6bangerwanab
Well-known member
as a general rule of thumb, how far can stock 200's be bored out? i know that its nessisarry for sonic testing, but im just looking for a general number
over bore
- Thread starter 6bangerwanab
- Start date
Over the last year, I've gone against the anything more than 30 thou, based on the recomendation of people on this forum. At 40 thou, people run into greyt iron, and it is likely to fail in service.
Use the least you can get to clean up the scratches, tapper and ovalarity of the bore. If you can get away with only 20 thou, and there are 20 thou pistons around, do so! The old rule that there shouldn't be less 180 thou of wall thickness at the thrust face of the piston hasn't ever worked with any engine made in Windsor or Cleveland. The last engines like that were the Lima Fours, Lima 385 big blocks, and old Y-blocks and FE's. Everything else, bar an aftermarket V8 block, is thinwall, and a liability.
From the factory, the Ford I6 and Windsor V8 and Clevleland V8 castings were as thin as 130 thou on the thrust faces from the late 60's to 1984. Pre 1968 blocks were reputelty thicker. The rust will take that down to 90 thou in some bad cases. Bore it out 30 thou, and there is less than 115 thou of wall thickness, less the rust and scale that has formed over the years.
On a Chev 350, the thickness on a good block wih no core shift at the thrust faces is about 180. 60 thou overbores possible.
A Slant six has up to 250 thou, and can take 100 thou over bores.
Ford guys are put on the back foot.
30 thou tops for most thin wall Henries. In the 70's, Chevies could cope with 40 or even 60 thou over bores, but there are few engine around like that. The exception is slant six Mopars and L6 Chevys.
I've seen Aussie x-flow blocks taken to 40 and 60 without too much problem, but iron was cheap, and Aussie blocks were less thin wall than the American engines.
I took my 250 block out to 56 thou for 305 Chevy forged pistons, but the walls have very little thrust support, and I'm now thinking of using liners.
Use the least you can get to clean up the scratches, tapper and ovalarity of the bore. If you can get away with only 20 thou, and there are 20 thou pistons around, do so! The old rule that there shouldn't be less 180 thou of wall thickness at the thrust face of the piston hasn't ever worked with any engine made in Windsor or Cleveland. The last engines like that were the Lima Fours, Lima 385 big blocks, and old Y-blocks and FE's. Everything else, bar an aftermarket V8 block, is thinwall, and a liability.
From the factory, the Ford I6 and Windsor V8 and Clevleland V8 castings were as thin as 130 thou on the thrust faces from the late 60's to 1984. Pre 1968 blocks were reputelty thicker. The rust will take that down to 90 thou in some bad cases. Bore it out 30 thou, and there is less than 115 thou of wall thickness, less the rust and scale that has formed over the years.
On a Chev 350, the thickness on a good block wih no core shift at the thrust faces is about 180. 60 thou overbores possible.
A Slant six has up to 250 thou, and can take 100 thou over bores.
Ford guys are put on the back foot.
30 thou tops for most thin wall Henries. In the 70's, Chevies could cope with 40 or even 60 thou over bores, but there are few engine around like that. The exception is slant six Mopars and L6 Chevys.
I've seen Aussie x-flow blocks taken to 40 and 60 without too much problem, but iron was cheap, and Aussie blocks were less thin wall than the American engines.
I took my 250 block out to 56 thou for 305 Chevy forged pistons, but the walls have very little thrust support, and I'm now thinking of using liners.
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