B18CRacer

So after reading this thread several times, ive think i got it straight on the afc hack that liam821 was talking about. Please if anyone want to add to this, feel free. Here is what i have on my gsr boosting 8psi.

vafc wired as stock normal
440 rc injectors
no missing link or check valves on the stock honda map sensor (connected as stock)
No Fmu
afc set at -.35% in high and low settings

I use this formula:


83% larger (b-a)/a=c c=percentage larger
-.45% set afc using formula (a-b)/b=c, where a=original injector size, b=new injector size, and c=value for afc. (add 10% on top of that to keep the honda happy)

integrx

are you using stock fuel pump?

racinskittle

stock fuel pump will be find for lower boost.

But yeah, that looks right.

USDM 4G VTEC

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B18CRacer &raquo;</TD></TR><TR><TD CLASS="quote">So after reading this thread several times, ive think i got it straight on the afc hack that liam821 was talking about. Please if anyone want to add to this, feel free. Here is what i have on my gsr boosting 8psi.

vafc wired as stock normal
440 rc injectors
no missing link or check valves on the stock honda map sensor (connected as stock)
No Fmu
afc set at -.35% in high and low settings

I use this formula:


83% larger (b-a)/a=c c=percentage larger
-.45% set afc using formula (a-b)/b=c, where a=original injector size, b=new injector size, and c=value for afc. (add 10% on top of that to keep the honda happy)

</TD></TR></TABLE>

so you saying that someone with the VAFC hack and 450cc DSM injectors shopuld??

(240-450)/450=C
(-210)/450=C
0.5333=C
0.5333 +10%= 43% on the VAFC???

B18CRacer

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by USDM 4G VTEC &raquo;</TD></TR><TR><TD CLASS="quote">

so you saying that someone with the VAFC hack and 450cc DSM injectors shopuld??

(240-450)/450=C
(-210)/450=C
0.5333=C
0.5333 +10%= 43% on the VAFC???</TD></TR></TABLE>

Your math is wrong

(240-450)/450=C
(-210)/450=C
-.4666=C
-.46% and take away another 10% to make the honda happy
so it would adjusted to -.36%

B18CRacer

im using holley fuel pump with a flow rate 50gph supports up to 600hp

liam821

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B18CRacer &raquo;</TD></TR><TR><TD CLASS="quote">

Your math is wrong

(240-450)/450=C
(-210)/450=C
-.4666=C
-.46% and take away another 10% to make the honda happy
so it would adjusted to -.36%

</TD></TR></TABLE>

Its a good starting point at least! Ive seen so many different settings. -35% is a great place to start though.

Also if you have the means - checkout uberdata. It has come along way!

liam

USDM 4G VTEC

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B18CRacer &raquo;</TD></TR><TR><TD CLASS="quote">

Your math is wrong

(240-450)/450=C
(-210)/450=C
-.4666=C
-.46% and take away another 10% to make the honda happy
so it would adjusted to -.36%

</TD></TR></TABLE>

well u gotta forgive me then

i just used my calc here at work.... damn SHARP's one.. and thats what it said.

anyways

TurboBumblBee

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B18CRacer &raquo;</TD></TR><TR><TD CLASS="quote">


afc set at -.35% in high and low settings
</TD></TR></TABLE>

the vafc confuses the hell out of me.. where would you put these settings in?? is this where its a graph and you can raise and lower it? and i should have -35% all the way across?

B18CRacer

Dammit_Dan_954

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by liam821 &raquo;</TD></TR><TR><TD CLASS="quote">

Its a good starting point at least! Ive seen so many different settings. -35% is a great place to start though.

Also if you have the means - checkout uberdata. It has come along way!

liam</TD></TR></TABLE>

Liam..... is -35% dumping more fuel than say -38%? or is it the other way around?

I am currently using the VAFC Hack on my freinds car with 450cc DSM injectors and have been for over a year now with out any problems until now. We changed his turbo and motor now it is acting up. Previously he had a saab t3 on a b16a which dynoed 231whp on 9lbs. We recently swapped in a gs-r motor and a sc52 and now it is runing like ****. It stumbles when accelerating lightly and the egt goes above 1500 deg Faren. The settings on his VAFC with the old setup was -33% for idle and -38% everywhere else. It still idles fine at -33% and we tried all settings from -36% to -41% all the way across all settings with no luck. Could the resistor box being wired wrong affect anything (I don't know if it is or not just asking since I'm not the one that wired it up.)

Any help would be greatly appreciated.

B18CRacer

how is your a/f ratio looking?

Dammit_Dan_954

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B18CRacer &raquo;</TD></TR><TR><TD CLASS="quote">how is your a/f ratio looking?</TD></TR></TABLE>

Fine.

Dammit_Dan_954

is -35% dumping more fuel than say -38%? or is it the other way around?

twkdCD595

with bigger injectors, yes -35 would me more fuel than -38.

