331 max overbore size

Johnny Cliche · Post by **Johnny Cliche** » Thu Aug 31, 2006 10:34 am

I'm new here, and I already searched for an answer and all I found were pissing matches from people who apparently know everything, but I figured I'd ask to see if anyone has any real world experience with something that I'll be doing shortly...

I have a '53 331 hemi extended bellhousing motor that I will be boring over to fit .030 oversized 354 pistons(.155 overbore from 3.8125 stock bore to 3.9675 bore), has anyone else done this before, and if so did you have good results? I'm planning on running this engine with the stock 331 small port heads, oversized valves, dual quad Hot Hemi Heads tunnel ram, aggressive cam, Mallory dual point/ Hy-Fire box/Pro-Master coil and fenderwell headers in my '40 Plymouth 2 door sedan straight axle gasser with a '46 dodge parallel leaf straight axle, A833 4 spd, and '62 Pontiac posi rearend with 3.23 gears...thanks for any info...

scootermcrad · Post by **scootermcrad** » Thu Aug 31, 2006 10:51 am

Excellent! I want to hear more! I too have an extended block '53 331 Hemi that I plan on over-boring. People seem to think they're "junk". I'm no pro, but I don't see any GOOD reason to junk this motor. In fact I now own TWO of them and plan on building both assuming the blocks come out in good repair. Thumbs up from me sir!

MAW · Post by **MAW** » Thu Aug 31, 2006 2:42 pm

Hi Johnny,

Welcome from another relative Hemi newbie.

One more here with an early extended bell motor. Our block needed a minimum of 0.060" to clean up so we had the walls sonic tested. Due to core shift ours will take a max of 0.100" and be safe (in the mind of the machine shop owner). We ended up going out 0.080" for this build and one more at a later time. We'll make up for the smaller displacement with another half pound of boost

.

I've read that 90% of the blocks will take a 0.125" bore (std 354), but I was one of the 10%

.

Ours now has a Wilcap adapter and a A833 OD four speed behind it.

Cheers, Mark

Bailiesdad · Post by **Bailiesdad** » Thu Aug 31, 2006 10:09 pm

"we had the walls sonic tested."

That is the only way for anyone, anywhere, to be able to tell what size any block can be bored safely.

Good shop.

Johnny Cliche · Post by **Johnny Cliche** » Thu Aug 31, 2006 11:05 pm

I figure worst case scenario I'll just have the sucker sleeved or fill the water jacket in and call it a day, it would just give me more motivation into turning my car into a drag only vehicle...no big deal...I was just wondering if anyone here actually had the balls in the past to do what I want to do...surely someone here has "gone big" on an overbore in the past?

MAW · Post by **MAW** » Fri Sep 01, 2006 7:29 pm

Sounds like a lot of downside risk (and $$) for a potential 2% gain in displacement. If you're running the early small port/valve heads (which I am also) you're not in it for the big HP numbers anyways.

BTW we're running 0.100" oversized Manley SBF SS ProFlo valves with small stem guides installed. Cheap and easy upgrade.

Why take the chance with the block?

Regards, Mark

Johnny Cliche · Post by **Johnny Cliche** » Sat Sep 02, 2006 12:20 pm

mainly because I can...everyone considers these blocks to be boat anchors anyway, so I might as well have some fun with it before it becomes one...a friend of mine just called me and told me he found some early hemi heads in the trunk of a car at a junkyard, he's gonna call back if they're the later model front water crossover...(keeping my fingers crossed)...

johnny5 · Post by **johnny5** » Sat Sep 02, 2006 8:59 pm

Bailiesdad wrote:"we had the walls sonic tested."

That is the only way for anyone, anywhere, to be able to tell what size any block can be bored safely.

Good shop.

I second that. For an extra 75 bucks you can be sure you won't hit water. 4 inch bores in 331's are common but most people don't sonic check them. I would, but mainly for core shift which isn't very common in the early hemis.