Why can you time aluminum heads higher than iron heads? For example, corvettes have much higher timing than camaros with the same size engine. The only difference I am aware of is the aluminum heads. Can aftermarket iron heads be timed as high as stock aluminum heads?

 

aluminum dissipates heat much faster than iron, therefore you can get away with more timing with aluminum heads...to a point.

 

Are there any port differences between the two, i.e. swirl in the iron, and not in the aluminum?? I don't recall what differences there are, but it would influence the part throttle and low RPM timing. High swirl will speed up combustion as the flame folds over on itself, requiring less timing to get the job done in time for best power.

And, as LeePerryRacing said, it can tolerate more timing before knock which can allow you to reach MBT (minimum timing for best torque).

 

The farther the spark timing is advanced. The more the engine is trying to compress a burning expanding combustion chamber. This increases piston, rod, and crank loads. There is a increase in power, but at the expense of more internal heat. Which will raise oil temps. To the extreme melt bearings.

There are limits and disadvantages to the "more is better"

As a "rule of thumb", Aluminum heads can take one CR ratio higher: 9:1 iron to 10:1 Aluminum. If you do this change to Aluminum heads, spark advance can remain the same. This is a very general rule, there will be special cases.

Not all vette spark tables are more advanced, some Broadcast codes are not optimized for long engine life. Remember they only had 3 years and 36000 miles warranties.

Rear end ratios play a big part in the spark table numbers.

 

Nah, it's worse to have way too little timing.

The closer you are to MBT without knock, the colder the EGT and water temp will be. Late timing can lead to flames out the exhaust and melted parts.

As a thought experiment - assume the engine takes in 14.7 grams of air, and 1 gram of fuel and burns it all. No matter what, the energy released is the same. The engine will send that energy either out the crankshaft as torque, to the cooling system as heat, or to the exhaust as heat. If more of that energy is put to the crankshaft as torque, then automatically less went to the coolant and exhaust (oil and coolant are similar in function).

With too little timing, the burn is slow and late. The peak temp is less, but the average temperature is more. Less work is achieved from the combustion, but the same energy is released, and it goes to whatever is cooling the piston and chamber, and the exhaust.

You could argue that with more timing the oil may have a little more load on it at the bearings to make it hotter, but it's hardly a difference, since the rotating assembly and oil pump is still turning at the same speed, and that sloshing and pumping is the main energy input to the oil (aside from the actual cooling system transferring bore and head temps to the oil.

 

I agree about too little timing. Higher CR don't need as much. Everybody says 30-35 degrees at WOT for the avg SBC. This is another "Rule of thumb".

I am not an engineer, just trying to relate observations.

If you read Grumpy's (RIP) notes on timing, he suggested to use the least amount to get the results you wanted.

I was referring to an extreme example. Usually happens at Part throttle and higher loads, it was my own experience with the higher temps. Detonation (ping) is usually the first to be noticed.

Per Grumpy, with rich mixtures and lots of spark advance, detonation is masked.