Speed Density Vs. MAF / Pros and Cons.

[Jpb972]

Those who have actually switched over to SD, what are your thoughts ?

[thahemp]

There should be very little difference assuming you have a good MAF+VE tune already. If you are running MAF only, then there are improvements to be made by getting the VE table done. You might as well keep it as a hybrid tune if you aren't flowing more air than your MAF sensor can measure. The MAF sensor is better for calculating airflow at more constant rates and the VE table is better for calculating airflow during transient conditions.

[Jpb972]

Originally Posted by thahemp

There should be very little difference assuming you have a good MAF+VE tune already. If you are running MAF only, then there are improvements to be made by getting the VE table done. You might as well keep it as a hybrid tune if you aren't flowing more air than your MAF sensor can measure. The MAF sensor is better for calculating airflow at more constant rates and the VE table is better for calculating airflow during transient conditions.

Thanks. You sort of answered another question for me which was if my VE is untouched would I benefit from tuning the VE tables anyway? I dont think I would need to go MAP only. Im not sure how my tune is set up and will not know until my HPT software arrives. If im not mistaken, if my VE has not been tuned then the values would all be zeroes?

[thahemp]

Originally Posted by Jpb972

Thanks. You sort of answered another question for me which was if my VE is untouched would I benefit from tuning the VE tables anyway? I dont think I would need to go MAP only. Im not sure how my tune is set up and will not know until my HPT software arrives. If im not mistaken, if my VE has not been tuned then the values would all be zeroes?

No it will just be filled with stock values. If it was not tuned, then most likely your tuner just set the dynamic airflow RPM enable/disable values to something unrealistic like 1 and 2 RPM. It will keep the ECM from referencing the VE coefficients in most cases. I have been told that the VE table can still be referenced during tip in/out even when dynamic airflow is disabled. I tend to believe this because I used to spike pretty lean for a split second in the logs during tip in/out running MAF only.

The car seems to be more responsive to quick throttle changes with a good VE table. Although to be completely honest, it runs pretty well MAF only.

The "VE table" doesn't really exist in a stock E38 ECM just fyi. You will have to use EQ<>VE to import the VVE coefficients and generate a table that you can modify with log data. Then you have to use the same tool to export the coefficients back to HP Tuners. It's a huge pain in the ass. You have to do it every time you re-log the vehicle and apply new data to the tune file, which will be a million times since you're just getting started! I would recommend you put in a little time up front getting the 2.5 bar custom OS working with your vehicle.

The VE table will be all zeros in the custom OS. You will need to generate starting values with EQ<>VE from the VVE coefficients in your current tune. You will also need to input the correct values for your MAP sensor in the "Engine Diag" section. You will also need to edit the axis of the VE tables in the custom OS to make use of the increased 33x33 cell resolution table. When you enter the existing VE data into your custom OS table, you will have an empty square between every cell since it came from a 1/2 resolution table. You will have to interpolate the table top to bottom and left to right to get it filled all the way in.

Then you're ready to start calibrating the VE and MAF airflow tables. You may have to start in closed loop and make a quick pass using fuel trims and part throttle, easy driving. All final calibrating should be done in open loop with your wideband.

Good luck!

[Jpb972]

Originally Posted by thahemp

No it will just be filled with stock values. If it was not tuned, then most likely your tuner just set the dynamic airflow RPM enable/disable values to something unrealistic like 1 and 2 RPM. It will keep the ECM from referencing the VE coefficients in most cases. I have been told that the VE table can still be referenced during tip in/out even when dynamic airflow is disabled. I tend to believe this because I used to spike pretty lean for a split second in the logs during tip in/out running MAF only.

The car seems to be more responsive to quick throttle changes with a good VE table. Although to be completely honest, it runs pretty well MAF only.

The "VE table" doesn't really exist in a stock E38 ECM just fyi. You will have to use EQ<>VE to import the VVE coefficients and generate a table that you can modify with log data. Then you have to use the same tool to export the coefficients back to HP Tuners. It's a huge pain in the ass. You have to do it every time you re-log the vehicle and apply new data to the tune file, which will be a million times since you're just getting started! I would recommend you put in a little time up front getting the 2.5 bar custom OS working with your vehicle.

The VE table will be all zeros in the custom OS. You will need to generate starting values with EQ<>VE from the VVE coefficients in your current tune. You will also need to input the correct values for your MAP sensor in the "Engine Diag" section. You will also need to edit the axis of the VE tables in the custom OS to make use of the increased 33x33 cell resolution table. When you enter the existing VE data into your custom OS table, you will have an empty square between every cell since it came from a 1/2 resolution table. You will have to interpolate the table top to bottom and left to right to get it filled all the way in.

Then you're ready to start calibrating the VE and MAF airflow tables. You may have to start in closed loop and make a quick pass using fuel trims and part throttle, easy driving. All final calibrating should be done in open loop with your wideband.

Good luck!

Thanks for taking the time to post this. I'm thinking I may just want to start out small and work my way up to this. Lol. I still have to figure out how to tune for new injectors running a return system with a boost referenced regulator.

If I attempt the VE / map tune can I use the ZL1 3bar map with the 2.5 bar os?

Thanks again!

[granatl]

GM VE is a value calculated from numerous PIDs. etc. You can log GMVE in the HP Tuners VCM Scanner software, MAP kPa vs. RPM.
This way, you get VE numbers that are spot-on with what the car's computer is calculating.
Once you get as many as you can, you extrapolate/interpolate the rest, then use the BlueCat tool to build the equations for the table data.
One of the experts on the HP Tuners forum gave me the explanation of the pros/cons of each. To condense, the car is far more drive-able below 4000 RPM w/ both VVE+MAF feeding the computer.

