Xu9jaz - Tdc At Tooth 20 - Yes/no

[andy0075 9 1 Cars]

Hi !

 

I have two short questions ( GTI with Motronic 120hp XU9JAZ now on 45 Weber) :

 

1) I have found out that tooth number 20 is under the original vr sensor when cylinder 1 is at tdc. But exactly is it at the beginning of tooth 20, or at the end or beetween teeth 20 and 21 ?

For me it looks like it is beetween teeth 20 and 21. Can someone confirm that ?

 

2) I want to lighten and balance my flywheel. How many kg less can you recomend ? The car will be used for 1/4 mile and slalom races.

I have heard when i lighten the flywheel that the torque of the engine will drop ? I can't believe that. What are your experiences ? Why should the torque decrease ?

 

cheers, Andy

[pip470 61]

Im not sure why you need to know where exactly tdc is. I think the ecu will be able to cope with telling it its 60 minus 2 and 20 teeth before the gap. A tooth out is only 6 degrees and wouldnt make that much differance.

 

As for the flywheel it will not increase or decrease torque or power at a certain rev range. It will however make the engine accelerate quicker because it wont take as much power for the engine to accelerate the flywheel. The job of the flywheel is to store energy so that between strokes when there is not an explosion the flywheel uses its kinectik energy to smooth out the lumpyness, If you lighten it this will be affected slightly when the engine is revolving at low speeds.

[andy0075 9 1 Cars]

Im not sure why you need to know where exactly tdc is. I think the ecu will be able to cope with telling it its 60 minus 2 and 20 teeth before the gap. A tooth out is only 6 degrees and wouldnt make that much differance.

 

 

I use the igniton from an xu9ja on my xu9jaz engine with 45 weber carbs. the xu9jaz flywheel has no marks for tdc and so it is not so easy to adjust the correct ignition timing.

6° more or less advance is a lot. When i adjust the max advance with a strobelight to 30° it then can be 24 or 36 in real ! Thats why i want it to know exact.

I think tdc is beetween teeth 20 and 21. Maybe someone knows it better.

[welshpug 1,657]

surely if you are using distributor ignition it would be best to time it by ear rather than eye?

 

(i.e advance to pink then retard as necessary, then test under load until a happy medium is found)

 

stock timing is all well and good but it was for 97ron leaded some 20 years ago, and on standard injection at that.