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Old 10-29-2008, 04:09 PM
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Heads Up !!!!

Hey everyone. new guy here. Question: I have a crate 383 stroker (360hp/410lbs) on Sealed Hyperutectic Pistons(yields 9.5:1 CP, flat top, 2valve relief); GM Cast Iron heads (Valves: 1.94int/1.5exh)(72cc/170 runners)...Compressed Head Gasket of .041..Standard deck height..Comp Cams Hydraulic Flat tappet .477/.480 lift; 110 lsa; 224/230 dur. @0.50" Advertised Dur. 268/280. I want to run Aluminum Heads (preferable trick flow's, AFR, Dart) with 190 or 195 intake runners & 2.02/1.6 valves. What size Combustion Chamber should I use to keep a CP ratio of nothing greater 10.5. (Street Driven/ Maybe some Track car).....Thanks

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Last edited by BG383; 11-02-2008 at 11:18 AM.
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Old 10-29-2008, 05:14 PM
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First off, Welcome to the board!

No one is really going to give you an accurate answer until all the details are known. Just guessing I would say either a -5cc flat top or a 12cc dish. Try to find out what you have and post back.
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Old 10-29-2008, 05:49 PM
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Quote:
Originally Posted by BG383
Hey everyone. new guy here. Question: I have a crate 383 stroker (360hp/410lbs) on Sealed Hyperutectic Pistons(yields 9-9.5:1 CP..don't know if flat top or valve relief); Cast Iron heads (1.94int/1.5exh)(76cc/175 runners).....I want to run Aluminum Heads (preferable trick flow's, AFR, Dart) with 190 or 195 intake runners. What size Combustion Chamber should I use to keep a CP ratio of nothing greater 10.5. (Street Driven/ Maybe some Track car).....Thanks
It takes 5 values to figure static compression ratio:
1. cylinder volume
2. combustion chamber volume
3. gasket volume
4. piston deck height volume
5. piston crown volume
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Old 10-29-2008, 06:43 PM
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If you are 76cc right now then go with whatever dart, afr, trick flow have for a large cc SBC 190-195cc head... I think afr's come in 74cc, dart in 72cc, and not sure about trick flow stuff. Even if they are 2-4cc smaller you should come out to (worse case) a shade over 10:1 and as long as the cam is decent size, the aluminum heads will help you out in regards to detonation.

But everyone else is right, it's best to know the details.
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Old 10-30-2008, 11:15 AM
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Heads up

The Pistons are Sealed Power hypereutectic (flat top) with two valve reliefs (part #H860CP)cp ratio 9.5:1. The heads (Cast Iron) have 72cc chambers with 170 cc runners. The cam is Comp Cams Hydraulic Flat tappet .477/.480 @.50lft.

Last edited by BG383; 10-30-2008 at 11:55 AM.
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Old 10-30-2008, 01:17 PM
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If you are truly at a 9.5:1 static ratio right now and the heads are 72cc - strictly changing head cc you can go down all the way to 62.5cc to get a 10.48:1. This is kind of a "dummying up the numbers" estimation as I don't know the deck height or anything to verify your starting ratio is exactly 9.5:1.

The one I really like to use for compression calculators is: http://www.diamondracing.net/cocalc.htm - it's a lot more detailed then most. Good luck!
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Old 10-30-2008, 01:47 PM
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cam???

I'm assuming those numbers are your valve lift??? and I don't think its @ .050", I could be mistaken but I don't think so. The STATIC CR is important, but the Dynamic is what you really need to look at ALSO. This is what is actually happening when the motor is running....

To get an honest answer on here your gonna need to provide more info about the cam, such as the duration, overlap, LSA, ect... Or you'll never get it accurate. Do you have these numbers??? If you ask me dynamic CR is way more important, cuz the cam will force you to go higher or lower with the static # based off these other figures... eg... your not gonna run 10.5:1 with a stock cam on pump gas, however, you throw in a radical cam say 245*@050" with 520/520 lift and a 108LSA you CAN run 11:1 on pump gas.... Hope this makes since, Please provide more info or a part number so we can lookit up for ya
Danny
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