[badlefthand]

Have a 59 SR 389 that I tore down ,Low comp. Dished piston GM#532289. I think std bore but have no way to measure. My Thanks, Machine shops are far away here. Last time I went through this one guy brought out a 12 foot tape,said "yup 4 inches."so drove to a couple machine shops 40 miles away and got a differant measurement from each WTF. Have checked web and nothing.Live on a pretty close budget to buy tools to check size.

[gmil60]

Dear Member,
The Bore diameter for your SR 389 is 4.063 Compression with the dish pistons 8.6

Regards Gerry

[pfilean]

If the pistons are oversise I would expect some stamping on the top surface like 030 060 etc.

[Stuart]

Originally Posted by pfilean

If the pistons are oversize I would expect some stamping on the top surface like 030 060 etc.

^ this. Every oversize piston I've ever seen was stamped.