It's my understanding that iron is a better material for "managing" heat than just about any other material, if a modern design head was made out of iron it would have advantages over aluminum but nobody does this.ClassicRob wrote: ↑Fri May 21, 2021 8:29 pm Ive heard the rule of thumb. 9.5:1 MAX compression ratio using an iron cylinder head is the widely accepted advice. However there is so much more to this topic. For instance, would you say it depends on chamber, piston, engine temp, timing and quality of fuel?
What I am asking, is using an old style chamber (lets say a camel hump head) is there a deduction as compared to a say... vortec style head?
Same with pistons. Will a flat top allow more compression because the flame front can travel better vs a dome?
What about engine temps? How does this affect your detonation on a point per 10 degree scale?
Bottom line, I would like to know how using a 10.1 or so engine on pump gas and iron heads would fare and what good information is there to mathematically configure what allowable compression you can run?
I hope this doesn't sound too vague or simple minded. Im trying to understand when it's safe to use more compression on pump gas. Even if its terrible quality fuel.
Aluminum is lighter and easier to manufacture.Things that help avoid detonation which will enable you to run more compression are:
- centrally located spark plug
- proper squish and quench
- flat top piston
- small volume combustion chamber
Spark plug location on a 2-valve engine is difficult to optimize. Squish and quench requires the proper piston, head gasket and/or block deck height. Since iron heads are more difficult to modify I'd assume there is a list of heads which already have a good design and are known good candidates.
Modern fuel injection and ignition timing control can allow for a wider range of acceptable fuel vs. compression. The best timing advance isn't necessarily right on the edge of detonation rather to create max cylinder pressure at the optimal time say 10 to 20 degrees ATDC depending on other factors. Timing control can be used to save the day by retarding to prevent detonation and assist with tuning if you are able to log it.
Otherwise you would have to find someone with a proven combination and duplicate that build.
