1--I know I have to change injector constant, whats the formula? What are my stock injectors rated at?
2--Do I need to ramp up the flow rate to compensate for boost ramping up, or will the MAF take care of that?
3--Do I need to ramp it up to compensate for the pressure differential between fuel pressure and manifold pressure to keep flow the same?
4-- I will be tuning for the 8psi I have now, then upping the boost. Once I get 8lbs dialed in, what will I have to change to raise the boost?
5--What else? I know that can't be everything.

 

1. A constant of 5.42 should get you close with those injectors. Some tweaking may be necessary depending on what your Ltrims currently are but, that constant will get you close. Stock injectors are in the low 2X# range.

2. No, you don't need to worry about ramping up the flow rate. Our fuel systems compensate some for boost increases since they are manifold referenced. You may have to adjust the PE vs. RPM table later on but, this should be done with a dyno tune or in truck wideband to get it accurate.

3. Our fuel systems pretty much take care of that. Evidently it doesn't raise pressure at a 1:1 rate but, it does compensate some.

4. When you up the boost you may want to pull some timing out and gradually work it back in to avoid getting any detonation. The A/F ratio may also need to be tweaked after increasing the boost.

5. I don't know. Hopefully someone else will chime in.

A wideband setup would go a long way in tuning your own truck with EDIT. If you keep your O2 readings in the .930-.940 range you should be OK but, don't take my word for it because every O2 seems to read a little different.

 

I have an FJO wideband on board. So if I change to 5.42, it will get me close enough to drive? My LTRIMS are about +9 right now. Does that change that 5.42 figure? Once I can drive it, and get wideband readings do I change PE RPM to tweak the AFR, or injector constant? Hey, this doesn't sound quite as hard as I thought.

Thanks man.

 

Cool, that wideband will make tuning simple.

5.42 will get you close enough to drive. If you're Ltrims are still positive with that constant you can lower it and the trims will come down. Just go a little at a time though, maybe like .2 at a time.

What you want to do is get your Ltrims just slightly negative at cruise/idle with the IFR. You do this so that the computer doesn't add fuel at WOT and make WOT tuning inconsistant. Once you have the ltrims just slightly negative(1-2% is fine) then you can tune WOT with the PE vs. RPM table. Keep a VERY close eye on your wideband while doing this. Does the FJO have a display? If not just do short WOT runs and work your way up threw the rpms after checking the logs and making sure everything is OK with the previous run.

If you're already tuned for the 8psi I bet everything will be pretty close.

I've also just recently read that the VE table may be better to tune WOT with but, I've never actually used that method so I can't say anything about it.

Might want to talk with GMC SKI about tuning the ATI also since he actually has one.

 

dont touch your PE rpm yet, work with your injector constant till you see negative ltrims, then start on your wot tuning. dont go all out with a WOT full 1/4 mile run either, give it a quick couple second blast and see where your a/f ratio is and then start adjusting with the PE RPM table.

it really is easy when you have a wideband. if it is lean for some reason go ahead and overcompensate on the PE rpm table and then work your way up from a rich condition, you dont want to be flooring it over and over again trying to get your a/f ratio down but it is ok to do that when you are rich and trying to get it up. i shot for 11.5-12.0 but that is without an intercooler, i think you could shoot for a little leaner.


edit...doa, john beat me to it.

 

XLR8NSS- yes it has a big display on my laptop screen, so that shouldn't be a problem. Thanks for all the info!
PARISH- did you have to change your tune when switching pulleys back and forth?

GMCSKI feel free to chime in too.

 

We used the same injectors on the escalade project. I thought the number would be 5.25 (according to the Magna guys values), but it turned out to be 4.77. This was tuning with a wideband and ending up with ltrims at -1. At WOT, it was prett fat, so numbers went from the stock ~1.2x to 1.07 in the PE table.

 

i didn't change my tune, seems like the a/f ratio held prety steady once it was dialed in, i ran 92 octane at 6psi and ~100octane at 8psi. right at the end i bumed it to 9psi when i had the good gas in and it ran strong, tried the 11psi pully and got knock.

 

BigTex - One thing I've noticed about injector constants is that they always seem to be smaller than the "calculated" values. My new injectors are the same way.

Black Blown 02 - Whatever value you put in just give the Ltrims a minute or so to correct at idle and adjust them accordingly. If the Ltrims are positive lower the IFR and if they are way negative you raise the IFR.

 

sounds good, thanks guys.