Injector Question!

[93lxmustang]

I have a 1989 ford mustang notchback. I have a sn93 Paxton Supercharger on it running 8psi and when i get to about 4500 RPM it cuts out. I was thinking that this was the injectors and wasnt getting enough fuel. So i was just wondering what would be a good size for the injectors on a sc mustang. I have 24lb injectors right now but was told by few people they are way to small and the car is running way to lean!

 

[Mike92GT]

There are a lot of variables here. Are you running an FMU? You can get by with 24lb injectors provided you are using a properly calibrated FMU. Otherwise you most likely will need something bigger. How big depends on your other mods. Is it an otherwise stock engine? What size fuel pump? Another common problem is blowing out the spark in the higher RPM's. What is your plug gap? Should be .035 or so.

 

[5spd GT]

Yep, what is your spark plug gap, if it isn't "tight" enough it could be blowing out...

What size fuel pump?

24lbers could work...I wouldn't say they are "way to small" if your engine is stock.

 

[93lxmustang]

My motor is not stock. my other mods consist of

-Paxton Supercharger (Polished Chrome)
-GT-40 Upper and Lower Manifold
-373 Gears (brand new in box)
-SVO Racing Seats (Front and Backs)
-Brand New Paint Job
-65mm Throttle Body
-Electric Fan
-3 Core Radiator
-Weld Draglite Wheels(8 hole)
-Rear Tires: G/T Qualifier Dunlop P265/50R15
-Front Tires: Master Craft 165R15
-Intake
-1 5/8 MAC Headers
-X Pipe No cats
-24 lb/hr. Flow Rate Injectors
-5 Inch 10,000 RPM Tach with Shift Light
-A-Pillar Full Pod Holds 3 Gauges (Volts, Water Temp, Oil Pressure)
-White Face Gauges
-Optima Red Top Battery
-Brand New Clutch Stage 2
-B&M Short Throw Shifter
-Brand New Speedometer cable
-Brand New Clutch Cable

It is a stock fuel pump on the car also.
Also what is the FMU??

 

[Mike92GT]

FMU is the fuel management unit. It raises fuel pressure in direct proportion to boost. If you don't have one I would just put one on there and leave the injectors alone for now. Eventually you can step up to larger injectors and ditch the FMU if you decide to add more mods. Also if your fuel pump is stock you need a new one for sure. The stock pump can't supply nearly enough fuel for a supercharged motor, especially with an FMU. Go with a 255 lph in-tank pump.

 

[Mike92GT]

You also should have the car tuned on a dyno to make sure your air/fuel ratio is safe.

 

[93lxmustang]

Ok thanks alot I really appreciate the help! Yeah i just set up an appointment to have my car dynoed and tuned. So insted of putting a FMU I can just upgrade the injectors to like 32 or 36lb injectors?? Because I was told you are safer to upgrade the injectors than run a FMU. Is that correct?? So i deffinly need to upgrade the fuel pump tho to a 255 lph in tank pump??

 

[Mike92GT]

I would definately do the fuel pump, unless you have a second in-line fuel pump, like a T-Rex or something. Yes, it is usually better to run larger injectors without an FMU. 36lb would probably be good for your set-up. However this may require a new mass air meter, as well as a custom chip to get your A/F ratio where it needs to be. It will end up being quite a bit more expensive. For your power level the FMU might be a simpler option, provided you don't have one. You can pick them up pretty cheap on Ebay.

 

[JunkyardTurbos]

Yep, what is your spark plug gap, if it isn't "tight" enough it could be blowing out...
stock.

Also, check that your timing is not knocked too far back. I had the same thing happen when too much timing was taken out. If you don't have an ignition solution, go get an MSD 6AL with the boost retard.

 

[93lxmustang]

yea my timing is knocked back to far dad just figured that out as he was out there working on it. I just ordered the 30lb injectors and a 255lph in tank fuel pump. Also just called up performance dyno and they are taking my car on tuesday to be dynoed and tuned. Any one have an idea on what i may put down for numbers to the wheels running 8psi?? my other mods are listed above in the post.