I've decided to have a 383 built for my 68 vert. The builder has given me two options at the same price.
Dart Iron Eagles, 200cc runners, 72cc chambers, flat-top pistons.
Pro Comp Aluminum Heads, 190 cc runners, 64cc chambers, dished pistons.
I'm looking for a streetable "pump gas" engine with compression around 9.5:1. What are the pros and cons of 64cc chambers with dished pistons versus 72cc chambers and flat tops?
My vote is for 72cc with flat tops.I think you get better combustion and the ability to make more power with flat tops.9.5:1 will work good with iron heads and 91 octane.With everything dialed in good 89 should be enough. My 327 is 9.42:1 and runs on 89.JMO
If I could add to the question asked here, I think what is being asked here is if the compression ratios are the same, what is the advantage of a larger or smaller chamber size.
In my plans for a 383, I was looking to keep my compression ratio down to 9 - 9.5 to 1. My thinking was to get the heads that will give me this ratio with the bottom end of the engine having flat top pistions that are zero decked and using normal .039 - .041 head gaaskets. My thought is you get a better burn across a flat surface of the piston.
Any other thoughts???
P.S. Don't hit the ESC key when typing your message, It goes away...
go with flat tops
the domes will require higher octane and bump compression up to 12:1 or close to it.
sure its good to have high compression but will you be willing to pay the price for higher octane?
or even racing gas at around 7 bucks a gallon now.
Assuming the compression ratio is the same my preference of combustion chamber design is as follows:
1. D-dish piston, small combustion chamber
2. Flat top piston, medium combustion chamber
3. Dome piston, large combustion chamber
4. old style dish piston (no quench pad) and small combustion chamber
There has been some tests and some debate about how much (if any) advantage there is to a D-dish piston over a flat top piston. I personally believe that if the compression ratio is the same the D-dish has a slight advantage due to combustion chamber shape -- being more compact in the center of the chamber will IMO burn a little faster and more efficiently than a larger, flatter chamber.
Pretty much everyone accepts the idea that the design of the combustion chamber makes a big difference in power production, but a lot of the time people forget that the cylinder head is only the "top half" of the combustion chamber -- the piston crown makes up the other half.
I wonder how much difference there is between a modern fast burn style 64cc chamber vs. a 72cc chamber of the same design. I bet the difference isn't near as significant as the old 64cc gm iron heads vs. the 76cc iron heads.
Interesting too is the fact that the few dyno tests that I have seen of small vs large chamber heads always shows the larger chamber making more power on the top end due to less valve shrouding.
That's true Travis . . . larger chambers can flow better. Especially if the extra volume is in the right place.
Anyone ever seen a set of SB 2.2's up close -- like a used set that had been worked for a cup team? The chambers are a work of art themselves . . . the ones I saw had a shallow flat chamber -- only 44cc's if I remember correctly.
Sounds kind of strange -- larger valves with smaller runners . . .
It depends on the cam you pick and the RPM range you want to run. If you use smaller runners don't plan on making good power much over 5500, sure it will rev higher but you will be giving up power up top. I don't think you would loose power down low -- you might even pick up some low end grunt.
What cam are you going to run? How much are the heads setting you back?
The builder is recommending a Wolverine Blue Racer (Crane) camshaft #WG1064 (Crane grind# 300-2H). .488/.510 lift, 234*/244* duration @ .05, and 112* lobe separation. I first thought it sounded too big for a street driven car. What do you think? I'm mostly looking for low end street power on pump gas.
I'm pricing a complete engine build, so it's hard to say what the heads really cost. But he said that an upgrade to 200cc heads would cost an additional $250 to $300. He has five sets of 180cc heads in stock and I guess he really wants to move them.
They just dropped one of these engines in the owners Chevy pickup. I'm going to arrange a test drive before I make my final decision.