What's the maximum bore that can be acheived with the 6L Iron Block? I know 4.03 is standard and 4.06 is used, but what about 4.08 or higher? I ask because it doesn't cost extra to open up the combustion chamber a little more than usual, giving a little more power and some more cubes.

4.03 bore x 4 stroke = 408
4.08 bore x 4 stroke = 418

 

4.060 w/sonic approval is the max.

 

Most only go 4.03 but you can go to 4.060 in some cases.

/Thread Jack

How's the new engine running Levi?

 

4.03 is the normal
4.05 is the most i would go with out a sonic test if you plan to go FI (I would not DD it though)
4.06 is the most you can go with out a sonic test if you plan to go N/A(I would not DD it though.

 

Decent

 

I have heard that some rare blocks can take an 0.080" overbore, sonic test first of course.

Keith

 

It is possible to go 4.080 if you sonic test and offset bore, but you would really be taking a chance. I have a 4.060 bore and had to sonic test 2 blocks at 90 dollars a pop to find the block I used. Best bet is to just go 30 over for no issues.

 

I'm running .080 over. Runs like a champ. Occasionally sees the street, made ~100 mile trips to the dragstrip and back before.

 

Hmm, seems like these blocks could be bored out more? What's holding them back vs Gen 1/2? The water jacket? At least the BBCs can be bored out like crazy.

 

i dont see the purpose of boring the block to the max.... if anything goes wrong with it, it will be useless.
if you can, always leave it std, or .030, so there is room for the future, IMO.

 

The cylinder wall thickness is what is holding them back. Many of the iron blocks are close to .100 thick brand new on one or more of the four inside cylinders meaning 3,4,5,6. You need wall thickness for strength so that cylinders don't distort under high load. More material also displaces more heat. Typically you want to keep cylinder wall thickness at .100 thick. If the wall is only .110 thick untouched it doesn't leave much room to bore it out a lot. I'm sorry if this is not clear. I will include a sonic test of my current motor. I recommend people stay at 4.030 to avoid any thin wall issues.

 

running 4.060 here

 

I was just going to create a new thread to ask this question, LOL
I bought a used iron block I thought and the old owner thought was .030 over, but it turned out to be .060 over. I am going to have it sonic checked and I am praying a hone job will clean up the cylinders.