Ring Gear as crank signal?

[Rob Stevens]

Has anyone ever successfully used the starter ring gear as a crank trigger + a distributer based single cam signal.

I'll go and count how many teeth there are on the flywheel as I see I can go up to 80

The engine is a 16v 1400 Polo, from early 90's I think, with injection, but no crank trigger, just what looks like a 4 point hall trigger in the dizy. I can't see how VW ever got any sort of accurate performance out of it like this taking crank position from effectively 4 cam points only. It even has a knock sensor fitted.

Any pointers as it looks like a bitch to try and fit a trigger wheel on the front of the engine.

[gnutz2]

I've thought about it but my audi starter ring has about 135 teeth so its a no go!

[stevieturbo]

I think main thing will be finding a sensor happy with the teeth and rpm's involved.

Didnt some old Quattro's or Porsche turbos used the ring gear though ?

Surely cant be that hard to adapt something up front though ?

As for accuracy....number of teeth wont really affect "accuracy" that much other than belt deflection etc. But whether it had 1 tooth or 100 teeth....belt deflection would still cause the same amount of deviation.
Or at the other silly extreme, Nissan go for a fancy optical based trigger with 360 teeth....and then mount it on the camshaft after that big wobbly belt lol But they use it on some high end engines, so it must be ok.

Could DTA even run off the dizzy trigger only ? Is it a dizzy/trigger with an actual 4 tower dizzy and single coil ?

[Rob Stevens]

Yeh single coil, DTA can't generally work from cam speed only, it can with that weird Mitsubishi (or Nisan) trigger however.

Ring gear has 112 teeth any way so that idea is a non starter as there is a max of 80.
It looks like I might be able to mod the flywheel and mount a sensor in the bellhousing.

[stevieturbo]

Could you stick a trigger ring onto the flywheel like some old Fords did ?

Or have it drilled with the holes creating the teeth ?

Why no room up front though ?

Or at a huge push....actually stick a Toyota, Nissan, Mitsi, Honda dizzy unit onto the engine instead of whatever is there now ? Something the DTA might be able to work with ?

[katana]

From the Google images of that engine I can find - putting a 36-1 tooth wheel on or behind the crank pulley does not look too difficult. Certainly no worse than old skool Fords or Mini's for example!

[Rob Stevens]

I could probably do it on the front of the engine, but I have to make a guard for it, its a low car and the lad may rally it one day. So I think I can machine the flywheel and drill a hole in the bellhousing to point the sensor at. Slightly anxious about making the flywheel off balance, I guess I can drill a hoke in the flywheel to balance out the missing tooth.

How deep do you think the teeth need to be 5mm ?

[stevieturbo]

Tooth depth/dimensions in general would depend on sensor used.

Or you could simply drill/tap the flywheel for say 8-12 holes and screw a cap screw into it to create teeth.

It doesnt need to be 36 etc.

[molecular bob]

I remember from my megajolt days that some users got a 72 tooth wheel with 2 opposing missing teeth to work inside a distributor housing and using an rx7 sensor, could something like that work for you?

[molecular bob]

2 examples in this thread.

https://www.autosportlabs.org/viewtopic ... a34d0801ec