Dish pistons vs. Flat tops
Thread Starter
Joined: Dec 2005
Posts: 4,795
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From: St. Cloud, MN
Car: 1984 Trans Am
Engine: LS1383 in work
Transmission: Magnum F - to be installed
Axle/Gears: Zexel Torsen 3.73, 28-spline mosers
Dish pistons vs. Flat tops
Ok, this should be a fairly strait forward question.
I'm building a 383 for my 84 Trans Am. In doing so I've been trying to do some research on what all I will need. And I'm a bit stuck...
I contacted scat to see what rotating assembly I would need. Looks like I'll be getting a cast crank with forged pistons and rods. I've got a good set of 64cc Vortech heads. Now I want to run somewhere in the neighbor hood of 9:1 or 10:1 compression to be able to run on pump gas if I'm not mistaken. That said, the tech guy from scat says I need to run dish pistons to get the correct compression ratio. I would really prefer to run Flat Tops but I think that will push my compression ratio too high and will not let me run on pump gas.
I've done some research on the dish pistons vs. flat tops and I know about the obvious design difference, but I would love to hear your comments on them. Which is better, will one run better than another? Thanks in advance!
I'm building a 383 for my 84 Trans Am. In doing so I've been trying to do some research on what all I will need. And I'm a bit stuck...
I contacted scat to see what rotating assembly I would need. Looks like I'll be getting a cast crank with forged pistons and rods. I've got a good set of 64cc Vortech heads. Now I want to run somewhere in the neighbor hood of 9:1 or 10:1 compression to be able to run on pump gas if I'm not mistaken. That said, the tech guy from scat says I need to run dish pistons to get the correct compression ratio. I would really prefer to run Flat Tops but I think that will push my compression ratio too high and will not let me run on pump gas.
I've done some research on the dish pistons vs. flat tops and I know about the obvious design difference, but I would love to hear your comments on them. Which is better, will one run better than another? Thanks in advance!
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Joined: Mar 2004
Posts: 388
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From: Kansas, where the wind howls
Car: 84 Z28 H.O. w/Megasquirt II
Engine: semi-stock L69
Transmission: T-5 non W/C
Axle/Gears: 3.73 open
The current trend in thought is that a smaller chamber and a dished piston is more efficent than a larger chamber and a flat top. I'm no engineer, but I believe the smaller chamber puts more of the power pushing on the piston and less on the head(that's how it works in my head).
A dished piston with a flat around it would be best to take advantage of quench(another effiecency theory).
Using mathmatics, you can find the exact compression ratio(CR) of your particular setup. I believe the equation is actually here on the site. Make sure you have the exact cc of the chamber with the plug in it.
My suggestion is that you figure your CR with the flat tops, and start building out the dish until you lower it down to 9.1(for iron heads, 10.1 for aluminum).
I believe this to be a safe number for the street. If you find you need to remove very little, maybe just put in some valve reliefs.
A dished piston with a flat around it would be best to take advantage of quench(another effiecency theory).
Using mathmatics, you can find the exact compression ratio(CR) of your particular setup. I believe the equation is actually here on the site. Make sure you have the exact cc of the chamber with the plug in it.
My suggestion is that you figure your CR with the flat tops, and start building out the dish until you lower it down to 9.1(for iron heads, 10.1 for aluminum).
I believe this to be a safe number for the street. If you find you need to remove very little, maybe just put in some valve reliefs.
Last edited by pizza_guy; May 18, 2006 at 02:00 PM.
Joined: Sep 2005
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Car: Yes
Engine: Usually
Transmission: Sometimes
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What heads?
It's like, how loud is one hand clapping? CR is determined by the pistons and heads together. You can't specify compression without both. Along with the deck clearance, and the head gasket thickness.
It's like, how loud is one hand clapping? CR is determined by the pistons and heads together. You can't specify compression without both. Along with the deck clearance, and the head gasket thickness.
Thread Starter
Joined: Dec 2005
Posts: 4,795
Likes: 15
From: St. Cloud, MN
Car: 1984 Trans Am
Engine: LS1383 in work
Transmission: Magnum F - to be installed
Axle/Gears: Zexel Torsen 3.73, 28-spline mosers
I appologize, you are correct! I'm running (will be running) Vortec 64cc heads.
From the Keith Black piston web site,
With the Dish pistons and 64cc heads, I can run...I believe it's right at 9.6:1 compression.
With the flat tops, to get under 10:1, I would need to mill my heads to 76cc chambers which would then make it some where in the 9.7:1 range.
From the Keith Black piston web site,
With the Dish pistons and 64cc heads, I can run...I believe it's right at 9.6:1 compression.
With the flat tops, to get under 10:1, I would need to mill my heads to 76cc chambers which would then make it some where in the 9.7:1 range.
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