I am rebuilding a 85 se/gt with a 2.8 v-6
I have been looking around and would like to know if I can use a 3.1 crank in the 2.8 block and if so what casting number should I look for and can I use the 3.1 rods with new pistons without a clearence problem.

you need 3.1 pistons which are shorter by the difference of the stroke between a 2.8 and 3.1... Be careful on picking your pistons. Aluminum head 3.1 pistons are dished and 2.8 pistons are flat topped with valve reliefs... I still think the factory used different pistons in 1988 vs. 85-87. Don't alot of people find dished pistons in their 2.8's... This may be why I've seen the compression listed as 8.5:1 for 88 and 8.9:1 on specs for pre 88.

You can use the 3.1 crank as long as it's from a first-generation 3.1 (1989-1991 I think?). Also, the 3.1 and 2.8 connecting rods are interchangeable. And last but not least, make sure you use pistons from an iron-head 3.1.

Cast Iron head 3.1L engines use dished pistons. ALL 3.1L engines use the SAME piston regardless of the head. The application data for the 3.1L pistons used in my new engine, Sealed Power H562CP, indicate an 8.8:1 compression ratio. The 1988 2.8L in my 88GT had flat-top pistons, stock, with valve reliefs. The increased stroke of the 3.1L means that a larger volume of air-fuel-mixture is being compressed.
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