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Trigger wheel Tooth Count

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Hey Guys,

Google has failed me on this one...

I am converting my 1985 911 to standalone using a Syvecs S6+, however Porsche decided to use a 129 tooth count on their flywheel which is incompatible with most aftermarket ecus, I plan to use a sensor from a later model (996) rather than the 33 year old item as it fits in the OEM place and a custom flywheel which is readily available, however what I would like to know is, how do I determine the tooth count of the flywheel that is best to use? Usually this is defined by what is used OEM, however I have full choice, is 60-2 the best option, a few people seem to use 36-1? I know Porsche used 45-2 on later models (but they are incompatible with my gearbox anyway)

I am sure any will work, but as I have the choice which is best or how do I work out which is best?

TIA Andy

G'day Andy. I'll move this post out to the genetuning discussion forum, as its likely to get more traction there.

In theory, the more teeth you have, the more resolution you have. If it were me though, I'd probably go for a 36-1, as its really common, and could keep your ecu options open further down the line.

I havent setup a Syvecs before, but have a bit of experience with Life Racing ECU's and understand they're very similar. The Life Racing ecu had a trigger pattern setup that was extremely flexible, and could be configured to read almost any pattern though, is the Syvecs more locked down?

Hi Andy,

Clewett in the USA is a good source for just about anything you'd need engine management-wise for air-cooled 911s, including bolt-on crank trigger kits, and even cam sync kits if you want. We have used their components on several 911s at my shop and they are great quality and fit:

I have a VEMS ECU on my 1986 Porsche 944 Turbo, which is one of the few aftermarket ECUs that plays nice with the early Bosch DME engines with the 129+1 engine speed and reference sensors (same as on your Carrera 3.2, uses the starter ring gear). I actually got a "plug and play" kit from a guy in Estonia of all places who specializes in making such kits for Porsches of that era:

He is very responsive and helpful, and I got to meet him in person a couple of months ago when he was in California for Rennsport Reunion. Some people with the 944 Turbo setup have had some trigger issues, which may be interference-related. It seems that the early Bosch DME control units had a robust, custom chip to convert the noise-prone 129-tooth AC signal to a good square wave for the microcontroller in the DME---the VEMS might not be quite as robust in this regard, but my engine runs great.

EDIT: I just saw that you were planning to get a custom flywheel made (I think I know of the outfit in the UK that you might be using, TTV Racing, they make such a flywheel for the 944 as well). It looks like they offer a 36-1 flywheel, but in theory the 60-2 is ideal. It works with any ECU, and that tooth count will have a finer resolution in terms of ignition timing/knock control than does a 36-1. 36-1 is usually only used on the front crank pulley when the diameter and/or amount of space is limited.

Thanks for the responses,

Zac - I believe the Syvecs is actually less locked down than the Life (im still finding my way around the software right now), I can actually use any number of teeth between 4 and 360, I am just not sure I want to use this method incase I change ECU brands in the future, and for the noise issue that chris mentioned.

Chris - I have seen the clewett parts, I was looking into use the Cam Sync option actually, I just prefer to use the flywheel for the crank method in regards to "neatness" I also considered the Rasant solution.

TTV are indeed the company, they offer 36-1 as standard, but can do 60-2 no problem.

Personally I would go with a 36-2 or 60-2 rather than a 36-1 trigger. It's normal to see some engine speed fluctuation when cranking, and if you're unlucky this can interfere with detecting a single missing tooth.