This is what I have been posting about in a number of threads.The link does explain it much better than I have been.I want to give credit to the people who posted the article.

http://www.crankshaftcoalition.com/w..._compatibility

 

http://members.uia.net/pkelley2/DynamicCR.html

 

Not bad. Good for general hot rodders. Now there are some 9 to 1 comp circle track classes that use cams designed to build cylinder pressure and still pull 7k rpms+. definately not lazy. So to some degree you can compensate for lack of compression.
Also need to keep in mind aluminum heads vs iron. 10 to 1 on iron could have more power/cylinder pressure due to retained heat in the head vs aluminum one at same comp.

 

Yeah-one of the frustrations I have is to have to build around gas pump gas for a street car. Certainly compression leads to a great gains in hp and torque. I would just love to go at it with dome trw's or alike and not have to be concerned with it all. But race gas on the street isn't financially possible.

 

They sell 110 here at my local pump but man that wouldnt be cheap as a driver. E85 is best alternative. 12-13 to 1 comp is doable. But its not available in alot of areas either

 

In my past I had dual purpose cars with 12.5 or 13.0 compression ratio cars. Ya daddy,we just let them lope and buzz to the moon.
I guess we are smarter now than back then.............but still I miss those times.

 

More SCR with aluminum heads got disproved a few years ago. Really, the 5.0 Ford guys disproved it many years ago.

 

Its physics that proves heat removal from aluminum is greater than iron. I will go with that.

Love to see my old 11 to 1 383 run on pump with iron heads or my turbo car take 15+ psi on pump with iron heads at even 9 to 1.

 

You're forgetting the time aspect. We're dealing with engines that have surface exposure to the heat measured in thousandths of a second, even at idle. The aluminum heads do get up to operating temp quicker, thy do "grow" more. But they don't allow another full ratio of static compression. Learn the full extent of every applicable aspect before posting what you've read. Do the dyno testing I've done so you can post with authority.

 

I have dynod my own. It ran fine with alum i wouldnt try it with iron. Same reason reverse cooling helps on lt1's to run higher compression. Removing chamber heat. Aluminum does it better. Iron head lt1's dont run the same compression

Share your examples instead of quoting some magazine or what you read as well. I would like to see same back to back type tests

 

I worked in the Dyno rm Tonn,NY engine plant. One measurement made was the effects of aluminum ability to dissipate camber heat better than iron heads. It was/is the sole effect of that allows higher compression ratios and not the expansion of the material. Those are the facts posted with authority. Camber shape,sharp edges,is also a contributing factor. If aluminum allows a full point increase is questionable. Certainly many other factors do come into play.

But you have a industry selling flat top pistons to a 64cc head that relies on the aluminum heads to make them useful. With that in mind..........

 

You have to have two identical heads cut into the two materials to really test it properly. But i dont know of many heads out there that are like this. Rhs has some iron castings of their aluminum heads from what i seen. They could be used.

Like said above, i dont mean to say 1 full point increase is the rule with aluminum. You may not beable to increase any. Lots of factors come into play. But its generally known that same 2 heads, but one aluminum and one iron, at same compression, the iron head will make abit more power. Reason is heat from chamber. Heat is energy. But two different heads may show opposite results. Like stock L98 iron vs afr 195 using a decent cam and intake. Obviously the afr head is a more efficient higher flowing head capable of more power so it could have less comp and still out power the L98. Its not apples to apples.

This industry moved to aluminum heads for good reason. Machineability is improved for one. Weight is another. When looking at old iron heads that most ppl think are performance heads from 60-70's its obvious to see how aluminum modern chamber and port designed heads have advantage and can really increase comp ratio because of their detonation resistance by cooling and improved chamber shapes. May have issues with old school heads at 9 to 1 on pump gas and new aluminum could see over a point or 2 more comp just fine. Now a new modern iron head may run very close to same comps as aluminums. Again there are a lot of variables here to consider

 

[quote=Orr89RocZ;5403001]You have to have two identical heads cut into the two materials to really test it properly.

We did.

 

Just out of curiousity what castings were used?

 

None on off line test pcs.