12-14PSI on the original 16 year old stock fuel pump with no problems.

The injectors themselves are going to be the determing factor for you. Best suggestion is to start turning up the boost very slowly while keeping an eye on the injector duty cycle and A/F ratio. My bet is that 10PSI is gonna be pushing it on 305s.

 

not enough injector for 10 psi at stock fuel pressure.

 

question.... i dont have greddy but i still haev a question. I don't need a fuel pump if i have MS correct? I can simply use MS to tune and watch the duty cycle correct( as you mentioned).

 

Sounds good. I'll put the pierburg on there then ^_^ Thanks guys!

 

Do you have a FMIC or WI??? Just pushing HOT air if you don't.

 

the peirburg won't help you at all. you need bigger injectors if you want more boost.

 

You're not listening. The Pierburg pump isn't going to accomplish anything if you don't have an AFPR. That's the whole point of crazy aftermarket fuel pumps: to be able to supply fuel at the increased rail pressures that AFPRs attempt to generate.

That being said, you already have a Megasquirt, which is about as good as it gets. In your position, installing an AFPR would be stupid. Sell the Pierburg pump, and between that and what you'll save not buying an AFPR you can get some 440cc injectors and have money left over to buy liposuction for Loki's sister. (different thread...)

 

You do need a fuel pump for most automotive gasoline engines, otherwise no fuel will flow through the lines from the tank to the engine compartment. Very few automotive applications use gravity-fed fuel systems these days, although they are still common on motorcycles and high-wing piston aircraft.

However, the stock fuel pump in a Miata is perfectly adequate for anybody who is using larger injectors and proper engine management to meet their fueling needs, rather than relying upon an AFPR and higher-than-stock fuel pressure.

 

Sell your 305s and the Pierberg pump and buy a set of 460cc Rx7 injectors. They will take you to 10psi and well past that (I'm starting to max mine at 15-16psi).

 

DB, Sav and Joe are correct. Sell the pump, sell the 305's. Buy 440's or 460's.

After that... you still need an intercooler or water injection to get the charge temps down. You'll have to pull so much timing at high boost due to the air temp that you'll start getting negative returns at higher boost where more boost actually makes no more power... then you'll knock and blow your motor. I'd do the Intercooler before going with bigger injectors. You might find that getting the temps down will let you better manage your timing and give you the power you're looking for now until you can spring for the larger injectors.

 

yup id look into an intercooler.

 

If you aren't intercooled, 6psi is the max you can safely do. You need larger injectors and an intercooler to go beyond that.

 

Whoops, I forgot to mention that =P I have a spearco bar and plate intercooler, 23-24" x 3" x 8" core with 2.5" end tanks.

Joe, I totally blew over the "un" in unnecessary o_O I'll look into the RX7 injectors.

 

What's this OR business? FMIC and Methanol FTW!

 

I cannot remember what my duty cycle was (85%??) but I considered my 440's maxed out around 220HP and swapped to low imp 550's and resistors.

 

I just bit the bullet on a set of 550cc purple-top turbo RX7 injectors. Shouldn't have much of an issue with fueling when those go in

 

Except you won't be able to idle <G>.

I'm not sure at what point injectors become too large. My 550's don't have any issues. Do you have to run resistors with the purple tops?

 

According to Braineack's FAQ, they'll go right in. They're high-impedance injectors.

 

they are a little on the big side. idle quality may suffer a little. the 550s can supply enough fuel for 340 rwhp or so.

i'm running 440's. 74% duty cycle at 255 rwhp, stock fuel pressure.