Additional Crank Trigger Wheel

[TuckerE30]

I am interested in adding an additional crank trigger wheel to my engine so that I may utilize MegaSquirt. The BMW M20B27 I'm targeting has its own crank trigger wheel and sensors in stock configuration, but they appear to be incompatible without significant MS source code modification. Does the GCR allow the addition of a crank wheel and sensor? Just the trigger wheel or sensor? Thanks.

This would be for a BMW E30 325e running in ITA.

9.13.D.1.e
Any ignition system which utilizes the original distributor for spark timing and distribution is permitted. Internal distributor components and distributor cap may be substituted. Crankfire ignition systems are prohibited unless fitted as original equipment.

[JoshS]

I see no rule that would allow you to ADD a crank sensor.

You can replace the sensor per rule 9.1.3.D.1.a.6, but it's not clear to me whether or not that wording also allows you to substitute the trigger wheel. In my opinion the intent was to allow you to substitute both the sensor and the wheel, but I'm not sure that we got the wording fully right there.

[JeffYoung]

Rule actually says stock sensors can be substituted with any equivalent units.

I believe what you are doing is within the intent of the rule - you are using an equivalent unit to perform the function the stock one did.

There may be a hypertechnical argument that you can't add a wheel, you have to substitute, and to be 100% legal you may want to see if you can do that. However, I am convinced that what you are doing is within the intent of the rule.

[Andy Bettencourt]

It does not say you can add a second crank trigger wheel. You can replace your OEM CTW with a different one, but not add a second one. The rule clearly states IMHO that there are only two types of 'sensors' that can be added (in addition to what came on the car).

Why can't the original CTW be replaced with one that is compatible with MS?

[chuck baader]

Tuckere30..contact me directly [email protected]

[TuckerE30]

I'll try to explain the stock setup and hopefully it will make some sense.

The stock M20B27 crank trigger wheel is made up two sensors actually. One sensor counts all 120 flywheel teeth and one sensor is just for a a positioning key attached to the side of the flywheel.

The closest trigger wheel style that megasquirt is compatible with is a missing-tooth style where there are a number of teeth (like 30 or 60) with one or two missing. I could try to modify my flywheel by knocking off a tooth or two, but I am afraid that I'd end up breaking off additional teeth due to the added stress during starting. Basically, I didn't see an easy way to add a crank trigger wheel to the backside of the engine.

Later BMW M20 motors come with a missing tooth crank trigger wheel on the front of the engine which is compatible with MS.

I think I should be covered with regards to adding new crank trigger sensor since I currently have two and could just move and replace one.

[Eagle7]

The stock M20B27 crank trigger wheel is made up two sensors actually. One sensor counts all 120 flywheel teeth and one sensor is just for a a positioning key attached to the side of the flywheel.

The closest trigger wheel style that megasquirt is compatible with is a missing-tooth style where there are a number of teeth (like 30 or 60) with one or two missing. I could try to modify my flywheel by knocking off a tooth or two, but I am afraid that I'd end up breaking off additional teeth due to the added stress during starting. Basically, I didn't see an easy way to add a crank trigger wheel to the backside of the engine.

Would a dual wheel configuration work with this?

[Andy Bettencourt]

I'll try to explain the stock setup and hopefully it will make some sense.

The stock M20B27 crank trigger wheel is made up two sensors actually. One sensor counts all 120 flywheel teeth and one sensor is just for a a positioning key attached to the side of the flywheel.

The closest trigger wheel style that megasquirt is compatible with is a missing-tooth style where there are a number of teeth (like 30 or 60) with one or two missing. I could try to modify my flywheel by knocking off a tooth or two, but I am afraid that I'd end up breaking off additional teeth due to the added stress during starting. Basically, I didn't see an easy way to add a crank trigger wheel to the backside of the engine.

Later BMW M20 motors come with a missing tooth crank trigger wheel on the front of the engine which is compatible with MS.

I think I should be covered with regards to adding new crank trigger sensor since I currently have two and could just move and replace one.

Not knowing the exact config, you state you have two sensors. Replace 1 or both of those sensors with a sensor that performs the smae function that can talk with your ECU. Done. Just don't ADD any that weren't there before.

Modifying your flywheel by taking teeth out is not legal. And if anyone wants to argue that it could be considered balancing - save your keystrokes!