.060 Overbore reliable or Weekend Only Spec?

[klaymonster]

I've got a 302 block with some gouges in one cylinder wall. Assuming that is bad and may create excessive blowby I have planned to machine the bores over .060". I chose that for the maximum displacement and maximum HP gain for the money invested. Why do something halfway, right? Well thats where my question lies. I seem to remember reading the .040" bore was much more reliable, can anyone give some input/experience on that? The car will never see nitrous and its highly unlinkely to see turbo either. Its a daily driver of at most the 300 - 400 horsepower range.

Heres the plan:
1985 Lincoln Mark VII LSC
SEFI Conversion with Tuned Mustang ECU
GT40 Upper and lower intake
AFR 185cc heads
Shortie Headers
Cats and Smog intact
4.10 Gears and AOD Wide Ratio

p.s. i know the expolorer gt40 intakes are automatic smog fail on my car but i plan to do a quickchange trick at smog time to stock HO intakes everything else should be smog compliant.

[SHONUF816]

Alot of people state that a late model block is no good beyond .040 overbore because the cylinder wall become to thin and have been known to cause heating problems. The early model blocks can handle .060 overbore because of they have thicker castings.

[klaymonster]

well i am running a late model block so i guess i'll be in the .040 overbore club. Out of curiosity does anyone have any insight as to the timeframe of the block changes?

[5.0Mav]

ya 60 is probably going to be way too much. personally i wouldnt go above 30 on a 302 and if thats not enough to get the cylinders straight i'd just get a new block before i cut any deeper. you also have to make sure this motor has never been bored before

when you bore a motor its usually not the slight bit of extra displacment that gives you the power, its the added compression.

IMO i would never bore a motor anymore then it needed to be. having a cool running reliable long lasting motor to me is more valuable then adding 3 cubic inches and running hot. its better to get some hi-comp pistons or mill the heads and get your compression that way. just make sure you have everything clearenced when you pick a cam

[illdrag]

you can go .60 over...jasper reman engines are done this way and have no problems.i had one that had a twin turbo set up on it and never over heated

[gadget73]

The least amount of overbore you can get by with the better. The couple of extra cubes doesn't make for significant power. My motor is actually .020 over, which was the smallest over set of pistons my machinist could get. He said that keeping the cylinder walls as thick as possible would help keep the bores from deforming, and it would allow another rebuild later on if needed. He said .040 is all he'd consider doing without doing a sonic check on the bores to verify thickness. Sadly he's since closed up shop and gone to work for some tooling company as a sales rep because he couldn't keep up with the physical demands of running a machine shop alone after 30 some years of doing it.

[psychotexan]

had a ford t-bird with a 302 bored .040" over and we never had any problems out of it.it was a late model block.

[PaulS]

Some blocks have the cores centered well and others don't. If you really want to know how far you can go have the block checked for wall thickness. As a note from personal experience going .060 overbore on a SBF is asking for problems. Local hot spots on the cylinder walls are likely and so are the cracks associated with them. If you want to go to a larger bore have the cylinders cut out and put sleaves in the block. You can have them furnace brazed in place for strength or pressed in and seated with the head torque.