Does anyone know with expereince if a .060 overbore is safe? I have heard that this is about the limit, but is this dangeroulsly close to the water jackets. Also are there any risk going this big? I would not do it if I did not have to, but the spare engine that I have is already .040 and the cylinders are beyond what I hone can clean up. Thanks in advance. Also who makes off the shelf .060 over pistons?

 

That would be the same as running a 4g64 block.

The 64 and 63 block are the same except the 64 block is 6mm taller.

People have bored the 64 block .060 over, that would be 88mm, a full 3mm over the stock 63 block bore.

Now is that recommended? No, but .060 over on a 63 block is no different than running a stock bore 64 block.

Go for it, still some life left in it.

 

The best way to determine whether the cylinder walls in your particular block have sufficient material to go to an .060 is to have the block sonic tested, which will provide exact thicknesses of the cylinder walls in a variety of locations and let you know exactly what is available. Some blocks can have core shift, while others may be fine. If you have a lot of money in machining in the block already, you could also consider sleeving the block and going back to stock or first overbore.

 

.060 is 1.25 mm correct?
so that would make the 4g63 86.25mm?
i never hear of anyting boring that much before

 

Thanks for the advice. I never heard of anyone sleeving our blocks. How does that work? Also what is core shift? You are a bit over my head on this one. I am interested in hearing more. Thanks

 

I've had 4g63 blocks sleeved before. In my area, it costs about $75 per cylinder, although you don't have to do them all if only one is damaged. With DSM blocks, which are readily available, it's not worth it given that good blocks are inexpensive. Evo blocks are another story, and sleeving is a viable alternative to a new block when they're expensive. The sleeve is pressed in, and then the interior rebored to the specification that your piston choice requires.
Core shift is the shifting of bore centers when the block is being cast. Some foundries are more consistent in getting the cylinder center spacing dead on, but over time, some production foundaries have small changes in the spacing, and when the blocks are finish bored, the walls may be thinner on one side than on another, simply due to the fact that the "rough" casting centers were not exactly where they should be, and the finish bores were bored correctly, but are not in the center of the material that was left in the rough casting. Hope that's understandable.

 

Bringing this thread back from the dead. Just wanted to correct the poster above that .020" is .5mm, not 1mm. So a .060" overbore would be 86.5mm, not 88mm.

Is .040" overbore considered safe on these blocks without sonic checking? I know it's not a problem on 6-bolt DSM blocks since that's what I'm used to, but I'm new to the Evo stuff and would like to hear a little feedback on it. Thanks.

 

hello?

 

you need to be more specific. whats safe at 300whp may not be safe at 1,000whp.

 

It's just going to be a 400whp pump gas/500whp E85 car, nothing big.

 

.040" at 500whp "should" be just fine, but if a sonic check isnt expensive it would be worth it for peace of mind.

 

Theres a few 500whp 3g eclipse with a 4g64 block thats .040 over

 

We have a .60 over 2.3 that will be put to the test later this year.

We'll see how that goes.

 

Thanks for the responses. I figured it would be just fine but I didn't know if there was known core shift problems in a certain model year run or anything like that. I probably will have it sonic checked just in case, but with a head gasket job turning into a full longblock rebuild, my finances are taking a bit of a beating.