I just bought some 12:1 compression .30 domed top pistons off ebay. I was wondring if I would have to use race gas or some sort of octane booster for these pistons. I am running them with the chevy double hump heads. Any input is welcome. Thanks
Daniel

 

Seeing as the Chevrolet double humps are an iron head you are way up there in compression for pump gas. I don't know the intended use for your engine but most people with a street car are running around 9 1/2 with maybe 9 3/4 CR tops. So I would say racing gas is in order. Allen

 

How many CC are the combustion chambers on the heads you plan on using?

 

Hmm most NA car addicts run 9 3/4 + on the street. If tuned right you can get away with 11:1 with the right heads.

Also Honda's (not chevy but they still have compression also lol) are factory over 10:1 compression ratio.

If i was building a shortblock that I knew was going to be NA I'd go as high as 10:1 to be on the safe side, but if you know what you're doing, you can get away with much more.

 

Honda... when's the last time you saw a Honda with old school iron heads?

 

When is the last time you have seen someone choose 9:1 compression ratio for a performance application knowing it's going to stay NA...?

 

Well,....i was wanting it to be driven on the street daily....... I wasnt even thinking strait when I bid on the item. Maybe I'll get some 76 CC heads,....that should lower the CR to 10:1 right?,......I was also trying to run a 150-200 shot on it also. Maybe not anymore. Thanks for the input so far
Danie

 

if they're solid dome it's pretty easy to make a fixture and remove the dome instead of buying new pistons.

 

I see... we are going to play it this way.

On iron heads? Maybe, but you are really pushing your luck.

Not sure how this even applies. They use aluminum heads as opposed to cast iron, the heat dissipation characteristics are entirely different and the two shouldnt ever be compared. Not to mention the combustion chamber and port design to promote swirl and therefore minimize the chance for detonation.

Lets not forget either that the camshaft plays a huge role in cylinder pressures and can make or break you.

 

So I can remove the dome on the pistons?,........Wont that make them ghetto?
Daniel

 

LOL, I'm just saying that 9.75:1 compression ratio being the "TOPS" is a little low...

Some people (not necessarily me) know what they are doing... and know what to do to scroung up whatever HP they can...

 

Back in the 70's chevy had an 11:1 domed piston, they wanted to run lower compression in the following year, so they just shaved the 11:1 down rather then redesign a new piston.

 

guess it depends on how you define ghetto. maybe the way you'd remove the dome would be ghetto, if so leave it for someone that knows what they're doing.

 

Thanks alot for the replies and help,.....
Daniel

 

Get larger CC heads for it and while your at it get them ported. If they flow better you will be able to get away with more compression without pinging your car to death with pump gas. Also when you run that much compression DO NOT spray especially to that magnitude you will have SERIOUS detination problems.