What's safe .20, .30, even .40 over?

[qws2000]

I have a 109 block and it is already .20 over... How far can you take the motor going past .20 over? What are the benefits of going past .20? What is the most common bore?

 

[forcefed3.8's]

There are no benefits with that little of an overbore other than a true cylinder and ring seal, 1 or 2cu in doesn't do anything. The issue is wall thickness. Spend the $100 and have the block sonic tested. It might frighten you how thin some of the 109's are.

 

[OvaBoost]

The issue is wall thickness. Spend the $100 and have the block sonic tested. It might frighten you how thin some of the 109's are.

When is it too thin? Did you have a number in mind and is that usually reached at a certain over-bore?

 

[forcefed3.8's]

Every block is different, that is why a sonic test is needed. At the thinnest, .180" to .200" is what is considered safe.

 

[daves87gn]

i have a 60 over block and heard of a few people that have gone as far as 100 over, but like state above sonic check, my machinist had a block leak at 20 over