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The mkiv Supra Owners Club

FPR needed or not?


Steve

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Size the injectors to run the power output desired at a sensibly low duty rate at manufacturers recommended fuel pressure, nevr fudge fuelling by upping line pressure to compensate for marginal, or too small a size, injectors. If running at stock pressure the stock FPR is fine for even big HP engines, it's a fallacy that you "must have" a bigger FPR, or an adjustable one. Most aftermarket ones have less control and reliability than OE ones. IMO.

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Size the injectors to run the power output desired at a sensibly low duty rate at manufacturers recommended fuel pressure, nevr fudge fuelling by upping line pressure to compensate for marginal, or too small a size, injectors. If running at stock pressure the stock FPR is fine for even big HP engines, it's a fallacy that you "must have" a bigger FPR, or an adjustable one. Most aftermarket ones have less control and reliability than OE ones. IMO.

 

Yup, in a perfect world. I just like the option to adjust when developing the map. Two or three psi can make a big difference.

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Are you using fuel line base pressure to basically "fine tune" the injector sizing then?

 

Also , I've found that the OEM one, which I'm sure is as good as CW says, has the limitation that it supplies fuel at the base pressure that the stock injectors were calibrated for. Not all injectors are calibrated to run the same pressures. ie when a manufacturer says they have 550cc injectors, that is at a specific pressure, (Which there is currently no standard for, so could be 2.5,3, or even 4 bar) so if you were to run them at anything other than that base pressure, you would have an injector that would flow too much, or worse, not enough fuel as you were expecting it to.

 

I say source injectors that are man enough for the job (give yourself some leeway for upgrades - but don't go silly with it) and then find out if they were flow tested at the same base pressure as the stock system (I'd be suprised if you found any that were!). If not then get yourself adjustable regulator to set your base pressure to the pressure they were tested at. IMHO the only complete way to set the system up.

 

 

 

edit to add:- Just spotted that CW mentioined the stock FPR was good if you were running at the stock base pressure

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Yes it is - but I needed one as I junked the whole stock fuel system barring the return pipe. This was before the single-walbro-plus-PE650cc-injectors setup was thought of... Cost me a fortune doing a twin in-tank pump setup with -8 main hose and a twin entry HKS fuel rail... :)

 

If you have to have one, get an Aeromotive.

 

My 720cc injectors run at 81% duty to give 11.4:1 afr at 1.4bar on a T67. So you'd need about 90% duty on 650's to acheive the same delivery of fuel - about as far as you'd want to push them but they will do it :)

 

-Ian

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