Like the title says. Searched.

Any of you out there who have had their VAFC tuned also have to get the timming done? Im asking cause when mine was tunned the timming was not touched. And since the car is running on basically a new fuel map, some peple have told me the timming needs to be tuned also.

Also, are the # of sensors supose to be set at 6in 6out all the time, even after tunning?

 

Good questions, I would like to know that also.

 

I know alot of you have gotten VAFCs..............where are you?

 

V-AFC can't change your timing. You need a real engine management system or at least piggyback to do that. Your car is OBDII you can't even turn the distributor.

edit: Does not include the V-AFC hack of which I know nothing about.

 

When running the afc hack it can actually advance your timing.

Here you go:
https://honda-tech.com/zerothread?id=841443

 

Yeah the VAFC hack and turning the distributor is out of the question, im not really into that kinda of "engine tunning".

The reason i ask is because doesnt the stock computer have different timming maps for low RPM and in VTEC? Is the timming advanced or retarded in VTEC? If for example the computer retards timming by 2 degrees in VTEC kicking in at 5200, when ever the VTEC is changed to lets 4800 will the computer automatically adjust the timming? Again, this is only and example. Im not saying this is really what the engine does or even if even happens.

I guess the question im trying to ask is, does the computer keep that 15deg BTDC timming throught the entire RPM band regardless of High or Low cam?

 

from my understanding the way the vafc interrupts the map signal and adjusts the fuel, that in itself has an affect on timing in the ecu. But it isn't something you can control, the timing is affected merely by the different input that the vafc delivers.

I may be wrong but i have done alot of research on several different forums and that is what i have come to understand, hope that helps.

 

I thought when lowering your vtec engagement via a VAFC, it just switches to the high cam lobe earlier and doesnt actually change your map or timing. Thus you dont really feel a pull till you hit the stock point at 5200 when the ecu adds the extra fuel and timing changes.

or am i nuts ?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 98TypeSH &raquo;</TD></TR><TR><TD CLASS="quote">I thought when lowering your vtec engagement via a VAFC, it just switches to the high cam lobe earlier and doesnt actually change your map or timing. Thus you dont really feel a pull till you hit the stock point at 5200 when the ecu adds the extra fuel and timing changes.
</TD></TR></TABLE>

this has been my belief all along, of course you can lower it and add fuel between the new vtec point and the old, but still leaves you with low cam timing..

thats why i never really went witha piggy back, it seems that its just engauges vtec, but does nothign to the fueling and leaves the ecu thinking its still hiting at the stock point

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 98TypeSH &raquo;</TD></TR><TR><TD CLASS="quote">I thought when lowering your vtec engagement via a VAFC, it just switches to the high cam lobe earlier and doesnt actually change your map or timing. Thus you dont really feel a pull till you hit the stock point at 5200 when the ecu adds the extra fuel and timing changes.

or am i nuts ? </TD></TR></TABLE>

Thats what i was thinking. So if the ECU makes timming changes at the 5200 RPM crossover point from HI to LO cam. Does the ECU make the changes if the VTEC point is lowered to 4800? We know the fuel changes can be made via VAFC. But lets say in the stock LO cam side from 1000-5199 RPM the timming is 15deg BTDC, and in the HI cam the timming is advanced 2deg. Now, when we lower the VTEC point 400RPM to 4800RPM, the timming during this period will still be 15deg BTDC even though in VTEC the timming is advanced. And this wont take place until the RPMs reach 5200RPM which is the stock VTEC engagement point.

So if the computer does make timming changes during VTEC, will it recognize the VAFC change and make the timming changes then? If not, we are not really taking full advantage of the lowered VTEC point is all we are changing is the fuel.

This is a complicated thing to explain, maybe someone can clear it up.

 

Does anybody have any a/f ratio charts from when they lowered
their vtec point to say 4800? I'm wondering if it would run lean
between 4800 and 5200.

 

I dont think the vafc actually changes the timing, it just kicks the vtec solenoid open and engages earlier, hence you dont feel the real pull till you hit 5200. This is why i decided to go with hondata rather than a vafc. Full map tune-ability and full vtec control as well as other little goodies like launch control Its all about the same price as well.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by SKDRCR &raquo;</TD></TR><TR><TD CLASS="quote">Does anybody have any a/f ratio charts from when they lowered
their vtec point to say 4800? I'm wondering if it would run lean
between 4800 and 5200.</TD></TR></TABLE>

Im guessing it will run rich, because during this time my VAFC was tunned to subtract fuel. But i will also like to see a a/f chart.

 

I should be cool with 7psi, AFC, and injectors right? Timing won't be necessary?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Behan &raquo;</TD></TR><TR><TD CLASS="quote">from my understanding the way the vafc interrupts the map signal and adjusts the fuel, that in itself has an affect on timing in the ecu. But it isn't something you can control, the timing is affected merely by the different input that the vafc delivers.

