427 Tall Deck Balancing
I'm starting my build of a 496. Due to finding a great deal on a block, I have gone with a 427 Tall Deck block.
It can hold a 4.375 crank without a problem, but I'll stay with a 4.25 stroke.
I am going to source a 4.25 crank, 6.8 rods, and 1.27 pistons.
1.27"piston pin height, + 6.8" rod length + 1/2 of 4.25" stroke(thats 2.125") equals 10.195" or .005 below the 10.2" deck on a tall deck block
thats a 1.6:1 rod/stroke ratio.
My question is that from my research, I can internally or externally balance this engine.
What are the pro's and con's of the balancing methods?
427 tall deck
Internal balance. Makes swapping parts a breeze. And its the way most people are going. External is only if those are the parts your starting with.
I have the same combo. Currently two engines. Both 427 tall deck with 4.25 stroke. One naturally aspirated with nitrious, and one with twin turbo's. Good setups.
Excellent, thank you.....
Block/heads/intake are at the machinists we speak. The block was never used for a running motor. It was found in a crate, and subsequently sold to me for $250 after being checked by a machinist. Block was in excellent condition, with some VERY minor surface rust in the cylinders. It was very well preserved by whoever packaged it.
The block is stamped "marine" as well, as is already notched.
So this block is "new" never run ?
Originally Posted by FishWagon
It's funny , we have done lots of these factory Chevy blocks. Machined them after lots of miles. What we see is not very good machining from the factory ? Or is it that when they originally machined them, they were
" green " and after the engines have been run and heated up and cooled off so many times, seems the castings move and take shape. So what we are seeing really is not that the original tolerances are all over the place, but that the block takes a set after being run, now they need to be machined to get them to the right specs ?
We just did one that the main caps were not flat on the mating surfaces nor were they 90 degrees to the block surface. It took .008 off the caps to get the line hone to come back to .ooo ???????
When we decked the block, the deck was like close side to side, maybe .002 or so, and front to back was that close also. But talk about a lumpy deck surface. It was within .002 of being square, but took .011 to get it flat ?
What do you think ?
After we run one that we machined, the things look great.
( Sorry, I'm noit trying to hi-jack the thread, just curious about a new block if that is what this thread is aboiut ?)
I don't know if you have one, but GM ran off a boat load of tall decks before they shut down the line. Chet Herbert moved a ton of these as did a guy I know out of Pheonix. My understanding is a guy out Las Vegas bought a thousand of them from GM, and part them out to different vendors. I bought 2 of these. $250.00 is a damn good price. They are They can be ID pretty easy by two means. First, everything behind the flywhell is flush with the bell housing mounting flange. The cam bore, lifter galleries, etc. Like they were all made with the same cut. They were. You'll know if you go to but restrictors in and need to use the ones for a bow tie. Otherwise they will hit your mounting plate behind the flywheel. The other is, it will swallow a 4.250 crank and the biggest rods you can find and then some. With the right rods, 4.375 will go, with no grinding. Truck blocks just seem to have the worse tolerance of all BBC. Its not so much a green thing and they move a bunch after running. They are machined wack at GM. Maybe it was the low po thing. Don't know. But new ones I had were the worse. Line bore was OK, but not good, decks off by a ton, front to back, in opposite directions. Ended up taking off .020 to get there. Bore where all over the place. It was as if GM was just jambing them thru the door. They knew they weren't going to be building motors with them. Good luck on your build. thats a nice find
Yeah, I'll know more from my buddy once he looks it over. He's going to check everything. There is not so much as a scratch anywhere on the block, it looks completly virgin.
Anyway, internal balance it is, talking to my buddy, he said the same thing, internal balance is the way to go.....
Thanks all, I'll let you know about the block once Rob checks it out and runs it through his shop. Rob mentioned that years ago before aftermarket blocks were popular, these blocks were in high demand due to their ability to be seriously stroked compared to standard deck blocks.
Anyway, thanks again.