Who here is running a low impedance box to control those big injectors? Are you getting good results? How's the tunabilty with something like that? Who sells them?

 

The only one that I know of is http://www.acceleronics.com/
I don't know how good it is though.

 

Does anyone know which one Harlan has on his car?

 

His own, e-mail him and you can get some more details.

 

I think Speed Inc, one of the sponsors, sells a low impedance box also.

 

The Speed Inc. box is the same as the Acceleronics box, the just distribute them.

I had one on my car when I was running 83lb. injectors as a test...it worked as advertised.

 

Scott,

Would you recommend it? How is it for tunability and idle?

 

Well, I had it on a stock motor with heads/cam and I was using 83 lb/hr injectors and LS1Edit. Originally I installed the bigger injectors for my turbo setup, but I wanted to test it before the turbos were back on the car.

The car would idle for a little bit, then start to load up because the stock computer couldn't limit the injector pulse-widths enough in MAF mode. The same thing would happen during cruising if I stayed in the same fuel cell.

I spoke to Matt Harlan and he said that I should look into a closed-loop tune with my setup, but I started to work long hours at work and I didn't have the time to do it.

I took the box out and went with smaller injectors because I got tired of experimenting and I needed to drive the car daily.

I pretty much decided that I am going to go with a Motec M800 system, so I am willing to part with my Acceleronics box.

I'm sure that you could work out a tune if you spent a decent amount of time on it and ran the car in closed loop.

 

I think you meant an open loop tune was suggested (as opposed to closed loop). The issue is some sort of minimum pulewidth in the computer (if it's changeable I do not know - it currently isn't at this time with LS1 Edit though. The computer can not bring the pulsewidth down enough to achieve 14.7:1 (it is closer to 12-13:1) so your l-trims pull out a ton of fuel. then as soon as you accelerate you are over the artificial minimum pulsewidth cap, but you still have a large l-trim correction factor which can cause a stumble, etc.

If you have the problem during cruising (which I have not experienced) you would need to tune your car to run in open loop all the time (no o2 directed computer feedback loop).

The times I have seen it it has been at pretty much idle only, which can easily be solved by setting your TPS to enable WOT to 0% up to 1400-1600 or so. This will put you in PE mode (no o2 sensor feedback loop) at and below that rpm - and you can tune your idle directly with the PE vs RPm table for that RPM range. As soon as you accelerate over the range you will go back into closed loop, but you shouldn't have the same l-trim based stumble you would otherwise.


(I have the Acceleronics box also, it definitely works as advertised - I would just suggest getting it from speed inc to support the sponsors here ).


Regarding the minimum pulsewidth cap, it is possible that it is an artifact of the injector drivers used by GM in our pcm (since the boxes take the driver output). It would be interesting to put a scope on the signal to the injector driver and see if that suffered the same constraint - if not it would be easy to get around this.

 

Sorry, I meant to say open loop