Technical Guide: How to tune the VAFC

[hattech-v]

hopefully.. never been there... haha

 

[shiroitenshi]

Bottom line : Piggy Back cannot INDEPENDENTLY adjust fuel and ignition, any changes to fueling will produce a change in ignition too, and often this is undesirable. And also, tuning only piggy back without parts upgrade.. not give impressive result.

my 2c....

Maybe Mr. Zaki got more to chime in... heh heh

You're right, lillvee.. but there are workarounds around that.

Edited for the 4th time!!! Bwahahaah!! ...

Your post has my mind in tangles.. How come leaning out = ignition advance? I got confused for a while.. and edited this post a couple of times before realising where I went wrong... haha.. no wonder my knowledge conflicted.

Like zaki said.. too much can become 'merapu'... ROFL!

Let's consider a column of the ignition and fuelling map... from the left to right, you see that as fuelling increase, ignition advance increases as well, the severity depending on RPM.

What VAFC does is cheats the ECU to think that it's getting more air(flow) than usual, hence the advanced timing AND fuel enrichment.

So adding fuel with VAFC will ADVANCE ignition.. due to the fact that it doesn't really control the injectors, but rather cheats the MAF into thinking that there is more air(flow) present..

So, since VAFC doesn't allow you to do A LOT of enrichment without SIMULTANEOUSLY increasing ignition advance.. we use the fuel pressure instead...

Then if we have too much fuel at the mid bottom end, we trim it using VAFC, and compensate by advancing the static ignition.

This feels kind of short.. but I think if you played around with VAFC long enough.. you'd understand how to beat 'some' of the limitations of VAFC. It's initially meant for mild modded engines.. but you can really 'stretch' it's use for quite a while before actually needing a standalone unit.

That's why I said got workarounds... :P

Thing is.. if you need so much fuel enrichment and total control of timing.. WHAT THE HECK ARE YOU SHOPPING AROUND FOR A PIGGYBACK?? :P

Oh.. Observing unichip version Q being done... It's quite clever (the design.. not the ECU.. computers are stupid.. period.. :P ) in the fact that it intercepts the ignition timing as well.. so it's an old-minded belief that piggybacks do not allow ignition control :P It's near standalone capability.. but one has got to wonder.. do we have to go so far adding an EXTRA BOX that does almost everything?? It's cheap.. so that's probably one I have to consider a plus for unichip...:P

Piggybacks are the simplest to play with, but they're limited if you're comparing to standalones.. So I hope nobody misunderstand this.

There was no argument about piggybacks being THE ONLY TOOL for tuning.. rather.. it's quite a good option for those with mild mods... A LOT of people are sticking with the B16A and SOHC VTEC.. having a cheap method to tweak the maps is a good choice for them. The thing is.. the cost of the unit and 'one off' tuning cost kills the interest of most regular, slow-build modders.

Or do you think these fellas are going to put in a 3K standalone setup in their 'relatively' stock engine?

It's also the means to tweak a chipped ECU.. where the percentage changes are small, thus doesn't affect ignition so much.. a lot of people simply plonk in mugen/spoon/etc ECU without realising that it's not that great of a performance increase since it was programmed on a engine with a specific setup... So unless if you mirror that setup.. sometimes you get less performance gain than claimed.

A little tweak here and there... and you'd see some gains on the dyno.. sometimes more than expected.

If fact.. I think it will grow for quite a while along with the owner that does upgrade in stages, without an extreme step up in any of the stages.

 

[shiroitenshi]

Bwahaha.. pening kawe sementar taip belako ni..

Can't wait till I can play with a standalone setup of my own.. :P
But if cannot datalog.. probably won't learn anything from it.

 

[zaki]

You're right, lillvee.. but there are workarounds around that.

Edited for the 4th time!!! Bwahahaah!! ...

Your post has my mind in tangles.. How come leaning out = ignition advance? I got confused for a while.. and edited this post a couple of times before realising where I went wrong... haha.. no wonder my knowledge conflicted.

Like zaki said.. too much can become 'merapu'... ROFL!

Let's consider a column of the ignition and fuelling map... from the left to right, you see that as fuelling increase, ignition advance increases as well, the severity depending on RPM.

What VAFC does is cheats the ECU to think that it's getting more air(flow) than usual, hence the advanced timing AND fuel enrichment.

So adding fuel with VAFC will ADVANCE ignition.. due to the fact that it doesn't really control the injectors, but rather cheats the MAF into thinking that there is more air(flow) present..

So, since VAFC doesn't allow you to do A LOT of enrichment without SIMULTANEOUSLY increasing ignition advance.. we use the fuel pressure instead...

bro, u might want to edit for the 5th time. :regular_smile: that's why i said, i can only write two to three lines ony. after that i'm gonna `merapu'...hahaha
if you `lean' out the VAFC, you'll get less fuel AND more ignition. you `rich' the VAFC, you'll get more fuel AND less ignition. it applies to both NA and turbocharged fuel + ignition map. for turbo, the higher the boost, the more you need fuel, the less you need ignition. for NA, at high vacuum (~WOT), you need more fuel and less ignition while at low vacuum (cruising), you need less fuel and more ignition.

 

[zaki]

Oh.. Observing unichip version Q being done... It's quite clever (the design.. not the ECU.. computers are stupid.. period.. :P ) in the fact that it intercepts the ignition timing as well.. so it's an old-minded belief that piggybacks do not allow ignition control :P It's near standalone capability.. but one has got to wonder.. do we have to go so far adding an EXTRA BOX that does almost everything?? It's cheap.. so that's probably one I have to consider a plus for unichip...:P

unichip version Q, correct me if i'm wrong that the unichip is almost the same as e-Manage; Map sensor `cheater' + ignition modifier.

