[steve25]

There’s a fundamental problem with running too low of a compression for a given cam, and this is compounded by having too much deck clearance.

The problem is the speed of the burn .
To make the highest cylinder pressure out of such a combination you need to run as much timing as you can for a given rpm .
Here’s another factor within the above that I posted that has a big effect on how hot the motor runs.

The lower the cylinder pressure along with a slow burn rate leaves a bunch more heat in the cylinder.

It’s residual heat that was not able to be used when it would have been the most effective in the small crank rotation range where it could have been used to create the most force on the piston.

The motor running hot is due to this residual heat that was not used to make power.

To there for get rid of this unused heat the exh side needs really good low lift flow .
This helps the heat / high pressure to move out on its own and does not require as much the action of the piston rising up on the exh stroke to pump it out.

Unfortunately I have flow tested a good amount of home bowl ported heads who’s exh side now flows less then stock.

Also a big consideration if your running headers and have a temp issue is if they are rust scaled up on the inside.
This condition add’s a lot of restriction to the exh side.

It’s has also been seen by fully instrumented dyno testing that at full throttle it was found that for any given rpm that the exh temps recorded would go up anywhere from 25 to 30 degrees for every degree of timing that the motor really wanted!

It’ should be clear from all of this that a low compression motor combo ( under 10 to 1 depending on the cam) needs far more precise and detailed tuning then a average home street car builder of one or two engines in his life time is going to know how to deal with in terms of a wrong combo being used and or build issues compounding a problem.