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Old 09-29-2008, 06:25 PM   #1
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Default Stock 1.8 Injectors w/boost?

This is a general fueling question so Im posting it in general miata chat.

We're still tuning on my friends supercharged 1.8 miata with factory injectors and a MSPNP. The charger has an 8psi pulley but at times can peak at 10psi for a fraction of a second (and some RETARDED IATs!!) Looking through the data logs from our high load WOT runs I'm finding the injectors are maxing out for a few fractions of a second, like 100 - 110% duty cycle, which I know anything above around 80% is generally BAD...

I'm assuming we've reached the end of the injectors useful range at stock fuel pressure and stock pump, but I'm confused. The last dyno was 159rwhp w/P-P-P-Powercard!! and some crappy *** timing retard box and the AFRs were damn near dead on 10:1 from Boost onset to redline. Am I likley correct in my assumption that the car likely is closer to 180rwhp with a better fuel/spark map allowed by the Megasquirt or maybe more?

Playing with RC's fuel calculator I entered 180hp, .55BSFC, 0.99 duty cycle, 45.3psi fuel system and it comes up to 265cc injectors. Under full load without WMI running we have no detonation (under 200degree IATs anyway) at the top of fourth gear running pretty solid 11.5 - 12:1 AFR.

Are we going to kill the injectors and ultimately kill the motor? I have an older BEGI AFPR laying around, could this help matters out until he can afford his turbo setup or am I adding fuel to the WRONG fire thinking this way?
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Old 09-30-2008, 12:48 PM   #2
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You can use a RRFPR like the begi one to compensate for smaller injectors along with the MS. I ran 1.8 injectors that way (with a vortech 10:1) for a while before I went ahead and just bought proper injectors. The maps and accel values look alot different though.
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