MoTeC Global Forum

I'm getting ready to tune an approximately 400 HP at 8,000 RPM Porsche 3.6 air-cooled race engine with ITBs. I have a MAP sensor available to me and each ITB has a vacuum port if I choose to use it. The cams are not particularly aggressive so max vacuum should be reach relatively low in the RPM range.

I am trying to understand if trying to use a vacuum block of some kind and a MAP sensor for VE tuning is going to make any real difference versus tuning using throttle position only. It is my understanding that above 4,000 RPM or so I will be using throttle position only any way. So what do I gain using VE tuning at all on a race engine that will live on the track above 4,000 RPM 98% of the time? Sure, I want the car to idle nicely at ~900 RPM and I want it to be easy to drive in the pits. But can't I get that with throttle position tuning anyway?

I guess my question is what would I be giving up by not using a MAP sensor?

Thanks!

Scott

Since this is a race engine, I assume it doesn't use any sort of IACV/external idle control or has an A/C compressor etc. In that case, simply tuning via TPS in the main VE table and using a Baro sensor (ideally in the airbox AFTER any filters, but before throttles) for altitude correction should handle all use cases well. I have done extensive testing with this type of setup at wildly different altitudes and conditions. The only time I have found this to not work is when there is an external device that adjusts airflow/load, hence why I mentioned the IACV or A/C compressor. In fact, even in those cases, additional trim tables can be used to avoid having to use a MAP signal.

As you've probably guessed, even with a vacuum block, MAP vs RPM will not be indicative of load/airflow on a setup like this.

bbrtuning wrote:Since this is a race engine, I assume it doesn't use any sort of IACV/external idle control or has an A/C compressor etc. In that case, simply tuning via TPS in the main VE table and using a Baro sensor (ideally in the airbox AFTER any filters, but before throttles) for altitude correction should handle all use cases well. I have done extensive testing with this type of setup at wildly different altitudes and conditions. The only time I have found this to not work is when there is an external device that adjusts airflow/load, hence why I mentioned the IACV or A/C compressor. In fact, even in those cases, additional trim tables can be used to avoid having to use a MAP signal.

As you've probably guessed, even with a vacuum block, MAP vs RPM will not be indicative of load/airflow on a setup like this.

Apologies for the thread jack, but curious about the basis for your recommendation to connect a baro sensor in the airbox after any filters. Would you mind expanding? Currently running mine just exposed in the engine bay and have always wondered whether I should be doing otherwise.

Separately, while I understand the theory about MAP v. RPM not being indicative of real air flow, I'm always struck by the OEM counterexample of the BMW S54 CSL, which as you know deletes the stock MAF and replaces it with an air rail mounted MAP. Any speculation about why THAT particular setup not only works, but works really well, contrary to the typical wisdom?

--Peter

Herrubermensch wrote:

bbrtuning wrote:Since this is a race engine, I assume it doesn't use any sort of IACV/external idle control or has an A/C compressor etc. In that case, simply tuning via TPS in the main VE table and using a Baro sensor (ideally in the airbox AFTER any filters, but before throttles) for altitude correction should handle all use cases well. I have done extensive testing with this type of setup at wildly different altitudes and conditions. The only time I have found this to not work is when there is an external device that adjusts airflow/load, hence why I mentioned the IACV or A/C compressor. In fact, even in those cases, additional trim tables can be used to avoid having to use a MAP signal.

As you've probably guessed, even with a vacuum block, MAP vs RPM will not be indicative of load/airflow on a setup like this.

Apologies for the thread jack, but curious about the basis for your recommendation to connect a baro sensor in the airbox after any filters. Would you mind expanding? Currently running mine just exposed in the engine bay and have always wondered whether I should be doing otherwise.

Separately, while I understand the theory about MAP v. RPM not being indicative of real air flow, I'm always struck by the OEM counterexample of the BMW S54 CSL, which as you know deletes the stock MAF and replaces it with an air rail mounted MAP. Any speculation about why THAT particular setup not only works, but works really well, contrary to the typical wisdom?

