NEED HELP ON FUEL INJECTOR SIZE WITH PAXTON!

[bigmike32172]

OK guys i'm finally in the ballpark with the HP i should be running. first things first, i guess you don't want to gap your spark plugs at 32 like paxton says, as the spark was being blown at approx 4500 rpm and up, so i guess they should be gapped at around 28 to 30 to avoid this.
next i was told to install 60# injectors, which i did, only to find out that they are maxed out in the mid 5000 rpm range @ approx 700 rwhp.
the dyno was performed on an all wheel drive dyno, cant remember the name, but i do know that the readings are right on, unlike the overinflated readings with a dynojet.
so my question is: what is the next size up onjector i should go with. the dynop shop told me to try to find one that is at least around 75#'s.
thanx in advance for the help guys!

 

[Viper Specialty]

Hello Mike,

Can you provide some more information? What type of Engine Management are you using? Are the injectors you have now high or low impedance? (preference?) Fuel system? Fuel Pressure?

 

[bigmike32172]

i have the vec2, walbro 255 fuel pump, 60# siemens high impedance shorty injectors i got from cody at ART.

 

[Viper Specialty]

mike- are you still running stock fuel pressure or the Paxton booster pumps? It sounds more likely with that configuration that you ran out of fuel due to fuel feed volume...not injector size.

If you are already running boosters, it is time to overhaul the fuel system totally...

 

[britospeed]

At 50psi those injectors should support 850 crank HP @80% duty cycle.

 

[Russ M]

The injectors you have now are good for 950-1000rwhp @100% so you are either.

A) Running out of fuel pump
B) Not tuning the vec 2 properly
C) Making more horsepower than that.

C) is not likely with a paxton

 

[PBJ]

Mike,
I just finished a 04 with a paxton, water, nitrous, 60 # injectors with a vec2 and I made 866 with the water on 93 octane and 901 on 110 octane before the spray. My air fuel was a flat 12.0-12.2 across the board with no issues. It sounds like you don't have enough pump to me.
Joe

 

[bigmike32172]

Seems like a lot of people are saying the injectors should be fine. maybe the pump is a little too small. is there a bigger pump that will just slip in place of the walbro 255 in the tank, or are we talking big money into a crazy fuel system?

 

[Viper X]

Hey Mike,

Not enough info to help you, and you need help. I seem to recall that you posted on a similiar set up / fuel issue before. You didn't have enough fuel pump then and you don't now. You have a fuel volume and pressure issue with your fuel pump, not your injectors. Call DC Performance and ask for Dan. He will help you before you blow your engine.

I am running 60 lb injectors on my 925+ rwhp Paxton SRT-10 (pump gas) and have more than enough fuel with the same #60 Siemens shorty injectors. I am also running two Bosch 044 pumps rated at 400 LPH each with -8 line going up to the fuel rails and a -6 return through an Aeromotive regulator. Not sure of the exact duty cycle (I can't remember right now and the car is at DC being re-tuned) but the shorty injectors are no where near maximum with my setup. I am using an AEM and you can monitor the injectors duty cycle, pulse width, etc.

One 255 LPH pump isn't close to enough pump for your set up. You need at least 2 of these and some guys are runing 3.

Good luck,

Dan

 

[Joseph Dell]

Mike - the paxton kit comes with an additional pump. did you install it?

 

[NoRice]

It counded like all he did was replce the intank pump with a Walboro 255 and since he didnt use the split second, he ditched the paxton addon pumps. Sounds like not nearly enough pump. If you motor is stock, why didnt you just go with the paxton suppled setup?

 

[bigmike32172]

Thanx for the help guys. Well it sounds like the 60# injectors are good to 1000rwhp i guess it must be the pump then. When I talked to ROE & Paxton they said you can't use the booster pumps and/or the split second if youre using the vec2. Maybe they don't know what they are talking about then. So it looks to me like I am going to have to research adding extra pumps in the tank then, and possibly a bigger fuel line then.

 

[NoRice]

Why are you using the Vec2 and not the split second? If you are on a stock motor running the stock pulley, I would just reinstall the split second and the supplied pumps it came with. They have been proven reliable and able to support the HP you are seeing. If you do not want to use the split second and the supplied paxton pumps, then you will need a custom fuel system. Leading Edge Performance is working in an intank solution that will hold 2 or 3 walboro pumps. I think you will have to upgrade your fuel system to include a return line if going that route or any other custom route. Which isn't a bad idea, just a little more expensive to run the new fuel line up to the fuel rails and use the stock fuel liine as your return line. Are you doing this yourself or do you have a tuner there? You may be better off getting your car to Leading Edge Performance in Las Vegas for Garth to hook you up, or Dan at DC Performance in Los Angeles, as it doesn't sound like your tuner knows what he is doing.

 

[bigmike32172]

I was told you would get more HP with a vec2 over the split second, but if I had to do it all over again then I probably would have just went with the split second.

 

[repiv]

You can still use the supplemental Paxton pumps with the VEC2, you just allow the split second box to control those pumps, that is the way is was set up on my S/C car.

 

[NoRice]

In either case, it sounds like you need to go back to the start and start over. As Kelly Martin posted on the alley, he is using just the split secomd with his 900rwhp TT setup with no issues. Vegas used both the SS and VEC together with no problems and he was using smaller injectors than you are. I have 65lb inj. and a Vec2 with an Aeromotive external pump and have no problems. Since you already have the Vec, I would probably do as Vegas' car was setup and just use the SS to control the pumps and the VEC for the tuning. Only thing I dont like about that is now you have 2 potential areas for fault vs. 1 with just the VEC. You could also sell the VEC to recoup you money, as their is always someone looking for the VEC and go just the SS way.

 

[Viper X]

I'd go back to the stock Paxton set up on a stock motor. No need for adding the VEC II or anything else. The stock Paxton set up works very well, is dependable and makes plenty of power. The split second box is programable as well.

DC can tune your stock computer if you'd like to maximize power.

Dan