Understanding VVT tables

[RRRocketMan]

In trying to tune the VVT tables (particularly the WOT intake and exhaust tables), I have tried very hard to read all the available literature on the subject but have yet to find a single post where somebody explains what the numbers mean.

Let me preface by saying from an automotive knowledge standpoint I already understand the science of cam tuning and all about separation angles affecting torque, scavenging, etc. but what I can't figure out is how the HPT tables should be interpreted.

For example, say I open the intake WOT table and it says 2 to 14 degrees from low RPM to high RPM. What's that mean? Is that degrees BTDC for the intake valve to open? So at 6000 RPM, the intake cam is opening the intake valve 14 deg BTDC? Also, what does "opening" mean to HPT software? Is that 0.050 tappet lift or the center of the lobe or what?

Now what about the exhaust table? I open that one up and it's got a bunch of 12s across the board or maybe 20 to 14 back to 20... I've seen some pretty funky combos on various cars. What do these numbers mean? Is this exhaust closing BTDC? ... OR is it exhaust closing AFTER top dead center? To me it makes more sense that the exhaust would close after TDC, not before but maybe I'm wrong. If it's after, why are both intake and exhaust numbers positive? Shouldn't they be + and - to denote before and after TDC? This is what confuses me the most about these tables because I can't figure out if I'm advancing or retarding the timing. Sometimes different cars appear to have a different numbering scheme too, with negative numbers appearing, which again throws me off the scent.

Can someone please tell me if the HPTuners tables for intake and exhaust WOT under the VVT tab have a consistent logic and what that logic is? It's the only thing I continue to wrestle with. Thanks.

[RRRocketMan]

Can someone please give me a hand with this? The car I'm tuning is behaving funky and I don't know if it's the VVT or something completely unrelated I changed.


I just want to know how to read the units on these 2 tables and interpret them physically.

[5FDP]

You never said what you are working with though.

[RRRocketMan]

You never said what you are working with though.

Well, the impetus for the original post was just to understand the tables in general. I just happen to be applying it to a Jeep at the moment but I'm confident that by understanding the scheme that the tables use, I can easily audit my Jeep tune and see if it's correct or not. Mostly it's just figuring out what sign the numbers should be and whether it's advance, retard, BTDC, ATDC, etc.

Not to be deliberately cryptic, here's the intake WOT table stock.

?
544 120
736 120
992 116
1312 108
1504 108
1792 108
2048 108
2336 108
2656 108
3008 104
3296 104
3712 104
4000 105
4416 110
4992 115
5856 120
6400 120
rpm

...and the exhaust WOT stock

?
544 120
736 120
992 116
1312 116
1504 116
1792 116
2048 112
2336 112
2656 112
3008 112
3296 112
3712 112
4000 112
4416 112
4992 112
5856 112
6400 112
rpm

[RRRocketMan]

Using the above example, my thought process is this:

The intake cam starts at 120, which right off the bat, makes no sense. 120 degrees.... what? BTDC? That can't be right - too early in the exhaust stroke. ATDC? Maybe that would make sense if it was when the intake valve CLOSED... maybe.

Then the numbers start to drop with RPM. We all know that with increased engine speed, there is increased air column inertia so the intake valve should close later in the stroke. If 120 going to 104 represents retard, as it would if it was a BTDC angle, then it makes sense in that the valve would close later, allowing more air to fill on the intake stroke but if it's ATDC, then this actually represents ADVANCE, in which case it's closing and opening the valve earlier, which makes no sense. If scavenging were the goal, wouldn't the intake be retarded and the exhaust retarded even more to create that overlap?

Anyway I've seen tunes that have numbers ranging from 0 to 14, unlike this one, so there's no consistency from one tune to the next and that's bad enough but when you can't even figure out advance or retard, BTDC or ATDC, it just makes pea soup out of these tables to the point where I don't want to touch them at all.

Any input on this would serve the community and myself well.

[1332777976]

Did you ever figure this out? I'd like to understand it too. I'm very new to hptuners and I practice on my vehicles and my denali has VVT.

[RRRocketMan]

I half figured it out.

It seems like, at least as far as the Intake Open is concerned, the more + the number is (whether it's represented as a negative or a positive number), the further the cam is RETARDED from its "parked" position, which is probably defaulted to something like 20 deg BTDC but I don't know what that number is. If you leave the thing parked (fill in 0s in the table), the intake opens as early as it can and closes as early as it can. The important thing here is that the intake closes closer to BDC rather than sweeping past it. At low RPM this prevents intake charge from being pushed back out the intake, improves dynamic compression and gives more power. This is exactly opposite to the stock tunes, that show big numbers at low RPMs like 25. This makes the intake valve close late, on the up-stroke, preventing full compression and reducing pumping losses for better MPG.

