Fuel Injectors
Thread Starter
Racer
Joined: Sep 2006
Posts: 309
Likes: 0
From: Houston TX
Fuel Injectors
Note: With the recommedation of another member I'm bringing this question to you guys on this side... See below.
I've used the search, but really couldn't find the answer to my question. With that being said, I've come to ask for your help.
As of late, I've been wondering if I'm starving my system of fuel, possibly needing larger fuel injectors. Ultimately, leaving a little HP on the table. At what point do you cross the threshold of having to replace them? Presently making 460rwhp / 412rwtq.
Current Setup:
Stage IIE Heads
S+ Cam (238/242 113 LSA .605/.610)
Ported TB
Fast 90
CAI
1 7/8 LT w/ Hi-Flo cats
Underdrive Pulley
I've found a set of LS2 "Direct-Fit" 46lb/hr injectors from Racetronix website, but not certain if I stand to gain anything from the change. Even if nothing is gained, I still want to change them out if my stock injectors are no longer adequate for the job.
I've used the search, but really couldn't find the answer to my question. With that being said, I've come to ask for your help.
As of late, I've been wondering if I'm starving my system of fuel, possibly needing larger fuel injectors. Ultimately, leaving a little HP on the table. At what point do you cross the threshold of having to replace them? Presently making 460rwhp / 412rwtq.
Current Setup:
Stage IIE Heads
S+ Cam (238/242 113 LSA .605/.610)
Ported TB
Fast 90
CAI
1 7/8 LT w/ Hi-Flo cats
Underdrive Pulley
I've found a set of LS2 "Direct-Fit" 46lb/hr injectors from Racetronix website, but not certain if I stand to gain anything from the change. Even if nothing is gained, I still want to change them out if my stock injectors are no longer adequate for the job.
Moderator emeritus
Joined: Jun 2001
Posts: 18,599
Likes: 3,951
From: Jacksonville Florida BWO Dayton, Cincinnati, Bloomsbury NJ, Cincinnati
2015 C7 of the Year Finalist
Note: With the recommedation of another member I'm bringing this question to you guys on this side... See below.
I've used the search, but really couldn't find the answer to my question. With that being said, I've come to ask for your help.
As of late, I've been wondering if I'm starving my system of fuel, possibly needing larger fuel injectors. Ultimately, leaving a little HP on the table. At what point do you cross the threshold of having to replace them? Presently making 460rwhp / 412rwtq.
Current Setup:
Stage IIE Heads
S+ Cam (238/242 113 LSA .605/.610)
Ported TB
Fast 90
CAI
1 7/8 LT w/ Hi-Flo cats
Underdrive Pulley
I've found a set of LS2 "Direct-Fit" 46lb/hr injectors from Racetronix website, but not certain if I stand to gain anything from the change. Even if nothing is gained, I still want to change them out if my stock injectors are no longer adequate for the job.
I've used the search, but really couldn't find the answer to my question. With that being said, I've come to ask for your help.
As of late, I've been wondering if I'm starving my system of fuel, possibly needing larger fuel injectors. Ultimately, leaving a little HP on the table. At what point do you cross the threshold of having to replace them? Presently making 460rwhp / 412rwtq.
Current Setup:
Stage IIE Heads
S+ Cam (238/242 113 LSA .605/.610)
Ported TB
Fast 90
CAI
1 7/8 LT w/ Hi-Flo cats
Underdrive Pulley
I've found a set of LS2 "Direct-Fit" 46lb/hr injectors from Racetronix website, but not certain if I stand to gain anything from the change. Even if nothing is gained, I still want to change them out if my stock injectors are no longer adequate for the job.
B) What is your A/F during PE?
Answer those and then decide if you need bigger injectors. If you are over 80 to 85% utilization, you might consider bigger injectors. If I were at 85%, I would stand pat UNLESS I had more plans to increase the HP.
Elmer
Former Vendor
Joined: Dec 2006
Posts: 2,239
Likes: 1
A) Get it checked by a tuner for % utilization of injectors.
B) What is your A/F during PE?
Answer those and then decide if you need bigger injectors. If you are over 80 to 85% utilization, you might consider bigger injectors. If I were at 85%, I would stand pat UNLESS I had more plans to increase the HP.
Elmer
B) What is your A/F during PE?
Answer those and then decide if you need bigger injectors. If you are over 80 to 85% utilization, you might consider bigger injectors. If I were at 85%, I would stand pat UNLESS I had more plans to increase the HP.
