Injector questions.
Thread Starter
Melting Slicks
Joined: Oct 2001
Posts: 2,315
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From: Brandon Fl
Injector questions.
I have a Procharger 600b on a basically stock L-98 Just long tube headers and 3" exhaust. I am preparing to install a Holley Stealth Ram and want to upgrade my injectors. What is a good size to go to? I contacted ATI and they recommended I go with 42# and remove my FMU. If I remove my FMU will the bigger injectors pump enough fuel under power? My fuel pressure gauge jumps up to 80-100psi under WOT. Anyone have any experience with this? Thanks
Racer
Joined: Apr 2006
Posts: 300
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From: OKlahoma City OK 89 vert
36
I was told to put 30lbs from Ford SVT and keep the FMU. The stock ECM can not run any larger with out the FMU. The ECM can burn out. Stay safe keep the FMU with 30 and get a good tune from FASTCHIP.com
Last edited by dustmann; Nov 12, 2007 at 12:55 AM.
Supporting Vendor
Joined: Oct 2004
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Hello RaidMagic,
You didn't specify what year L98 so I'll give you an overview based upon my tuning experiences.
For 1985 thru 1989 L98 Vettes with the MAF sensor you will need the FMU. The reason is the MAF sensor is 'pegged' past 5 or 6 pounds of boost pressure. i.e., the ECM doesn't know to add more fuel. You should still run bigger injectors (24 to 42 lb/hr) with a re-calibrated E-prom. The bigger the injector the lower the FMU ratio. The lower the FMU ratio the better it works: generally more consistent. The lower FMU ratio does not require as much pump head. Whenever a FMU is used I always recommend the in-line fuel pump (like the GSL-392) and a good in-tank pump like the GSS-340M. The FMU in order to operate properly requires a rock steady amble supply.
On the 1990/91 L98 Vettes there is a little known problem with the stock program: it's called a PW cap (injector pulsewidth cap). Built into the program is this PW cap that calculates the maximum flow in lbs/hr. Say you put in 60 lb/hr injectors and use TunerCat to index program to same. Now you go to tune, altering the various variables; well guess what - you will not get any more fuel than what a 24 lb/hr injector would deliver!!!
I offer a program for the 1990/91 Vettes where this GM code has been removed. Now a 60 lb/hr injector will deliver full flow if needed. As such I have used 60's on a 1991 Vette delivering 600 RWHP without the need of the FMU.
Hence, without my chip, you can run larger injectors but you will still need the FMU.
Hope this helps - Best regards, Greg
You didn't specify what year L98 so I'll give you an overview based upon my tuning experiences.
For 1985 thru 1989 L98 Vettes with the MAF sensor you will need the FMU. The reason is the MAF sensor is 'pegged' past 5 or 6 pounds of boost pressure. i.e., the ECM doesn't know to add more fuel. You should still run bigger injectors (24 to 42 lb/hr) with a re-calibrated E-prom. The bigger the injector the lower the FMU ratio. The lower the FMU ratio the better it works: generally more consistent. The lower FMU ratio does not require as much pump head. Whenever a FMU is used I always recommend the in-line fuel pump (like the GSL-392) and a good in-tank pump like the GSS-340M. The FMU in order to operate properly requires a rock steady amble supply.
On the 1990/91 L98 Vettes there is a little known problem with the stock program: it's called a PW cap (injector pulsewidth cap). Built into the program is this PW cap that calculates the maximum flow in lbs/hr. Say you put in 60 lb/hr injectors and use TunerCat to index program to same. Now you go to tune, altering the various variables; well guess what - you will not get any more fuel than what a 24 lb/hr injector would deliver!!!
I offer a program for the 1990/91 Vettes where this GM code has been removed. Now a 60 lb/hr injector will deliver full flow if needed. As such I have used 60's on a 1991 Vette delivering 600 RWHP without the need of the FMU.
Hence, without my chip, you can run larger injectors but you will still need the FMU.
Hope this helps - Best regards, Greg
Last edited by BlowerWorks; Oct 9, 2007 at 06:34 AM.