B18CRacer

Yes

B18CRacer

this maybe a question for liam but anyone who knows may help me....I set it to -30 on high and low both narrow and wide. Is this correct because the narrow seem to want more fuel for it to idle correctly.

Cimburke23

i have a vafc2, wondering do i use the TDC, VTM, and VTC wires, if so, where do i wire them? any help would be greatly appreciated. thanks

hatchback_al

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cimburke23 &raquo;</TD></TR><TR><TD CLASS="quote">i have a vafc2, wondering do i use the TDC, VTM, and VTC wires, if so, where do i wire them? any help would be greatly appreciated. thanks</TD></TR></TABLE>

please make your own thread, don't jack others threads

p.s. i have a vafc ver 1 not 2 so i cant help you on that one sorry

TurboEH2

he wasnt jacking this thread, the guy is laying down information and he needed to ask a question that maybe this guy had an answer to. if u arent contributing to this thread then why are u posting? to try and teach someone a lesson on how to use h-t properly?

B18CRacer

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Cimburke23 &raquo;</TD></TR><TR><TD CLASS="quote">i have a vafc2, wondering do i use the TDC, VTM, and VTC wires, if so, where do i wire them? any help would be greatly appreciated. thanks</TD></TR></TABLE>

You gonna have to ask liam....I believe its hook up as stock as instructed in the apexi manual.

Just Checking In

It looks like some of you guys have the concept down to a degree but not really why its neccessary.

With the vafc hack, maximum amount of boost before 11 psi when the map sensor errors, is dictated by the injector size you choose to run. 450 cc injectors are popular with the vafc hack because they will allow you to scale the map sensor voltage nearest 3.09 volts with room to increase the amount of fuel needed above the percent differance between the injectors. This lets you clear the greatest timing advance section of the ignition table and lets you create a close 14:1 air/fuel ratio per psi of boost.

Mathematically heres an example.

Say you want to run 10 pounds of boost and you bought the correct 450cc injectors for this.
The differance of flow is 46% because (240/450)-1= .46
Then because larger injectors have to be compensated for latency we subtract about 5% for 450cc's leaving us with a 41% fuel difference
This means at -41% setting in your VAFC your 450's are giving you the same fuel your 240's were.
Now the map sensor goes into limp mode at 3.1 volts so you need to stay below that, and 10 psi is about 4.7 volts.......... so 4.7-(4.7x.41)=2.89
This shows us that 450's give us enough room to reduce the map signal below 3.1 volts with enough differance in volts between 2.77 and 3.1 to increase the fuel %cuts to accomodate for boost.

So what we do in terms of setting the vafc is this. We know the differance in flow between 450's and 240's is -41% and at idle air/fuel ration does not change with the turbo. So at idle, if you run 450's you will set your VAFC to -41%. As your rpms increase you want to add fuel to compensate for boost you could be making at those rpms. So on average, people add 1% per 1,000rpm's above 3,000rpm where boost begins to build with average sized compressor housings and wheels. You don't really want to go past a 5-6% overall increase though because you will be increasing your flow differential at the same time the ecu is increasing pulse duration. This can make for a really rich combustion.

Here is a good example of settings for a b16 running 450's and VTEC set at 4,500 rpm:
Same settings for wide and narrow with hi and lo
1000 -41%
1500 -41%
2000 -41%
2500 -41%
3000 -40%
3500 -40%
4000 -39%
4500 -38%
5000 -37%
5500 -36%
6000 -36%
7000 -35%
8300 -35%

Do you see how you want to transition into the air fuel ratio gradually? If you just set it at -35% across the board you are running entirely too rich at idle and anything below 4k roughly. Different setups will build boost at different rpms so this is just an example of something average.

Once you grasp the concept you'll notice some issues. You will see why the VAFC is a piece of **** for spirited city driving. It works for cruising below 3,500rpm or full throttle runs and thats about it. Otherwise all your settings that you input so that you have a correct a/f mixture when flooring it......creates entirely too rich a/f's when you're just trying to cruise around and you just happen to go past 3,500rpm with anything less then half throttle on the average sized compressor housing, on a small displacement motor. You will also see why to run safe with the vafc you should run 10 psi, so that your fuel correction values aren't putting you dead center of the highest ignition advance on the table. You also should slightly compensate your idle and low end power by retarding your base TDC timing down to about 12 degrees instead of stock 16-18.

I hope this helps.

Modified by Just Checking In at 9:11 PM 8/7/2004


Modified by Just Checking In at 9:18 PM 8/7/2004


Modified by Just Checking In at 9:20 PM 8/7/2004

SOHC_MShue

thats a good explanation . Also a good description of why the afc hack isn't all that great. I would highly recommend uberdata over the hack anyday.