Just in the market for some new injectors. I need to down grade and get some 48lb ones. Just making sure there not too big too :(

and 48lb/hr is close to what in cc/min ?

48lb/hr = 505cc/min

440cc (42 lb) is the max an S-AFC and your stock ECU can handle. If you're running engine management, etc the story is different obviously.

are you repeating what you heard/read on this board or have you actually tried using a 48LB injector with a S-AFC?

I'm repeating the sum of conversations with corbin, posts on here, and some math.

Here's the constants:
ECU limit:
Long term Fuel trim +-25% max
Short term Fuel trim +-25% max (this should be closer to 5-10% for idle and drivability)
S-AFC limit: +-50% max
Stock injectors: 235cc/min @ 47psi

Variables: BSFC, HP target, and Duty cycle

Good Reference: http://www.2gnt.com/www/corbin/chooseinj.html

Please someone correct me if I'm wrong, but if you start with 235cc/min stock injectors, max out the LTFT at 25%, STFT at 25%, and SAFC at 50% you end up with a 100% "bigger" injector. Which = 470cc, and the ECU is then helpless to adjust the fuel curve. (440cc would give you an acceptable 12% STFT.)

I definitely have not actually tried putting 48lbers in. Go for it! Just datalog your fuel trims :)

Dino is using 440cc injectors with -50% on the S-AFC. He has datalogged "0" long/short term fuel trim from the ecu.

That makes the 504cc injectors 64cc larger.

I am currently using 315cc injectors which are 80cc larger than stock. The car idles fine when starting after it has a chance to warm up a couple minutes. I also use NGK 7 plugs which make cold starting/idling slightly more difficult.

If the short term trim is 25% and I only use 10% of the long term trim, that is 35% of my original 235cc injectors. This is approx. 80cc of fuel trim for idle purposes. This is what I am doing now.

I have not datalogged the trims on my setup and I will do so before trying the 48LB injectors with the standard vortech fmu.

Thanks for the reply and I appreciate the extra data you used to make your opinion.

You can always cheat and use an adjustable FPR to lower the FP at idle & static. As I understand it, that helps bigger injectors whether or not you have an SAFC.

Hey Dan how did the injector install go?

dans car is not running still.. so install for him is easy, pop is off and all.. for u, u r limited to the room you have to work with to install them...



Michael 99gs
HRC Stage 2
http://www.dreamwater.net/purplebeast