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

**copgtp** · 04-19-2012

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.

**boostedcompg** · 04-19-2012

i dunno...but what did you do with your 42.5's

**copgtp** · 04-19-2012

Sold them

**Fivefingerdeathpunch** · 04-19-2012

You will have to change the numbers.

**copgtp** · 04-19-2012

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?

**copgtp** · 04-19-2012

Oh, and I'm a newb with the HPT, FYI

**99prixgt** · 04-19-2012

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*

**matt5112** · 04-19-2012

Originally Posted by 99prixgt

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*

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.

**copgtp** · 04-19-2012

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.

**99prixgt** · 04-19-2012

damn, i need hpt

**matt5112** · 04-19-2012

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.

**copgtp** · 04-19-2012

So, if I'm tracking.....by using the offsets from my 42.5 injectors, I'm running quite rich with the 80 injectors?

**matt5112** · 04-19-2012

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?

**copgtp** · 04-19-2012

Siemens Deka 80# Injectors

**matt5112** · 04-19-2012

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

**matt5112** · 04-19-2012

Building offset vs pulse width vs MAP table

**matt5112** · 04-19-2012

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.

**copgtp** · 04-19-2012

great, we shall see what happens! Thanks for the help matt

**matt5112** · 04-19-2012

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.