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Forced Induction All questions and problems regarding Superchargers, Turbos, NOS, ZEX, intercoolers, water injection, etc.

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Old 11-06-2003, 01:37 AM   #11
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Peeekabooooo...hahah. There is a lot of confusion about these (or is it just me) and I wanna try and clear things up. I'm just going to use basic math and throw this out to try and figure this out but lemme know if I'm way off. Fuel injectors that you see for sale are rated at 100% duty cycle. This isn't, however, what they run at. Generally you shoot for an 80-85% duty cycle. Lemme use this simple formula to explain:
(HP x BSFC) / Injectors x duty cycle
The rough BSFC (Brake Specific Fuel Consumption) for the supercharged engine is about 60. BSFC is how much fuel (in lbs) it would take to make 1hp for 1hour. Using the math (at 100% duty cycle) they work out to 20.5lbs. Close enough to the 21lbs that people are talking about. But wait...thats at the unreachable 100% duty cycle that people selling them rate them as, not people that put them in factory cars designed to last 100,000miles and more. things get hairy when you figure out how big an injector is needed to sustain 205hp with a BSFC of .60 and a duty cycle of a more reasonable 85%. It works out to a reasonably higher 24.1lbs/hr. So lets think about this. We know the injectors in your average engine should run a max around 80-85% duty cycle, why would GM install injectors that could only sustain 205hp if they were CONSTANTLY on (100% duty cycle). Its common knowledge that you should buy injectors rated at your 80-85%d.c. needs, why would GM sway from this? Of course this doesn't take into account fuel pressure which can make up a few lbs but taking 21lbs and raising the pressure 10psi will only get you 22.5lbs/hr...and thats STILL at 100% duty cycle! Any comments on this?

I said all that because the answer really depends on it. I'll do some hidden math here but suppose GM did the right thing and put 24lb injectors in there taking them up to 100% would be 27.7lbs, then raise the pressure 10psi (with boost control) and you get 30.5lb/hr injectors! 30.5 is capable, with 0.60 BSFC, of handling 305hp. Well above your ranges. If not and they put 20.5lb injectors in there and you only raise the pressure 10psi, since they are already running at 100% with 205hp, you'll have 22.5lb injectors that can handle 225hp. Crazy huh? Which injectors do you REALLY think are in there? hehe
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Old 11-06-2003, 01:41 AM   #12
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Ok, doc. What are YOU running now?
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Old 11-06-2003, 01:43 AM   #13
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were you reading that as i typed it? haha. I'm still at stock but 2 days of light breakin didn't give a lean condition time to rear its ugly head. I've seen software out there that can tell you your current injector duty cycle, can any scantool do this? I'd like to find out. Either way its obvious I need to upgrade but for break-in I should be ok.
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Old 11-06-2003, 01:54 AM   #14
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I can check my 'tool' tomorrow and see if it offers Injector DC. I'll let you know. Weren't the SSEi injectors factory rated at 24lbs?
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Old 11-07-2003, 08:40 PM   #15
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What is the stock fuel pump rated to hp wise? How much room over stock HP is it capable of?
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Old 11-10-2003, 02:56 AM   #16
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If you want serious Power you WILL need new ones. The guys with the MP112 GP said it needed a completely new Fuel system, for a turbo application, or a */C Nitrous application you will definetly want around 30#/hr injectors IMHO. I don't know the math behind it or formulas, but from what i've seen, that'* about average.
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Old 11-10-2003, 01:04 PM   #17
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Quote:
Originally Posted by BonneMeMN
If you want serious Power you WILL need new ones. The guys with the MP112 GP said it needed a completely new Fuel system, for a turbo application, or a */C Nitrous application you will definetly want around 30#/hr injectors IMHO. I don't know the math behind it or formulas, but from what i've seen, that'* about average.
But that'* a pretty extreme application. Ok, WAY extreme. The sheer volume the 112 produces (112 CFM per stroke, neat how that works, eh?) requires more fuel to keep the ratio correct. Alot depends on the type of Turbo he'* considering using, and how much boost he'll run. Stock injectors and fuel pump may be fine. It just depends on how far he intends to take it.
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Old 11-10-2003, 01:54 PM   #18
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Quote:
Originally Posted by DrJay
were you reading that as i typed it? haha. I'm still at stock but 2 days of light breakin didn't give a lean condition time to rear its ugly head. I've seen software out there that can tell you your current injector duty cycle, can any scantool do this? I'd like to find out. Either way its obvious I need to upgrade but for break-in I should be ok.
So if I read into this right.....

If I were to have a real time scan going of my car (which I can do) I need to watch to see if the 02 sends a lean signal back to the PCM that doesn't go away durring WOT? Or do I watch things like the short term fuel ratio, or one of the other couple dozen options I got?
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Old 11-10-2003, 02:00 PM   #19
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All of the above. The O2 should toggle fairly quickly. Not as quickly as at idle, but it should never go lean for more than a 1/2 second. Do it under load, hard accelleration.
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Old 11-10-2003, 02:37 PM   #20
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Quote:
Originally Posted by willwren
All of the above. The O2 should toggle fairly quickly. Not as quickly as at idle, but it should never go lean for more than a 1/2 second. Do it under load, hard accelleration.
Yup, I've already been watching the 02 on the way too and from our meet a week ago and at idle it was real quick between the two. I haven't had a chance to really watch the rest though. Something about trying to read and comprehend a statistics creen on a loptop while at WOT just doesn't work too good.
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