318 value
All of this is way over my head. Can I get decent performance from a 8.25:1- 9.0:1 compression ratio? The reason why I was looking at closed chamber heads is for the compression, flame travel. From what I've read on the magnum / 302 heads concerning them cracking it's not a matter of if but when they will crack. Seems they are prone to cracking between the seats and naturally the crack only gets worse. I can't see putting money into cracked cylinder heads. One guy claimed that the exhaust seat came loose due to severe cracking. Is it possible to run a decent torque cam with a 8.5:1 compression ratio? I'm wanting good throttle response and strong low to midrange torque, engine speed will probably never exceed 4,800 rpm's as that's what the cam pulls to that I looked into.
Yes, you can make good power with compression ratios in the area you are considering.
But like everything else there are other things to think about.
Lower compression ratios have less expansion ratios. You can look that up on the web and read on it. Expansion ratio is something that needs to be considered.
Also lower compression ratios generate way more exhaust gas temperature than does a higher compression ratio. The less dense air/fuel mixture in the combustion chamber burns slower so it makes more heat later in the cycle.
Lower compression ratios also require much different timing curves, including total and initial. They can be very detonation sensitive so getting the timing right is important.
Cam timing is always critical. Just as much so with those compression ratios. Trapped volume is a big deal so you want to think about how the cam numbers affect how well the cylinder traps the air/fuel mixture.
Exhaust guides could possibly need a bit more clearance depending on the valves and guide materiel. This is due to the extra heat.
Just like anything else, the more time and study you put into your combination the better it will run and behave when you are done.
The end goal is the most cylinder pressure you generate without detonation. Lower compression ratios do not always mean an engine is less detonation sensitive.