Would 42lb. injectors be good enough for a CCSB gmc denali, it has a LQ9, a STS T67 and a meth kit soon. Would they be good enought to run 12lb boost on them?

Thanks in advance

 

The Meth will compenstae some but I'd go for 60lb'ers.

 

That would be pushing the limits of the 42lbs'ers. Might want to look at 60lbs'ers. Think of it as insurance because if your skimpin on fuel your whole engine is gonna blow like a virgin on prom night with the prom queen.
If you have a tunning program check it's duty cycle.

 

42 lb./hr. injectors are good to approx. 450rwhp. MAX.

you should be WELL over that but the meth will help compensate for the lack of injector. however i feel that you should run an injector big enough to feed your motor without meth and then add meth and enjoy its benefits on top of having PLENTY of injector

we all know what happens when we run out of fuel and dip into the lean scale rather quickly

 

Think about this. I have a 4.8, and turning it 6200 and 12 lbs of boost with a T60 turbo, with a M10 meth nozzel and 11.2 AFR and I'm in the mid 90% injector duty cycle with 42lbs/hr injectors. I got some 60's ready to go in it.

If you want to keep the 42's, your will need to limit your RPM and spray a fare amount of meth.

 

also remember what 42s are we talking about....svo 42s are 48# injectors, thats alittle more room then a standard based 42. i had svo42s on the 408 and even at 7k i was only at 72% duty and alot of guys on tech are running them in the mid5xx rwhp range

 

On the dyno I ran the 42#rs up to 450 before I started to see "the slope of death" on my AFR log. This was at 62-63psi and spinning a supercharger, so you can figure in some parasitic loss there, you will be doing a turbo and not see it. My IDC's were 110% at 460 to the wheels. I am in the low 500's now and spray a good amount of meth, tach to 6100 and see 99% IDC's with a conservative 11.5 AFR. I have a set of flow matched green tops in the toolbox but may sell those for some 60#rs for the extra headroom. I am just not motivated to do the swap till the cool weather arrives.

 

My 4.8 at 10psi with a 11.5 AFR and no meth is getting damn close to the limits and I'm only probably making 400-425ish rwhp

I'd think 5-7psi on an LQ9 would be safe. You could always up the fuel pressure, but then you're just compensating.

 

these are the 8.1l marine injectors, I don't know if that makes any difference. Thanks for the help guys, I'm very limited on performance knowledge so all the advice helps alot.

 

Here's a scan of my truck... hard to read but the 91 percent duty cycle (on the 42's) is at 5650 RPM on a down shift if I remember correctly... with fuel pressure dropping rapidly. Power is in the sig...

Bill