How much longer beyond stock can the O2 sensor wire be lengthened...with the spfi con., I would like to move the present location of the 02 sen. to just "after" the cat for ease of o2 access...the original cat 25 yrs old, failed emissions 10yrs ago and has 240Kmi

Thats not really a good idea. The O2 sensor is meant to get hot in order to get an accurate reading. Moving it farther away from the engine will mean it wont get hot enough to work correctly and therefore you car will most likely run rich or throw an O2 code. You "can" get a heated O2 but im not sure why you would want to go through the trouble or the expense.

The closer to the motor the better

on my Brat my O2 sensor is in the H cross pipe I made for my duel exhaust setup which is actually the 2sd cross over the 1st one behind the oil pan is a x cross over and I didn't have the room for the O2 sensor there so I put it in the 2sd one under the trans and haven't had any problems yet and it been 2 years

It won't work after the cat. The cat changes the O2 content in the exhaust gases as it oxidizes the HC and CO, or reduces the NOx , so it won't see what's happening in the engine.

It won't work after the cat. The cat changes the O2 content in the exhaust gases as it oxidizes the HC and CO, or reduces the NOx , so it won't see what's happening in the engine.

 

good catch. Didnt even think that one through.

The "cat" is a long time dead

Just because it is old and failed emissions doesn't mean it isn't doing something. Keep it hot and upstream of the cat, or else you will miss out on the benefits of the SPFI: more power and good economy, as the ECU tries to adjust the mixture for conditions that don't exist.