i was told by a friend today that the cylinder walls on 327s are thinner than 350s and they blow up because of this? is this true? this is the frist i have heard of this. i am looking at building a 327 and do not want to run into this issue.
cylinder wall diff?
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Your friend is full of it. No real difference between the two as to thickness of cylinder wall.
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There are thin wall blocks and there are thick wall blocks in the same engine family. All production blocks are cast. Casting is a mature, but not particularly exact process. There will be core shifting and such going on that will make one block come down the production line with pretty much equally thick cylinder walls all around, then the one right behind it could have thin walls on one side of the cylinder and thick walls on the other side.
The thrust side of the cylinder on a small block Chevy is on the inboard side of the cylinder on the driver's side of the block and the outboard side of the cylinder on the passenger's side of the block. Most engine builders will prefer to have 0.200"+ on the thrust sides of the cylinder after boring and honing. Other areas around the bore can be slightly thinner. Smokey Yunick said he likes to see a minimum of 0.135" anywhere in the cylinder after boring and honing. He said further that there must be enough mass in the walls to quell vibrations set up by the piston rings skidding up and down the walls (yep, he said they SKID, rather than moving smoothly up and down). If these vibrations are not kept under control, they can transfer to the water jacket side of the cylinder wall and separate out little air bubbles from the cooling water, which then cling to the wall and prevent cooling water from getting to the wall to cool the cylinder.
Now you know why an over-bored block with thin walls will have a tendency to over-heat.
Ultrasonic equipment is used in most shops to determine the cylinder wall thickness of a block. This equipment has come down in cost over the last 20 years, but is still in the $1000 range. Affordable for a shop or even an engine builder who builds a few high-buck engines a year, but still a little pricey for the home-builder.
Invite your friend to sit down and get the real skinny from you so that he stops disseminating false information. :thumbup:
The thrust side of the cylinder on a small block Chevy is on the inboard side of the cylinder on the driver's side of the block and the outboard side of the cylinder on the passenger's side of the block. Most engine builders will prefer to have 0.200"+ on the thrust sides of the cylinder after boring and honing. Other areas around the bore can be slightly thinner. Smokey Yunick said he likes to see a minimum of 0.135" anywhere in the cylinder after boring and honing. He said further that there must be enough mass in the walls to quell vibrations set up by the piston rings skidding up and down the walls (yep, he said they SKID, rather than moving smoothly up and down). If these vibrations are not kept under control, they can transfer to the water jacket side of the cylinder wall and separate out little air bubbles from the cooling water, which then cling to the wall and prevent cooling water from getting to the wall to cool the cylinder.
Now you know why an over-bored block with thin walls will have a tendency to over-heat.
Ultrasonic equipment is used in most shops to determine the cylinder wall thickness of a block. This equipment has come down in cost over the last 20 years, but is still in the $1000 range. Affordable for a shop or even an engine builder who builds a few high-buck engines a year, but still a little pricey for the home-builder.
Invite your friend to sit down and get the real skinny from you so that he stops disseminating false information. :thumbup:
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15,336 Posts
No, in fact 350s and 327s and even the 302s use the same 4 inch bore block casting numbers. The 350 arrived in 1967 with 2.45 inch rod journal while the 327 and 302 used the earlier 2.3 inch journal. Starting in 68 and complete by 69, the 302 and 327 also got the 2.45 inch rod journal. All 3 of these engines have seen 2 and 4 bolt main caps and all three have been available in very high performance versions with an excellent reputation for durability and reliability whether using the 2.3 or 2.45 inch rod journal crank.blight said:
You should experience no problems with a 327 build compared to anything else.
Bogie
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The cylinder wall story is just another to add to the BS hall of fame.
Before 1968, small blocks had small journal cranks and rods. The rods were not that great. As they got older and clearences got to be greater, someone would rev on it hard and it would come unglued. I`ve seen quite a few small journal engines sling rods, but I`ve seen a some medium journal rods do the same under the same conditions.
And not trying to argue with you Bogie, but I`ve never seen a 4 bolt 327.
Before 1968, small blocks had small journal cranks and rods. The rods were not that great. As they got older and clearences got to be greater, someone would rev on it hard and it would come unglued. I`ve seen quite a few small journal engines sling rods, but I`ve seen a some medium journal rods do the same under the same conditions.
And not trying to argue with you Bogie, but I`ve never seen a 4 bolt 327.
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Sorry if I'm sounding confusing, I didn't mean 4 bolt 327, but rather that the common block casting for 302, 327, and 350 has been machined for 2 or 4 bolts at various times for 4 inch bore engines. But none-the-less, it's sloppy writting on my part.DoubleVision said:
It's also worth noting that not all 327s were built to castings common to the 302 or the 350 as is the case prior to 1968.
Bogie
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5,030 Posts
Speaking of commonality of castings, recently a post was made that wondered how it was that his GMPP 572 block had a casting number that came back as a 454 truck block.
After he contacted GM, he was apparently told the castings were somehow related- despite the 572 having a tall block, larger bores, etc. Go figure.
After he contacted GM, he was apparently told the castings were somehow related- despite the 572 having a tall block, larger bores, etc. Go figure.
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1,680 Posts
A sonic test will tell you if you have a good block or not as we see a lot of them that are not a good peice for a hing HP applications and don't go by core shift as we have found that not to be a good referance.
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10,722 Posts
Well Cobalt, Many have said the general never made a 454 tall deck block but they did two model years, 1979 and 1980 or it may have been 80 and 81. I had never heard of one myself until I was reading CHP and Kevin McClelland (I think that`s his name) looked it up in the GM books, even he was surprised to find out they did.
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