Increasing cylinder bore

[Shawn]

Does anyone know if it is possible to bore a 25” 218 block with a bore of 4 3/8” to 4 5/8”. Is there enough material without compromising the cylinder walls?
 

Thanks for the help

[Plymouthy Adams]

that is double the HIGH side of bore....you talking .250 and the highest most folks and being nervous with this number is .125 and trust me that is over twice the bore of later cars...over 4 times that of the current casting...

[Loren]

What you are looking for is cubic inches.

On these engines the 237, 251, 265 all use the same bore and pistons, the difference is in the stroke.

Rather than "artificially" wearing out your block, I'd change the crankshaft and rods.

When you start getting bigger bores you also find that the head gaskets wouldn't accommodate overbores much more than .060.

A very common crank & rod set will give you 237 cid, cheaply and reliably.

If you want more the price and availability reflect the scarcity.

A 265 4 3/4 stroke crank and rods takes a mighty wallet and determination.

It really is a "no pain no gain" situation!

That said, there's a big improvement going from 218 to 237. More stroke, more torque.

[Andydodge]

It maybe easier to just chase a complete 251/265 engine as they will essentially just bolt straight in with all the benefits that you are wanting already there...........andyd

[Shawn]

Great, thanks so much for the info, I have a pile of good 218’s motors, and trying to figure the most economical way to spruce something up.

[Tony WestOZ]

The Canadians used two different casting. The small bore ones are different to the large bore castings. Its to do with wall thickness. If they used the same casting for all blocks the small bore engines would have had to much wall thickness to properly cool the engine.

 

Tony