Elmer
Great info, I agree. You need to know what the duty cycle and fuel pressure is to know if you need larger injectors.
Former Vendor
Joined: Jan 2001
Posts: 262
Likes: 13
From: Decatur IN
LS2 injector replacement
Although I agree with the other people that said to check your air-fuel ratio (with a real air-fuel ratio meter) and to check your injector duty cycle, if you know how much power you are making at the rear wheels you can get a fairly close idea of how much fuel you are using and how close you are to being out of injector.
Since you mention drop-in replacement LS2 injectors, I am assuming your car is an LS2 Corvette (and not a Z06 with the LS7).
The LS2 injectors are rated at 33.9 lbs/hr (or 4.27 grams/second).
If you are making 460 rwhp that is around 520 to 540 hp at the crankshaft (using 12% to 15% losses assuming you have a manual transmission vehicle).
Brake specific fuel consumption (BSFC) is a measure of the amount of fuel it takes to make horsepower. The common units used in the US are lbs/hr/hp. A 0.45 BSFC fuel consumption is about as good as you are going to get on a naturally aspirated street engine on pump gas (and it could be slightly worse, a range of 0.45 to 0.50 is usually used for a naturally aspirated street engine). If this were a boosted engine then your BSFC would likely be closer to 0.55 to 0.60.
At 540 hp and a brake specific fuel consumption (BSFC) of 0.45, you are consuming 243 lbs/hr of fuel (540 hp * 0.45 lbs/hr/hp= 243 lbs/hr). With 8 injectors, that means each injector needs to deliver 30.4 lbs/hr of fuel (243 lbs/hr / 8 = 30.4 lbs/hr). Since the injectors are rated at 33.9 lbs/hr, you are at 90% duty cycle (30.4/33.9=0.896). This is assuming the 0.45 BSFC and 540 crank hp. At 520 hp, you would be at 86% duty cycle. At 0.50 BSFC and 540 crank hp, you would be at 100% duty cycle. These percentages are slightly off since it actually takes a certain amount of time to open and close the injector and during part of that time, fuel is not flowing through the injector. Most engine management systems have a minimum off time that they give the injectors (so you never really get to 100% duty cycle).
So, to make a long story short, you are likely out of injector or almost out of injector. Going to larger injectors would be recommended at your power level. You probably won't make more power (unless you are running much too lean) but you will be back in fuel control and are less likely to damage your engine.
If you are loosing fuel pressure for any reason, then your effective injector size is even smaller and you are even more likely to be out of injector. Also, as fuel temperatures increase, the density of the fuel decreases so you need more volume of fuel to maintain the same number of fuel atoms (the same mass of fuel) so as fuel temperature goes up you need more volume of fluid to keep the same air-fuel ratio.
Sorry if this ended up being longer than intended.
Since you mention drop-in replacement LS2 injectors, I am assuming your car is an LS2 Corvette (and not a Z06 with the LS7).
The LS2 injectors are rated at 33.9 lbs/hr (or 4.27 grams/second).
If you are making 460 rwhp that is around 520 to 540 hp at the crankshaft (using 12% to 15% losses assuming you have a manual transmission vehicle).
Brake specific fuel consumption (BSFC) is a measure of the amount of fuel it takes to make horsepower. The common units used in the US are lbs/hr/hp. A 0.45 BSFC fuel consumption is about as good as you are going to get on a naturally aspirated street engine on pump gas (and it could be slightly worse, a range of 0.45 to 0.50 is usually used for a naturally aspirated street engine). If this were a boosted engine then your BSFC would likely be closer to 0.55 to 0.60.
At 540 hp and a brake specific fuel consumption (BSFC) of 0.45, you are consuming 243 lbs/hr of fuel (540 hp * 0.45 lbs/hr/hp= 243 lbs/hr). With 8 injectors, that means each injector needs to deliver 30.4 lbs/hr of fuel (243 lbs/hr / 8 = 30.4 lbs/hr). Since the injectors are rated at 33.9 lbs/hr, you are at 90% duty cycle (30.4/33.9=0.896). This is assuming the 0.45 BSFC and 540 crank hp. At 520 hp, you would be at 86% duty cycle. At 0.50 BSFC and 540 crank hp, you would be at 100% duty cycle. These percentages are slightly off since it actually takes a certain amount of time to open and close the injector and during part of that time, fuel is not flowing through the injector. Most engine management systems have a minimum off time that they give the injectors (so you never really get to 100% duty cycle).
