Whats the diff?? .20 over vs .30 over
Thread Starter
Instructor
Joined: Feb 2006
Posts: 119
Likes: 0
From: Atlanta GA
Whats the diff?? .20 over vs .30 over
Guys,
My motor is in the shop being rebuilt and I specified with the builder .30 over. The builder started the other day and I stopped by only to find he's bored .20 over and half way through the rebuild. Clearly a breakdown in understanding on the builders part but good job otherwise! He's wanting to stick with .20 over rather than re-working and going .30 over.
What's the big difference? What differences will I see/notice? It's a 73' 350 with Edelbrock RPM Intake Manifold, Dart Iorn Eagle Heads, Holly 670 cfm, heads, .....
My motor is in the shop being rebuilt and I specified with the builder .30 over. The builder started the other day and I stopped by only to find he's bored .20 over and half way through the rebuild. Clearly a breakdown in understanding on the builders part but good job otherwise! He's wanting to stick with .20 over rather than re-working and going .30 over.
What's the big difference? What differences will I see/notice? It's a 73' 350 with Edelbrock RPM Intake Manifold, Dart Iorn Eagle Heads, Holly 670 cfm, heads, .....
Drifting
Joined: Aug 2004
Posts: 1,883
Likes: 124
From: Lubbock TX
You'll lose a couple of cubes but may get a rebuild at .030 or .040 over if you decide to change it in the near future. Has it been honed or just bored to .020? If just bored, it'll finish hone at .030. As long as you're ordering new pistons and rings, it's not a big deal at all, may even run a tad cooler (but not much)
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
The difference will not be noticeable ( less than 2 cu." of displacement). Clearly a misunderstanding, but some builders generally bore only as much as necessary for clean bores and to leave some leeway for a future rebuild should the need arise.
Race Director
Joined: Jan 2000
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From: Corsicana, Tx
2020 C2 of the Year - Modified Winner
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My only fear is that if he is using .020 over pistons, that they are a cheap rebuilder type cast piston. You will end up with deck height very low which when combined with normal rebuild type gaskets a very poor quench setup and low compression.
Cubes wise..you'll never know it...the other stuff WILL make a difference. I hate to see you spend all that money and not get a motor that runs and lives like you are hoping.
Unless you go to High $$ race pistons.....020 isn't a normal deal..it's a cheap rebuild type deal. I agree that keeping as much metal in the block is good...but just double check brand and measurements of pistons/deck height.
JIM
JIM
Cubes wise..you'll never know it...the other stuff WILL make a difference. I hate to see you spend all that money and not get a motor that runs and lives like you are hoping.
Unless you go to High $$ race pistons.....020 isn't a normal deal..it's a cheap rebuild type deal. I agree that keeping as much metal in the block is good...but just double check brand and measurements of pistons/deck height.
JIM
JIM
Race Director
Joined: May 2005
Posts: 10,674
Likes: 122
From: Millington Illinois
St. Jude Donor '08-'09
Originally Posted by MotorHead
No difference, machinists like to take as little metal out as possible for more options when rebuilding again. 
Sounds like a good shop. The .020 bore gives you another rebuild down the road over a .030 right now. Not noticable power difference and you actually have a stronger cylinder with less chance for cracking. Ask Msvetteman about his .040 bore on his crate engine.
The advice from all posters above is all good!
Last edited by 63mako; Jun 20, 2006 at 10:18 PM.
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Originally Posted by MotorHead
No difference, machinists like to take as little metal out as possible for more options when rebuilding again.
Yep that's it. And you will be able to get another rebuild out of the block that way, too.
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