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Multi-tooth vs missing tooth when used with cam sync

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Hi Guys,

After a bit of advice in regards to my trigger options, mainly being missing vs multi-tooth when using a cam sync. Engine is an SR20 and the rev limit isn't going to be changed from factory. ECU is going to be a Motec M130, running sequential injection and ignition.

I'm planning to run a crank trigger and cam sync kits from EFI Solutions. I have 3 options when it comes to trigger wheels on the crank - 12 tooth, 24 tooth, and 36-2 tooth.

I've seen the webinar and understand the differences between them, and believe the tradeoff I'm trying to weigh up is the resolution at low RPM vs the chance of 'overlap' between a crank sensor tooth and the sync signal. In my head I've struck out the 12 tooth wheel, but that is probably just a 'more is better' mentality.

Any advice or insight people could give this would be great, especially if they have dealt with SR's or the EFI solutions kits. I've included some pics of the kits as an FYI for people that aren't familiar with them.



Attached Files

36-2 would be my pick from those options. The reason being that resolution is good and the position of the cam tooth is not critical.

In a practical sense you can barely notice a difference in the visible timing drift between a 24T and 36T wheel, but a 24T multitooth (no missing) can be pretty fussy with sync position especially on a 4cyl that has a lot of valve train resonance and an alloy block that grows a lot with temp.

I dont think M1 has capability to do 360 deg sync start up at this time but if they did add that functionality in future then a missing tooth wheel would be nice to have from that point of view too.

Thanks Adam, that's some great info!

I hadn't even thought of the block growth affecting the sync signal but makes perfect sense.

Just to clarify, by 360 deg sync startup you mean the ECU running sequential injection and ignition instead of reverting to batch fire and wasted spark during cranking?

Some ECU's if using a crank wheel with some unique identifier on it (ie. missing tooth) can switch over to wasted spark/batch fire during cranking for a quick start up. This is what I call "360 sync". This means the engine can start as soon as the missing tooth gap is seen (i.e it will sync within 1 crank rev at worst case). As far as I know M1 (at least with the GP* packages) doesnt do this, it always runs in sequential (720 sync), so potentially needs to do two full crank revolutions before it can fire inj/ign.

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