Technical 331 Hemi question...

Quick question -- How far can one safely overbore a 331 Hemi, and what does the engine block weigh? Can it go to 4 or 4 1/8 inches safely for a supergharged, gasoline, application?

A buddy has one and I am considering what engine to use for an Opel GT G***er build I am starting. Was going to use a larger engine (392 or an aluminum block BBC) but if I can bore this one far enough to get to 370-ish cubes then I might buy it from him.

Thanks in advance

Al in CT

 

I, and several others, bored our 331 engines to 3 15/16 (354 size). Boring to 4 or 4.125 seems like asking for disaster. Many 354s ran a long arm with a .125 bore to get lots of inches. Lot of 331s got sleeved to make 300 inch engines. Or you cam modify a Pontiac crank to fit for shorter strokes.

 

Sonic check the block. That's the only way to truly find out how thick the walls are.

 

Chrysler castings were high quality and seldom had core shift. As Rich Fox says they were made to take a 1/8 overbore which allows the use of standard size 354 pistons. This was a common hop up trick in the fifties and sixties, as standard size pistons are cheaper than oversize.

However, there could have been 65 years of corrosion and rust pitting since then so, sonic testing is a good idea. An even better idea is to bore it to the minimum, just enough to clean up wear.

I have no idea what an open GT g***er is but if you really want horsepower a 392 will give it to you. In the long run a crate motor from Chrysler might be the best buy.

 

Scooter bought a 331 punched out to 4.00 + a little more. cyl walls paper thin & started coming apart9 can't remember if he got to even fire it up before failure.. Probably could check ScooterMcrad's Threads and read it. As was said, if you need CID get a 392.

 

I don't know what it's like today, but 20 years ago when I built my 331, 392 parts were more available and cheaper than 331 parts and you could build one quite a bit cheaper. The problem is finding a reasonable 392 core.

Also, the combination of "maximum overbore" and "supercharging" makes me feel a little bit queasy.

 

Scooter did get his all the way together and fired up. Whipped up the oil into a coolant flavored milkshake. I really felt for him when that post came on the build thread. His broke out at the bottom & well below the rings travel area or compression zone.

Sonic test is the only way to know. Folklore suggests it can be done because of stories told about it being done. Apparently not on every engine. However the little facts like filling the block to the bottom of the freeze plugs are left out of the stories. The bottom fill very well could have kept the water in scooters block.

 

You may want to talk with this guy....