hohl

Was the flow rate of the 8.1 injectors ever definitively answered? Searching the forum has yielded flow rates of 30, 38 and 42 -- Which one is it?

I am looking for drop in replacements of at least 36 lbs. Is RC Engineering still the only source?

Richard@WCCH

iTrader: (3)

Although I don't have much useful to add, I'd sure like to know what larger injectors will work too. My understanding is the 8.1l injectors are 30lbs. Will they bolt into a 5.3l engine?
I'm gonna stay tuned......

Richard

BigTex

iTrader: (16)

I'm 99% sure that they are right under 30 pounds per hour. They physically are the same size as the stock injector. I installed a set in a vahicle recently. Before tuning them in, the ltrims at most rpms were right at 17% rich. If you multiply the stock size by 117%, you get just about 30 pounds per hour.

hohl

Thanks for the info BigTex.

I found out that the 8.1 injectors flow 30.15 lb/hr and have a flow rate of 3.77 g/sec. They swap in with the 4.8, 5.3, and 6.0 with no problems. They are used on the LQ9 Escalade 6.0 Part number: 17124531

The other option for a drop in injector is a marine injector. Rated at 36 lb/hr at 3 bar, 41 lb/hr at 4 bar. It is a direct replacement and is part number: 25176061 (Marine part number, I can't find this at GM dealers)

Unfortunately there is nothing in between. I have to calculate what my pulse width at idle will be with the marine injectors, if it's too small I'll end up swapping to the old style. I refuse to spend a lot of money on the 8.1 injectors since they will not offer much room for growth since I am at 109% duty cycle of my current injectors.

Anybody swap the marine injectors for their application? How is idle and off idle performance?

I read Parish8 used values nowhere close to the flow rate of the 50 lb injectors he was using but compensated with the PE.

BigTex

iTrader: (16)

Hmmm. I'm going to have to do a little checking. I pulled the injectors out of an LQ9 Escalade recently. I would have sworn that they were the same part number that is on the 4.8/5.3/6.0 trucks. I have them in my garage, I'll look at them this evening.

We installed 8.1 marine injectors in that escalade. Your part number 25176061 is correct. Got them from Lingenfelter. Those are the injectors that autotap showed flowing 17% more than the stock injectors. If they were really 41 psi at 4 bar, autotap would have shown the LTRIMS maxxed at 25% rich.

I'm gonna do a little more research.

hohl

My bad -- You're right about the LQ9 injectors. I checked a few of the online parts stores and found 17113698 listed as the part number. Same as the 4.8,5.3, and 6.0.

The 41 lb rating for the marine injector came from the RC Eng calculations. According to RC they flow 370 cc/min @ 3 bar.

370/10.5 = 35.24 lbs/hr

sqrt(4/3) * 35.24 = 40.69 lbs/hr @ 4 bar

I know you have more cubes but what have you found your pulse widths at idle to be with those marine injectors? Idle and off idle tuning ok?

hohl

After looking at some calculations I think I should be able to tune the 41 lb injectors with no problem.

my current IFR is 3.13 g/s and my pulse widths average 4.78 at idle. So at idle i am flowing around. .015 grams of fuel.

3.13 g/s * .00478 s = .0149614 g of fuel

With the 8.1 injector the idle pulse width would be around 3.9 msec.

.0149614 g / 3.77 g/s = .00396 s

With the marine injector 2.9 msec

.0149614 g / 5.15 g/s = .00290 s

As long as the pulse width stays above 2 msec I should be fine with those delphi/lucas disc injectors right?

BigTex

iTrader: (16)

OK. Just checked. I pulled out a set of these from the LQ9 escalade: 25317628 / 17113698

We installed the 25176061 8.1 marine injector in that escalade. The Ltrims were only 17% off. That makes me think the marine is not a 40 pound injector. Of course, we added 60 cubic inches and a much larger cam at the same time. Having it professionally tuned on Tuesday. Will know the answer then.