Now the 1/2 I don't get yet is the exhaust. For cruise MPG, what GM wants to do is combine that late intake closing event with an even later exhaust closing event. What this would do is allow lots of exhaust to mix with the intake charge because of the big overlap. Lots of overlap reduces compression and also creates an EGR effect.

But here's the problem. I read elsewhere that the cam phasors are set up in such a way that if hydraulics fail, the fail-safe, allowing maximum overlap because this would allow maximum driveability? I dunno if I follow that since overlap creates idle lope but anyway, let's say it's true. If 0 degrees (parked) represents the fail-safe state for both intake and exhaust, then it would be maximum advance for the intake and maximum retard for the exhaust. However if you look at the stock tunes they don't make sense then because if you want lots of EGR gas + low compression for the cruise event, this would mean lots of retard (big + number) for the intake and lots of retard for the exhaust close (0). This isn't what you see.

Can somebody please clear this up? It's bloody annoying not being able to tune these tables on a DOHC when you can easily get huge tuning effects from them. I was able to tune an Impala no problem because the intake and exhaust phasers are locked to each other so I don't have to worry about overlap but for full VVT I still don't know what I'm doing on the exhaust side. I don't like it if the intake/exhaust numbers mean opposite things but at least if someone confirms this to be true I can memorize it and work with it. It's the not knowing that sucks.

[RRRocketMan]

Still hoping someone will eventually reply...

In the meantime, I just tuned a camaro 2.0T and have no idea what's going to happen:

Intake:

Values go from 10 to 20 between 0 and 6000 RPM

Exhaust:

Values go from 30 to 20 between 0 and 6000 RPM

Basically the intake was going the wrong direction (numbers decreasing) and were much higher, I shifted them down towards parked. I picked exhaust values to maintain a small overlap because the engine is turbo'd. I would have liked to drop the intake to 0 but unfortunately, to maintain a small overlap this would have raised the exhaust to 40 degrees. The problem I have with that is that with such an early exhaust closed event, the exhaust open is also early. If the exhaust valve opens 2/3 down the power stroke, as I assume it would at that angle, all the unburned fuel will get shot into the headers and turbine, causing them to glow red hot. This happened to me before because of very low spark timing but early exhaust opening would only make it worse. Therefore these number above are a compromise to get better low end torque than the tune had in it before, maintain small overlap for dynamic compression and VE and prevent nuking the headers, turbine and cat. This is all based on the theory I've extracted from countless vague posts on the topic but I still don't have any confirmation that it is correct and no access to a dyno to confirm by experiment.

[zmooney2011]

I?m in the same boat, per gm service info the exh cam retards and the intake advances. I?m not sure what they refer to on the stock tables I see numbers from +7 to -41 on the intake side. Hopefully someone has completely figured this out. Should be able to get good gains.

[smokeshow]

Looks a lot like lobe centerline angles on the Jeep, don't you think? Keep in mind they're different manufacturers, so it is apples to oranges. GM uses cam angle relative to ICL/ECL, Chrysler uses absolute ICL/ECL.

[BLUEBOY455]

Think your correct on the dodge stuff, it will be centerline angel and you can log that. Moving it in the wot on the dyno also show it respond to it as centerline. Being able to lengthen the torque curve but not really giving you much of HP gains. I also have been told this is part of the neural network but I'm still playing with that to find a good use for that info. Also was told it may make things more consistent when turning neural off if used correct. On the dodge you can only retard or advance only and would expect that on any brand unless it has a separate cam for exhaust or a two peace cam where intake and exhaust can move in different directions, not much chance the cam can move that fast to do more.
Being able to control this correctly makes a little cam make as much average power as a big cam with out the side effects. Good example is the hell cat cam for the dodge. Those guys did their home work when they designed it.

[Nigel Pitsch]

You only need to look at the exhaust , High Barro does most of the work and WOT , the numbers are ex lobe centre with the NN enabled it doesnt even use the data in the tables watch it on your HP log , you can set up to record ex position
If you are on hard mapping with NN off you will have to rescale the tables to something that makes sense or it will run like a pig
With NN on let it do its thing