OK so looking at going to a smaller pully on my M62,just wondering if I could do a 2.9 or 3.0 with the green top injectors,Or is it time to buy bigger injectors..

Thanks,Jason

What tune are you on?

Im on a 2.9" pulley with 63# injectors(custom HP Tuners tune) and they are currently maxed(85% duty cycle) at 7000rpms.



Edited 1 time(s). Last edited Saturday, August 20, 2011 8:14 PM



its an old concept. time for something new to take the reigns. - Z yaaaa

I'm on a 3.0 with 42.5 lb'ers and a racetronix f body pump n harness and @ 7,000 rpm's I'm not even pushing 50% duty cylcle.....so you you want to get the most out of you injectors upgrade your intank pump

Am on a hp tune right now. Not sure what I am am for duity cycle.

And I just installed a brand new factory pump last year.

So looks like new injectors then.

Im still on the stock pump and have 92k+ miles on it.




its an old concept. time for something new to take the reigns. - Z yaaaa

3.0 pulley
ford green tops
stock original pump
80% duty cycle @ 7000 rpm







Save your money. It might be worth something someday.

are the ford green tops bigger than the stock cobalt ss injectors..

Yes ford greentops are 42/lb

Id say youll need atleast 42's.....if you go with a 2.9 even 60's if you dont want to upgrade your fuel pump.

Ok thanks. I will order some new ones this week.

Is anyone using the GM reflash?

The GM flash is only "OK" with a 3.1 pulley.

Anything smaller requires a retune and larger injectors. Obviously a real tune is the better route to take in the beginning though.

Philly D wrote:The GM flash is only "OK" with a 3.1 pulley.

Anything smaller requires a retune and larger injectors. Obviously a real tune is the better route to take in the beginning though.

untrue....


depends what other supporting mods you have.

the gmflash is currently running on my car with a 3.0 pulley, and is running just fine. seeing low to mid 11's AFR at WOT. I however have a adjustable FPR that i used to bump fuel pressure a bit to make the injectors work better for my needs.

Safe and just fine are two different things.

Whats your duty cycle?

my duty cycle is safe! WHEN RATED, THESE INJECTORS ARE NOT RATED AT 85%. they are rated at 100%. after hours and hours of research and talking to some engineers at GM, I am perfectly fine with my 95ish% duty cycle.

EvoFire wrote:my duty cycle is safe! WHEN RATED, THESE INJECTORS ARE NOT RATED AT 85%. they are rated at 100%. after hours and hours of research and talking to some engineers at GM, I am perfectly fine with my 95ish% duty cycle.

That GM engineer does not design injectors nor does he calibrate cars anywhere near that limit if he is even in that department. What we engineers call Best Practice for both standard pintle and disk style low pressure fuel injectors is that above 80% duty cycle the injector innards react unpredictably, and the quality of the fuel and air mixing goes down.


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2002 Chevy Cavalier LS Sport Coupe: In a Junk Yard
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WPI Class of '12 Mechanical Engineering
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Im not saying you are wrong at all Jon. But I know of 2-3 people that have put 1000's and 1000's of miles on the GM Reflash with the injector duty cycle at or about 90% during WOT. If the injector was running 90% all the time then I would see issues arising, and would look into it more. But my car is at WOT for what 13 seconds at a time tops? AFR's are still good the entire run, and KR is minimal to non existant. So I personally do not think that injectors are maxed at 80%. I know that this is what is accepted at the "NORM". But sometimes the the 'norm' needs to be readjusted and/or broken. I'll let ya know when my injectors cause and issue with the GM Reflash.

Also for those that do not know, injectors are rated at 43.5 PSI. That number is the international standard for rating them. Our cars do not run 43.5 PSI. They run higher then that. Effectively making your injectors "bigger". Either way. I have deviated from this norm, and will continue to do so until said deviations cause issues.

Most injector companies do not recommend a duty cycle greater than 80-85% under full load. Most say a 70-80% at 43PSI is the most efficient range for their injectors. Induction dynamics is up to 75 psi at 80% if I recall correctly.






PRND321 Till I DIE
Old Motor: 160whp & 152ft/lbs, 1/4 Mile 15.4 @88.2
M45 + LD9 + 4T40-E, GO GO GO

yeah. and i am running my gmpp 36's at 65 under full load....

It's not just taxing the injectors at near 100% IDCs, it's loss of control of the injector. To each his own, but there is no good reason not to take steps to keep IDC in check <80% IMO...

It may seem correct on your wideband. But I bet if you had a magicaly fairy wideband that was so fast it could actually measure each firing pulse you would see I higher spread of afr's on each pulse than if you had larger injectors run at a lower dc.


1994 Saturn SL2 Home Coming Edition: backup car
2002 Chevy Cavalier LS Sport Coupe: In a Junk Yard
1995 Mazda Miata R-package Class=STR
Sponsored by: Kronos Performance

WPI Class of '12 Mechanical Engineering
WPI SAE Risk and Sustainability Management Officer