I bought 4 720cc injectors. Now what do I need to use them efficiently?

 

unless you have some form of fuel control you will be running way rich! Also what year is the car? You may need to run a resistor pack if its an 88, though judging by the picture, its an 87. What mods are on the car?

Im running 720's in my secondaries only for now.

 

you only need 2 unless you are making huge power...

 

K&N Intake
3" Straight pipe
Custom downpipe
Air Pump Removed
ACV Removed
BAC Removed
Solenoids removed
Spider Removed
Fast Idle Cam Removed
TB Coolant line removed
Secondary Butterflies removed
Twin Scroll Removed
Intake Manifold Ported
Turbo Compressor Housing Ported
3" Custom Cold air TID
Fuel Cut Defencer
A'PEXi Twin Chamber Blow Off Valve
HKS Type 1 Turbo Timer
HKS MBC

and now Im putting in a street ported JSPEC engine

should I get an FPR, fuel pump, safc?

 

btw...youre right 87

 

stock turbo and IC ?? get the pump first. that is good till 12psi or so...

if you wana run more. buy an AFC and put 2 of the injectors in the secondarys.

 

yep....FPR, pump and safc.....with that u will be able to lay down some very decent numbers with what u already have....

 

FPR is not needed... that is just band aid for not having big enough injectors.

 

how much boost would I be safe to run?

 

About 12# I guess. Getting a good fmic should help out alot. Thats what really limits you.

 

stock 87-88 turbo boost limit is about 12-13psi, after that its pushing the limits of its efficiency, and its life span. you really only need the 2 720s in the secondaries. you can get away with running them by themselves. but some kind of fuel controler would help for sure. the Apex S-AFC is prolly the best fuel controler on the market in my opinion.

 

I say put all 4 injectors in if you plan on getting a larger turbo or hybrid in the future. You'll just have to get a fuel controller. With all 4 you can get a nice hybrid and make some good power.

 

thanks for all the replies. You guys have been really helpfull

 

OK, time to smack down some misinformation...

First off, the car can and will run lean before the 3800 RPM crossover - this is really where a lot of motors go at. Especially in higher gears where you're putting a lot of load on the motor. 4 720's is a great way to go.

For the original poster, a Super-AFC is a great way to tune them in - inexpensive, easy to use, and works great.

On fuel pressure regulators - a rising rate FPR IMHO isn't the best idea, that's the "band-aid solution". An adjustable base rate FPR is a whole 'nuther story. With a hefty fuel pump (Walbro) that's been rewired, you'll easily overrun the stock FPR and run WAY too rich - too much fuel pressure. The stock FPR can't bleed pressure off fast enough to keep up. So, with an FPR you can adjust your base rate with, you can set you fuel pressure where it needs to be and rock.

Anyhow, 720cc primaries is an excellent idea - the car CAN and WILL go lean down low, even with a stock turbo - I've seen it myself on a wideband. During a drag race or something, that really won't be an issue since the revs won't fall that low, but during regular street/highway driving is when it's a problem.

Dale

 

another question...What fuel pressure regulator do I need? Ive found some that compensate for boost (which I assume isnt the one I need). What range does it need to be adjustable to? etc

 

I was told by RX7.com that a S-AFC does not control the injectors untill the car is started .. and that 720 primary's will tend to flood the engine very easily on start-up. I ordered my 720 primaries just the other day .. I already have 1000cc secondaries.. I am going to find out how true this is very shortly.

 

That is totally dependant on your setup.. with my hybrid & the clip on it .. Etc. Etc. I don't even begin to hit boost till after that .. so ther eis no way I am running lean before 3800. With a good rewired fuel pump .. i think it is very unlikely to run lean at that low of RPM .. plus with a ECU upgarde you can boost the duty cycle to prevent this also... the above statement is just way to general.

 

Nothing a fuel cut-out switch can't solve...


-Ted

 

Ya, i already have one wired up .. I needed it to start my fresh rebuild .. I am going to keep it wired up, and make a permanent mount for it. I'm thinking I will need it.

 

720cc primaries don't contribute to flooding. My old roommate Jay (Opec) has 4 720cc injectors and a Super-AFC and has no problems whatsoever.

Heck, when we first installed the 720cc primaries we forgot about them (we were doing a LOT of other things at the time) and started the car without even touching the Super-AFC. Car started right up and idled no problem. You could tell it was rich, but it idled just fine.

Anyhow, I don't feel that this is a problem.

Dale

 

all the AFC does is mess around with the signal coming from your AFM going to your computer. it tricks your ecu into running richer or leaner. i dont see how it could affect the car at startup

 

are you using a stock FPR? I figured my 255 FP Im buying will be too much for a stock one

 

okay this guy is only sending me 2 injectors now...I guess I was mistaken...or something. Im not going to blow my NEW engine up at 12 psi with 550 primaries and 720 secondaries, a 255L FP, SAFC and maybe a FPR am I???