[bluegoat06]

Is all theory until you've tried it

But you can run MAF only with a good tune, and you'll never notice the lack of the SD, post#2 summarized it very nicely. SD mode with E38's kind of suck because we have to use the dang SD calc to build the table, if you're used to the E40 pcm's, you'll know exactly what I'm talking about, the calc does the job, I just wish I had better control of the zones.

Thahemp, for your lean spikes during tip-in (I believe GM does this on purpose for emissions purposes), try adjusting the transient enable delay from 56 crank references to 15, and then the impact factor/maximum mass from 2048 to 1024. also make sure your part throttle fuel in CL is within -+2%, you should not have any more lean spikes, in fact, watch your WOT fueling during the initial hit, if you go too rich in one shot, add 100 at a time to the maximum mass, but 1024 should be about right. this works for LS2's, L76's, LS7's etc, even the trucks, my 2010 5.3L Silverado Crew cab runs great with this settings.

The VE is not referenced if the dynamic airflow high rpm disable/re-enable is set correctly, but you can always check your dynamic airflow status bit, high means MAF only, VE is not referenced
http://www.hptuners.com/forum/showth...-Calc-Mode-PID

[Jpb972]

Originally Posted by granatl

GM VE is a value calculated from numerous PIDs. etc. You can log GMVE in the HP Tuners VCM Scanner software, MAP kPa vs. RPM.
This way, you get VE numbers that are spot-on with what the car's computer is calculating.
Once you get as many as you can, you extrapolate/interpolate the rest, then use the BlueCat tool to build the equations for the table data.
One of the experts on the HP Tuners forum gave me the explanation of the pros/cons of each. To condense, the car is far more drive-able below 4000 RPM w/ both VVE+MAF feeding the computer.

Thanks !

[Jpb972]

Originally Posted by bluegoat06

Is all theory until you've tried it

But you can run MAF only with a good tune, and you'll never notice the lack of the SD, post#2 summarized it very nicely. SD mode with E38's kind of suck because we have to use the dang SD calc to build the table, if you're used to the E40 pcm's, you'll know exactly what I'm talking about, the calc does the job, I just wish I had better control of the zones.

Thahemp, for your lean spikes during tip-in (I believe GM does this on purpose for emissions purposes), try adjusting the transient enable delay from 56 crank references to 15, and then the impact factor/maximum mass from 2048 to 1024. also make sure your part throttle fuel in CL is within -+2%, you should not have any more lean spikes, in fact, watch your WOT fueling during the initial hit, if you go too rich in one shot, add 100 at a time to the maximum mass, but 1024 should be about right. this works for LS2's, L76's, LS7's etc, even the trucks, my 2010 5.3L Silverado Crew cab runs great with this settings.

The VE is not referenced if the dynamic airflow high rpm disable/re-enable is set correctly, but you can always check your dynamic airflow status bit, high means MAF only, VE is not referenced
http://www.hptuners.com/forum/showth...-Calc-Mode-PID

More good info. Thanks for your contribution.
Lol. Agree completely with the first sentence. Looking forward to it. My brain hurts from all this theory.

[thahemp]

Originally Posted by bluegoat06

Is all theory until you've tried it

But you can run MAF only with a good tune, and you'll never notice the lack of the SD, post#2 summarized it very nicely. SD mode with E38's kind of suck because we have to use the dang SD calc to build the table, if you're used to the E40 pcm's, you'll know exactly what I'm talking about, the calc does the job, I just wish I had better control of the zones.

Thahemp, for your lean spikes during tip-in (I believe GM does this on purpose for emissions purposes), try adjusting the transient enable delay from 56 crank references to 15, and then the impact factor/maximum mass from 2048 to 1024. also make sure your part throttle fuel in CL is within -+2%, you should not have any more lean spikes, in fact, watch your WOT fueling during the initial hit, if you go too rich in one shot, add 100 at a time to the maximum mass, but 1024 should be about right. this works for LS2's, L76's, LS7's etc, even the trucks, my 2010 5.3L Silverado Crew cab runs great with this settings.

The VE is not referenced if the dynamic airflow high rpm disable/re-enable is set correctly, but you can always check your dynamic airflow status bit, high means MAF only, VE is not referenced
http://www.hptuners.com/forum/showth...-Calc-Mode-PID

Thanks for that. I'll give it a shot. I do actually swing a bit rich entering PE. It has never really bothered me too much, but that's an easy fix if your method works out.

Jpb972 I don't have a boosted car and have never tuned one, so I won't even start to pretend to know what to do with your different MAP setup. Best advice I can give you is to take it slow and be gentle with the throttle until your confidence catches up to your tune changes.

All theory till you try it is 1000% the truth. Half the time it doesn't matter a bit what someone else says will work.

[Jpb972]

::

Originally Posted by thahemp

Thanks for that. I'll give it a shot. I do actually swing a bit rich entering PE. It has never really bothered me too much, but that's an easy fix if your method works out.

Jpb972 I don't have a boosted car and have never tuned one, so I won't even start to pretend to know what to do with your different MAP setup. Best advice I can give you is to take it slow and be gentle with the throttle until your confidence catches up to your tune changes.

All theory till you try it is 1000% the truth. Half the time it doesn't matter a bit what someone else says will work.