What size injectors do I need?
Thread Starter
Burning Brakes
Joined: Sep 2009
Posts: 1,239
Likes: 2
From: Naples FL
St. Jude Donor '12
What size injectors do I need?
I currently put out 420 RWHP, getting ready to replace the heads, cam and intake, will probably put out in the 470-480 RWHP after these mods.
I'm figuring about 45lb injectors by my math,sound about right?
I'm figuring about 45lb injectors by my math,sound about right?
Thread Starter
Burning Brakes
Joined: Sep 2009
Posts: 1,239
Likes: 2
From: Naples FL
St. Jude Donor '12
I believe they're stock, but I plan on checking. I figured these injectors at 80% duty cycle.
the guy I bought the car from had almost no information on it. He bought it and it sat in his garage, the previous owner to him did all the mods.
the guy I bought the car from had almost no information on it. He bought it and it sat in his garage, the previous owner to him did all the mods.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
LS injectors are rated at 4 bar ( 54 PSI) however most aftermarket injectors and most other stock injectors are rated at 3 bar ( 43 PSI) make sure you address this correctly
As an example a popular mod is to install FORD 30 lb injectors on an LS engine--These are rated at 3 bar --so on a LS application they are actually apprx. 34 lb !!!
Here is a great site with multiple injector calculations---
It uses BRAKE HP rather than RWHP which would make your engine (after mods) with a 6 speed apprx 540 brake HP
Chart shows to get 80% duty cylcles you would need only approx 38 lb injectors rated at 3 bar in order to end up with the desired 42 lbs
Running injectors that are larger then needed---does NOT make more HP !!!
Also too large of an injector will most always create idle/issues--surging/dying etc.
This can be fixed with tuning somewhat but the injector rate is so large the ECM can't command a small enough pulse -that's where the problems arise from--
http://www.witchhunter.com/injectorcalc1.php4
As an example a popular mod is to install FORD 30 lb injectors on an LS engine--These are rated at 3 bar --so on a LS application they are actually apprx. 34 lb !!!
Here is a great site with multiple injector calculations---
It uses BRAKE HP rather than RWHP which would make your engine (after mods) with a 6 speed apprx 540 brake HP
Chart shows to get 80% duty cylcles you would need only approx 38 lb injectors rated at 3 bar in order to end up with the desired 42 lbs
Running injectors that are larger then needed---does NOT make more HP !!!
Also too large of an injector will most always create idle/issues--surging/dying etc.
This can be fixed with tuning somewhat but the injector rate is so large the ECM can't command a small enough pulse -that's where the problems arise from--
http://www.witchhunter.com/injectorcalc1.php4
Thread Starter
Burning Brakes
Joined: Sep 2009
Posts: 1,239
Likes: 2
From: Naples FL
St. Jude Donor '12
Thanks, all good info.
Someone else is doing the tuning.
I know I'll have to do something with the fuel pump, I was thinking a boost a pump, but I'll look into the lingenfelter. I was going to buy one of their 2 stage launch controllers anyway.
I noticed that about the aftermarket injectors being rated at 3 bar. I'm aware that going too large with the injectors causes driveability issues, but too small causes short life and potentially running lean. I'm guessing just a few lbs oversized is ok - example would be 42lb injectors when the calculation shows 38lb. Or 45lb vs 42lb. I'm not off base here, am I?
Someone else is doing the tuning.
I know I'll have to do something with the fuel pump, I was thinking a boost a pump, but I'll look into the lingenfelter. I was going to buy one of their 2 stage launch controllers anyway.
I noticed that about the aftermarket injectors being rated at 3 bar. I'm aware that going too large with the injectors causes driveability issues, but too small causes short life and potentially running lean. I'm guessing just a few lbs oversized is ok - example would be 42lb injectors when the calculation shows 38lb. Or 45lb vs 42lb. I'm not off base here, am I?
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Thread Starter
Burning Brakes
Joined: Sep 2009
Posts: 1,239
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From: Naples FL
St. Jude Donor '12
Melting Slicks
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Safety Car
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Burning Brakes
Joined: May 2007
Posts: 911
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From: Southern IL
Thanks, all good info.
Someone else is doing the tuning.
I know I'll have to do something with the fuel pump, I was thinking a boost a pump, but I'll look into the lingenfelter. I was going to buy one of their 2 stage launch controllers anyway.
I noticed that about the aftermarket injectors being rated at 3 bar. I'm aware that going too large with the injectors causes driveability issues, but too small causes short life and potentially running lean. I'm guessing just a few lbs oversized is ok - example would be 42lb injectors when the calculation shows 38lb. Or 45lb vs 42lb. I'm not off base here, am I?
Someone else is doing the tuning.
I know I'll have to do something with the fuel pump, I was thinking a boost a pump, but I'll look into the lingenfelter. I was going to buy one of their 2 stage launch controllers anyway.
I noticed that about the aftermarket injectors being rated at 3 bar. I'm aware that going too large with the injectors causes driveability issues, but too small causes short life and potentially running lean. I'm guessing just a few lbs oversized is ok - example would be 42lb injectors when the calculation shows 38lb. Or 45lb vs 42lb. I'm not off base here, am I?
Otherwise use the bosch green injectors, they are 48lb injectors.
Thread Starter
Burning Brakes
Joined: Sep 2009
Posts: 1,239
Likes: 2
From: Naples FL
St. Jude Donor '12
There is a REALLY good deal on the Bosch 48 lb injectors on one site I found, they're rebuilt, but really cheap.
So a boost a pump isn't a good alternative?
So a boost a pump isn't a good alternative?
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Cheapest and best way to get larger injectors is to send YOURS off to someone who can port the nozzles with a C&C machine--Usually costs around $150 and you know you won't have any fitment issues cause you are usuing your same ones !!--I know a great company that I have used in the past to do them if interested---
Thread Starter
Burning Brakes
Joined: Sep 2009
Posts: 1,239
Likes: 2
From: Naples FL
St. Jude Donor '12
Modifying mine is a great idea, but I'll probably go back to stock some day (like you are) so that's not a great option.
As far as the Ford, thanks but I think I'll probably need a bit bigger.
WKMCD, you ran 34 lb injectors with 460 WHP? that seems small by the tables. I believe you of course, but according to the math that just doesn't work out. What am I missing????
As far as the Ford, thanks but I think I'll probably need a bit bigger.
WKMCD, you ran 34 lb injectors with 460 WHP? that seems small by the tables. I believe you of course, but according to the math that just doesn't work out. What am I missing????
Race Director
Joined: Dec 2004
Posts: 13,760
Likes: 75
From: Haymarket VA
Modifying mine is a great idea, but I'll probably go back to stock some day (like you are) so that's not a great option.
As far as the Ford, thanks but I think I'll probably need a bit bigger.
WKMCD, you ran 34 lb injectors with 460 WHP? that seems small by the tables. I believe you of course, but according to the math that just doesn't work out. What am I missing????
As far as the Ford, thanks but I think I'll probably need a bit bigger.
WKMCD, you ran 34 lb injectors with 460 WHP? that seems small by the tables. I believe you of course, but according to the math that just doesn't work out. What am I missing????
Here's a good site.
http://www.rceng.com/technical.aspx
Last edited by WKMCD; Sep 16, 2012 at 10:29 AM.
