MoTeC Global Forum

I have been tuning my NA engine with tps and rpm as the main efficiency calculation with pretty good success. I notice though a lot of people are talking about tuning secondary tables etc with MAP. I am working on all the accel advance sections using tps but was wondering if MAP may be a better way, there seem to be a few tuning holes I cant seem to crack, can anyone give their opinion why it would be beneficial use MAP for these enrichments over TPS ? Also some thoughts on how you went about tuning it rather than just typing in random numbers and ' seeing what happens '
Thanks

20B wrote:...with pretty good success...

Generally "pretty good success" is an indicator that you are on the right track.

I have no idea where you are located, but Australia is generally pretty flat.
If are in a place where altitude change happens, then MAP can be used for altitude (Barometric) compensation.

Someone wiser than I will tell you more.

Out of interest what engine is it?
I would not be surprised if MAP compensation was difficult with wild cams.

Out of interest what engine is it?

N/A 20B rotary , no cams here
I'm pretty happy with everything I just notice some people use it, I find I tend to go off blindly down a particular tuning path sometimes but it helps somwtimes to stop and look at what other people are doing and why they are doing it.
There are mountains here so Baro comp will be factor for that.

You can tune a NA engine based on TP but with a MAP comp and connect the MAP sensor to the manifold. This normally works well but there are exceptions where a stable MAP reading is difficult to obtain, for example on a multi throttle setup or an engine with a lot of cam overlap (or in the case of a Rotary a lot of "port overlap"). The advantage of tuning this way is that the ECU will respond bettter to load changes at low or closed throttle and/or if an idle control valve is being used. I would still trigger the accel enrichment from TP but you will find that you do not need as much. This setup will also do a reasonable job of compensating for changes in altitude. You can have a seperate baro compensation though if you find that there are changes in mixture that the MAP compensation is not correcting.

Ross,
Thank you for your helpful comments.
It has standard ports so idle is pretty good although it has multi throttle setup.
I did notice that if I just touch the throttle ever so slightly the readings will go lean but no TPS reading will show higher than 0 so I guess there is slight airflow increase that is being unaccounted for on the fuel map. Maybe reading from the MAP sensor instead on 0 - 5 % TPS positions as a secondary table will give me more resolution for the minor changes which aren't seen by the TPS sensor ?
I have idle control working nicely with no MAP sensor input, I just wrote a PWM table to drive the idle valve which seems to work nicely.

I would still trigger the accel enrichment from TP but you will find that you do not need as much.

Can you elaborate what you mean ?

You can have a seperate baro compensation though if you find that there are changes in mixture that the MAP compensation is not correcting.

Would it better to have separate Baro sensor as well as MAP sensor connected to manifold ?

RossB wrote:...
You can have a seperate baro compensation though if you find that there are changes in mixture that the MAP compensation is not correcting.

Ross,

How does that work?
Is it a different sensor?
and a different mounting location?

Or is it just a MAP sensor that sits in the airbox rather than in the manifold(?)
...along with a different compensation scheme?

20B
If you tune your engine based on TP with MAP comp the fuel table will be flatter because the MAP compensation is also contributing to the calculation of the fuel requirement. The change in MAP when you open the throttle also helps provide more acurate fuelling during transient opperation and can reduce the requirement for Accel Fuel.

If you are touching the throttle and seeing no change in TP but you are seeing a change in mixture it is likely that there is a bit of play in the throttle likkage causing one or two throttles to move before the one that is connected to the TPS or that your TPS Hi/Lo settings are wrong.

When your idle valve opens you let in more air but without the compensation from the MAP sensor the corresponding amount of fuel will not bee supplied to the engine which can cause idle in-stability. You could do a compensation based on the duty cycle of the idle valve to help overcome this as an alternative.

A seperate Baro sensor can be used and is a good idea if the engine is opperating at different altitudes. Normally Baro compensation is the standard "double the air double the fuel" formula but if it is used in conjunction with a MAP sensor it can be used to compensate for changes in VE as a function of ambient air pressure. For example if you run an engine at altitude with 80 KPA this will have an effect on the exhaust back pressure which can change the VE even on a turbo engine. In other words if you have a turbo engine runnig with 1 Bar of boost at sea level the fuelling requirements will be different if you run the same engine at 1 Bar of boost at the top of a mountain where the air pressure is lower. The pressure in the intake manifold is the same but the exhaust pressure is not and this affects the efficiency of the engine. On an NA engine this also changes, partly because of the lower air pressure in the intake but it also effectively changes the "tuned length" of your manifolds.

Holmz
A normal MAP sensor can be used for Baro comp. It just needs to be mounted where it is exposed to ambient pressure.

Ross,
Some great points there, thanks.

You could do a compensation based on the duty cycle of the idle valve to help overcome this as an alternative.

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This is exactly what I ended up doing and it worked remarkably well, I found the idle control function a little too advanced for my experience so just made an aux output table with duty cycle and rpm as the two channels, I then just tried all sorts of different values until I could see I was heading in the right direction, it now starts straight off the key from stone cold with no drive input all the way up to idle where closed loop kicks in, very nice.
Not many performance rotaries can boast that, they just want an ecu that does WOT
The BARO sensor to atmosphere comp sounds the easiest for me I think.