I would like to share my experience with e-manage. still fresh from doing a turbocharged civic last week, I found that e-Manage is a good unit especially if you have bolt on turbo kit. the car was a 4 door civic, 1.6 litre single cam no VTEC. td04h turbine + vr4 intercooler + e-Manage + auto gearbox + 0.6~0.7 bar
the only problem I have is that I have no idea what kind of ignition map (max timing etc) the car has, since it is the MDM not JDM :regular_smile:.

Honda ECUs will show CEL when the MAP sensor detects positive boost, eventhough the MAP tensor capacity is 1.7 bar (absolute). To `disable' the CEL, I need to cheat the ECU, whenever the car goes positive boost e-Manage will give signal as if the car is at WOT (~atmospheric pressure ~ 1 bar (abs) aka high vacuum).

As boost climbs up, more fuel and less ignition are needed. The ECU still sees high vacuum (e-Manage cheat laa) whereby the engine is already at positive boost. The fast way to correct this is by raising the adj fuel regulator pressure or swapping to a bigger injector. let say, the injector is too big, then you have to `reduce' fuel at high vacuum column. but wait a minute, if you `reduce' fuel at high vacuum column, won't it increase the ignition? do we know how much ignition is added? much worse, at full boost the car has enough fuel but the ignition is higher that the high vacuum ignition. There you go...

luckily the e-Manage can manage the ignition and it is based on MAP sensor. sigh. but then again, do we really know how much ignition to be retarded? right now I feel retarded.....:confused_smile::retarded:

so far the car runs better than before and no signs of knock can be heard...

 

[shiroitenshi]

bro, u might want to edit for the 5th time. :regular_smile: that's why i said, i can only write two to three lines ony. after that i'm gonna `merapu'...hahaha
if you `lean' out the VAFC, you'll get less fuel AND more ignition. you `rich' the VAFC, you'll get more fuel AND less ignition. it applies to both NA and turbocharged fuel + ignition map. for turbo, the higher the boost, the more you need fuel, the less you need ignition. for NA, at high vacuum (~WOT), you need more fuel and less ignition while at low vacuum (cruising), you need less fuel and more ignition.

hmmm.. I think remember that adding fuel also adds ignition advance on the VAFC.. It's due to the way it references the lookup tables in the ECU at WOT.

Let me check again.. I forgot which is which..

 

[shiroitenshi]

luckily the e-Manage can manage the ignition and it is based on MAP sensor. sigh. but then again, do we really know how much ignition to be retarded? right now I feel retarded.....:confused_smile::retarded:

so far the car runs better than before and no signs of knock can be heard...

Hahaha.. but isn't that's why people run piggybacks in the first place? So they have a starting baseline for tuning? :P

For me.. tuning is still a trial and error affair due to the fact that we can't really calculate airflow due to various other factors. But it's important to keep in mind what's going to work and what's not.

That's why a conservative tune usually causes less problems.. sure.. you can tune it to the max for sea level.. but I'm not sure it won't cause problems when the car and engine goes up the mountain (higher than sea level) for the west -east travel up north. :P

Hmm.. damn.. forgot to shine the timing light when I tuned the VAFC... should have got it confirmed then as to how much air correction % increase or retard ignition advance.

 

[shiroitenshi]

hmmm.. I think remember that adding fuel also adds ignition advance on the VAFC.. It's due to the way it references the lookup tables in the ECU at WOT.

Let me check again.. I forgot which is which..

Lol.. stupified... :P
Yup.. my mistake.. ignition advance increased by RPM, not manifold vaccumm... :P
haha.. mixed up the two...

So my initial 1st and 2nd edit was right..
So.. this is roughly what I mentioned in my 1st and 2nd edit. (A lot shorter than the real thing)

Add fuel with FPR, maintain peak rpm ignition timing.

Lean out with VAFC, get higher ignition advance at lower manifold pressures, for a more aggresive ignition curve.

Play with static timing to achieve target total timing.

But from what I know about VAFC.. the ignition advance isn't much of a concern unless you're using very high air correction rates... (around 15-20% plus)

Thanks lilvee & zaki for pointing that out.. :P

Still.. I think you can tell the forummers here that VAFC is usable for mild mods... Limited, yes.. but can't beat the price.. :P

 

[hattech-v]

aisey... baru mau cakap... hehe... sleep la weii....

 

[shiroitenshi]

aisey... baru mau cakap... hehe... sleep la weii....

Baru bangun tido.. :P

Not so soon.. how about you? wife feels lonely at night when hubby sit in front of computer you know???!!!

Ahahahahaha!

 

[hattech-v]

hahahaa... only if the distance is close... 500km woooo.... different story... haha

 

[shiroitenshi]

Wah.. you left your wife behind ah?

"hmm.. macam terlupa sesuatu jer masa balik ke sri kembangan.. apa dier ye?"

(after parking the car, logged on to zth, and read my post about 'wife')

"Cilakak!! Tertinggal bini aku rupanya!!!"

Bwahahaahaaha!!!!

 

[hattech-v]

chaits.... hahahaahaha....
then u still not sleep this time, where is ur wife?

 

[shiroitenshi]

Single buggerlah.. where got wife?

Currently posting at zth while doing maintaince/cleanup on my computer.

 

[hattech-v]

aiyaaa.... no wonder u very fast typing.... too much training for ur hand... kekekkekekekkekee