71 340 Compression Test

nm9stheham said
FWIW.... Only worry about the hardened seats for regular pump fuels, not for 100LL AVGas. 100LL has MORE lead in it than leaded automotive fuels ever had; 100LL is 'low lead' only in reference to the older lead AVGas.

I know people who have run the 100LL and they recommend the hardened valve seats. As do I. I know the 100LL has more gas than regular leaded gas ever did. But it's more than capable of being run in a vehicle.

nm9stheham said
Mmmmmm... well I ran 8.2-8.3 DCR on the street years ago with iron heads and quench and premium fuel... ran over 90k miles that way. I di have to be careful with ignition timing. A 7.5:1 DCR limit is way to low and unnecessarily limiting in my view. Use quench and small combustion chambers and don't fear going into the low 8's with iron heads....IMHO.

I'm not sure at what elevation/fuel you ran that. But the rule of thumb I've always used is 7.5:1 on iron, 8.5:1 on aluminum. This is safe for 91 octane. As you mention, you had to be careful with ignition timing. Of course you can run more DCR if you want to risk bad timing/fuel problems. Which might be fine if you are sure your timing is good. That you won't run into any fuel problems. And have access to higher quality fuels at all times. Or you can run less DCR and be safer with timing and fuel. Remember, 1 point of compression is really only good for 10-20 horse, depending on the setup of course. I would rather be down 5-15 horse from 8.2 DCR to 7.5 DCR and not have to worry about timing, overheating, fuel, etc. Than get that extra 5-10 horse. Especially in a street vehicle. If it was a race vehicle? I wouldn't worry, cause it would be on methanol.