255lph intank fuel pump and T-REX (190lph) external fuel pump combo question!

**Goliath 5.0** · 02-11-2003, 10:33 AM

Okay... I have heard mixed reviews about running a 255lph intank fuel and the vortech T-Rex (190LPH) together...

Some people say it is a solid combination, whereas the external fuel pump keeps the fuel pressure constant incase the internal fuel pump becomes incapacitated at anytime plus other added benefits of running the two pump in conjunction with each other...

Whereas some people say the obvious... For example if you were to have a 255 lph intank fuel pump and a 190LPH T-REX external fuel pump, the T-REX would be restrictive and lessen the flow rate of a 255 lph intank fuel pump since the external T-REX pump flows mathematically "65 LPH" less than the 255 lph intank fuel pump.

That is the general feedback I have been getting from many people when I ask for their opinion on that particular subject

SO...

What it boils down to is...

Some say it works! Some say it won't work!

Okay VortechPower.com peeps, chime in with your input.

Will the external T-REX pump restrict a 255lph intank pump? Will Batman ever let Robin cruise the Batmobile? Will we all get free vortech superchargers if we promise to put vortech stickers all over our stangs?

-Chris

**Forcedpower** · 02-11-2003, 12:37 PM

1. I don't think that it will. I ran this combo on my car and it worked very well. I made 425hp with it and my a/f was good. I held fuel pressure steedy at any rpm.

2. Robin will never get to drive tha Batmobile.

3. If they would then I would.:p

**91GTFiveO** · 02-11-2003, 01:18 PM

I would have to see the pump curves for both pumps (if available)and calc the system hydraulic requirements to confirm thou.

Under certain conditions, like using a high ratio fmu, an intank 255 lph may not have the capability to flow 255 lph at max conditions because now the pressure required of the pump is like 115 psi (pure guess, system loss = 35 psi + backpressure at the injectors = 80 psi = 115 psi required of the pump). Same applies to the 255 lph/t-rex combo which may not flow the 190 at the high backpressure the fmu exerts. I think the pumps are typically rated at 70 psi discharge, except for the GSS-340 high pressure which I think is rated 20 psi higher?

Typically, with any given non-positive displacement pump system, pressure produced is inversely related to flowrate. Increase the pressure the pump is required to develop and capacity is reduced. Or conversely, increase the flowrate of the pump ( say the rated 255 goes to 300 lph) and it may be able to do that but at like 30 psi discharge pressure. There may be a crossover point in which increasing the backpressure would cause the 255 intank to flow less than the 255 intank/t-rex combo.

Not sure if that answers your question or causes more confusion, but I'd need to do the system hydraulic calcs and check the pump characteristics of the specific pumps to give you a much better answer.

**Kevin89notch5.0** · 02-11-2003, 11:51 PM

Originally posted by Goliath 5.0
Will the external T-REX pump restrict a 255lph intank pump? Will Batman ever let Robin cruise the Batmobile? Will we all get free vortech superchargers if we promise to put vortech stickers all over our stangs?

I honestly don't know. Thats the exact combo I run, and the few miles i have put on my car with them both, seemed fine. None of those miles were with boost.

I don't think so!

Maybe? I'll take a free sticker!

**Trey** · 02-12-2003, 01:12 AM

Very interesting guys. I have a 255 intank right now and a T-Tex sitting on my work bench. What to do....What to do......:D

**MoDo** · 02-12-2003, 02:05 AM

i have a 255 intank and a t-rex in my car and my air/fuel is dead consistant

**Parker Dean** · 02-14-2003, 01:38 AM

FWIW, the LX out in the garage has a 255/T-REX combination. The 255 was added sometime after the original SC install.

When the car fist came to me it had an adjustable FMU on it that was a used unit from someone somewhere and it never seemed to work right. Anyway with a FP guage on the car when boost was first built the FP would spike to over 90psi and then drop steadily to about 65psi@6000rpm. That tells me the fuel system is not completely capable of supplying the engine demand. How much of that drop is fuel pump related and how much is due to stock lines I don't know.

I've removed the erratic FMU and run 36's where it had FMU/30's before. After I get some sort of Tuner/Tweecer I'll move to 42's or something and get some real fuel line in it too.

**blownaway** · 02-16-2003, 08:33 PM

I have heard that a 255 in tank will be plenty for 400 or so horsepower and you don't even need a T-rex. My car with an adjustable FMU and 36 pound injectors would always hold perfect fuel pressure under boost,with or without the T-Rex. I didn't ever dyno tune it though and now it is apart with the new motor on the way in. P.S I think I was running way on the rich side cause I cranked the FMU up so it would have like 70 lbs under boost. I might try it without a FMU next time. It is going straight to the dyno before I run it had. In conclusion, I don't think I will run the external fuel pump.