Will I need new Injectors?
03-07-2008, 02:50 AM
#1
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Will I need new Injectors?
I heard the stock injectors are only good up to around 315 horsepower. With my current set up (mods in sig) plus a CC503 Cam and 1.6 Roller Rockers, do you think I will need to upgrade my injectors? If so, what size should I go with?
03-07-2008, 08:36 AM
#5
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Somebody please post the formula that suggests the theorectical power limit of the oem injectors.
03-07-2008, 09:34 AM
#6
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I don't think he is close to the limit. I haven't done the math lately, but I would think you can run the oem injectors to at least 350rwhp without concern for locking them up.
Somebody please post the formula that suggests the theorectical power limit of the oem injectors.
Somebody please post the formula that suggests the theorectical power limit of the oem injectors.
Stock injectors at 90% (most only recomend going to about 80%) duty cycle will be good for about 360 flywheel HP N/A.
O.P. I would highly recomend new injectors for you with the 503 cam. FYI, stock GTP injectors flow about 33.5lbs at stock LT1 fuel pressure and can be had for about $5 each on GTP forums.
03-07-2008, 10:48 AM
#7
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I upgraded recently because I'm now probably in the 400 fwhp range. The stock
injectors worked fine for 316 rwhp but they were at the upper limit. I would think
with everything working properly you will be in the 330-350 rwhp range and larger
injectors will be necessary.
injectors worked fine for 316 rwhp but they were at the upper limit. I would think
with everything working properly you will be in the 330-350 rwhp range and larger
injectors will be necessary.
03-07-2008, 11:16 AM
#8
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Location: Moore Oklahoma
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Check with the person doing your PCM programming, as the duty-cycle will be a key factor in your revised tune. The programmer will know the duty-cycle limit of the stockers and exactly when to move-up on injector size. Additionally, what injector size to use (probablly SVO #30s).
WD
WD
Last edited by The Engineer; 03-07-2008 at 12:33 PM.
03-07-2008, 12:01 PM
#9
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Check with the person doing your PCM programming, as the duty-cycle will be a key factory in your revised tune. The programmer will know the duty-cycle limit of the stockers and exactly when to move-up on injector size. Additionally, what injector size to use (probablly SVO #30s).
WD
WD
03-07-2008, 12:28 PM
#10
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Location: Hell was full so they sent me to NJ
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Injectors are sized based on flywheel HP. Citing performance vs. rwHP is not usefull, without a detailed description of the drivetrain losses.
The typical injector sizing formula is very conservative, assuming a brake specific fuel consumption (BSFC) of 0.500 #/HR/HP. A good tune, good heads, etc will produce a more efficient engine, and reduce the BSFC.
The typical injector sizing formula also plays it safe and recommends an 80% maximum duty cycle. My experience says you can push it a bit... say 85% max.
Combine the BSFC a more efficient tune (but not a "race" engine tune) and the higher allowable duty cycle and you can come up with a rule-of-thumb that says to get the minimum recommended injector size for a normally aspirated, modified engine running a custom tune, multiply flywheel HP x 0.07
Example....
350 flywheel HP x 0.07 = 24.5 #/HR
The stock injectors are programmed at 24.9 #/HR. You can get into trouble running a fuel with a very low specific gravity, since the injector is really flowing in volumetric units, not mass units, so a low density fuel would supply less #/HR for a given injector size and pressure.
While I'm sure there are people who have managed to produce 350 rwHP (guessing that would be about 400 flywheel HP with an M6) the injectors would be close to 100% DC with a mediocre tune. Above 85-90% DC, the injectors may actually flow less than rated, the spray pattern starts to deteriorate, and they may overheat, shortening their life.
It makes no sense to see how far you can push an injector, when there is no down side to using a larger-than-needed injector, other than the cost.... and really, a set of injectors and a tune one of the cheaper mods.
The typical injector sizing formula is very conservative, assuming a brake specific fuel consumption (BSFC) of 0.500 #/HR/HP. A good tune, good heads, etc will produce a more efficient engine, and reduce the BSFC.
The typical injector sizing formula also plays it safe and recommends an 80% maximum duty cycle. My experience says you can push it a bit... say 85% max.
Combine the BSFC a more efficient tune (but not a "race" engine tune) and the higher allowable duty cycle and you can come up with a rule-of-thumb that says to get the minimum recommended injector size for a normally aspirated, modified engine running a custom tune, multiply flywheel HP x 0.07
Example....
350 flywheel HP x 0.07 = 24.5 #/HR
The stock injectors are programmed at 24.9 #/HR. You can get into trouble running a fuel with a very low specific gravity, since the injector is really flowing in volumetric units, not mass units, so a low density fuel would supply less #/HR for a given injector size and pressure.
While I'm sure there are people who have managed to produce 350 rwHP (guessing that would be about 400 flywheel HP with an M6) the injectors would be close to 100% DC with a mediocre tune. Above 85-90% DC, the injectors may actually flow less than rated, the spray pattern starts to deteriorate, and they may overheat, shortening their life.
It makes no sense to see how far you can push an injector, when there is no down side to using a larger-than-needed injector, other than the cost.... and really, a set of injectors and a tune one of the cheaper mods.
03-07-2008, 12:40 PM
#11
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WD
03-07-2008, 01:31 PM
#13
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Location: Downey, CA
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the flow matched injectors. I ended up getting a set of Racetronix 32# injectors.
So far they are working very nicely.
03-07-2008, 01:40 PM
#14
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Location: Mooresville, NC
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