OK guys ever since we all started messing around with this VAFC hack business I kinda figured it was a great way to get fuel taken care of, but I always had some concerns regarding what it would do to ignition timing.

Reasoning: we're altering the MAP signal that reaches the ECU so it will trim fuel out. IE at full boost, the ECU sees 40% less pressure, so it thinks you're at 0 boost. At 0 boost, the ECU thinks you're at like -10 inHg vacuum. The ECU drastically advances timing in vacuum, so I worried a lot about how this would work out with the VAFC.

Well, thanks to the Hondata site posting so much info about their maps and fuel/timing concepts, I was able to do some rough projections of how our timing advance works out under two situations:

Situation one: Hondata base map - essentially GSR base map plus 0.75 degrees retard per PSI of boost. Most of you Hondata guys are probably running something pretty similar to this.

Situation two: "VAFC hack" technique of -40% across the board, no other control measures for ignition timing.

These are the results at 3000 RPM and 8025 RPM just for example:




What you're seeing is that the VAFC setup is between 5 and 8 degrees MORE advanced than the Hondata map at 0 boost, and at 8 psi boost, it's nearly 10 degrees more advanced than it should be.

I dunno about you guys but that looks DANGEROUS to me. Good thing the VAFC hack tends to run really rich, but timing advanced that far spells bad news any way you look at it.

I figured I'd see how close I could get using static retard and boost retard to what looks like a "safe" timing situation.

Best scenario I could come up with is about 4 degrees STATIC (distributor) retard (not 4 degrees AFTER tdc, but 4 degrees retarded from stock) and 0.5 deg/psi boost retard. This comes pretty close except of course that it puts you 4 degrees retarded in vacuum, which could hurt your fuel economy and make you run a little warm but nothing too terrible. This is what that looks like:




Obviously not as great as we might like, and still pretty aggressive timing at low boost, particularly in the 3000RPM band where it could be dangerous if you're lugging in a high gear, but an improvement anyway.

Anyone care to discuss this? I know these are just projections, but if the ECU is reading the map based on what we're feeding it from the VAFC, this IS what should be happening. Maybe we've been rich enough not to detonate (stock pump, pressure, DSMs, I was running like 9.8:1 AF at first) but this tells me we have a lot to learn.

I'd like to get some feedback from some Hondata or other standalone tuners on how they like a boost timing map to look as well...

(apologies for the psycho colors on the charts - excel is freaking out here)

 

Nice Post!

 

Wait wait

You're saying the hondata map has 14deg of ignition advance at 8000rpm @ 8psi?

That's definately not right. Should be like 22-24deg.

Dustin

 

BTW...this wouldn't be limited to just the "hack" people. Anyone using MAP trickery (missing link, check valves) would be effected in a similar way. I say similar because using a missing link or check valve, the vacuum portion of the ignition map would be unchanged from stock, which is fine. Those using the hack (raises hand) will have altered timing everywhere on the map.



[Modified by DSF, 1:42 PM 6/19/2002]

 

You honestly didn't expect this? The Honda ECU uses two inputs to reference a look-up table for BOTH fuel and ignition [MAP & Rpm]. Mess with fuel....your automatically messin' with ignition.

But the idea from the get go was pretty slick - no doubt.

Hopefully people will have a better idea of whats going on now.

on the post.

 

Thanks for the heads up dustin - you are correct, my 8000 rpm boost timing figures were messed up - posting corrected charts now based off the actual Hondata maps!

 

nice post...and this is why the afc hack is really only good for low boost operation. I dont have a problem on pump gas and low boost with stock timing. For anything 8psi+ you should really get something better.

I still think this is a good option for the true honda hacker

liam

 

so you could really have a poor mans hondata with the vafc and say the 6al btm. that would cover almost all bases.

right?

 

OK guys I re-did the charts with the REAL numbers from the Hondata GSR base boost map - Hondata says their boost timing is still slightly conservative so a little advance from that is probably not too bad.

Anyway also notice that I changed some numbers in the post to reflect the modified data; my solution is now 4 degrees static and 0.5 deg/psi boost retard.

NOTE: IF YOU STILL SEE PURPLE CHARTS YOU NEED TO RELOAD THE IMAGES!!!


Covert - yeah you could have something KINDA like a poor man's hondata with this setup and a good boost timing retard setup. I trust it enough to run it myself but not enough to recommend it to a friend.

[Modified by dbman96, 11:13 AM 6/19/2002]


[Modified by dbman96, 11:18 AM 6/19/2002]

 

My MSD allows me to retard the timing by boost psi - would this solve most of the timing issues brought up? How much should I retard to correct with the hack?

 

OK after like 50 edits I think I'm on track here. Sorry I jumped the gun.

Looks like 4 degrees distributor retard and 0.5 deg/psi is pretty decent.

That 5 degree advance at 3000RPM, 1-2 psi boost looks like tip-in detonation city to me, but it might be OK...

 

Well, I can understand the concern for right around 0 PSI when the ECU thinks you're ~7-10"Hg and the timing being advanced there, but under full boost it's no different than your typical FMU setup with base timing retarded. I still run ~11 degrees BTDC with the hack just like I did with my Cartech. I don't expect the hack to address my timing.

The thing is, us JRSC'ers are pront to "tip in detonation" right around that 0 PSI range but the hack seems to help out there too which is contradictory to the graphs.

The timing alterations are almost a bonus IMO. It adds back some timing while not in boost so you don't loose so much low end, non boost power.

I wouldn't say we're looking at a major fault in the hack methodology but it's good research.

 

I agree - I only did this so we would actually KNOW what it's doing to our timing rather than just saying "I'm pretty sure this is ******* w/ our timing really bad..."

 

Sweet.

 

if you have an OBD2 datalogger, you can make very nice timing graphs that will tell you exactly what is going on.......... i was fooling around with this before to determine what the effect of the ever popular JR "IAT Hack" was...



this one was throttle position vs timing



and RPM vs timing



ignore the blue line on that one, i was just making sure that the effects of the BTC settings on the JR EMS were "after" the ECU.

 

Yeah although road testing like that it's hard to keep MAP or RPM constant long enough to get a solid timing curve - if you used it on a dyno and forced it to hold RPM constant, it would be really cool.

 

now i'm scared....

 

okay, so if i'm running the VAFC hack and i'm running 12psi what should my igniton be retarded to? 4 degrees always on the distributor?

 

Here's a question... What are the effects of reseting your timing while the hack is in place? Would that reset your ignition tables to compensate for the new MAP signal?

 

It shouldn't matter since when you short out the service connector it is taking the ECU out of the picture.

 

Yeah I'm pretty sure the ignition tables are non-adaptive, it doesn't have any sort of "long term ignition trim" like it does for fuel.

 

i really hope that's true. i've seen no mention of this parameter, so if it exists it's stealth.

 

Well, there is no way for the ecu to know whether it can safely add timing like it can add fuel when it reads lean on the O2 sensor. It's not going to automagically add ignition timing until it detects knock... hehe.

 

Could you even imagine the havoc that you would see if you put every system in the ECU into closed-loop operation?

 

Hrm...? This thread made me a bit nervous, so last night, just for the heck of it I turned my BTM up to 1deg per pound (from it's usual .5 setting). Now, you have to realize I'm still running stock timing (16deg BTDC), so I just wanted to see how the boost portion was affected. Seat of the pants...it was a dog. Maybe it's a combination of a lower than predicted CR and richer than I thought fueling, I don't know. Of course, I can turn the BTM down to 0 and still not "hear" any detonation (not to say that there isn't any) .

*scratches head*


[Modified by DSF, 7:31 AM 6/20/2002]