Technical Engine overbore heating

Remember, you are still moving the same amount of weight, maybe a tad faster! Usually the OEMs build a little cushion in most things. So that the car can survive driving in the dessert! I bet your cooling system. Was in good shape!






Bones

 

Good explanation, Steve.

 

My personal opinion is when engines are bored out they usually get decked and the heads machined for more compression. To me that's where the extra heating comes from not to mention anyone who does these modifications is gunna get into it harder with the loud pedal. Extra revs means extra heat.

 

I have a .040 over 289. I asked my machinist about going to .060 over. He said he's done hundreds over the years and never had issues. I will go with his expertise, and the fact that, if it was a issue, why do, and have all the major, reputable piston suppliers been making .060 Pistons for 50 plus years. If it was a real issue, there would be no market for them

 

https://mustangsandmore.com/ubb/BudgetSmallBlock.html

great read on building a 300 hp 289 on the cheap….look at the comments on boring..and Alex knew his stuff

 

General go/no-go cylinder wall thickness is 0.200-inch. This is found by sonic testing. Sonic testing does not show porosity or other iron deficiencies/flaws, Magnaflux or other similar tests will reveal those.

One thing to consider that hasn't been mentioned is that when a proper overbore is done, it isn't as simple as enlarging the hole evenly 0.010-0.020-inch or whatever the overbore spec might be. If the machine shop retains the original bore center spec (and not what the engine measures out to), one side of the cylinder might only be bored 0.005 while the other side sees 0.015-inch. So that sonic test result that showed cylinder wall thicknesses of 0.215 and above might get awfully close to that 0.200 minimum if the bore centers are off (they probably are) and the machine shop fixes that (they definitely should).

If the cylinder walls are of sufficient thickness after a overbore, I couldn't imagine this causing overheating issues in a sufficient cooling system. Consider this, a 350 Chevy engine with a .060-inch overbore is only 360 +/- cubic inches. All other things equal, that small of an increase in displacement isn't likely to over stress a properly functioning cooling system.

I think the larger, looming problem with too thin a cylinder wall would be piston ring blow-by caused by distortion of the cylinder wall or cracking.