compression ratio

[mac]

here i go again! ok, it's about the set of stealth heads i have to put on the car. with all the measurements from the machine shop and a set of felpro head gaskets i will be at 9.9 to 1. machine shop guy is saying to play it safe and leave it there, but i have to ask, should i try to get a little more like 10.5 to 1? they are aluminum, and i run 93 octane. should i just leave the way it is or not? :loco:

 

[Big John]

I'd leave it alone. Three reasons. First, I don't see gas getting any better in the future. Second, it's hard to go back to lower compression without cutting pistons or replacing heads. Third, it let's you cut them in the future if you need to.

 

[SomeCarGuy]

Call it good. :cents:

 

[A31PKG]

X3

My set up is similar, although with 906's...Flat tops with the Fel-pro gasket. My macinist estimated C.R. about what you have. I also use 93 octane with no issues.

 

[mcmopar]

Leave it alone. If it ain't broke don't fix it... :cents:

 

[Hoosier Bird]

Have your builder figure your dynamic compression. Static compression means nothing. Keep your dynamic at 8 and you can run 87 octane with no problem. My static is 10.75 and I run 87 with no problem. The more duration the higher Static you can run.

 

[george68hemirr]

bullshit .....go 10.5 to 1.....more compression more horsepower....forget about mileage....alot of new cars running high test....it aint going no where

 

[ykf7b0]

I have 10.15 to 1 compression ratio with no problems what so ever. I have ran 87 octane but I try to make it a priority that it get 92 or 93 octane. Your cam selection will determine how much compression is going to be bled off. My cam of choice is a single pattern Mopar Purpleshaft with 242 duaration at .050. I agree that you would more than likely be safe at 10.5 to 1. Mopar's love compression!!!!!!!!!!!!!

 

[moparchris]

Without going into some of the other things said I would have to say that 9.9 to 1 with an aluminum head is pretty weak. You should raise the compression 1.5 points when going to aluminum to make similar power. You are going to be disappointed with the performance since a point of compression, in theory, is worth roughly 8% in the compression range your at. Say your 440 makes 500hp, with the aluminum head it will make 450. That would be tough to make up in head flow. Just sayin'. :cents: If I were in your shoes I would cut the head and run the thin cometic MLS gasket, Fel Pro makes a cool one too, and later on if you want to lower the compression I would remove material from the combustion chamber to enhance flow. I would probably cut it .040 for a full point.

 

[mac]

i couldn't take it anymore and cc'd the heads myself twice to find an average. machine shop tells me 88.2. my first time was 83.2 and the second was 84.8. so with the average being 84 and that being the advertised measure of a out of the box stealth head, with my gasket thickness of .039 and a flat zero deck piston with a 5 cc valve relief, that gives me a cmop of 10.293 to 1. that makes me a little happier.

 

[mac]

just an update. i put the stealth heads on and had a few problems with getting things running. first, i was not getting enoungh voltage to the coil. second, i had a bad spark plug wire going to #2. with those 2 problems out of the way all i can say is nice difference in performance with just changing heads. car pulls nice and strong with no bog from the carbs. very pleased!!!! :drive:

 

[moparchris]

I'm glad to hear that. A pair of these may be in my future.