VVT Tuning on the Street
 

Tonight, my boyfriend I mean my girlfriend was studying for her law school exams so I whipped out the ole Dell and went for a drive.

I messed around with the VVT map in the hydra a bunch and did about 15 sets of modifications and logs in my 1:1 gear in the crucial 2000-5000RPM range.

Since I didn't have a dyno, I was tuning VVT for boost ramp rate. Correct me if I'm wrong, but more boost = more power. The earlier I can pressurize and make more boost at a given RPM, the better. I didn't mess with the map over 5000RPM since I didn't have a dyno. One could however, infer power gains by looking at air fuel ratios. Advancing/retarding the cam does significantly affect your AFRs- I saw variances of up to 1.5AFR points. If you log lean AFRs after a VVT change, that means you are flowing more air. More air means more power capability.

I tried a few things including going full retard when above 9psi at any RPM. That resulted in my turbo hitting full boost over 1000RPM later :jerkit:. Also tried: Retarding earlier, Retarding later, Gentler ramps from advance to retard, Steeper ramps from advance to retard

With the logging and tuning I found about 2psi under the curve that I didn't have before. Not sure what that would work out to on a dyno but it's a lot more than 0hp.

That was kind of a ramble so here is a how to:

To tune VVT on the street:
-Pick a stretch of road that you'll drive on repeatedly.
-Don't change the weather conditions
-Log in as tall a gear as possible for the highest resolution logging
-Before making any changes to your VVT or fuel map, do a baseline log
-Futz away with your VVT map.
-Log the bitch
-Pull over and look at your log. Note the RPM/speed and and how fast you build boost. Compare RPM and PSI between each log and map change.
-Repeat

Full Boost VVT Tuning
-If you want to try to tune VVT after you hit full boost e.g., 4000-5500RPM, note your AFRs. Compare the AFRs between logs.
-If you're lean vs. your baseline, you are flowing more air. That's good. Depending on your knock voltages and AFRs, keep on adjusting your VVT map to try to get more leanness. When your AFRs don't get any leaner it's time to adjust your fuel/VE map to compensate for the extra air. Adjust your fuel map and log to hit your target AFRs.
-If you're rich vs. your baseline, you are flowing less air. Try adjusting your VVT map again.

--Notes
-Watch your AFRs and make sure you don't knock.
-Watch your AITs because if your temp sensor is in a sucky place it will heatsoak and fuck up your AFRs and therefore affect your spool. And your AFRs. And your spool.
-Make your VVT map smooth not choppy or you'll break shit
-Here's a link to Y8s work that started it all. Read it before doing any VVT tuning. http://forum.miata.net/vb/showthread...highlight=tale



Comments/criticism is welcome.

Boost is a measurement of restriction, not power. An example: if you were to install a freer flowing intake mani, you'd be making less boost but more power. But making full boost faster will help you get max power faster.

also, never go full retard. [on a cell phone so imagine tropic thunder pic here]

just use my map then at the dyno day do a few runs to determine where to set it. I will halp.

secret pro tip: boost / MAP value doesn't really have much bearing on VVT tuning. only RPM does. above 80kPa anyway.

Skidude wants VVT, and wishes he was man enough to handle alpha version.

megasquirt users should hold out for the y8s approved alpha code. it's getting there.

Do you HONESTLY think I'm man enough for any alpha code, y8s approved or not? I just assumed I'd have to wait for a beta at least. I do hope I get something soon!

Also, I can't imagine how VVT tuning on the street would really work, since you're just tuning it for power, not necessarily boost. It SHOULD make more power at the same boost when tuned right...

Did you actually notice quicker spool to always follow your leanest AFR rule?

Where do you think power comes from? It comes from airflow. More psi should equal more airflow.

I don't know. I will look at the logs again tomorrow. BTW higher EGTs which should accompany leanness should also improve spool. Real world application means don't go 11.5:1 as soon as you hit 1psi.

If you make a change that causes the engine to be restricted you will have more PSI with less power. I'm not saying your philosophy is entirely wrong, but I think there's more to it and it may be hard to really get a good tune going without some kind of dyno data.

Does the VVT code adjust the injection timing to sync with the cam timing? Reason I ask is:

the lean theory worries me. While I see your logic, when tuning injector timing you do the opposite: you time the injectors so that the AFR's are the most rich for a given PW, then lean back out to optimal. The logic here is that for a given injection point, the most fuel makes it into the combustion chamber and isn't fucking about in the runner.

What concerns me here is that your logic is considering the air, and that makes sense, but couldn't adjusting your cam phase also help/inhibit the flow of fuel into the combustion chamber? That would cause your lean condition just as the injection timing. Except it would mean BAD things instead of good things.

Finally, and this may not really matter for the discussion at hand much (if you are always below 14.7-15AFR), but peak EGT is typically at stoich and tapers off if more lean or more rich.

hmmm that's a good question about the injection timing. The megasquirt does allow you to vary the timing with the cam angle directly.

BTW FaeFlyper, I wont be at your dyno day so you're kinda on your ownz.

WTH I was kind of expecting you to play with my VVTz some them.

Um. Do you mean can the Hydra adjust the crank angle that the injector opens at based on the cam angle sensor?

BTW with the VVT head the injectors are in the head. Yes you're right dyno is the best place to do it.

Oh my bad on the ECU, I always think in terms of MS, but that is essentially what I was asking. What happens to injector timing as the VVT changes the cam? It either moves dynamically with it, or doesn't, which would effectively change the timing.

Doesn't matter where the injectors are, unless you have DI, you are injecting against a closed valve. Injecting JUST prior to is opening is the most advantageous time, and injecting while it's open makes the engine run like ass.

And the real reason we need a dyno is to tell which logic to follow. One line of thinking says "aim for lean" the other "aim for rich." one of them is right. They both seem equally plausible, but we have verified results for injection timing (if you research it on the MS forums). My question then, is it apples to oranges?