Fuel injector debate!!!!

**BenGSX** · August 3rd, 2006, 08:51 AM

This should be goin on in here not in the garage guest book!!!!

http://www.sacramento-dsm.com/garage...estbook&CID=14

**my3awds** · August 3rd, 2006, 09:43 AM

RRFPR's (Rising Rate Fuel Pressure Regulator) are what n/a people who turbo their car usually use. Since the stock n/a fuel pressure regulator doesn't see boost ratio and raise fuel pressure on a 1:1 basis like a turbo one, an RRFPR does this. It can do 1:1, 1:8, even 1:10 increase depending on the setup. The reason why people use this instead of a regular fuel pressure regulator is that they use the stock n/a ecu with close to stock injectors. By doing this, since the RRFPR only raises fuel pressure during boost, you don't have to tune your idle/partial throttle settings as the pressure remains at stock levels. Neat.

Using this on a turbo application would work to. The downside is that unlike the AFPR, the RRFPR cannot fine tune itself since they use "ratio plates". You're stuck with whatever you install (ie 1:1, 1:8, 1:13, etc etc).

**BenGSX** · August 3rd, 2006, 11:32 AM

Right This is all understood.. The factory FPR is a RR fpr with an ECU controlled solenoid sitting between it and the boost source... THe only reason to swap it out is to accomodate increased flow from the pump or if you want to be able to adjust the pressure..

The basic debate here is if 550's will ever push enough fuel to feed a 70+lb/min 62-1 turbo.. :)

(And were not talking about c16.. 91 pump )

**my3awds** · August 3rd, 2006, 11:50 AM

Right, because it's undersood, running an rrfpr with an injector upgrade can be equivallant to increasing to huge injectors, but with the stock fuel pressure ratio. And, a turbo size does not determin the actual airflow a tuner will see. So if he only plans to run 15psi of boost, he may only see 50lbs/min of airflow, in which case he might not need to compensate as much.

This is why some people get away with using stock 450's, an evo 16 g at 18psi, walbro255, and an afpr to raise the amount of fuel delivered to the injectors.

**my3awds** · August 3rd, 2006, 11:59 AM

Originally Posted by turbocooker

i dont know why people run freaking huge injectors. with my to4b vtrim i was running 20psi and my injectors were running at 25% duty cycle.

If this is the quote that you're concerned about Ben, he can say whatever he wants, but until we know the rest of his setup and a log for this, it really means nothing. What was his knock count? What did the logger read as karmen ariflow input? What was his fuel pressure ratio?

**BenGSX** · August 3rd, 2006, 01:04 PM

True true.. I just wonder what the physical limits are of a 550.. Yes increasing the pressure will increase the amount of fuel delivered but its not a perfect linear ratio And there are physical limits that the injector can withstand.. you cant just increase the pressure by 400% and expect it to function without locking or overheating. Not to mention heat and increased wear on your fuel pump due to the added pumping resistance.. Heres a good article about it.. Not super detailed but he makes a good point at the end

http://autospeed.drive.com.au/cms/article.html?&A=0349

"The equation shown above can be used to fairly safely predict the increased injector flow that's possible by increasing fuel pressure. But as with any modifications, it's best if it's done in moderation. Going ballistic with the fuel pressure will cause the pump to wear fast, and may cause the injectors to overheat if they are always working against a much higher than standard pressure. But for gains in fuel flow of 20-30 per cent, increasing injector fuel pressure is a viable and cost-effective approach."

sure the 550 will cover the gap to a point.. Maybe if he doesnt run much boost outta that turbo.. But then whats the point of such a super huge turbo if your not using it? Tons of lag for nothin :) Im not trying to spark a fight or anything.. just trying to be helpful

**BenGSX** · August 3rd, 2006, 01:08 PM

Heres another good one..

http://www.ttmtechnical.com/fueldelivery.htm

"However, buying bigger injectors can be an expensive option. If the existing injectors are only slightly too small for the power in your engine, then sometimes the extra fuel flow can be achieved by keeping the stock injectors and upping the fuel pressure so that more fuel flows for the same duty cycle. In some systems you can get good flow while upping the fuel pressure by as much as 1bar upto a max of about 4bar. This is as much pressure as any stock injectors should be pushed to. Once 4bar fuel pressure is exceeded, injector life is dramatically cut, and in many cases there is no corresponding rise in fuel flow once the pressure is pushed beyond 4bar."

4 bar is around 58 psi..

**my3awds** · August 3rd, 2006, 01:31 PM

Yeah, the downside to using smaller injectors and an rrfpr is that you REALLY abuse the injector. It's nice that injector duty cycles aren't effected, but pushing that much pressure through a pinhole is never good for an extended period. And the results should be pretty linear up to the point of wear, which will of course be premature if done too often. So that type of setup, in the end, is really up to the tuners goals. If it's a car for primarily the track every other weekend or so, its perfect. But for the normal joe-blow who knows nothing of tuning and how it works, or for the guy that likes to push it alot and often, then the huge injectors become the popular school of thought.

Manny

(On a side note, That first link you posted still works with the rrfpr concept, you just have to calculate what actual psi your fpr will read once it hits atmospheric pressure. 400bhp, 4 injectors, .65 BSFC, 80% IDC (pushing it), System FPR 100 (if you are using a 1:2 rrfpr and your base is 50psig. 563cc injectors is roughly what you would need with a 1:2 rrfpr and a 400bhp goal).

**OldDirtyNoSeven** · August 3rd, 2006, 01:42 PM

I ran 11's on 550's a 20g and cams so untill you get to low 12's you should worry about the tune not the injector size.

Or just run it untill you fry a piston and go from there!! HAHAHA

**98spydert** · August 3rd, 2006, 02:13 PM

Originally Posted by BenGSX

Heres another good one..

http://www.ttmtechnical.com/fueldelivery.htm

"However, buying bigger injectors can be an expensive option. If the existing injectors are only slightly too small for the power in your engine, then sometimes the extra fuel flow can be achieved by keeping the stock injectors and upping the fuel pressure so that more fuel flows for the same duty cycle. In some systems you can get good flow while upping the fuel pressure by as much as 1bar upto a max of about 4bar. This is as much pressure as any stock injectors should be pushed to. Once 4bar fuel pressure is exceeded, injector life is dramatically cut, and in many cases there is no corresponding rise in fuel flow once the pressure is pushed beyond 4bar."

4 bar is around 58 psi..

That is cute. Raising your fuel pressure from the base 43.5 by 4 bar is rediculous enough. Then add the additional PSI from the 1:1 ratio to boost. Run 20 psi and your fuel pressure is now 121.5psi!!!! Someone needs to read up about how actual fuel delivery isn't linear to the rail pressure. These Walbros we use are not efficient at extremly high pressure, they are only efficient at certain ranges, depending on model. Not to mention the rest of the fuel system taking pressure 3 times that of factory? Get real.

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