SkidPalace

Hi all,
I have spent the last several days reading and reading regarding the options for feeding the supercharger the necessary amount of fuel.
I have been running my 1st gen s/c since the truck was new and I have not paid much mind to the fuel mods, since I don't get much ping at all.
However, the more I read, the more I feel I need additional fuel as there is HP sitting on the table and I know I have burned through some exhaust components as a result of higher EGTs due to the S/C running lean.
Currently my 1st gen has on the "free FMU" mod. The fuel pressure regulator is connected to the boost port.
My question is, will ~315cc fuel injectors alone provide adequate fueling and are they plug and play with the existing connectors and stock ECU?
Gadget's website (although outdated) actually says "I currently have my stock FPR connected to the boost port and I am using the 305 cc injectors." under the Free FMU section of the Fuel Delivery page.
Also, Speedy's supercharger thread on this site mentions that the stock fuel pump is sufficient, even for a 7th injector upgrade.
I don't have the cash to drop a grand on the URD kit at the moment. I can however pick up some used '93 Supra injectors for $50, or a set of flow tested and matched units for $100.
They don't look like a walk in the park to install them, so is it worth my effort to install the injectors?

mt_goat

Dude, you can't just throw in bigger injectors without a piggy back to control the fuel. The stock ECU isn't programed for them. You must have some type of FTC (piggy back) to control them.

To answer your question, yes, 315cc is big enough and they will plug in if you get the right ones. I'm not sure what the right ones are though. I rewired all my injector harness for the URD injectors.

okie81

There's not many other options I've seen to provide adequate fuel delivery for the s/c other than the URD system.

slacker

iTrader: (1)

ok, school me as well !! I've looked at lots of Supra sites and indeed have built a 400HP (est) HP engine without computer mods .. adding larger injectors of course with intake and exhaust mods WORKS .. but the engine is turbo charged , not super charged ... is this the big differance ? supra engine is computer controlled as well as EGT are an issue ... and ultimatly , piggy back would be the best for max tuning , but bottom line with min mods .. I got's 400 out of this engine !!

let me know your thoughts , as I'm wanting to do this as well

.

mt_goat

Well its pretty much the only way to tune it. There is a difference between a building a race car and adding a SC to a daily driver. With a daily driver you don't want it running around pig rich all the time or you'll waste more money on gas and cats than you'd ever save by not adding the proper tools to tuning it. A race car is pretty much tuned for WOT. At WOT the ECU is mostly out of the loop (open loop).

That being said running too rich IS safer (for the engine) than running too lean. But there are still dangers, like washing the oil away with too much fuel.

The 315 cc injectors without an FTC to control them would probably run very rich (like around 7-8 on an A/F guage). I have my fuel cut quite a bit with them to get it close to 11 at WOT. And good luck getting it to idle. For some perspective, the ECU will try to keep the A/F at 14.7 in closed loop.

mt_goat

No, the method of boosting is not the reason.

SkidPalace

I recall reading on this forum that the ECU will adjust the out of whack A/F ratio by dialing down the injector pulses. At WOT, the injectors just spray at full capacity, which happens to be perfect for this engine's HP level. I guess I read incorrectly.
So the 315cc injectors and a fuel management unit like the SMT6 or the URD controller should handle the bulk of the issues with the superchager with the stock fuel pump and pressure regulator?
I really appreciate all the research and advice provided to the community by Gadget but, damn, his kit is ridiculously expensive for what it is.
I believe in the 80/20 rule. If you can get 80% of the benefit for 20% of the cost or effort, then I call it a win.

mt_goat

Yes... it will try, but it has limits of adjustment. Not sure exactly what they are and it does depend some on the year ECU. And it will only adjust in closed loop, for the most part. Go ahead and let us know how the experiment works.

If you don't think the price of the kit is reasonable, buy the parts on your own and put one together yourself.

Personally I'd rather stay stock than boost without a good tuning.

vandert

There is one way you can get an adjusted MAF and match it to the injector's, but with the cost your almost better off to go with the URD setup.

spaugh

you can toss in bigger injectors, they will run at 14.7 until you go into open loop. then you will probably be running way rich unless you are making like 10lbs of boost. In open loop, my truck will dump gas with the stock fuel system down to 11.5 with just the blower, no add ons. The best thing to do honestly is buy and AFR meter and gauge and see where you are right now in open loop.

UKrunner

Remove stock fuel pressure regulator.
Replace with adjustable external fpr.
Install wide band for a/f.
Test and adjust
If running lean in closed loop, move O2 sensor 18 inches towards the tail pipe.

mt_goat

Interesting, info. But keep in mind the newer 2001 and up models like you and I have are better programed to adjust to the SC fuel needs. I doubt the results would be as good with a 98-2000 truck, and especially a 96-97 truck.

Good advise.