SilverFish
Well-Known Member
I've never been a fan of running more than a .030" overbore on anything, anybody else feel nervous about a .060" overbore on a small block Mopar? Especially if it's stroked???
Max overbore for LA 340 block? .060" too much??
- Thread starter SilverFish
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hcarr
Well-Known Member
.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
Howard
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.
SilverFish
Well-Known Member
Its a 72 340 block, and yes a sonic check will be performed before I scuttle the block. I'm just trying to decide if I want to use it for my stroker project or acquire a 360 core from a friend. The 4.10 bore opens up some pretty ridiculous displacement combos, and yes they are tempting. I just was wondering if anyone had any experience with uber-thin-wall builds.
As an aside I am only planning on running 10:1 (hcarr) but thanks for the input on the o-ring recommendation as well. It may still be applicable even at the lower CR.
Thanks for the input. :toothy10:
fishy68
Tyr Fryr's Inc.
It might be ok but I wouldn't even think of it without sonic testing it. In fact if I have to go more than .030 over I sonic test them. Sonic testing is the only way to know the limits of it.
1wild&crazyguy
Banned
u'll b fine.
.060 over ain't sht.
.060 over ain't sht.
raced a .060 340 for ever.....with high old heavy 12.5 trw pistons...
have a 360 that is .060......have never thought twice about going .060
dgc333
Well-Known Member
How does the head gasket have anything to do with the amount of overbore you do?
Most small block head gaskets have a 4.150 bore much larger than the discussed overbore.
Well like hcarr said you only have 10 bnolts and if you also go high compression it has always been a weak link, but the cometic gaskets as compared to old thin metal stampings help a bunch.
It is also i nthe old Direct Connection Mopar Bible too, that they recomend a racing gasket and or o-rings above 11.5 and the bigger you go this also has an effect on your static ompression too.
but good point and question.
It is also i nthe old Direct Connection Mopar Bible too, that they recomend a racing gasket and or o-rings above 11.5 and the bigger you go this also has an effect on your static ompression too.
but good point and question.
I picked up a 72' 340 block that was in a machine for about 20 years. Somebody brought it in and had it gone though and never came back and picked it up. It got shoved in the back and forgotten about. It has crank, cam, pistons .040 over and a timing chain. The bores look kind of rough and I don't know if they will clean up to uses the .040 pistons. So I might have to go to .060 over. I should be ok to punch it out bigger? I'm not planning on a radical rebuild. Just a good running moter with a little pep.
Mad Dart
Nothing to see Here!
You could mag and sonic check the block to be sure but It would be just fine...........also this is NOT 1970 anymore............there is a company called Cometic that makes MLS Head Gaskets and another company called ARP which makes High Strength Head Studs that will cure your OLD issues in a heartbeat!
dodge freak
Well-Known Member
Can you read man--its been answered, Sonic test is like $125-$150, otherwise you are gambling
That's right. You can't tell some of these people anything. A .060" over 340 would be a .100" over 360 in of same year. They'll GO that far no problem. I've built four like that myself. In fact, one has been pulled and bored .030" FURTHER. LOL You just can't tell some people anything, so I generally give up at that point. LOL Great comparison with the 340.
ateam
A motor can
Dugans in Riv.,Ca. $80. (12) reads per bore,quaility work-always. Because mine will be raced, who's won't?,I'll using "Hard Block", in a half-fill. Ateam:cheers:
dodge freak
Well-Known Member
Yeah but if you want to drive on the street in summer, the hard block fill will cause overheating problems...big time.
Prices do vary, not all shops up here have the equipment, those that do charge...make that over charge. I believe even sonic testing isn't all the same, I mean some check better than others.
Longer strokes put more stress on the cylinder walls, what might be ok with a 3.31 stroke might fail and crack with a 4 inch stroke.
dgc333
Well-Known Member
I understand increasing the compresion and the 10 bolt heads but I don't see the connection to the size of the bore.
Hcarr stated that you can't go .060 over on the bore because you will blow head gaskets. I just don't see the connection between a safe overbore and whether you blow head gaskets or not.
Certainly increased compression or boost has a big impact on how head needs to be clamped to the block to prevent head gasket failure.
It has and can be done like mentioned above, sonic testing is a good idea though because each block is different and what works on one block may cause issues with another block.
The one big issue some may have is overheating, I know of a few local guys that went .060 over with 360's and neither could keep them cool on the street. It may make a difference on what part of the country your in also.
The one big issue some may have is overheating, I know of a few local guys that went .060 over with 360's and neither could keep them cool on the street. It may make a difference on what part of the country your in also.
green1
Well-Known Member
Boring raises the compression.
EL5DEMON340
Well-Known Member
Also remember the more miles a block has, the more erosion it might have in certain parts of the block from water running through the jackets. Sb are not as robust as the bb if i was going to build any hot SB i would pay the $100 or so for the sonic before i dump thousands in it.
dodge freak
Well-Known Member
Here is a GUESS why a large overbore could create a head gasket sealing problem. If the bore gasket size is 4.150 and the bore is 4.070 and not 4.100 there is a longer gap that is just .040 wide before the head gasket ring. That extra .030 of distance could weaken the combustion pressure/heat on the gasket rings.
Surely the father the ring is away from the flame/heat the better.
Then again, who runs 12.5 to 1 compression on the street anymore? 10 to 1 is a big difference when it comes to sealing the head.
Surely the father the ring is away from the flame/heat the better.
Then again, who runs 12.5 to 1 compression on the street anymore? 10 to 1 is a big difference when it comes to sealing the head.
Mad Dart
Nothing to see Here!
Almost every head gasket that is over the counter and not custom is 4.172-4.180 bore size. Unless you get a custom gasket such as a Cometic most are that way. I dont believe such is the case of a head gasket blowing because of an over bore and a gasket bore problem at all. Almost every small block around is running the over the counter gasket without any issues at all.
Nice69
Well-Known Member
My 419 stroker is 1975 360 bored .085 over, walls sonic checked, W2 iron hds & ARP head studs with Cometic gaskets. Only 10:1 CR but no problems so far. ususally runs 180-195 depending on ambient temp. Made 537 HP.
mopardude318
Well-Known Member
Sweet man! any pics of this beast??
I hear you. The later blocks aren't as thin as everyone thinks. I did a 77 360 .070" over for a 416. It was a 12.1 motor. I don't own it anymore, but the guy I sold it to rebuilt it with lower compression and it's still runnin around on the street.
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