[tirod]

Tetra ethyl lead additives were eliminated a long time ago. At that time most engines were already being built with better valves and hardened seats in anticipation. Rebuilders began adding them to motors they were selling to avoid warranty issues, another reason the prices went up.

Unless you know you have a lead era motor from the early days that hasn't been retrofitted, you likely have the hardened seats. You can get the block casting numbers off the heads and then know what time period they were made in history and go from there.

Since pump gas is what most of us run, most crate motors are built with it in mind, and the complete lack of lead additives, too. These days, a high compression motor is rare - and running it problematic. They are mostly track motors and it's expected that knock will be a factor, the guy who selected the components knows to choose with care and the warranty he words with it.

It's part of why most motor rebuilders don't sell short blocks anymore, weekend racers were slapping on small chamber heads and blowing them up with uncontrolled preignition. So now, all the rest of us have no choice but to buy the motor long block or not at all. Read the warranty language on short blocks and see what little coverage you get. Read the crate motors compression and what cam is used - actual PSI isn't as much as we'd like to conform to the reality.