Max overbore for LA 340 block? .060" too much??

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....oh and if you gotta overheatin problem, it ain't the overbore, it's the coolin system. Seen more people blame overbores for that than I can count. It just ain't true. long as you gotta good coolin system overheatin ain't gonna happen.
 
StrokerScamp said:
....oh and if you gotta overheatin problem, it ain't the overbore, it's the coolin system. Seen more people blame overbores for that than I can count. It just ain't true. long as you gotta good coolin system overheatin ain't gonna happen.
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I agree 100%
 
have it sonic check

over heathing aint bore size problem but a cooling problem

sure a nice rod ratio will keep the engine happyer

but can someone tell me whats the rod ratio to a small bock chebby?
 
StrokerScamp said:
....oh and if you gotta overheatin problem, it ain't the overbore, it's the coolin system. Seen more people blame overbores for that than I can count. It just ain't true. long as you gotta good coolin system overheatin ain't gonna happen.
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I agree too. I sonic check everything that gets an over bore. I have a coffee table at my shop (440) that is standard bore and couldn't take .030. Lol. F-in POS. Okay where was I, oh most people that have head gasket issues are having detonation problems and dont know it. Dont ask how I know that one, lets just say it involves a turbo. Plus head gasket and head bolt technology has come so far that these issues are pretty much a thing of the past. Sonic check that baby and then run it if it passes.
 
what about real late model blocks? i have a 91 360, the last year before they went magnum...how far over can one go safely on something like this?
 
StrokerScamp said:
It depends on the year. the 70-73 date coded 360s were cast off the same mold as the 340. Most of them can go a LOT over. I personally have gone .120" over with one and .100" over with another. Sonic checking of course is a must, but the earlier 360 castings have a lot more meat in the core. .060" is just fine for any of the 360 engines. If companies make .060" over pistons, you better believe the engines will go that far safely.
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I agree with Strokerscamp, I have a 72 360 in my Duster it's 60 over thats how I got to a 412" I had my machine shop check the block over good before I did it though as I do not know what to check.
 
hcarr said:
.060 is to much for small block mopars. Because of the weak ten bolt pattern heads you will continue to blow head gaskets unless you have the cylinders o-ringed. I know from experience cuase in the early 70's I had mine bored .060 over and trw 12 and a half to one pistons and was constantly changing head gaskets.
Howard
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'o' ringed cylinders? blown head gaskets? ever hear of cylinder head studs? they work wonders, and now with a 40 year advancement in gasket tech.. 12.5:1 should be a cakewalk. perfect for some E-85. and as others have already said, I wouldn't think twice about giving a 360 a .060 over. don't count out the later 360's either. there tougher then you think.
 
............Unfortunately in the end the donor 340 block had cracks in two cylinders so it never made it to the sonic check. :angry7:

Looks like I'll be using a 360 block for the stroker project instead, but obviously the same tools/principles apply.:supz:

Cheers!
 
Nice69 said:
Heres a few....:cheers:
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That W2 motor makes me drool. What headers do you have in the images?? I would like to run large tube headers for my stroker build, but most that I have seen have the drivers' side #1 primary drop straight down, which won't work with the AlterKtion rails. Yours sweep back towards the firewall which would be ideal for my application.

Thanks in advance!

p.s. - so what did the 419 pull on the dyno?!?!?
 
I'm in the same boat. Bought a 340 block years ago. It has a rebuild tag from 1973 showing .030 (4.040 + .030 = 4.070). After all these years I want to see what I have. Measuring showed the largest bore at 4.076. The service manual says max overbore at .040. That doesn't leave a lot of room for boring but a hone cleanup. The question is, after sonic testing what is the recommended minimum cyclinder wall thickness? I have seen .180 to .225 but don't know for sure. I would like to use this block for a street stroker since it is a bare block.
 
Someone asked the rod ratio of a small block chevy...it sux at 1.52 (350)

The head gasket issue with a big overbore comes from block flex. As stated, that problem is pretty much eliminated with good hardware and mls gaskets.

As stated, running hot can be fixed with a good cooling system.
 
5.7/3.48=1.62 and change, still not so great

400's use the 5.6 rod which would give the 1.5999 w/3.48 stroke or 1.484 w/3.75 stroke=even worse






then you do a 408/410/416 sbm and get 1.53 rod ratio....hmmmm I guess the '350' chevy rod ratio isn't all that bad.....
 
I run .060 over when I can, but going larger can get pricey for custom (larger thann .030 over on the 4.04 bore) pistons. You have to sonic test. I have yet to find a block I would feel good about going beyond .060. Besides, boring on its own does not gaurantee more power. As far as the head gaskets... On a small mopar, until you reach above 12.5:1, you should not need anything fancy. Mopars do suffer from detonation especially with the factory heads and it' usually this that pops the head gaskes. That and really poor block machining from the factory that isnt corrected during the rebuild/build.
 
Something else to bear in mind when overboring an engine, with time and water jacket corrosion, thin bore walls will flex and allow increased blowby. Thus bleeding off precious horsepower. I've read of motors which (All other factors being eqaul) were able to make more horsepower with the standard or smallest overbores, than when taken right out. Albiet they weren't mopar engines. But it does make you think. An Iron block isn't as rigid as some might think.
 
IMO, boring is to clean up the cylinder bore. Increase your cubes with stroke.
If you are going for max cubes, you're probably going for max power...thin walls aint good for that.

And I was going by memory on the chevy ratio...either way, it aint good.
 
max overbore? gotta sonic check it first, then get the block in a cnc and see how far the bores are off crank cl.........then you'll know how much you can safely overbore.....
 
I've seen ones that would go .060 on occasion but usually 6-7 are fine and one is too thin for comfort.

I never take more out of a bore than I have to, the last 340/414 I built cleaned up at .020 so that's where I went with it. Why not save a good block for 1 or 2 more builds someday. I like as much bore thickness as I can get, stable bores make and hold a lot more power than a thinner (and marginally/insignificantly larger) walls. I'd rather have 8 sleeves with standard bores than most .060 over blocks running around. Sleeves are stronger as long as they're properly done.

Hard thing is most 340's are either already .030 to .040 and some are already at .060, that's what happens when even the newest oem castings are close to 40 years old.
 
hcarr said:
.060 is to much for small block mopars. Because of the weak ten bolt pattern heads you will continue to blow head gaskets unless you have the cylinders o-ringed. I know from experience cuase in the early 70's I had mine bored .060 over and trw 12 and a half to one pistons and was constantly changing head gaskets.
Howard
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in 1970 they didn't have o ringed head gaskets like they do now.

the felpro 1008 has wire rings to keep from pushing out the gasket, better yet, they have head gaskets designed around that high of compression.

technology is great.
 
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