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How much to retard when using VAFC?

Old 12-11-2005, 03:08 PM
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Default How much to retard when using VAFC?

I will be running a D16Y8, with 14b @ about 9ish psi, 450ccs, yada yada....anyways i will be running a VAFC because i have an automatic tranny. So I hear the VAFC advances your timing. I plan on buying the MSD Universal Boost Timing Master, which alows me to retard my timing 1-3 degrees for every lb of boost.
Why does the VAFC advance the timing?
How much does a VAFC advance my timing?
About how much should I retard my timing per lb of boost?


Thanks for any help.
GrenEggzandHam is offline  
Old 12-11-2005, 03:32 PM
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Default Re: How much to retard when using VAFC?

the afc advances timing when you use it as a afc hack.. the purpose of the afc hack is to fool the ecu by lowering the map signal %40 so that your ecu thinks you dont have positive pressure in your manifold. the map sensors in hondas generate a signal of up to 5 volts max but the ecu throws a CEL over 3 volts because its the output for 0 manifold pressure and over that you would have possitive pressure.. when you boost about 10 psi that makes a map reading about 5 volts and -%40 setting makes that 3 volts for your ecu.. so you have fooled the ecu for boost now you have to change your injectors because at -%40 your sending your engine %40 less fuel while you have to get more fuel with FI. stock honda inj are 240cc and if you use 450 it will give just right amount of fuel needed using those values for the afc because they push more fuel to the engine for the given ecu signal to them.. the problem is that when you set your afc setting to lower your ecu uses levels for less airflow which have more advanced timing to that you should be using in that air pressure.. you can easily see this in uberdata.. load a stock map and see the timing in the last column; when you hack with afc and use -%40 the reading of the map decreases and it uses the 6th column and you have more advanced timing in that coloumn according to the last.. so to say that gives you about 6 dergrees of timing advance with afc hack you have to retard it about 6 degrees according to the table (thats the max value you have to retard it it should cahnge according to the rev and MAP) and when you boost the car you have to retard some more about 3-4 more degrees for about 10 psi.. finally you have to retard it about 10 degrees but you have to do it gardually according to the afc hack and at what rev you get what boost..

a bit long post but it should explain the whole thing i guess
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Old 12-11-2005, 08:22 PM
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Default Re: How much to retard when using VAFC?

Thanks, that kinda helped. I didnt know the vafc was that complicated . Y cant Civics just come turbo charged, it would make my life alot easier!

So i need to retard it aprx. 10 degrees.
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Old 12-13-2005, 11:51 AM
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Default Re: How much to retard when using VAFC?

MSD BTM does nothing to address the extreme ignition advance associated with the AFC hack, except cost a couple hundred dollars and lend a false sense of security.

The best solution for those who insist on running the AFC hack, is to not run the AFC hack. If that isn't an option, and you have to run the AFC hack, then don't run the AFC hack. If that still can't be done, then take about 3 degrees out of your base timing by fiddling the distibutor, run a full 9-10 psi right at the max of the MAP sensor's reading ability which will get all the ignition advance out, and avoid situations where it takes a long time to build your full 9-10 psi of boost like WOT in 4th or 5th gear from 1500 rpms. Which you can't do, because OBD2 timing is locked regardless of how you twist on the distributor.

Gimme a minute, I'll find my HT writeup of the problem.
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Old 12-13-2005, 11:58 AM
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Default Re: How much to retard when using VAFC?

Alright, here it is: http://www.honda-tech.com/zerothread?id=841443. It was on here at one point in time, but everyone pissed on the thread with bullshit and it was unstickied. *shrug* So the HT haters can deal with a link offsite.

FYI, I don't see any reason why you have to run the AFC hack since you have an auto transmission. I know automatic OBD1 cars, properly tuned via the ECU, happen even if I don't know all the details. I also know that after all the work you put into a turbo Honduh, swapping out for a 5 spd transmission isn't that much work or expense.

Just my $0.02, what do I know?
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Old 12-13-2005, 03:26 PM
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Default Re: How much to retard when using VAFC?

OK so im hearing that ur saying "...take about 3 degrees out of your base timing by fiddling the distibutor...", but then u say "Which you can't do, because OBD2 timing is locked regardless of how you twist on the distributor." So wouldnt that mean that the MSD BTM would do nothing for my automatic car.

Also on hondatech you said "...if you have retarded your distributor 2-3 degrees you should have adequate ignition retard under boost."
So pretty much the MSD BTM will not do anything and I should retard my distributor 2-3 degrees? and How do i retard my distributor? Would it be just as safe for me to just run my FMU?
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Old 12-13-2005, 09:38 PM
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Default Re: How much to retard when using VAFC?

You can retard your distributor, but the OBD2 ECU "sees" this and puts the timing right back in, so you effectively accomplish nothing.

If you have no idea how to adjust ignition timing on a not-OBD2 Honduh, or 95% of the other cars on the roads, /yourself. If basic DIY maintainence is beyond you, a turbo Honduh is not for you.

At ~ 6 psi boost, with the typical 12:1 FMU, you will have 72 psi of fuel pressure. That's right about the point where excess fuel pressure starts pushing the injectors shut when the ECU is trying to hold them open, so you don't get as much fuel as you think you are going to. Also, the stock fuel pump at stock pressures is good for ~300 whp... at 72 psi it's probably good for 225 or less. Okay, you upgrade to a Walbro high pressure 225... and sustained high fuel pressure causes a ---- ton of fuel leaks over time. God help you if you try to run more boost... and you still can't do anything with that OBD2 ignition timing.

Tom-Guy is offline  
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