So i had a couple jspec engines and a few aspec t2 engines laying around the garage. I was rebuilding my 6 port for my fb and decided to use a few 13bt housings and picked the best out of what i have. I ported them and cleaned and then noticed plug timing was different. They are all off s4 engines so im confused. My main question is i cannot use these together, correct.

 

No, you cannot use them together.

S5 (and some later S4?) housings have different plug timing.

 

Weeeeeell... You might be able to use them together, but I certainly would recommend against it. Your ECU will assume the plug timing is x for both, when really one is x and one is y. The trouble is that the results may be unpredictable (unless you REALLY do your homework) and more importantly probably dangerous to the motor, even under light use because each combustion cycle from front to back will be different.