Injector sizing
Thread Starter
Burning Brakes
Joined: May 2007
Posts: 911
Likes: 27
From: Southern IL
Injector sizing
I am wondering if I would be much better off downsizing my injectors. I know it has alot to do with tuning, but I have am really curious if there would be any benefits with dumping my 42lb. greentops for something smaller.
Would there be any improvement to low RPM driveability going with a smaller injector? What size would be best for me?
My engine specs:
LS6 intake
Vararam & Kooks LT's
64cc 317 heads
and this camshaft http://www.compcams.com/Company/CC/c...csid=1400&sb=0
Would there be any improvement to low RPM driveability going with a smaller injector? What size would be best for me?
My engine specs:
LS6 intake
Vararam & Kooks LT's
64cc 317 heads
and this camshaft http://www.compcams.com/Company/CC/c...csid=1400&sb=0
Last edited by Vicarious.; Feb 10, 2013 at 06:00 AM.
Tech Contributor
Joined: Aug 2008
Posts: 2,902
Likes: 21
From: Oak Hill Virginia
Injector Size = Horsepower X Brake Specific Fuel Consumption
______________________________________
Number of Injectors X Desired Duty Cycle Percentage
Since you're N/A and using conservative numbers
440 X .5
_______
8 X .8
Gives you 34.35 lbs/hour per injector and I purposely overestimated on the high side.
So yeah... you could go smaller.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
YES------ Too large of an injector will cause a tuning nightmare as well as idle/starting/surging issues----
Common knowledge is to not let your "injector duty cycles " go much over 80%---That is the way you decide which injector size you need-
ALSO most injectors are rated at 3 bar (43 psi) --A C5 injector is rated at 4 bar (58 psi)--
Your green top 42's are rated at 3 bar so at 4 bar they are actually
48 psi !!!
That is a huge size for a 6.0 N/A motor---But check the duty cycles to prove it to yourself---I will guess thay are like 40%--
A too large injector on a street car will never have a small enough pulse to have it idle right--The injector hole size is just too big !!
You can try to tune the Min pulse width by asking for a smaller amount of fuel but that usually won't do it either--It just can't make the fuel amount that low--
On my 98 with approx 400 RWHP I still run my STOCK 28 lb injectors !!
idles fine-no surging-starts perfect-- My Duty cycles do go up to 90 % when drag racing--But as long as I let the injectors and eng cool down between runs- its NOT an issue-- I'm gonna guess the Ford red top 30's
are your best choice--as they are actually 34 lb at 4 bar---make sure your tuner scales your " injector flow rate " table accordingly---
Common knowledge is to not let your "injector duty cycles " go much over 80%---That is the way you decide which injector size you need-
ALSO most injectors are rated at 3 bar (43 psi) --A C5 injector is rated at 4 bar (58 psi)--
Your green top 42's are rated at 3 bar so at 4 bar they are actually
48 psi !!!
That is a huge size for a 6.0 N/A motor---But check the duty cycles to prove it to yourself---I will guess thay are like 40%--
A too large injector on a street car will never have a small enough pulse to have it idle right--The injector hole size is just too big !!
You can try to tune the Min pulse width by asking for a smaller amount of fuel but that usually won't do it either--It just can't make the fuel amount that low--
On my 98 with approx 400 RWHP I still run my STOCK 28 lb injectors !!
idles fine-no surging-starts perfect-- My Duty cycles do go up to 90 % when drag racing--But as long as I let the injectors and eng cool down between runs- its NOT an issue-- I'm gonna guess the Ford red top 30's
are your best choice--as they are actually 34 lb at 4 bar---make sure your tuner scales your " injector flow rate " table accordingly---
Thread Starter
Burning Brakes
Joined: May 2007
Posts: 911
Likes: 27
From: Southern IL
YES------ Too large of an injector will cause a tuning nightmare as well as idle/starting/surging issues----
Common knowledge is to not let your "injector duty cycles " go much over 80%---That is the way you decide which injector size you need-
ALSO most injectors are rated at 3 bar (43 psi) --A C5 injector is rated at 4 bar (58 psi)--
Your green top 42's are rated at 3 bar so at 4 bar they are actually
48 psi !!!
That is a huge size for a 6.0 N/A motor---But check the duty cycles to prove it to yourself---I will guess thay are like 40%--
A too large injector on a street car will never have a small enough pulse to have it idle right--The injector hole size is just too big !!
You can try to tune the Min pulse width by asking for a smaller amount of fuel but that usually won't do it either--It just can't make the fuel amount that low--
On my 98 with approx 400 RWHP I still run my STOCK 28 lb injectors !!
idles fine-no surging-starts perfect-- My Duty cycles do go up to 90 % when drag racing--But as long as I let the injectors and eng cool down between runs- its NOT an issue-- I'm gonna guess the Ford red top 30's
are your best choice--as they are actually 34 lb at 4 bar---make sure your tuner scales your " injector flow rate " table accordingly---
Common knowledge is to not let your "injector duty cycles " go much over 80%---That is the way you decide which injector size you need-
ALSO most injectors are rated at 3 bar (43 psi) --A C5 injector is rated at 4 bar (58 psi)--
Your green top 42's are rated at 3 bar so at 4 bar they are actually
48 psi !!!
That is a huge size for a 6.0 N/A motor---But check the duty cycles to prove it to yourself---I will guess thay are like 40%--
A too large injector on a street car will never have a small enough pulse to have it idle right--The injector hole size is just too big !!
You can try to tune the Min pulse width by asking for a smaller amount of fuel but that usually won't do it either--It just can't make the fuel amount that low--
On my 98 with approx 400 RWHP I still run my STOCK 28 lb injectors !!
idles fine-no surging-starts perfect-- My Duty cycles do go up to 90 % when drag racing--But as long as I let the injectors and eng cool down between runs- its NOT an issue-- I'm gonna guess the Ford red top 30's
are your best choice--as they are actually 34 lb at 4 bar---make sure your tuner scales your " injector flow rate " table accordingly---
I forgot to mention I am also running a racetronix fuel pump. Does that change anything?
Safety Car
Joined: May 2003
Posts: 3,814
Likes: 105
From: Dearborn Heights Michigan
For what it's worth; my 5.7 L 2000 is highly modified to about 475HP with a more agressive cam than yours, a ZO6 intake, ported heads, complete exhaust.
The tuner who did the work stuck with the original 26 lb injectors.
The car has always ran strong with decent MPG.
The tuner who did the work stuck with the original 26 lb injectors.
The car has always ran strong with decent MPG.
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