85 5.0 block vs. 94 5.0 block (gas mileage)

[jruppert]

Hey guys whats up? I have a '94 GT and a year ago I broke the crank on it. When I did this I split the whole engine down the center. I found a '85 block real cheap that had about 70,000 on it. I set the block in (mild cam, stock heads) and put my factory headers back on, edelbrock upper and lower intake. I have notice a considerable drop in MPG. I have done some reading and found that the '85 block orignally only had 8.4:1 compression as opposed to the '94 9.0:1 compression. The '94 pistons are fly cut for valve clearance where as the '85 pistons are dished deeper. With this in mind, I thought about throwing on my '94 factory heads. These heads have 35,000 miles on them. Do you think this will help? I am wondering if this compression difference would be affecting my gas mileage. I am getting between 16 and 18 miles per gallon. On my old engine I had a e-303 cam, gt-40 heads, edelbrock upper and lower, with much more and was getting a good 22 miles per gallon. Anyone have any suggestions? I do not have any codes either. Thanks