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Discussion Starter · #1 ·
I just installed a 2.3" pulley on my JRSC and have a question about the MAFS voltage. From my understanding, once the voltage reaches 5V, no more fuel will be metered and excessively lean conditions will result-not good. What happens when my engine starts drawing even more air due to higher blower rpm's from the smaller pulley? Will I reach that 5v cutoff? How do I tell if the mafs is maxed out? What do I do next? get bigger injectors/recal MAFS combo? I have 30lb injectors/recal MAFS (no chip) on the car now, with aquamist water injection and do not get any detonation at all. The car runs great, awesome power and throttle response but these questions.....
Thanks for any info on this!
 

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First off, you will need bigger injectors, but 36 or 42? I have the 42's, but that was to let the excess fuel work towards cooling the charge. You have an aquamist for cooling so who knows? It sounds like time for you to have a custom chip burnt. How much boost are you getting with the 2.6, and how much from the 2.3? Secondly, remember that you NEVER want to work your injectors so hard they go to full (static wide-open). They lose the ability to spray and just dump fuel so the mix becomes uneven. I think you need to calculate what injector will do the job at no more than 85% capacity, so bigger is better here. (a custom chip won't let them spray too rich)
 

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I'd be a little worried with the MAFS and not having a chip. It is my understanding that this will advance timing. Tom seems to know a lot about this stuff so maybe he'll chime in.
 

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Discussion Starter · #4 ·
I think you're right about the custom chip-I have been putting it off because with the 30lb injectors, I haven't been getting any detonation at all but with any bigger injectors and the higher boost, I will definately need to pull some timing.
BTW, how would I calculate what the best sized injectors would be? I s there a rule of thumb about HP and injectors? I got 169whp before the race header and 2.3" pulley.
I am now getting 7.5 lbs boost with the 2.3" pulley, and got about 5.5 with the 2.6". I will be getting a dyno test next week to check out how much additional power the 2.3 is giving me.
 

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Injector formula is:

(bhp x bsfc) / (No. injectors x DC)

bhp = peak crank horsepower (note this is PEAK power at crank not whp, not average, etc.)

bsfc = which is the 'brake specific fuel consumption"; basically .50 for blown engines, .45 for NA

No. of injectors is 4 for most of us

DC = duty cycle which should be .85

so...

(bhp x .5) / (4 x .85)

should give you to lbs/hr fuel injector size (always ROUND UP to nearest available size).

My guess is you will want to keep your 30's or maybe go to 36 but you will need a good estimate of the amount of hp you are pulling at the crank which you should be able to derive from your upcoming dyno run.
 

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Assuming you have a manual with OEM clutch, I think the consensus is 15% loss though I do not have any real data for that number, so chp = .85 x whp.

If you have auto the loss is more like 25%.

If you have getrag or something similar you may be down around 10%. these are all just off the cuff though.
 
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