VVT mapping discussions (VVT/Mivec/Vanos etc.)

[LeNainCapable]

Hello guys,

I'm running G4X pnp for 1jz vvti, stock cams for now

I've seen the base maps on VVTI were based on RPM/TPS.. What is the advantage of that compared to RPM/MGP pressure ?

I'm street tuning for now but trying to get a sensible tune and only have to adjust a little on the dyno

Let's take an example :

At 3000rpm and 100kpa, you can be either at low throttle (~15-20%) or at max throttle.

However the V.E. is only based on your rpms and pressure. If the cam is retarded at 20% tps but fully advanced at 100% tps, wouldn't that create a difference in V.E. for the same cell ?

I know cam timing is mostly in regards to air velocity : 

• Really low air velocity (low/mid rpm, high vacuum) : max retard because no power is required, also avoiding overlap (unsure about this one)
• Low air velocity (low-midrange rpm, low vacuum to max boost) : max advance in order to help scavenging (overlap), but still close at or near BDC to prevent air from going back out of the cylinder
• High air velocity (high rpm (4000/4500+), high vacuum to max boost) : max retard to remove scavenging effect and closing later than BDC since air still going in due to velocity

 

Also, I assume high duration cam will not really change the VVT mapping all that much ? it'll just shift the powerband and maybe lower power at lower revs due to closing event happening later, and maybe overlap), and supposedly allow more air to enter during the midrange - highrange ?

 

Please tell me if I missed something, feel free to discuss VVT stuff here !

Thank you

[Adamw]

Generally TP works better for cam control in my experience. 

Many tuners still use MAP or MGP as the load axis for VVT so cam position is referencing the same variable as the fuel (VE) table lookup which should in theory make tuning the VE table easier - so it is fine to do it that way if you wish.  It does work ok. 

But in my experience in some operating regions, especially light throttle this can cause a self perpetuating cam position oscillation and when it does happen you can feel the torque oscillating with it while driving.

This is because moving the cam changes the MAP, so having MAP also controlling the commanded cam position is not ideal.

[LeNainCapable]

Hello Adam,

Thank you for the explanation, that does make sense.

The example would be : 2000rpm, 10% throttle.

If the 2000rpm/10%TPS is steady, no issues.

But if it's referenced in KPA, it might advance, then we have less kpa, so it retards, so we have more kpa, so it advances... then fluctuating torque ?

 

As my VE is still being tuned I think I'll try to first reference the MAP for vvti, and if I encounter these kind of oscillations I will try switching to TPS.

I fear TPS might induce some jerkiness in the V.E. tuning, as for a given cell I won't know how much advance I actually run (aside of checking logs but still), I'll experiment with both as they should aim for roughly the same values with RPM, I can probably switch without throwing off the whole thing.