MAX stroke on 348 block.

1964SuperStocker

Well Known Member
Supporting Member 2
#1
I was thinking 4 inch (which one of my blocks already has and is common). I would think with special pistons, rods and a little more work to clear the rods on the bottom that a 4.25 crank would work. I know someone has tried or at least did the math on this. What is the scoop on this? I know there might be issues with an oil pan which may need some mods too.
 

1964SuperStocker

Well Known Member
Supporting Member 2
#2
It would seem that you can put a 4.25 stroke in a 348 but it would also seem like no one has according to the few people I have reached out to. Everyone wants to build big cube motors to go fast or build a pulling motor but few people think of great grandpa big block as the platform to do it because the Beach Boys didn't sing about it. I have both 348 and 409 blocks but the 348s are way cheaper because of a bias against not simply being a 409 block. Maybe I'm missing something but if a 348 can achieve up to 454 cubic inches by bore/stroking it then you would think that someone would try it. I might have to do it just to create a proof of concept. Yes there are easier ways to do anything but that kind of thinking would mean less tire smoking fun. One consideration is I'm not yet sure whether the parts to do this are going to need to be completely custom. If it is done in a 409 block then a 348 should be close. :read More to come!
 
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Don Jacks

Well Seasoned Member
Supporting Member 3
#3
Reach out to Jack Gibbs about that.He's reportedly one of the few people in the world that can keep the bottom end in a 4.25 stroked engine.
 

1964SuperStocker

Well Known Member
Supporting Member 2
#4
Thanks so much! After seeing how it was done in my 434 build with a 4inch stroke I thought that a 4.25 would be the next step. Plus I like to think of all of those poor 348 underdogs out there showing up to race with a little extra stroke to race the 409 boys and beating a few of them. :winner
 

Don Jacks

Well Seasoned Member
Supporting Member 3
#10
Yes,but there's parts for that.I've heard that it has to do with the W main bearing size is too small.From what I heard,if you bore the mains out to the larger big block size,you'll be fine.
 

buildit

Well Known Member
Supporting Member 8
#12
Big block mains, I fitted BBC four bolt caps center three, a full width BBC two bolt on the front, BBC two bolt rear cap. Line bored and then line honed. Re-drilled pan rail and used BBC pan. Timing cover upper two thirds, 409; lower third BBC. 6.385 rod, ring pack squeezed together a little, counterweight OD reduced .200", required several slugs of Mallory metal to balance. If I ever get retired, I will finish the engine. Bob Walla raised port heads, 3/4" spacer plates, M/T CrossRam. Many of these parts were leftovers in the shop. All the machine work was done without CNC tools.
This kind of project will soak up a lot of enthusiasm.
I have also built a 476" engine with BBC size journals and caps, done a different way.
 

1964SuperStocker

Well Known Member
Supporting Member 2
#13
Big block mains, I fitted BBC four bolt caps center three, a full width BBC two bolt on the front, BBC two bolt rear cap. Line bored and then line honed. Re-drilled pan rail and used BBC pan. Timing cover upper two thirds, 409; lower third BBC. 6.385 rod, ring pack squeezed together a little, counterweight OD reduced .200", required several slugs of Mallory metal to balance. If I ever get retired, I will finish the engine. Bob Walla raised port heads, 3/4" spacer plates, M/T CrossRam. Many of these parts were leftovers in the shop. All the machine work was done without CNC tools.
This kind of project will soak up a lot of enthusiasm.
I have also built a 476" engine with BBC size journals and caps, done a different way.
I was fearful that you would tell me its a lot of work. Thankfully I still have another 40 years in me. I have been pondering the BBC caps too.
 
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