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Stock injectors vs stock fuel line....

1031 Views 5 Replies 2 Participants Last post by  TT_6SPD_95
There's been discussions about the duty cycle of the stock 550 injectors for the Supra. I had what I considered a full fuel setup (twin intank Walbro, SP fuel rail and SP injectors with an additional all Earls -6 run), this fed the rail from one end the the stock along with a fresh fuel filter was feeding the other end.

Well, I no longer have the car but was able to walk away from what could have been my last ride (this is kind of why I live on the never know :D).

Anyway, I have another Supra, this time a 6pseed and I would like to do my fuel a little different and would like some opinions from people that like to play with formula's. We talk about the stock injectors, what about the stock fuel line? I want to use the stock fuel line to feed 720cc injectors supplied by twin intank Walbro's. My goal is to put down numbers similar to Steve Jarvis (around 500 or so at resonable boost). I plan to go to Pocono and learn how to drive the car. I never have felt the need to put down huge numbers or run very high boost. I like the idea of being able to run 18-20 pounds and make decent power.

Any suggestions regarding the fuel setup are greatly appreciated. Btw, I had a PHR Stage 2 and decided to go with a SP63 .70. I'm willing to discuss my reasons off line, due to the huge respect I have for Jarrett, great guy but we all have our little quirks.

Ok Lar, Gary said he was going to phone me at work today. I've been here since 6 am and still no call :D j/k. Hope to hear from you guys before I leave my office for the day. I can't help it...I'm impatient, but having the time of my life.....


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If your goal is only 500rwhp, you might want to consider just raising the fuel pressure with the stock injectors and using a good high pressure pump like this one: Its OEM so supposedly its quite. As you can see, it flows a ridiculus amount at high pressures.

Raising the base fuel pressure 10 psi should give you 11% more flow through the injectors. Of course you don't want to raise it too high.

Even if you replace the stock injectors and use the stock rail, the stock FPR has been known to go bad (I don't think its that common, but still) so if your going to get an aftermarket FP anyways might as well try raising the pressure before buying injectors. Jonas had his aftermarket FPR attached to the stock one, so you don't have to pull the rail and weld it. Should work ok, given that the higher pressure setting would override the stock FPR.

Please don't wreck another Supra.

how do you calculate the % of fuel increase thru increase in FP?
right now I'm runing my FP to stock spec, which is 2.2bar at idle, 3.0bar at atmosphere pressure, and 4.3 bar at full boost (1.3bar+3.0bar). should I try to increase fuel pressure to see if I can get more fuel out of those injectors?
Zerosoul said:
how do you calculate the % of fuel increase thru increase in FP?

This calculation is for INJECTORS. Fuel pumps generally LOSE flow as you increase pressure, as they are having to work harder. The drop off in flow all depends on the pump. The stock MKIV pump does not appear to do too well at higher pressures from tests I have seen. You might end up switching your limiting factor from injectors to pump as you increase FP.
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I appreciate the responses

Grant, I appreciate the concern for the Supra. More important (to me and my family) is not killing myself or anyone else. I've been driving for 33 years and this was my first've probably never had any :)...I can't say that anymore but hey, was a good accident free 33 years....

So, the stock fuel line should be fine? I did say I planned to use 720cc injectors but neglected to ad that I will use a different fuel rail and fpr. The pumps will be either Walbro or the Bosch that the guy on the main MKIV list is using in his setup.


Does anyone know what max hp the stock fuel line will flow by itself?
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