Now i have me exhaust fitted time to move onto next mod, was thinking of going with VAFC but there are lots of mixed views especially on usa part of forum.

short and sweet is it worth it and if so where from?

or should i spend the money on something else.

cheers

 

I've got one, and on an NA tune I got about 4/5 bhp across the entire rev range, and a chunk where the vtec cross over was flattened out.

But i missed the kick that early cars give on cross over.

Only issue is the ECU learns that it's running rich/lean (the adjustments) and tweaks accordingly. You'll need to reset the ECU every week or so to get the performance gains back.

I'll be getting it re-done with the charger next weekend to see if it's good enough, or if a full aftermarket is *really* needed.

 

i dont know if i could be arsed with resetting the ecu every week.

what about the unichip?

 

I think it also needs a regular ECU reset.

 

Does the Unichip not alter the date the ECU recieves? in simple terms if you want to run richer the Unichip fools the ECU that its running lean and the ECU compensates.

 

Yes.

Assuming the Unichip it the same as any piggyback (like the VAFC). The VAFC is fueling only, the Unichip is fuel & timing.

But the ECU also then gets the readings from the O2 sensors (which are not being tweaked by the Unichip), and then realises it's running rich/lean (due to the piggyback tricking it) and will then slowly compensate for the piggyback.

So you add 10% more fuel (via the piggyback) .. the ecu adds 10% more, realises, and then thins out the fueling. Now you have a piggyback adding 10% and an ECU taking 10%.

The problem with this is that the Piggypack can be tuned for a fine readings, and then the stock ECU starts taking away the fuel, you run lean and *BANG*.

It's best to setup the car so it's running richer, and then reducing the fuel via a piggyback. Then when it starts to re-learn, it's adding fuel (loosing power, but running safe).

That's the way I understand it anyhow.

 

Any piggyback does that, ie HKS F COn, Apexi VAFC, Unichip etc...

It adampts the signal from the MAP sensor to fool the ECU into thinking what it wants. It sounds a bit dodgy but IMO its not at all. The key thing is that if the car is mapped with a wideband lambda, and the AFR is safe then it will be fine. I know of people running Unichip on Impreza's with good results too!

The difference with the Unichip, it also adjusts the ignition timing, which is where the gains will come from.

As said, the ECU wants to keep to its original settings, so it will learn its way around what you do eventaully. A reset is a 2 min taks really.

MB

 

Bibbs, the O2 sensor (singular) is not used to control fuelling by the ECU when on VTEC or WOT.

AFAIK.

That makes me wonder now... The o2 sesnor is there to optimise fuelling when you dont have your foot down, on cruise etc etc. It searches for a stoich voltage from the 02 sensor. When you put your foot down, the ECU uses lookup tables within its memory, taking inputs from the MAP for load, the IAT, TPS, speed etc etc to go for the right fuelling. THe fuelling is governed by fuel pressure as the injectors are held wide open, rather than injector pulse.

The 02 sensor is passive at this point, in that it has no fuel control.

What I can't remember is if it is still monitoring (it is most definately still switched on) and feeding back into the fuelling trims.

Will find out.

MB

 

I know on warm up and WOT it's "open loop".
On part throttle it's "closed loop".

After 2 months, on part throttle I could feel the car pop and bang and struggle with the fueling after the VAFC was tuned. After a reset it was fine.

Under WOT it was okay.

 

I see.

Only odd thing is that normally they only tune the car on WOT so effectively only messing with the open loop fuelling...

MB