boring too much?

[chevy art]

my buddy had an engine built by a builder that supplies the block. its a 350 sbc with an overbore of .080, he sahy the overboore is never a problem. i always thought that .060 was max. block is not filled and it is a steel headed engine with hydraulic cam aprox 10,0 comp,. ratio, engine builder says its 525 HP but i dont believe it even comes close to that. has a edelbrock regular performer and a carb that is 870 cfms(i believer its way overcarbed). dont believe this builder is a good one with his combo and overstated horsepower. any comments on the overbore. thanks art

[SupStk]

I've done them at .080" but that was block which passed a sonic test and was filled.
Not saying it can't be done but without knowing wall thickness its a crap shoot at best.

[Paul Kane]

0.080" overbore was a common rebuilder piston size for the SBC since forever, manufacturers still offer them, and we're not hearing endlessly about windowed cylinders.

The engine sounds like a mild build to me given the components used. And so in that regard 0.080" ought not be a problem. Of course, the more the power increase, the more one must scrutinize details such as the one you bring up.

There is no steadfast rule that says "0.060" max," and certainly no such rule can be applied as a maximum dimension on a component that has as much variability as one which is casted.

[David Vizard]

I've done them at .080" but that was block which passed a sonic test and was filled.
Not saying it can't be done but without knowing wall thickness its a crap shoot at best.

Chevy art,

I think that anyone who is good at finding power will run into a problem sooner that some one who has less skill in that department. I use a sonic tester on every block I come across. That S/T was the best tool I ever bought. Paid for itself the first test session I had with half a dozen blocks. During that session I found a stock 350 block with cylinder walls about the same as a bow-tie block!

0.080 is OK if the wall thickness is there but finding a block that will tolerate 650 plus hp is rare . I think they are all used up. However there are still blocks that will go 0.060 OK and hold a decent amount of power ie 600 plus.

So what I believe here is that Supstk's advice is well worth serious consideration.

As for Paul Kanes post he is talking about mild builds so what he has to say is valid but just in case I would limit the overbore to 0.060 on a sonic selected block.

DV

[user-23911]

We had a Toyota 4 cylinder diesel block which we overbored by the usual 0.5 mm.

It came back due to water in one of the combustion chambers.

We found a pinhole leak in a wall caused by rust, almost impossible to see.




So even though the wall thickness on average is OK, it isn't always OK to overbore.

[PackardV8]

The max overbore is inversely proportional to the horsepower and the RPM developed. We've proven to our satisfaction that on a all-out effort build, especially with power adders, standard bores make more power than max overbores.

Some, i.e. Cleveland and other thin-wall Fords, Pontiac, as well as SBCs, can suffer if bored very much.

Having said that, the stock rebuilders have sent out thousands of .080" SBCs and .060" small-block Fords without too many problems. They don't make enough horsepower to hurt themselves.

Also, torque plate boring/honing and main bearing bore line honing should be considered a requirement for a performance SBC, but certainly needed on one bored .080".

Thin rings are better able to cope with larger bores than the old school 5/64".

We found a pinhole leak in a wall caused by rust, almost impossible to see.

For true; those of us who work with 50-75-year-old rusty iron get bitten by that too often. My theory is a bit of slag in the iron is a weak point which attracts rust.

Then, there are the old-car-criminals who won't get the radiator leak fixed or the blown head gasket replaced; instead they pour the cooling system full of unknown home remedy crud and/or the snake-oil commercial stop-leak. We just had a numbers-matching block which required two sleeves because whatever was in there was corrosive.

[dwilliams]

I had more than a few of those, almost all on Ford FEs, though. When boring for a repair sleeve, it often looked like there was a bubble in the casting. Sometimes it was just porous brown crud.