Hey guys I was wondering if their would be any problems running 6.9 precups in 7.3 heads, some of my turbo cups are cracked past the fire rings and I have being hunting for a set will the early 83 84 6.9 cups work in the later heads. I imagine compression and cold starting would be slightly effected. Thanks Mitch.

 

The pre cups will not change the compression. The volume difference between 6.9 and 7.3 is in the head itself. The only difference is throat size. They should be just fine to use.

 

The early cups have thicker or thinner walls than the 7.3 cups. But would in theory work. There is a thread with some good info on this subject somewhere.

 

I think R&D talked about this in his smogie build... I think when he rebuilt the engine he was going to use a set of 6.9l heads because that's what he had but then found a set of 7.3 heads