Something For You Guys To Think About Before You Throw On Bigger Injectors

[fromtheshadows]

:lol: nicce. Bump for making the most from my tiny stock injectors (although I still think orange is ugly)

[The Poi]

While under boost they also have to overcome the manifold pressure...the reason why FP goes up with boost in the first place

3 poking pages and only one person has mentioned this? Good god people, this is how fuel injection works. jesus christ.

[Tadek]

3 poking pages and only one person has mentioned this? Good god people, this is how fuel injection works. jesus christ.

You're completely right, this is really an unbelievable thread!

I wonder why so far no one has mentioned that when you double your fuel pressure, you increase the flow of your injectors by roughly 40%.

[Johann]

3 poking pages and only one person has mentioned this? Good god people, this is how fuel injection works. jesus christ.

The thread starter mentioned this already...

0 vac 45 lbs of FP

7 lbs boost- 52 lbs of FP

15 lbs of boost- 60 lbs of FP.

52-7=45

60-15=45

Looks like his FPR is working A-OK

The 850T5's use a higher base pressure compared to the later models. Basically the new multi nozzle injectors will give more fuel on an 850T5 than what they are rated for.

Also the idle behavior and accelleration enrichment levels will change. Anything closed loop will stay more or less the same. Anything over ~4500 RPM will get richer with larger injectors.

I measured a lot of difference between orange and white injectors at 5000-6500 RPM, almost 16% and proof that the white injectors were providing more fuel that their higher rating would suggest. At 20.5 psi, KKK turbo + Atech IC, the white injectors were near their max. Starting 6000 rpm and up they had a hard time keeping 12.5. I guess this also more or less confirms the basic rule of max HP=CC rating at max DC. We did Dyno Volvo KKK's at 340+ crank HP, they are rated 335 HP. Blue injectors in this same setup without a retune, '97 850T5 M4.3, would flood the engine in several area's, mainly cold start and fuel enrichment putting the throttle on from closed loop. Higher end will totally flood the engine. Greens it completely totally overkill unless the software is completely rewritten... Every injector change needs a retune.

Another thing is that the stock 850 fuel pump appears to have a hard time providing fuel over 340-350 crank HP.

Same goes for stock blue injector setups changing to green.

Rev down to idle the greens will go rich for a moment after which the ECU will recover to Lambda, the blue injectors always behave spot on. Closed loop will stay near lambda but load will see faster and a tad more enrichment. Near 6000 RPM the difference is roughly 12.5% more for green injectors vs blue at the same DC.

It is not only the maximum values but also the acceleration enrichment near peak torque which determine the correct injector size needed. Accelerating hard from just before peak torque can make a to small injector run after the facts. It needs a reserve to get a headstart for proper fuel levels during full boost acceleration.

[WhiteT5]

And that's why I say, when this man speaks, you should listen.

Iterating my earlier point, the wideband is one of the most useful tools you could possibly have. It is worth every dollar. Don't even think about touching any component of the fuel system until you have sufficient data to say that it's necessary. Even then, the effort is futile if the fuel program is not reprogrammed.

[Gioseppe]

this thread is absolutly amazing. i nominate for stickey.

[Yellow95]

While under boost they also have to overcome the manifold pressure...the reason why FP goes up with boost in the first place

Understood, but surely you dont believe that fuel that is already pressurized to 45 lbs at 0 boost needs 60 lbs to squirt against 15 lbs of pressure? The FPR is also set up that way for fuel enrichment.

Gary

[JCviggen]

If they wanted enrichment they could play with the duty cycle. Its to keep the pressure differential steady

basic math.... lets say you ran 20 lbs boost and 20 lbs fuel pressure...what would happen :)

[Yellow95]

If they wanted enrichment they could play with the duty cycle. Its to keep the pressure differential steady

basic math.... lets say you ran 20 lbs boost and 20 lbs fuel pressure...what would happen

I didnt learn that in basic math. I am just telling you that when you have a pressure differential of 4-1 (60 lbs of fuel vs 15 lbs of boost) the additional pressure needed to overcome the manifold pressure is not 1 for 1. If all variables where equal, then you are correct, it would be a one for one trade off.

Gary

[WhiteT5]

If they wanted enrichment they could play with the duty cycle. Its to keep the pressure differential steady

basic math.... lets say you ran 20 lbs boost and 20 lbs fuel pressure...what would happen

Oh, let's make this fun! Someone add a poll and see how many get it wrong. :sheep:

[Mogatu'r]

This is good info, poking ever1 should be reading this!

[paulr]

I think the real point isn't the debate between 310 and 350cc but those considering or running 500/750/800/1000cc injectors (especally without a remap). 310 to 350 is a 12% increase, while 350 to 500 is a 42% increase. ouch. 500 to 750cc is a 50% increase. double-ouch.

If you're smart enough to remap it's just waste,and if you're not, then you'll just be rich as all hell for no good reason.

You need extreme after-market hardware (and new internals) to justify that much fuel flow, and I'd argue that 750cc and up doesn't have any place on our blocks, period.

[JCviggen]

I didnt learn that in basic math. I am just telling you that when you have a pressure differential of 4-1 (60 lbs of fuel vs 15 lbs of boost) the additional pressure needed to overcome the manifold pressure is not 1 for 1. If all variables where equal, then you are correct, it would be a one for one trade off.

Gary

The differential remains an absolute 45 lbs, hence the injectors will have a constant rate.

Doesnt matter if its 4x higher than boost or whatever, you add the boost to the fuel pressure to keep the same amount of flow, done!

[ViperVette]

I am currently running 1600cc injectors. I was thinking about getting a remap but instead I just got some Pegs and a SpeedTuning ECU. Has been working out pretty well.

[Gioseppe]

The differential remains an absolute 45 lbs, hence the injectors will have a constant rate.

Doesnt matter if its 4x higher than boost or whatever, you add the boost to the fuel pressure to keep the same amount of flow, done!

example of a knowledgeable post.

I am currently running 1600cc injectors. I was thinking about getting a remap but instead I just got some Pegs and a SpeedTuning ECU. Has been working out pretty well.

example of a worthless post.

what Jc is saying makes complete sense, so i don't know why you are still debating it...