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Going from 42.5* injectors to 80*......change my tables?

copgtp

copgtp

Your ClubGP Liason
My topic pretty much says it all, do my tables need to be changed with these injectors? I haven't done anything to require more injector, I installed them thinking I might go E85 in the future, but for right now I want to run them at the same percentage as my 42.5's were at.

Thanks.
 


I haven't done any tuning in a while, could someone lead me in the right direction? What tables to I have to change, and what type of change do I need to make?
 


Divide your old injector size by the new injector size to get the variance. For example: 36 / 42.5 = 0.847. So... your new IFR table shall be 84.7% of the old table (highlight all cells in the IFR table, right-click, select CUSTOM, click on PERCENT, enter 84.7, click ok, this is what i would have to do since i have a DHP.

*taken from the tuning bible*
 
99prixgt said:
Divide your old injector size by the new injector size to get the variance. For example: 36 / 42.5 = 0.847. So... your new IFR table shall be 84.7% of the old table (highlight all cells in the IFR table, right-click, select CUSTOM, click on PERCENT, enter 84.7, click ok, this is what i would have to do since i have a DHP.

*taken from the tuning bible*
Click to expand...

Why?

Why not just insert the correct data from the start?

Jason, have a rewire?

If so, the IFR is the same all across.

Same with the offsets.

You'll want to find good data on your injectors and use that.

Also use the rated flow rate and the calc built into HPT to find out the flow of your injectors at 3.5 BAR.
 
Matt: Yes I have a re-wire

And the rest of what you said I believe was in a different language....... LOL!!

I wish they had a class I could take for this HPT! Maybe it's my old age, but it seems harder to use than the PT.
 
Your injectors have a "flow rate" when run static.

Thats the rated flow at 43.5 PSI or 3 BAR.

our fuel system namely the FPR is setup so that the injector always sees an effective pressure of 58 PSI or 4 BAR.

Since the injectors inject a fluid, they do not flow linearly and follow Berneroulli's principle. Bernoulli's principle - Wikipedia, the free encyclopedia

Injectors respond mostly linearly after 2-4 ms. Before that, they respond slower than expected. The smaller the pulse width (the on time commanded by the PCM) the longer they take to flow the expected rate.
 
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So, if I'm tracking.....by using the offsets from my 42.5 injectors, I'm running quite rich with the 80 injectors?
 
Well offsets only affect idle and low throttle situations.

The first thing you need to look at is your injector flow rate table.

Which injectors do you have specifically?
 
Offset vs volt:

4.1033433 4.1033433 4.1033433 4.1033433 4.1033433 4.1033433 3.3738600 2.6291792 1.9604862 1.6261397 1.3069908 1.1702127 0.9726443 0.8358662 0.7446808 0.5927051 0.6079027 0.5927051 0.5775076 0.5775076 0.5775076 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000 0.0000000
 


Use this in each collum in that last table:

0.5471124
0.4711246
0.3951368
0.3039514
0.2279635
0.1671732
0.0911854
0.0759878
0.0000000
0.0000000
0.0000000
0.0000000
0.0000000
0.0000000
0.0000000
0.0000000
0.0000000

That should give you a pretty accurate fuel model granted your fuel pressure always changes 1:1 with manifold pressure/vacuum.

You'd need to check your fuel pressure to make sure it doesnt drop off and changes properly with manifold conditions.
 
Well it seems I might have mucked that up.

Some sources say we have a 3.5 BAR FPR, not 4 bar.

GM service manual is inconclusive as it gives a range of 51-59 PSI.

Try it out, see how it runs, if it runs lean, then you might need to lower those values to reflect this mistake.

I guess the real mistake is not finding out your true fuel pressure without vacuum on the FPR.
 
Jason...how new is your HPT? The most recent software has all the good stuff that we never before had to truly tune in the injectors.
 
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