Hirth F-33/MAP sensors at the limit

[ColorDog]

Hi folks,

I would like to apply a megasquirt system to a Hirth F-33, but before I spend the >$1000 on it, I wanted some basic advice.

This engine has the following characteristics:

Single cylinder, two-stroke, aircraft engine
Displacement: 313 cc (19.1 cu in)
28hp @ 6500rpm

I'd like to use high resolution MAP sensor pulsations rather than CPS or cam trigger sensor as my basic "where is the engine at in its cycle" sensor. If the MAP sensor is connected to the crankcase, it should tell me not only the max vacuum, but also the supercharge pressure, before the piston port opens. From that sudden dip in the crankcase pressure, I should know exactly what part of the cycle the engine is at, and I should be able to time EFI and ignition. It would seem to me there are a couple limiting factors: (1.) The resolution of MAP sensor output, (2.) the latency of the MAP sensor output, (3.) Telling the MS to use X time before peak pressure as BDC.

Any advice on if this is mechanically possible and what MS system to use would be helpful.

[Drew442]

Hi folks,

I would like to apply a megasquirt system to a Hirth F-33, but before I spend the >$1000 on it, I wanted some basic advice.

This engine has the following characteristics:

Single cylinder, two-stroke, aircraft engine
Displacement: 313 cc (19.1 cu in)
28hp @ 6500rpm

I'd like to use high resolution MAP sensor pulsations rather than CPS or cam trigger sensor as my basic "where is the engine at in its cycle" sensor. If the MAP sensor is connected to the crankcase, it should tell me not only the max vacuum, but also the supercharge pressure, before the piston port opens. From that sudden dip in the crankcase pressure, I should know exactly what part of the cycle the engine is at, and I should be able to time EFI and ignition. It would seem to me there are a couple limiting factors: (1.) The resolution of MAP sensor output, (2.) the latency of the MAP sensor output, (3.) Telling the MS to use X time before peak pressure as BDC.

Any advice on if this is mechanically possible and what MS system to use would be helpful.

I would run alpha-n and leave the map open to atmosphere for barometric correction.

Sent from my MI 5 using Tapatalk

[jsmcortina]

Sensing of the engine phase using the MAP sensor is supported in MS2 and MS3, but a crank sensor is still required.

James

[cdb]

Did you go ahead with this on the Hirth?
I’ve got a Hirth F23 and am looking into the microsquirt.

Thanks