So, to make a long story short, you are likely out of injector or almost out of injector. Going to larger injectors would be recommended at your power level. You probably won't make more power (unless you are running much too lean) but you will be back in fuel control and are less likely to damage your engine.
If you are loosing fuel pressure for any reason, then your effective injector size is even smaller and you are even more likely to be out of injector. Also, as fuel temperatures increase, the density of the fuel decreases so you need more volume of fuel to maintain the same number of fuel atoms (the same mass of fuel) so as fuel temperature goes up you need more volume of fluid to keep the same air-fuel ratio.
Sorry if this ended up being longer than intended.
Note: With the recommedation of another member I'm bringing this question to you guys on this side... See below.
I've used the search, but really couldn't find the answer to my question. With that being said, I've come to ask for your help.
As of late, I've been wondering if I'm starving my system of fuel, possibly needing larger fuel injectors. Ultimately, leaving a little HP on the table. At what point do you cross the threshold of having to replace them? Presently making 460rwhp / 412rwtq.
Current Setup:
Stage IIE Heads
S+ Cam (238/242 113 LSA .605/.610)
Ported TB
Fast 90
CAI
1 7/8 LT w/ Hi-Flo cats
Underdrive Pulley
I've found a set of LS2 "Direct-Fit" 46lb/hr injectors from Racetronix website, but not certain if I stand to gain anything from the change. Even if nothing is gained, I still want to change them out if my stock injectors are no longer adequate for the job.
I've used the search, but really couldn't find the answer to my question. With that being said, I've come to ask for your help.
As of late, I've been wondering if I'm starving my system of fuel, possibly needing larger fuel injectors. Ultimately, leaving a little HP on the table. At what point do you cross the threshold of having to replace them? Presently making 460rwhp / 412rwtq.
Current Setup:
Stage IIE Heads
S+ Cam (238/242 113 LSA .605/.610)
Ported TB
Fast 90
CAI
1 7/8 LT w/ Hi-Flo cats
Underdrive Pulley
I've found a set of LS2 "Direct-Fit" 46lb/hr injectors from Racetronix website, but not certain if I stand to gain anything from the change. Even if nothing is gained, I still want to change them out if my stock injectors are no longer adequate for the job.
Last edited by jhaines; Feb 7, 2008 at 02:45 AM. Reason: Added fuel temperature and pressure information. Clarified some math.
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Former Vendor
Joined: Jan 2001
Posts: 262
Likes: 13
From: Decatur IN
SC fuel requirements
Yes, but a supercharged car would use the 0.55 to 0.60 BSFC figures I mentioned.
BTW - the total fuel flow before you devide by the number of injectors is how much pump flow you need. You actually need a margin of extra fuel pump flow as well to compensate for hot fuel handling and to run the jet (venturi) pumps that fill the canister and transfer fuel from the passenger side tank to the driver side tank. We normally like to see 10% to cover hot fuel handling and jet pump operation. When we flow test pumps in our test cells we usually try to test the complete system including the jet pumps.
BTW - the total fuel flow before you devide by the number of injectors is how much pump flow you need. You actually need a margin of extra fuel pump flow as well to compensate for hot fuel handling and to run the jet (venturi) pumps that fill the canister and transfer fuel from the passenger side tank to the driver side tank. We normally like to see 10% to cover hot fuel handling and jet pump operation. When we flow test pumps in our test cells we usually try to test the complete system including the jet pumps.
Thread Starter
Racer
Joined: Sep 2006
Posts: 309
Likes: 0
From: Houston TX
Actually, I appreciate the long explanation, so there is no need to apologize 
.
With everything you said, it only makes sense to replace the injectors. Especially if I want to be in control of my fuel again. Granted, fuel pressure isn't dropping, but with Texas summers being as hot as they are, it's better to be safe rather than sorry. Consider it cheap insurance!
. With everything you said, it only makes sense to replace the injectors. Especially if I want to be in control of my fuel again. Granted, fuel pressure isn't dropping, but with Texas summers being as hot as they are, it's better to be safe rather than sorry. Consider it cheap insurance!
Although I agree with the other people that said to check your air-fuel ratio (with a real air-fuel ratio meter) and to check your injector duty cycle, if you know how much power you are making at the rear wheels you can get a fairly close idea of how much fuel you are using and how close you are to being out of injector.
Since you mention drop-in replacement LS2 injectors, I am assuming your car is an LS2 Corvette (and not a Z06 with the LS7).
