VVTi - link to TP% or MAP?

[M1tch]

Hi all,

I have recently copied over the table for VVTi from the WRX V10 basemap as suggested, the table is linked to throttle position rather than load via the MAP KPa.

Should I look to link to to the engine load or keep it linked to throttle position?

The engine in question is a Toyota 1zz running NA, happy with the fueling and ignition at the moment but just want to make sure the VVTi is working as best as it can safely.

Thanks in advance!

[Davidv]

I've been in two minds about this, currently with a MAF based tune on my engine (NA Toyota) I've got TPS as the load axis for VVTI.

But I think with a MAP based tune it makes more sense to have it on same load axis as your fuel, because unlike MAF, MAP has no way to tell how the VE of the engine changes with cam angle.

But the catch 22 here is that changing the cam angle can change the map reading at part throttle so it's a bit of a circular reference.

Realistically I doubt you'll have much trouble using either.

[M1tch]

13 hours ago, Davidv said:

I've been in two minds about this, currently with a MAF based tune on my engine (NA Toyota) I've got TPS as the load axis for VVTI.

But I think with a MAP based tune it makes more sense to have it on same load axis as your fuel, because unlike MAF, MAP has no way to tell how the VE of the engine changes with cam angle.

But the catch 22 here is that changing the cam angle can change the map reading at part throttle so it's a bit of a circular reference.

Realistically I doubt you'll have much trouble using either.

Thanks for that, yeah it seems to work fine at the moment, might look to swap it to the MAP as the load axis - they are probably quite similar as 100% throttle would be max load, I guess its the part throttle bits as you mention might be a bit different. I will look at other VVTi maps in the basemaps and see if there are any which are known safe settings but use the MAP rather than TP.

[Davidv]

12 hours ago, M1tch said:

Thanks for that, yeah it seems to work fine at the moment, might look to swap it to the MAP as the load axis - they are probably quite similar as 100% throttle would be max load, I guess its the part throttle bits as you mention might be a bit different. I will look at other VVTi maps in the basemaps and see if there are any which are known safe settings but use the MAP rather than TP.

Okay so here is why I switched back to a MAF from a MAP based setup.

When you are at part throttle and have cam overlap, the low pressure in the intake manifold pulls some exhaust gas back into the cylinder and intake manifold. 

The more advance you have at lower load, the more this happens. 

It's good for economy, but unfortunately when intake manifold pressure is the load axis it throws things out of whack. Because you are measuring the pressure with the assumption that all of the air in there is fresh air giving you a certain amount of pressure. 

When you have some internal EGR happening, for a given MAP reading you want less fuel and more ignition timing, but the ECU sees a higher map reading so puts in more fuel and then less timing. 

When you use a MAF as a load axis, it only ever reads fresh air coming in, rather than making assumptions about the composition of the gas inside the manifold, so its always way closer to correct. 

As well as the multitude of other accuracy benefits that a MAF has. 

This is on a single VVTI beams 3SGE engine.

 

[JMP]

I'm working through a new map for a turbo 1zz I've been tinkering with for many years.  When I next get to the dyno I'll be trying a 4D fueling setup, with MPG for the main table, TPS for the 4D table, and TPS for the VVT table.  Will be tuning the main fuel table with the VVT and 4D tables zero'd out, when the main table is done I'll then do the VVT and 4D tables after that.

If that doesn't work out nicely I'll give it a go with TPS as the load axis for the main fuel table with a BAP/MAP XOver equation load source.  

Have had the turbo setup running for years with the VVT load set to TPS and Fuel table as MAP, but looking to make it a bit cleaner

[M1tch]

On 8/12/2018 at 2:12 AM, Davidv said:

Okay so here is why I switched back to a MAF from a MAP based setup.

When you are at part throttle and have cam overlap, the low pressure in the intake manifold pulls some exhaust gas back into the cylinder and intake manifold. 

The more advance you have at lower load, the more this happens. 

It's good for economy, but unfortunately when intake manifold pressure is the load axis it throws things out of whack. Because you are measuring the pressure with the assumption that all of the air in there is fresh air giving you a certain amount of pressure. 

When you have some internal EGR happening, for a given MAP reading you want less fuel and more ignition timing, but the ECU sees a higher map reading so puts in more fuel and then less timing. 

When you use a MAF as a load axis, it only ever reads fresh air coming in, rather than making assumptions about the composition of the gas inside the manifold, so its always way closer to correct. 

As well as the multitude of other accuracy benefits that a MAF has. 

This is on a single VVTI beams 3SGE engine.

 

I agree with the MAF being a better option, however the stock MAF is too restrictive for the airflow I am planning and running a MAP sensor tidies everything up.