Thread: Lucas 42.5# Injectors. When are they too small?

I have a brother running E85 on a cammed Regal with exactly the same mods that I have on my car in the sig. Except he has 42.5# Lucas injectors and I have 60# Siemens. We both have completely stock fuel systems besides injectors. He sees about 20 msec duty cycles in scans and I'm barely above 10 msec at the same commanded fueling. His fuel trims are near perfect and the commanded vs actual AFR is verified by wideband to be spot on.

Does anybody know when his Lucas injectors become too small for the application? I cant find much info on those injectors, especially specific to our application. I need help from someone that's been down this road before with these injectors on something like this. I'm just wondering if the injectors are nearing the non-linear end of the spectrum at 20 msec and if it's time to upgrade.

Thanks Guys!

I have 42's in my regal with E85, with the 3.5" pulley I'm at almost 80% IDC. About the same IDC I had with the stock injectors and stock pulley. At what RPM is he seeing 20 ms?

Edit: And what size pulley is he running?

Originally Posted by 99GT2dr

I have 42's in my regal with E85, with the 3.5" pulley I'm at almost 80% IDC. About the same IDC I had with the stock injectors and stock pulley. At what RPM is he seeing 20 ms?

Edit: And what size pulley is he running?

He is having good luck with a 3.0" pulley. The 20ms pulse is at the 1-2 shift, about 6300-6400 rpm. Keep in mind that we are at 6000ft+ elevation, air here is about 20% thinner than sea level. On an average day we scan 80 kpa MAP with the engine turned off.

Is there a way to determine IDC from pulse milliseconds? We use UVscan and Tiny Tuner to build tunes. Use DHP Powrtuner to flash.

Thanks again for your help!

Yeah, just Google "injector duty cycle calculator", you put in your ipw and rpm and it gives you your idc. If he's seeing 20 ms ipw's at 6400 those injectors are maxed like a mofo. Looking at my scans, I think the 42's will only get me to a 3.2, if even that, then I'll be out of injector.

http://www.stealth316.com/2-calc-idc.htm. Can use that site for your idc calculations, that's the one I usually use.

IIRC 20-22 is max.

Sounds like it's time to upgrade

20 is maxing the injectors.

The point he's at now, he needs to upgrade.

Uvscan has a fake pid for IDC too.

Lean it out and he'll have more injector room.

But anything over 90% duty cycle and I'd think about upgrading.