This is all about heat transfer to a point.
Initially, heat from ignition, friction, etc. is retained in the cylinder walls. At the point that temperature exceeds the coolant temperature heat is transferred to the coolant and the cooling system has to do it's job. It doesn't matter if the bore is standard or overbored, this is always true.
As you bore the cylinders, the amount of iron left to to retain the heat is reduced and heat is transferred to the coolant sooner. ,030 doesn't sound like a lot but when you calculate the surface area it becomes significant.
Normally surface area is your friend in heat transfer. But in this case, the surface area contacting the coolant doesn't change so no help there.
So, to a point whether increasing the bore creates overheating problems is singularly a function of whether your cooling system is up to snuff.
At some point the walls become thin enough that hot spots are created causing localized boiling and vaporization of the coolant. Mechanically, this is destined to fail.
I have seen 289/302 blocks running .060 over with no issues. Motors that are otherwise stock had no more heating issues than they did before.
Modifying the motor for more HP creates more heat, creating more demand on the cooling system necessitating the need for cooling modifications.
Personally, if I was modifying a motor I'd go no more than .030 over. For a stock build I'd go as high as .060. Past that I'd be concerned about localized overheating.
And by the way - if you are using a pre 73(?) block, be sure to drill out the coolant passages on the block deck. This will eliminate some localized steam pockets and does make a difference.
Initially, heat from ignition, friction, etc. is retained in the cylinder walls. At the point that temperature exceeds the coolant temperature heat is transferred to the coolant and the cooling system has to do it's job. It doesn't matter if the bore is standard or overbored, this is always true.
As you bore the cylinders, the amount of iron left to to retain the heat is reduced and heat is transferred to the coolant sooner. ,030 doesn't sound like a lot but when you calculate the surface area it becomes significant.
Normally surface area is your friend in heat transfer. But in this case, the surface area contacting the coolant doesn't change so no help there.
So, to a point whether increasing the bore creates overheating problems is singularly a function of whether your cooling system is up to snuff.
At some point the walls become thin enough that hot spots are created causing localized boiling and vaporization of the coolant. Mechanically, this is destined to fail.
I have seen 289/302 blocks running .060 over with no issues. Motors that are otherwise stock had no more heating issues than they did before.
Modifying the motor for more HP creates more heat, creating more demand on the cooling system necessitating the need for cooling modifications.
Personally, if I was modifying a motor I'd go no more than .030 over. For a stock build I'd go as high as .060. Past that I'd be concerned about localized overheating.
And by the way - if you are using a pre 73(?) block, be sure to drill out the coolant passages on the block deck. This will eliminate some localized steam pockets and does make a difference.
. A cast iron radiator would be retaining the heat in comparison - no way to get the kind of surface area you can with a finned copper or aluminum radiator. Not to mention would weigh over 100 lbs.
