adding fuel to PE trim after upping injector constant

[NC87GN]

When injector constant is raised in a chip to improve BLM, does the PE trim table need to change by a given percentage also? Here is where I'm at. Car has 55# injectors but BLM's are 90. Ran the car WOT and 02's are 720-750 (very lean). Chip I am using has injector constant at 45.1. I did correct for the lean condition in the chip at WOT but did not mess with the injector constant yet. When I raise injector constant to 45.1 to 55# (around 18% difference), do I need to add the same percentages (18%) to my PE trim tables to keep it from going lean??? TIA

Mike Banas
87GN

 

[TurboJim]

Why would you be using a 45# constant with 55's? No wonder your BLM is 90. Depending on the car I'll use 54-56# and have minimal BLM correction. I say depending on the car, I dont know why some cars like it one way or another. Maybe differences in MAF's I guess.

 

[Eric Stage I]

Mike,
Yes, you're going to have to add the fuel back in for PE if you change the injector constant. You can do it in the PE trim tables for specific areas, or you could do it in the A/F in PE vs. Coolant table to move the whole "range" up or down. Either way works. Although I calculated a 22% increase.

Good luck,
Eric

 

[TurboJim]

Actually Eric:

It depends on if he NEEDS the fuel.

ie:

Lets say his car is mild mid low 12 car. Lets say he had 36's in it and his PE trime were maybe as high as 30%. If he ONLY changes the constant, the 55's will act like 36's. ie: if with the 36's he blew 800's out the exh, he *should* blow 800's with the 55's (not accounting any difference in inj characteristic) and heres why: Lets say he had a 38h in his constant. That equated to a multiplier of .219. Fuel calcs are done and mult by .219 for IPW. Now lets say he puts a 24h in for the 55's, which equated to a .145 multiplier. The IPW is gonna be almost 1/2 without changing anything else. Now, if his 36's were maxed and he needed more fuel, lets say he was at +40% which should put the 36's close to static, putting just a 55 constant will put the 55's at roughly the same mixture, but at like 60% instead of 100%. Adding fuel will will realize a richer mixture as the 55's CAN flow more than the 36's.

So, the point of my babble here is if he does nothing but change the constant, it should put him exactly where he left off, give or take a little. (Provided he wasnt over ~ +70% in PE/RPM which would put the 36's at like 150%+ would send the 55's pretty high as well, my aSSumption would be somewhere in the 95-100%)

Of course, this is all pretty general, and doesnt take into account he might have his PE stuff up high already which would INCREASE the rich condition if present and cause him to need to REMOVE fuel with the 55's.

If I were doing the chip, I'd use a 54.9 or 56lb constant, and my PE's would look something like:

My 132* and 218* PE AF in a street chip might be 13.4:1 or so and PE/RPM might look something like:

800 1600 2400 3200 4000 4800 5600 6400
-12 -8 2 8 14 25 38 45

That would be my start. I'd adjust as needed from there. Thats been my experience anyway

 

[NC87GN]

Reason I ran a chip with a 45.1 injetor constant is I had no other chip for 55# that would work properly. He has an old version of an extender chip (one of the very first revisions) for 55#, and the car would not move 60' without stalling. I needed a quick baseline to record some readings with direct scan and the only chip I had in my possession was for 009's. Long story short, the car ran MUCH BETTER with 009 chip than his old extender chip. Just need to work tweak the chip to account for low BLM's.

Jim, what is a typical base fuel pressure you start off with on the 55# with injector constant ~56-57? We have the translator set to 3" MAF with no fuel correction @ base. WOT MAF is also 0 (no change).

Thanks for all the help!!!

Mike Banas
87 GN

 

[Eric Stage I]

Jim, I understand and agree with your method. In this case, Mike said his wot O2's are good and he wants to change the inj constant from 45lb to 55lb to help the blms. So I would think that to keep his wot O2's the same, he's going to have to add PE fuel back in because its gonna get leaner when he goes from 45 to 55. That was my line of reasoning anyway...

Eric

 

[bruce]

Originally posted by NC87GN
When injector constant is raised in a chip to improve BLM, does the PE trim table need to change by a given percentage also? Here is where I'm at. Car has 55# injectors but BLM's are 90. Ran the car WOT and 02's are 720-750 (very lean). Chip I am using has injector constant at 45.1. I did correct for the lean condition in the chip at WOT but did not mess with the injector constant yet. When I raise injector constant to 45.1 to 55# (around 18% difference), do I need to add the same percentages (18%) to my PE trim tables to keep it from going lean??? TIA

Put together or buy a WB.

Then set the constant at 55.

Then calibrate the MAF tables and scalars for light throttle, and then use the PE stuff for PE.

Until you take the time to get it right you'll be chasing ghosts.

It's worth doing it right.....

 

[TurboJim]

Originally posted by Eric Stage I
Jim, I understand and agree with your method. In this case, Mike said his wot O2's are good and he wants to change the inj constant from 45lb to 55lb to help the blms. So I would think that to keep his wot O2's the same, he's going to have to add PE fuel back in because its gonna get leaner when he goes from 45 to 55. That was my line of reasoning anyway...

Eric

I see what you mean, and you're probably right...but its gonna depend what cell 15 learned to. It cell 15 is 90, then once you up the constant and let it relearn, it will probably be OK

 

[Eric Stage I]

Your right...I assumed a blm lock. I always tend to lock cell 15 so its non-changable.

Eric

 

[BM Computer Src]

Mike,

Shoot me an email, I've got an update for you.

Bob

 

[NC87GN]

Hey Bob!,
Been out of the turbo scene for a couple weeks and just seen your reply back to this post. I will give you a call when I get back to the office Monday Dec. 1. Thanks for the response on the update..

Mike Banas
87GN