Yeah buddy on this! X2^3Overkill
For.
The.
Win.
Hey I said a few weeks back that 'Mike is right', I gotta crawl back to sanity a little
Just for fun, what's 1200lb/hr with a 12 feet of -8 line through the calculator? 43psi base pressure.
You present a good question if the pump really is large enough.
80lb/hr injectors at 58psi base pressure flow 92lb/hr which is 14gal/hr per cylinder or 428lph for the entire engine. I need 428lph of fuel flow (at the pump) to max out 80lb/hr injectors.
But, that's assuming the injector would be firing all the time, which it can't. If the engine is running at 6000 rpm its making 3000 combustions per minute, and you only have half the cycle to use because one half is intake and the other is exhaust, which means essentially the injectors run at a max duty cycle of 50%, even if they are at 100%. Can't inject fuel on the exhaust stroke. Really I need 214lph to max the injectors out on a 4 stroke engine. That's 56 GPH which according to this chart is achieved below 105psi on 12v or 115psi on 13.5v.
Gotta keep the pressure AT THE PUMP below ~100 psi on a 450 lph pump with 94lb injectors.
Not sure about ^^^. I have to do some more checking. But I believe that is not correct, but I can't find/figure out how to prove it - yet.
See bold - I'm not clear about how GM did this, but I'm not aware of an aftermarket ECU that does this. I'm quite sure that your ECU is operating with sequential injection. If it operates like a Megasquirt, Holley or Haltech, then your statement is erroneous (please correct me if you know I'm wrong about GM). Batch fire, doesn't really care much about valves events, other than it is setup to have at least one of the events occur with the valve open if it's designed for 2 squirts per 720 degree crank cycle. Many systems will allow for 4 squirts per 720 degrees of crank cycle, which implies that there is definitely fuel being injected against a closed intake valve. The reason the OEM's run sequentially is to allow for a cleaner burn in high vacuum/low KPA conditions - which implies emissions standards.
The reason to run sequential in a performance situation is to make your injector bigger. Every injector has a dead time - more accurately referred to as off time. I'm sure you know about this, but .... it's the minimum amount of time that an injector takes to turn off fuel flow and turn it back on. A Deka 80 is somewhere in the .8 of a millisecond, or .0008. At 6000 rpm's it takes 20ms, or.020 seconds for a 720 degree cam cycle (if my math is correct). So this means that the injector can only be open .0192 seconds for a sequential setup. If you run batch fire with 2 squirts, then you're down to .0184 seconds and if you run 4 squirts per cycle your only have .0168 seconds of available time to inject fuel. The difference between from sequential to 4 squirts is .0024 seconds of additional time injecting fuel. So this mean that an injector with .8ms dead time is 10% larger running sequentially - that's freaking HUGE if you're on the edge of your injector. The trade off is idle quality - it's very easy to make a 4 squirts per cycle batch fire run super smooth at idle as opposed to sequential with one squirt per 720 of crank cycle. It can be done, but it has to be at a precise interval related to intake valve opening. The OEMs have the testing ability to do this - the hotrodder (or me - not so much lol.
I messed around with this with my sons 421 and set of 80lb Dekas alot, and I mean alot. I did manage to get it run pretty well sequentially, but I could never get it to idle as well as with 2 or 4 squirts per cycle. On 93 octane at 18 psi of S480 boost with sequential injection and 20 gallons per hour of 50/50 meth injection fluid his duty cycle is at 85% which is an 18-18.4 ms injection cycle. Those same injectors run in batch fire with 4 squirts per cycle are maxed out at 14 psi of boost.
My point to these several paragraphs is to point out that the injector cycle doesn't give a crap if the intake valve is open when the rpm's are up. And boost keeps the mixture atomized without effort. which also makes the timing of the injection less important.
I believe, repeat believe, GM did the same.
p.s. - great discussion, hopefully you appreciate it. Let me know if you don't so that I'll stop it.
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