I like Mitchell's manuals personally. I got the whole collection for 2006 from my mechanic.

 

You can get combustion chamber sizes the same for iron or alluminium heads. Alluminum heads do change compression beacuse the heat transfer from the chamber is much greater than the iron heads. The general rule is to reduce compression by 1 point when running iron heads. So if you have 9:1:1 compression with iron heads and install alluminiums you will have 10:1:1 compression.

 

No, I still think, nay, know, that's wrong. the aluminium does nothing to change what the compression ratio IS. It allows you to run higher compression because it transfers heat to the coolant more eficiently, and the result is less chance for detonation, which is caused by over heating/compressing fuel air mixtures of a given caloric content. The higher the caloric content (I.E: Lower octane) the sooner this threshold is reached. The aluminium will allow you to go a point higher because it doesn't stay hot the way the iron heads do. Volumes don't change just because of the material. a CI of gas and air inside an aluminium box is the same as a CI of air and gas in a iron box.

 

Well if you don't believe me then contact an engine machine shop they will tell you the same thing, or you can look it up in books or the internet but its the truth. I had then same thoughts about different materials in heads changing compression ratios but its true.

 

All things being equal the compression is the same iron or aluminum it is basically a volumetric ratio calculation. If you have an internet source telling you different please post a link I would like to read it.

 

I'm with you on that one, Griff.

 

if i were to run 93, or even 110 octane gas in a regular street vehicle (i.e. my mom's 3.8 v6 ford winstar, around 200hp), the higher octane means it wont ignite at the compression and ignition system of her stock engine. if the engine would run at all (likely it will), it would only manage to put out around 150 hp because the engine cant burn the fuel.

most lawn mower type engines specify a minimum octane rating of 79. i think that most cars in america can run on 81-83 octane and not run into an problems