Right injector size??

[CrazyLT1]

hey guys, my dyno appointment is next week and I am wondering whether or not I should upgrade my fuel injectors in order to get the best results. Last year, I added 36 lb. injectors when I installed the supercharger and they were more than enough. But now, after my internal engine work over the winter, I am told to expect around 450 RWHP, give or take a few. Any advice as to whether my Venum 36 lb. injectors will be ok for that, or will I need to upgrade AGAIN...???

[Kevin - Blown 95 TA]

Sounds like you have a nice setup there! You may need a little more than 36# though with no FMU, but it's hard to guess, so I'll go by my own similar setup and also what I know others are using. On my stock motor with baby blower cam & heads, I was using 42# and seeing some pulsewidths over 90% at the track (which is OK), but of course, for normal driving they were just fine. From my mph and race weight, I estimated my rwhp at maybe 450-480 or so on a cool day - probably very similar to yours. Most guys with a 7# blower and no FMU run about 42# injectors, the guys with built motors run larger, but that's cause they usually run more boost. Alternatively, you can get a little extra flow out of them with higher fuel pressure, but that's up to you. I am going to go with some 60# injectors and a bigger blower as soon as I feel like dropping another wad on the car. I am just finishing up the new motor and have a feeling the S-Trim is too small for the 383. I am going to breakin on the 42# injectors and S-trim blower, then kick it up ANOTHER NOTCH

Here's a few links to help out...

http://users.erols.com/srweiss/tableifc.htm
http://www.sdsefi.com/injectors.htm
http://www.racetronix.com/
http://www.camaroz28.com/calcs/index.shtml
http://www.rceng.com/technical.htm#WORKSHEET

[CrazyLT1]

Thanks a lot for the advice! I'll probably end up going with some bigger ones to just get it over with. Especially since I would also like to turn up the boost soon. Sounds like you have quite the set-up there also, good luck with your projects. I would love to have a moser 12 bolt rear right now, cuase I know it is just a matter of time till my stock 10 bolt gives in!!

[Injuneer]

450rwHP through an A4 would indicate about 550 flywheelHP. Using the normal 0.60 #/HR/HP for a blower setup....

550 x 0.60 = 330
330 / 8 = 41.25 #/HR
Assuming an 85% duty cycle 41.25 / 0.85 = 48.5 #/HR

That would indicate even a 42 #/HR injector might not be enough. If you had a really efficient tune and pushed the injectors to a 90% DC, you'd get exactly 42.0 #/HR

Maybe start with 42's and stock fuel pressure, knowing that you could bump the injectors up to 4bar (58psi) if you find it running a bit short on fuel.

I think its safe to say you'll run lean with the Venom 36 #HR injectors.

[fastTa]

Those 36lb Venom's ain't going to cut it. At a true 550-560 crank HP and roughly a rail pressure of 43-44 PSI, you might be able to squeeze by using a high-impedance 42 pounder, but if you ever get any boost spikes or if you juist plan on ever upping the boost, you will want an injector bigger than 42lb. You will not find very many high impedance selctions out there over 42lb, but there are some available.

If you do decide to go with a low impedance 50 pounder, the cool thing about those is that just about all of the manufacturers flow match them.

[Kevin - Blown 95 TA]

FYI, the Siemens 60# that I am getting are high impedance, matched, and they are running well with fast turn-on times in a quite a few cars. Apparently easy to tune.

[CrazyLT1]

how much do those cost??

[Kevin - Blown 95 TA]

how much do those cost??

Heres a link - Harris Speed Works

[CrazyLT1]

thanx a lot