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The VAFC Hack: How it works, & Why it's Gay

Old 05-28-2004, 12:26 PM
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Default The VAFC Hack: How it works, & Why it's Gay

How it Works
Many of you may already know that an alternate method of tuning a boosted honda is to run what is called the VAFC hack. Now, the way this works is simple. When running larger injectors on a factory ECU, it's easy to understand it will dump too much fuel. Common knowledge says that the more load your car is under (i.e. higher RPMS, wide open throttle, etc.), the more fuel you are going to need.

Hondas run on what is called an MAP sensor, or Manifold Absolute Pressue sensor. What this does is tells your ECU how much air, in terms of pressure, is entering your engine. From that, your ECU can calculate exactly how much fuel your engine needs to dump in order to get the proper mixture of air and fuel. When you are at wide open throttle, more air is entering your engine, thus you need more fuel.

NOW, when you upgrade your factory fuel injectors to larger injectors, such as 450cc units, your ECU was not designed to run them. The ECU is only capable of calculating how long the STOCK injector needs to be open in order to give a certain amount of fuel, based on the readings of your MAP sensor.

Get it? No? alright...lets put it like this. Say you're microwaving something. The directions say to microwave it for 2 minutes. Cool. You pop it in, and cook that bitch for 2 minutes. All is well. Now, take that microwave, and double the power, meaning it cooks ---- twice as fast/gets twice as hot, and you don't know that. So you read the directions, and as always, it says 2 minutes. You pop that bitch in for 2 minutes and what happens? you burned the ---- out of your food.

In this scenario, You are your ECU, the MAP sensor is the directions, and the microwave is the fuel injector. Instead of getting a more powerful microwave, we're getting bigger, better flowing injectors, meaning if you keep them open the same amount of time, you will run too rich. So how do we fix this? Change the directions. Since the MAP sensor is telling the ECU how long to keep the injectors open, the VAFC intercepts the signal, scales it down to whatever it needs to be, then lies to the ECU so it keeps the injectors open for the correct amount of time. It erases the box and writes on the right cook time on the box so your dumbass doesn't burn your food with your new badass microwave. Got it? good.

Why it's Gay
*Note: if you don't know how the AFC hack works, Read my other post first.

So, you think you have a tuning tool there, do ya? Lets see what you've done by comparing hacked numbers to a factory numbers, layed over the ECU's Fuel Map:

(The mBar readings in black represent the ECU's programmed mBar values that the AFC is making the ECU think that you are at, where the readings in red represent what you are really at, but your AFC has hacked down to the base value. These maps were made with a -40% AFC setting. )

Now follow the transition into boost (any value over 1055 mBar) at 3000 RPM on your stock map (black numbers) to column 10. Holy ----! 555! You would flood your motor keeping your injectors open that long! luckily, you have your badass -40% afc hack, which dropps it down to 280 at column 5 (based on the red numbers).
Good job! Since you have larger injectors, the amount of time they stay open has been scaled down to where they need to be at (hypothetically), by tricking your ECU of course. Now you have a nice AFR all throughout your powerband.

Done with tuning right? your AFR in boost is at a nice 12:1 or whatever, and everything seems good. Wrong. What about timing?

Again, these maps show Red/Black, just like the fuel map.

Just for reference sake, follow the 3000 RPM field over to the factory transition into boost, or column 10. 24.5* of timing right? good stuff. Now remember, every tuner will agree that when you boost, you want to retard timing to thwart detonation. So, any value under 24.5 will work right?

Now, follow the 3000 RPM field over to your newly hacked values, or column 5. Holy Detonation, Batman! 32* of timing!

So, let me get this straight. If a rule of FI tuning says that when you boost, you retard timing to prevent detonation. Now, since you are a retard yourself, you decided to jack UP the timing 7.5*. NICE! that's a wonderful idea.

This, my friends, is why VAFC hacks are a poor excuse for timing. Yes, you CAN successfully control bigger injectors, but at the cost of jacking up your ignition, the exact opposite of what you want to do.

P.S. You will notice the screen shots were made with a Demo version of hondata. Demo? yes a demo. Honestly, the only reason I used Hondata for this explanation is becuase Uberdata, which I am loyal to, displays vaccum readings in in/hg, and i'm too ------- lazy to convert that ---- to mBar. I personally think Hondata is the equivalent of paying your neighbor $10/gal. for tap water, when you have a god damn faucet in your own house, but thats for another discussion.


EDIT: HA! How do you like them paragraphs now Beeotch :P
street_kings is offline  
Old 05-28-2004, 01:07 PM
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Default Re:The VAFC Hack: How it works, & Why it's Gay

Your lack of paragraph's is even more gay.

Ok, I'm going to read it now...
Wally is offline  
Old 05-28-2004, 01:36 PM
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Default Re:The VAFC Hack: How it works, & Why it's Gay

this is why ppl install a MSD BTm and retard base timing :/
88crxSi is offline  
Old 05-28-2004, 01:42 PM
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Default Re:The VAFC Hack: How it works, & Why it's Gay

Looks like some impressive work, I'll read it when I get back. :P
quadnie is offline  
Old 05-28-2004, 05:44 PM
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Default Re:The VAFC Hack: How it works, & Why it's Gay

Know and respect your roots...

So much hatred towards the hack. Yeah its not the best fuel management but it gets the job done. Fuel management is always evolving, it started with FMU's, than the hack was created and now the future is turboedit and uberdata. The hack and a BTM is actually good fuel management for people who are starting out with low power levels.

The hack is a good tuning tool for people just starting out. Some people don't even know the physics behind turbocharging when they start building a kit, are you expecting them to learn how to tune a standalone fuel system on top of that?

Your talking about the hack like it raped your mother and made you watch...
Reddy is offline  
Old 05-28-2004, 06:08 PM
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Default Re:The VAFC Hack: How it works, & Why it's Gay

^^^yeah, what he said. :P

This is also in the wrong forum. :P


I was in love with "the hack" for the longest time because it worked. I got to experience boost and it didn't cost me an arm and a nut. It was easy to use and it was simple to install. It was a large step up from the previous "FMU" setup just as TurboEdit is a large step up from "the hack".
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Dr.Boost is offline  
Old 05-28-2004, 06:33 PM
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Default Re:The VAFC Hack: How it works, & Why it's Gay

All of this is covered in the Engine Management FAQ.
TurboEF9 is offline  
Old 05-28-2004, 06:38 PM
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Default Re:The VAFC Hack: How it works, & Why it's Gay

Whoops, I honestly forgot to read the FAQ , anyway, my intentions weren't to completely bash the hack and say anybody has ever used it is a fucktard. There was a guy I was arguing with on another board about the hack, and if/how it advances igntion timing. I just thought it might be helpful to someone if i posted it here also. The people this was aimed twards is the people like that guy, who believe that hack is a solve all god-like tuning tool, when there's actually better tools out there that make more sense. Yeah, it is one of the roots of tuning like when back in the day the only option was $450+ hondata, and for some setups that's the AFC is the only option. However, now since there's so many options for the honda guys, it may not be the most practical. (and that little ****** pissed me off so I was a lil heated :P)
street_kings is offline  
Old 05-28-2004, 07:40 PM
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Default Re:The VAFC Hack: How it works, & Why it's Gay

awesome right up, this really clears alot of things up, espicially for people who don't know(like quadnie) I hope there is a link to this is tha FaQ, it's good stuff.
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Old 05-28-2004, 09:15 PM
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Default Re:The VAFC Hack: How it works, & Why it's Gay


Originally Posted by TurboEF9
All of this is -----> covered <----- in the Engine Management FAQ.
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