Is it possible to run without MAP?

[olie05]

I was talking to a porsche guy about programmable ecu's and we were talking about inputs and sensors and such. I told him how many sensors Megasquirt uses, and he said that he only uses a TPS, IAT, Coolant Temp and RPM readings for his N/A race cars.

 

Now it makes sense to me why he is able to do this, since N/A engines are much more predictable then boosted engines when it comes to guessing what manifold pressure there will be, but is there any advantage to this?

 

-Oliver

[mobythevan]

That is alpha-n mode right? You only use the TPS sensor, not map or air flow meter. The only time I would use this is if I was out driving and the MAP sensor failed (maybe bad backfire broke it). Then maybe TPS only would get you by for a few days. You can run mechanical fuel injection also and not have an ECU. Run as many sensors and control as much of your engine as your pocket book will allow. Thanks to Megasquirt no one should be running alpha-N mode.

[Drax240z]

alpha-n mode is only necessary on engines with unstable vacuum signals, such as cars with ITB's or very large cams. Otherwise I'd run a MAP based system.

[mobythevan]

In the large cam scenario you can run megasquirt with a ford mass air flow sensor using the extra code. I forgot about large cams causing problems with MAP based systems. I have become so use to thinking of performance engines being built with a relatively small cam and using supercharger or turbo.

[Tony D]

Electromotive's Control Scenario allowed a blend between a MAP signal and the TPS to allow for low speed drivability with unstable signals. Even with fairly big cams and ITB's, the MS usually is easily dampened with a fuel filter in line with the MAP sensor for some capacitance. This of course causes some lag in response, but we are talking on the range of Microseconds because of the relatively strong signals an ITB will produce.

Where Alpha-N comes in is with single TB's and verrrry low manifold vacuum availability. Then you have no resolution between the vacuum you have at idle, and the vacuum you have at 80% of throttle opening. This is particularly an animal bred of port fuel injection!!! Before, these same engines wouldn't IDLE below say 2200 rpms, but now with port fuel injection supplying atomized fuel to the back of the valve head, velocity at idle in the engine is almost irrelevant---velocity sufficient to transport fuel mixture, that is! Our L28 wouldn't idle below 2200rpms with a single four barrel on it (shaddap, already!), idled at 1700 with Triple Weber 45DCOE's, and then idles as low as 450rpm with TWM 45mm ITB's!

 

Not having to transport fuel in the airstream lets you use a FAR larger cam than ever was possible for a street car even 20 years ago. And that gives you no vacuum. So for resolution, you either use Alpha-N, or like Moby said, meter actual airflow through the engine with a MAF, and fuel accordingly.

 

I would not go Alpha-N, it's far too coarse. For that I would go with a MAF---especially on a street car.

 

If you are racing, however, Alpha-N may be an option, as you only really care about WOT and higher RPM operation, with an idle quality that "just keeps it from stalling". My bet is that your lap times would be slower than a properly mapped out MAF system, though. Having to drive WOT and not having tip in transition power makes for a particularly ham-handed way to barge around the track. John Concialadi at AEM would always say "I can pick you up three seconds on the track per lap with proper midrange fuel delivery", and generally, what John says, John can deliver!

 

I digress! LOL