injector size----HELP ME

riceboyskiller · 09-22-2001, 09:53 AM

Good morning guyz!!!!

I am planning to built an healthy street small block that can put about 400-450hp.

I already have a 6lbs powerdyne and trick flow street intake.I also have a 12:1 fmu given with the blower kit.

what is the best injector size for my engine.I heard 24lbs will be fine with a 12:1 but 30lbs are better without the fmu but i have to recalibrate the EEC on a chassis dyno!!! What do you thinck about that

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92 black LX

smokedchevy · 09-23-2001, 03:20 AM

I'd go with the 30lb injectors.The computer chips are mandatory for large injectors because the engine loses control of the injectors at low speed. The pulse width required is smaller than the injector can respond to when turning on and off again. This results in hard starts and fouled plugs. You want an injector to run at about 80% duty cycle, that way it's meterd carefully and you're getting all the fuel you can handle. However this requires larger injectors that need tuning, so you could even go with 38lbs on a 450 horse engine, but it's going to need to be tuned with a chip by an experienced person.

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92 GT, 4:10 gears, centerforce clutch, 6# powerdyne blower, bbk h-pipe, flowmasters

riceboyskiller · 09-23-2001, 07:02 AM

Tanx a lot man. So if i understood i can put 30lbs on with the correct mass air and scratch the fuckin fmu without any trouble??

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92 black LX

smokedchevy · 09-24-2001, 02:39 AM

I'd leave the FMU on even with the injectors. If the manifold had 6psi of boost, and the regulator was set for 40 psi and has no connection to the manifold, the pressure on the injector is 34#'s. You need to overcome the pressure working against the injector inside the intake, that's where the FMU comes in handy. Confused yet?

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92 GT, 4:10 gears, centerforce clutch, 6# powerdyne blower, bbk h-pipe, flowmasters

09-24-2001, 04:02 PM

I'd go w/ the 30#ers. Also, if you got another grand lying around

, I'd ditch the stock heads if I were you. Those stockers are holding your car back....BIG TIME!

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'90 LX 5.0;12K original miles (no sh*&);3.55 gears; March pulleys;Edelbrock Performer Heads;BBK 1 5/8" equal length shorties;MSD 6AL ignition w/ blaster 2 coil;FMS E303 cam;Pro-M 75mm MAF;BBK 70mm TB; Eibach drag-launch spring kit;Southside welded subs;9" K&N cone filter charger;Hurst shifter;Cervini's 3" turbo hood;A/C delete; gutted cats;2 chamber Flomasters;Corbeau racing seats;FMS 30# injectors;JMS chip; Holley 190lb fp;TFS track heat Intake (12.299 @ 113 - 1.78 60')

09-22-2001, 09:53 AM	#1
riceboyskiller Registered Member Join Date: Sep 2001 Location: sherbrooke,quebec,canada Posts: 46	injector size----HELP ME Good morning guyz!!!! I am planning to built an healthy street small block that can put about 400-450hp. I already have a 6lbs powerdyne and trick flow street intake.I also have a 12:1 fmu given with the blower kit. what is the best injector size for my engine.I heard 24lbs will be fine with a 12:1 but 30lbs are better without the fmu but i have to recalibrate the EEC on a chassis dyno!!! What do you thinck about that ------------------ 92 black LX

09-23-2001, 03:20 AM	#2
smokedchevy Registered Member Join Date: Jun 2000 Location: ventura,CA Posts: 438	I'd go with the 30lb injectors.The computer chips are mandatory for large injectors because the engine loses control of the injectors at low speed. The pulse width required is smaller than the injector can respond to when turning on and off again. This results in hard starts and fouled plugs. You want an injector to run at about 80% duty cycle, that way it's meterd carefully and you're getting all the fuel you can handle. However this requires larger injectors that need tuning, so you could even go with 38lbs on a 450 horse engine, but it's going to need to be tuned with a chip by an experienced person. ------------------ 92 GT, 4:10 gears, centerforce clutch, 6# powerdyne blower, bbk h-pipe, flowmasters

09-23-2001, 07:02 AM	#3
riceboyskiller Registered Member Join Date: Sep 2001 Location: sherbrooke,quebec,canada Posts: 46	Tanx a lot man. So if i understood i can put 30lbs on with the correct mass air and scratch the fuckin fmu without any trouble?? ------------------ 92 black LX

09-24-2001, 02:39 AM	#4
smokedchevy Registered Member Join Date: Jun 2000 Location: ventura,CA Posts: 438	I'd leave the FMU on even with the injectors. If the manifold had 6psi of boost, and the regulator was set for 40 psi and has no connection to the manifold, the pressure on the injector is 34#'s. You need to overcome the pressure working against the injector inside the intake, that's where the FMU comes in handy. Confused yet? ------------------ 92 GT, 4:10 gears, centerforce clutch, 6# powerdyne blower, bbk h-pipe, flowmasters

09-24-2001, 04:02 PM	#5
bada$$lx Guest Posts: n/a	I'd go w/ the 30#ers. Also, if you got another grand lying around , I'd ditch the stock heads if I were you. Those stockers are holding your car back....BIG TIME! ------------------ '90 LX 5.0;12K original miles (no sh*&);3.55 gears; March pulleys;Edelbrock Performer Heads;BBK 1 5/8" equal length shorties;MSD 6AL ignition w/ blaster 2 coil;FMS E303 cam;Pro-M 75mm MAF;BBK 70mm TB; Eibach drag-launch spring kit;Southside welded subs;9" K&N cone filter charger;Hurst shifter;Cervini's 3" turbo hood;A/C delete; gutted cats;2 chamber Flomasters;Corbeau racing seats;FMS 30# injectors;JMS chip; Holley 190lb fp;TFS track heat Intake (12.299 @ 113 - 1.78 60')