AFR's and different fuels.

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AFR's and different fuels.

Postby Holden202T » Thu May 12, 2016 1:50 pm

In other threads there has been talk of changing AFR's for different fuels v's not and then changing other things to make the tune read correct on the wideband for petrol even though the fuel is not actually petrol.

Some people are under the impression that changing the open loop AFR table to suit a different fuel has no effect and theres various other things in there as well, so with the assistance of VL400 and Jayme i have made a little spreadsheet to show you how simply changing one constant effects the output of the injectors.

in the attached spreadsheet BPW output is effectively the injector opening time and for the purpose of this subject, this is the only real output we want to look at.

Explaining AFR's.xlsx
(12.25 KiB) Downloaded 266 times

The spreadsheet is roughly populated with an injector rate from V6 commodore (19lb injector), standard petrol AFR and battery voltage offsets from the delco tables.

if you were to change the injectors in your car to 60lb then you would change the injector constant from .1299 to roughly .0433, so if you do that in this spreadsheet you will see that the BPW output pretty much drops to 1/3 what it was.....

ok so that now establishes that putting 3 times bigger injectors into the motor means you need to open them 1/3 the time to get the same fuel flow for a v6 commodoore.

now that you have the capacity in the fuel injector to flow 3 times as much fuel, you can now start looking at changing the target air fuel ratio in the spreadsheet to show you the sort of offset it will have on the injector opening time (BPW output)

So now we want to change our petrol v6 to E85, so you would go through the tune and offset all AFR related tables from 14.7 petrol stoich to 9.7 E85 stoich..... (approx 66% change)

Petrol open loop afr table

petrol afr table.jpg
petrol afr table.jpg (270.64 KiB) Viewed 1971 times

the same table offset by 66% (the difference between petrol and E85 requirements.)

E85 afr table.jpg
E85 afr table.jpg (251.29 KiB) Viewed 1971 times

now if you put any of the E85 afr numbers into the spreadsheet you will see that it will increase the bpw output by pretty much 66% more than the same given number in a petrol AFR table.

and if you wanted to apply the same theory to methanol it will similarly increase petrol bpw output to approx 2.3 times by simply changing the target air fuel ratio from 14.7 to 6.4 for methanol.

methanol afr table.jpg
methanol afr table.jpg (248.17 KiB) Viewed 1971 times

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Re: AFR's and different fuels.

Postby vlad01 » Thu May 12, 2016 1:55 pm

:thumbup:. this should be in the FAQ
I'm the director of VSH (Vlad's Spec Holden), because HSV were doing it ass about.

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Re: AFR's and different fuels.

Postby immortality » Thu May 12, 2016 2:24 pm

Good work and agree it should be part of the FAQ.

I like where this is going :thumbup:

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Re: AFR's and different fuels.

Postby TdracerTd » Thu May 12, 2016 3:12 pm

I'm pretty sure that it is in one of the guides. And I understand why you do it that way.

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Re: AFR's and different fuels.

Postby Holden202T » Thu May 12, 2016 3:18 pm

there is plenty of information in the tuning guides on how to change stuff, but not so much why and what result it has.

as far as tuning a car this information is not so much part of a tuning guide, its more a thing of general understanding of how it all works, and alot of the tuning guides assume you know all these things and just gives you the specifics of how to change them in $11/12P environment.

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