The LS2 injectors are rated at 33.9 lbs/hr (or 4.27 grams/second).
If you are making 460 rwhp that is around 520 to 540 hp at the crankshaft (using 12% to 15% losses assuming you have a manual transmission vehicle).
Brake specific fuel consumption (BSFC) is a measure of the amount of fuel it takes to make horsepower. The common units used in the US are lbs/hr/hp. A 0.45 BSFC fuel consumption is about as good as you are going to get on a naturally aspirated street engine on pump gas (and it could be slightly worse, a range of 0.45 to 0.50 is usually used for a naturally aspirated street engine). If this were a boosted engine then your BSFC would likely be closer to 0.55 to 0.60.
At 540 hp and a brake specific fuel consumption (BSFC) of 0.45, you are consuming 243 lbs/hr of fuel (540 hp * 0.45 lbs/hr/hp= 243 lbs/hr). With 8 injectors, that means each injector needs to deliver 30.4 lbs/hr of fuel (243 lbs/hr / 8 = 30.4 lbs/hr). Since the injectors are rated at 33.9 lbs/hr, you are at 90% duty cycle (30.4/33.9=0.896). This is assuming the 0.45 BSFC and 540 crank hp. At 520 hp, you would be at 86% duty cycle. At 0.50 BSFC and 540 crank hp, you would be at 100% duty cycle. These percentages are slightly off since it actually takes a certain amount of time to open and close the injector and during part of that time, fuel is not flowing through the injector. Most engine management systems have a minimum off time that they give the injectors (so you never really get to 100% duty cycle).
So, to make a long story short, you are likely out of injector or almost out of injector. Going to larger injectors would be recommended at your power level. You probably won't make more power (unless you are running much too lean) but you will be back in fuel control and are less likely to damage your engine.
If you are loosing fuel pressure for any reason, then your effective injector size is even smaller and you are even more likely to be out of injector. Also, as fuel temperatures increase, the density of the fuel decreases so you need more volume of fuel to maintain the same number of fuel atoms (the same mass of fuel) so as fuel temperature goes up you need more volume of fluid to keep the same air-fuel ratio.
Sorry if this ended up being longer than intended.
Since you mention drop-in replacement LS2 injectors, I am assuming your car is an LS2 Corvette (and not a Z06 with the LS7).
The LS2 injectors are rated at 33.9 lbs/hr (or 4.27 grams/second).
If you are making 460 rwhp that is around 520 to 540 hp at the crankshaft (using 12% to 15% losses assuming you have a manual transmission vehicle).
Brake specific fuel consumption (BSFC) is a measure of the amount of fuel it takes to make horsepower. The common units used in the US are lbs/hr/hp. A 0.45 BSFC fuel consumption is about as good as you are going to get on a naturally aspirated street engine on pump gas (and it could be slightly worse, a range of 0.45 to 0.50 is usually used for a naturally aspirated street engine). If this were a boosted engine then your BSFC would likely be closer to 0.55 to 0.60.
At 540 hp and a brake specific fuel consumption (BSFC) of 0.45, you are consuming 243 lbs/hr of fuel (540 hp * 0.45 lbs/hr/hp= 243 lbs/hr). With 8 injectors, that means each injector needs to deliver 30.4 lbs/hr of fuel (243 lbs/hr / 8 = 30.4 lbs/hr). Since the injectors are rated at 33.9 lbs/hr, you are at 90% duty cycle (30.4/33.9=0.896). This is assuming the 0.45 BSFC and 540 crank hp. At 520 hp, you would be at 86% duty cycle. At 0.50 BSFC and 540 crank hp, you would be at 100% duty cycle. These percentages are slightly off since it actually takes a certain amount of time to open and close the injector and during part of that time, fuel is not flowing through the injector. Most engine management systems have a minimum off time that they give the injectors (so you never really get to 100% duty cycle).
So, to make a long story short, you are likely out of injector or almost out of injector. Going to larger injectors would be recommended at your power level. You probably won't make more power (unless you are running much too lean) but you will be back in fuel control and are less likely to damage your engine.
If you are loosing fuel pressure for any reason, then your effective injector size is even smaller and you are even more likely to be out of injector. Also, as fuel temperatures increase, the density of the fuel decreases so you need more volume of fuel to maintain the same number of fuel atoms (the same mass of fuel) so as fuel temperature goes up you need more volume of fluid to keep the same air-fuel ratio.
Sorry if this ended up being longer than intended.
