The Stovebolt Site Forums The Shop Area Engine Shop 250 mods... what makes the biggest difference

I'm rebuilding a 250 from the ground up. What modifications make the biggest difference for gaining power? The engine will be going in a truck which will occasionally pull a trailer but mainly be a daily driver. Should I use I use a 4bbl carb or two singles? what cam? any other helpful hints to get the best all-around performance out of the old girl.

The cheapest and easiest is to add 307 Chevy flat top pistons to raise the compression up around 9 to 1. They bolt right in with out any modifications. Add a 292 exhaust manifold, 3 bolt outlet are 2 1/2" diameter pipe. A small 450 cfm four barrel may help and a little head work, add bigger valves if doing a valve job, not worth it if head is OK.

Joe

bad news... got the the engine completely torn down today... its already been born .40 over. Its a piece of junk. back to the drawing board.

They bolt right in?
You mean, after taking the engine apart down to the bare crankshaft? Not my idea of "bolt in".

How much taper wear do the cylinders have? If there's less than .005" of taper, a re-ring job at .040" oversize won't be a problem. I've built a few 250's to .060" oversize, but they were short-life race engines so a long-lasting rebuild was not a concern. The 307 pistons have all the same dimensions as the 250, including weight, so they're a direct swap. They just have flat tops instead of dished, which raises the compression. I've also done a .050" head mill job on a few engines along with the 307 pistons without getting into piston/valve interference problems with a stock-lift cam, and the engines still ran regular gas without detonation problems. The 292 exhaust manifold is a good suggestion, but they're a little hard to find. If you decide to find another block, the 230 can be used to build up a 250, with just a crankshaft change. The bore size is the same.
Jerry

What I mean is, they fit with out any modification to the rod or piston, they are a direct replacement for the stock piston only they have provide more compression.

Joe

Water in the cyls and pretty bad scoring. I just junked it and cut my losses. But if any one has a 230/250/292 for sale near by let me know.

Since you are on the hunt again, go for a 292. It will make more power and torque right off the bat.

Joe

Not nearby, but I've got a rebuildable 250 long block, serial # FO421CAB in south central Tennessee. Standard bore, no rust, with what appears to be a good cylinder head. IM me if you're interested. I love to horsetrade- - - -what ya got?
Jerry