Wormhole

Can anyone tell me definitely at what HP output 55lb injectors MAX out at with 3bar fuel pressure on our cars?

Wormhole

No one?
Seems like a pretty straight forward question.

fortysixandtwo

http://www.rceng.com/technical.aspx
About 250hp at the wheels with 80% duty cycle and about 300hp with injectors at MAX (100% duty cycle).
You shouldn't go past 80% duty cycle, so 250rwhp.

Ski

They'll support 350 rwhp, running 48# fuel pressure with a stage III MAF, VR software and a piggyback.

Wormhole

That's obviously not correct. I’ve been to that website before and it is flawed for some reason.

Wormhole

Ski, that's at 100% duty?

theedge

No, you never run injectors at 100% duty. 80% duty cycle is the usual max.

Wormhole

That seems to high then. I think he is saying they max out at 350hp(100%), not that he runs them at 100%. If he got 350hp at 80% then they would be capable of over 400hp.

Ski

I'm not sure of the duty cycle, don't have a monitor on it. I can tell you we've had no problem with the car going lean at any time, we've been able to add fuel and take away - at 17 psi.

If 350 is the target, 55 will support that...actually I hope they support 365, which is what the new engine should produce when we get it to the dyno.

There are several dyno sheets out there with 380-400 with 55# injectors, not sure of the duty cycle - I do remember that Robs old car maxed them out around 410+ or so, if my aging memory serves me correct.

Jeremy Himsel

Yeah those calculators can be misleading a bit. For example if you plug in Turbo S HP with a .60 BSFC then the factory injectiors are undersized. Use a .45 or a 110% duty cycle and it'll put you in the ballpark. Another consideration is the static fuel pressure. Under boost, where we make max power, fuel pressure rises based on boost signal @ the FPR. That also changes the max. That calculator is a VERY conservative estimate. If I use that I'll need 115 lb injectors for my 3.0l......

Porschefile

Better safe than sorry I say. Are $250 worth of injectors worth risking your motor over? With higher fuel pressure, you can squeeze some more flow out of the stock 37# injectors to support around the 300-350whp area. 55# injectors would be much more appropriately sized for say the 350whp area, and that would definitely keep the duty cycles low. It has been proven for decades by the automotive industry as a whole that it is generally not a good idea to run injectors past approximately 80% duty cycle for long periods of time. Doing so can wear them out quickly and cause them to fail, stick 100% open, etc etc. In my experience, for some odd reason the stock Bosch 951 37# injectors as well as some other Bosch/Siemens injectors seem to withstand constant high duty cycles a bit better than many other brands of injectors, though it's still an unnecessary risk IMO when $250 worth of aftermarket injectors can completely bypass any potential problem.

Rogue_Ant

Perhaps I'm not understanding what you're trying to convoy here... but fuel delivery rate does not change under boost/vacuum. The actual pressure differential does not change from what the base pressure is set too. This is the purpose of having the FPR source manifold pressure. I.E. when manifold pressure is +15psi, fuel pressure rises the same to keep fuel delivery constant.


-Rogue

anders44

just slap 95 in there and be done, if you have good aftermarket efi, it won't be a problem

eniac

Or 86# injectors which have been proven to run fine with the stock DME with batch injection. You can simply increase fuel pressure from there if you need more fuel.

If your going with a standalone EMS then yeah, might as well throw in something a bit larger and use sequential injection.

sawood12

I've been told that if you size injectors too large such that you are running low duty cycles then the flow of fuel through the injector nozzle never really gets established properly due to the short time they are open meaning you don't get proper atomisation of the fuel and therefore poor mixing with the air in the combustion chamber. Is this an issue anyone has observed?