I may be wrong but i have done alot of research on several different forums and that is what i have come to understand, hope that helps.</TD></TR></TABLE>

I really don't think H22a Ignition timing tables are that complex that this point, if even true, makes a difference.

 

also. one of the reasons your search probably didn't turn up anything is because you can't spell TIMING. I ave edited your title out of frustration.

 

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

So if the computer does make timming changes during VTEC, will it recognize the VAFC change and make the timming changes then? If not, we are not really taking full advantage of the lowered VTEC point is all we are changing is the fuel.

This is a complicated thing to explain, maybe someone can clear it up.</TD></TR></TABLE>

the only way the computer knows that vtec in engauged is when the tach reads the predetermined rpm,

i think the vafc just opens up the solinoid, so you can add or remove fuel, but you can;t touch the timing,

thats why i belive in a ful stand alone, and have always kind of snickerd when people brad about having a vtec controller or having their vtec lowerd for MaDpOwER , because it really doesn't make and changes your just slaping the solinoid open early on the low cam map,

 

When running the hack, you want to boost as much as possible to deter timing advance from taking place.

On the last prelude I did, we used the hack to 7psi on an obd2 set up (you cannot retard timing). It pulled quite nicely. Before boosting I did a compression test, one of the cylinders was about 20-25psi lower than the other cylinders so that gave me a little worry especially since the guy said his car would overheat every now and then. Well about 2 weeks later the guys headgasket gave. I tend to believe the boost finally polished off what was giving on the headgasket and the amount of ignition advanced increased cylinder pressures to also lead in letting the headgasket let go.

I'm not trying to scare you, just let you be aware of what can happen. If you are obd1 you should knock your timing by about .75 degrees per psi and you should be safe. I have done 2 other obd1 afc hacks and nothing detrimental has happened in the past 2 months.

 

Lowering VTEC to 4700 or so on a 5th gen will cause you to run super lean, I've seen it on the dyno the guys power tanked till he added fuel with the V-AFC.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by satan_srv &raquo;</TD></TR><TR><TD CLASS="quote">Lowering VTEC to 4700 or so on a 5th gen will cause you to run super lean, I've seen it on the dyno the guys power tanked till he added fuel with the V-AFC. </TD></TR></TABLE>

so could one surmise this was due to the fact that the ecu still hadn't swapped over to the high cam map and due to the lower engagement point he was still on the lo fuel map and the added air caused a lean condition?,,

also how does the vafc control the secondarys, or do they just open at the preset rpm?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by satan_srv &raquo;</TD></TR><TR><TD CLASS="quote">Lowering VTEC to 4700 or so on a 5th gen will cause you to run super lean, I've seen it on the dyno the guys power tanked till he added fuel with the V-AFC. </TD></TR></TABLE>

Hmm thats weird, my VAFC never added fuel to the engine at any time. Only subtracted. My car ran rich when the vtec point was lowered.

Does anyone know what the timming, excuse me, TIMING during VTEC is? On a naturally aspirated application.

 

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

I really don't think H22a Ignition timing tables are that complex that this point, if even true, makes a difference.</TD></TR></TABLE>

I seem to remember reading this info on S2ki.com , so it may not be applicable on a prelude.

 

Ignition timing is affected, but not controlled by, use of a VAFC. The ignition lookup tables in the ecu have MAP sensor voltage as a variable, just as the fuel tables. When you change the MAP voltage to trick the ecu into fueling differently, it is going to change ignition timing as well, as the computer is seeing a different votage than what the MAP sensor is actually producing. This can be dangerous with the AFC hack, as the load on the engine during boost is much larger than what the ecu thinks it is (because you have greatly cut back the MAP voltage), causing ignition timing to be more advanced than it should during boost. If you are using the hack, you must cut back the timing at the distributor (OBDI), or use some sort of boost timing device (OBDII), or boom.

 

This is all gibberish to me right now; I am NOT in the mood to be thinking!

But I do remember readin on the MR2 turbo boards about how using an AFC on their motors will cause the timing to advance significantly. I think what they suggested doing was using an adjustable FPR to change the fuel pressure first........

:runs to go search:

 

What i dont understand is how some people have better 1/4 times after tunning the VAFC and others (my self) dont. I initialized my VAFC and it runs way better now than when it was tunned. One noticable thing is the engine and exaust sound during VTEC. With the VAFC tunned and VTEC set at 4700 the engine was higher pitched and with stock settings the engine sounds deeper and stronger during VTEC, alot smoother too.

If lowering the VTEC point causes you to run lean in that RPM range, then that means fuel needs to be added to compensate. But i have NEVER seen a naturally aspirated 5g Prelude with basic bolt ons have a +fuel change on their VAFC. I know for a fact that my car ran super rich all throuigh the RPM range even after the VTEC was lowered.

Im begining to think getting a VAFC was pointless, adjusting fuel and not timming is not working for me.