--Peter

Baro reading atmosphere is generally OK but I've worked on a few race cars that have had filters slowly clog up during a race; the vacuum/restriction generated behind the filter would be read by the Baro sensor and compensated for in the ECU. If you don't have a MAP sensor it would also give you an indication of restrictions upstream of the throttles.

As far as the CSL, I'm pretty sure it uses total throttle area (IACV commanded position + ITB angle from TPS) vs RPM as the input to calculate a VE/RF value, which is then used as the "load" input to various tables. It uses the Baro sensor inside the ECU (hence the vent on the ECU case) along with the IAT sensor for air density calculation. From what I understand the MAP sensor is only used for emissions (measuring vacuum to determine EVAP and EGR strategies among other things), and plausibility checks. It is also used in case of a failure of the TPS.

Beau

bbrtuning wrote:
Baro reading atmosphere is generally OK but I've worked on a few race cars that have had filters slowly clog up during a race; the vacuum/restriction generated behind the filter would be read by the Baro sensor and compensated for in the ECU. If you don't have a MAP sensor it would also give you an indication of restrictions upstream of the throttles.

As far as the CSL, I'm pretty sure it uses total throttle area (IACV commanded position + ITB angle from TPS) vs RPM as the input to calculate a VE/RF value, which is then used as the "load" input to various tables. It uses the Baro sensor inside the ECU (hence the vent on the ECU case) along with the IAT sensor for air density calculation. From what I understand the MAP sensor is only used for emissions (measuring vacuum to determine EVAP and EGR strategies among other things), and plausibility checks. It is also used in case of a failure of the TPS.

Beau

Thanks, Beau. I have always understood that the CSL used the MAP sensor signal for load in lieu of the MAF signal. Interesting.

--Peter

Im borrowing this thread a little.

Im about to setup an m150 on my s54b32 engine.

With my previous ecu, i tuned the fuel table with tps and rpm with an map compensation for the turbo.

I only had to compensate if 1bar boost didint make 100% more power. Otherwise the ecu did the calculation automaticly because the map sensor was connected to the vaccum source.

Do the Motec GPRP work like this also with turbo setups and tps load source?

Mobne wrote:Im borrowing this thread a little.

Im about to setup an m150 on my s54b32 engine.

With my previous ecu, i tuned the fuel table with tps and rpm with an map compensation for the turbo.

I only had to compensate if 1bar boost didint make 100% more power. Otherwise the ecu did the calculation automaticly because the map sensor was connected to the vaccum source.

Do the Motec GPRP work like this also with turbo setups and tps load source?

Unfortunately it seems that the M1 GPx firmware does not support this strategy that most other ECUs do. I ended up having to write this in M1 Build, for a turbo ITB engine. Seems that if you want to do anything other than very basic level control with this ECU you'll need to built it into your own firmware package, or buy someone else's 3rd party firmware. Luckily, Build itself as well as the M1 hardware is quite powerful.

Beau

With GPRP m150 1.10.0075 you could just do manifold estimate to move the fuel load axis to throttle based and then use engine efficiency > boost pressure compensation where needed. If you wanted to have throttle position as the native load axis for the fuel table, you'd need build for this of course.

If you have a stable map signal with the iIGB (s54b32 has a vacuum rail and it gives a pretty good vacuum source.) why can’t I use a map sensor instead of estimate table?

Is there any way tuning against VE with tps and map/boost compensation?

My setup has both map sensor after throttles and turbo/airbox (map before throttles).

Please advice.

Hi,

If you are wanting to us the Multi Throttle Tuning option, then I would advise upgrading your Firmware to one of the 1.11.0.x version, rather than remaining on the 1.10.0.x release as there has been some work done in the background on how this system works.

Mobne, if you have a stable MAP signal from your rail, that will give an accurate reference of Engine Load for the M1, then I see no issue with using VE mapping and your ITB's. Most ITB setups will not provide this and give a flat response to throttle position changes once the throttle position exceeds a fairly low number as the pressure on both sides of the throttle plates equalises to typically ambient pressure.