John, I cant wait! This should be a real treat! Only thing here is you have me questioning my injector selection now. What size were you originally intending to run?
Scott, I was originally planning on running 650's, but if you run the numbers, they're just a tad undersized for what this engine "might" do, once you consider supercharger losses.
John,
Scotts not the only one starting to question injector selection.
My 440's are starting to sound light on.
Rod, I'm pretty sure my 460's were on the ragged edge last time, and the only thing that saved us was the methanol injection. We know the motor made 498 HP to the dyno, and at the boost we were running, my calcs showed it was taking 60-80 HP to drive the SC, so to produce 498 HP net to the dyno, the engine was actually making 498+80=578 HP gross. The injector math shows that 460's "should" be good for (sorry in advance for using imperial units):
460/10.5 = ~44lbs/hr
44x8x0.80/0.55 = 512 HP
The 8 is the qty of injectors, the 0.80 is their duty cycle, and the 0.55 is the BSFC in lbs/hp-hr. (My BSFC was probably actually a little lower than 0.55 because at max output we were running AFR's of around 12:1)
So 512 HP worth of injectors @ 80% duty cycle really wasn't enough to run this motor with 80 HP lost through the supercharger, but we were also putting somewhere between 600cc/min and 800cc/min of straight methanol through the motor too, so IMO, that added sufficient fuel to keep the injectors at 80% and the AFR at 12:1, although we did see some duty spikes up to 90% in some places, IIRC.
Doing the same math now, "if" we assume this motor could give the dyno 700 HP, plus is still losing 80 HP to the blower, then I need:
780x0.55/8/0.80 = 67 lb/hr injectors or 67x10.5 = 703 cc/min
So the 650's I'm planning on using might be a bit light, but I think with the amount of methanol we'll be putting through the motor, they'll probably be "just" OK. But it's the "just" part that has me a bit nervous
My economic side is telling me it's stupid to buy a set of 850's "just" to run the motor on the dyno with C16, then another set of 650's for running the motor in the real world on pump gas at reduced boost. So I may just get the 650's and run the static rail pressure a bit higher to compensate. The Siemens DekaIV's apparently don't mind running at "much" higher rail pressures.
That is, of course, unless someone here would want to buy a set of "slightly" used 850cc DekaIV's when this is over!
Boys calm down
I run the 7MGTE 440's...although they flowed much higher on the test rig at more like 480....and they did 400rwkw easy off a 45psi base pressure and 16ps boost.
Because i'm now going to run E85 i have gone up to 560's that are a diffuser plate style for better atmomisation.
Fuel needs are just maths John so right down your alley to work out exactly what you need
Give yourself some headroom for safety and any future gains you might find and just a little bit extra again for the 'black art' component. Just be sure to check what pressure and duty cycle whatever you buy is rated at as there doesn't appear to be a standard as such.....one man's 500s may only be 450s in the real world world.
Yep, you got it Justen. The thing we SC boys have to contend with, that you TT boys don't, is the power the SC consumes. While it doesn't appear at the flywheel of the motor, we definitely have to include it in our injector calcs, and it's considerable - depending on the SC and its efficiency, we're talking 60 - 80 HP or more.
I think John originally run 460cc injectors from the RX7, but not sure about now. I'm running those same injectors at 13-14 psi and they seem to burn rich at 20 psi fuel of pressure at idle. I feel like they can still have more juice to squirt at more boost.
Right Steve, those are what I ran before. BTW, getting your AEM idle map and IAC setup correctly is one of the great mysteries of the AEM as far as I'm concerned.
