ValiantRacing
Well-Known Member
This is a piece of a 340 cylinder that is .040 over, its .145 thick. i think another .020 or more is not going to make a dent in amount of materiel here, its very unfortunate that i have this piece.
Been some talk lately about boring 340 blocks and how much over, i have a picture
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Picture doesn't work.
What year block? My former machinist had to use 1970 and earlier castings to pass sonic test on all eight holes for a .60 overbore. But all of the early 340 blocks I’ve seen have cylinder walls like early 360 blocks with the cylinder walls at the core plug holes almost touching each other.
The problem is that not every cylinder in the block has the same thickness walls, and even within a cylinder the wall thickness isn’t necessarily uniform.
So having that one section at .145” doesn’t mean that you’ve got .145” in every part of every cylinder.
And it’s not even just an early vs late casting thing, it varies from block to block. The only way to be sure is to sonic test the block you’ve got.
ValiantRacing
Well-Known Member
Block is was a 71
65TerrorCuda
Well-Known Member
Looks meaty
I guess I'm in the minority. I don't think it looks all that good. Look at how much porosity it has in that casting. It's sure not very dense. Look at all those pockets. That's not good, regardless of how thick it is. Thanks for posting this. This seems to possibly prove the theory that casting quality got better through the years.
9secRR
Well-Known Member
My 71 340 is 4.100”. Been together for 3 years running 9’s
These blocks are really a pretty crude casting.
Especially as I recall Mopar used the molds up
to 9 or ten times.
Thirty years ago, we were honing a
Brand new R Block. Part way down the bore the
hone did a strange chattering. We had sonic checked
the block and it tested great. We found a bubble about
050 to 060 below the surface in that cylinder that was in
an area the sonic testing had not revealed.
These were a special block that Mopar had found left over
from the early 70's Trans Am program. I obtained all 8
from a Ohio warehouse that they had lost for 20 years.
It broke my heart to have to sleeve a brand new expensive
block, but what could you do.
I am still using 7 of those blocks currently in our race cars.
The eighth one had issue that made it unusable for our bores (4.10 often)
I ending up letting one of our friends acquire it for his 318 Superstock car (3.965 Bore)
Especially as I recall Mopar used the molds up
to 9 or ten times.
Thirty years ago, we were honing a
Brand new R Block. Part way down the bore the
hone did a strange chattering. We had sonic checked
the block and it tested great. We found a bubble about
050 to 060 below the surface in that cylinder that was in
an area the sonic testing had not revealed.
These were a special block that Mopar had found left over
from the early 70's Trans Am program. I obtained all 8
from a Ohio warehouse that they had lost for 20 years.
It broke my heart to have to sleeve a brand new expensive
block, but what could you do.
I am still using 7 of those blocks currently in our race cars.
The eighth one had issue that made it unusable for our bores (4.10 often)
I ending up letting one of our friends acquire it for his 318 Superstock car (3.965 Bore)
following...
What I have seen over the years as well many other builders, is that the first pours out of the ladle the blocks are very clean and have less porosity due to the heat of the metal and the freshness of the heated molds. This gives a more consistent core. A 340-1 or 318-1 is a much stronger and cleaner block verses a higher number like a 340 -8 and up. Here is a X-block 318-11 . The block was missing the top of the lifter bore and had other deformities so we spray welded it and sold it.
The 2 blocks stacked 273-8 vs. the 340 -5, look at the porosity on the 273 in the crevices where the trans attaches . This can also be seen internally. The higher the number the worse it gets. Steve spray welds/repairs many blocks for numbered matching cars that most shops won't tackle My suggestion is to look for a low dash number.
Most mopar sprint car builders looked and paid top dollar for Dash 1 blocks. The block being attached to the flexing frame torquing off the turn with front and rear engine plates, They need to be strong.
Race blocks have higher nickle content then stock blocks. But still sitting in the ladle that is cooling. Also the slag starts to go into the mold. When the ladle is first poured we would scrape most slag off on the top and hold the rest back with a paddle. When reaching the bottom some of that scrap sticking to the side makes it through due to the ladle tilted more and dropping off the top side. Low numbers are the ticket for a stronger block.
Just an FYI use it or not its up to you
The 2 blocks stacked 273-8 vs. the 340 -5, look at the porosity on the 273 in the crevices where the trans attaches . This can also be seen internally. The higher the number the worse it gets. Steve spray welds/repairs many blocks for numbered matching cars that most shops won't tackle My suggestion is to look for a low dash number.
Most mopar sprint car builders looked and paid top dollar for Dash 1 blocks. The block being attached to the flexing frame torquing off the turn with front and rear engine plates, They need to be strong.
Race blocks have higher nickle content then stock blocks. But still sitting in the ladle that is cooling. Also the slag starts to go into the mold. When the ladle is first poured we would scrape most slag off on the top and hold the rest back with a paddle. When reaching the bottom some of that scrap sticking to the side makes it through due to the ladle tilted more and dropping off the top side. Low numbers are the ticket for a stronger block.
Just an FYI use it or not its up to you
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