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compression calculations help
#2833897
10/17/20 02:44 PM
10/17/20 02:44 PM
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Joined: Jan 2008
Posts: 35 Livonia,MI
1968fury
OP
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OP
member
Joined: Jan 2008
Posts: 35
Livonia,MI
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just wondering how accurate the compression calculations that 440 source has listed for there stroker kits.
I'm building a 440-512 kit 30 over (505) with the .17 dished pistons and trickflow heads. They say I should be at 10.6. With pistons .015 in the hole. I went 0 deck and I'm trying to figure out what my compression is going to be and I'm having a hard time. Even when I enter there numbers in summits compression calculator get a lot higher numbers than what they say. Any help is appreciated. My goal was 11.1 or so. Thank in advance
71 scamp 340 509 cam 456 gear,68 fury1 318 3spd on the tree,50 merc flathead 3x2 3spd w/overdrive
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Re: compression calculations help
[Re: 1968fury]
#2833910
10/17/20 03:18 PM
10/17/20 03:18 PM
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Joined: Jan 2003
Posts: 31,049 Oregon
AndyF
I Win
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I Win
Joined: Jan 2003
Posts: 31,049
Oregon
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A 505 with 17 cc dish and zero deck and 78 cc heads will be 10.9 compression with a 0.041 gasket.
You made some sort of input error. I used the Summit calculator and got 10.85 compression ratio. You probable used the wrong sign on the dish volume.
Last edited by AndyF; 10/17/20 03:29 PM.
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Re: compression calculations help
[Re: fastmark]
#2834177
10/18/20 11:14 AM
10/18/20 11:14 AM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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good to know that the online calculators ain't right (I woulda never thought). I will figure out that formula & use it
live every 24 hour block of time like it's your last day on earth
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Re: compression calculations help
[Re: 1968fury]
#2834225
10/18/20 01:59 PM
10/18/20 01:59 PM
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Joined: Aug 2003
Posts: 43,223 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,223
Bend,OR USA
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Try using the United machine on line calculator and or the Wallace on line Using the same numbers will result in slightly different results on both sites Make sure and try using the - and+ sign on the piston deck heights and piston dome volume, you should get less compression with the dish than with the same amount of dome volume. Which ever sign gives you the less compression using the dish volume will be accurate, if using the + sign on the disc volume gives you 10.5 to 1 and the - sign gives you 13.5 to one then you know which sign to use on THAT sight Both will get you in the ball park though Have fun and learn
Last edited by Cab_Burge; 10/18/20 02:00 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: compression calculations help
[Re: 1968fury]
#2834238
10/18/20 02:45 PM
10/18/20 02:45 PM
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Joined: Jan 2003
Posts: 5,394 Pikes Peak Country
TC@HP2
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master
Joined: Jan 2003
Posts: 5,394
Pikes Peak Country
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One of the areas most mistakes with this happen are around chamber volume and down fill volume. Many simple step calculators just use published figures from piston and head manufacturers and should be fairly repeatable if you use the right figures. That isn't to say they will all be exact, but they should be within a narrow range of each other. One I like to use for static figures is here: https://www.rbracing-rsr.com/compstaticcalc.htmlOnce you have accurate static numbers, I use this one to account for cam, altitude, and boost variations to figure out what needs to change for pump gas livability: https://rbracing-rsr.com/comprAdvHD.htm
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Re: compression calculations help
[Re: TC@HP2]
#2835331
10/20/20 10:25 PM
10/20/20 10:25 PM
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Joined: Jan 2008
Posts: 35 Livonia,MI
1968fury
OP
member
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OP
member
Joined: Jan 2008
Posts: 35
Livonia,MI
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Thanks for the help. I should be good at that comp ratio. Now to finish assembling it and getting it on the dyno
71 scamp 340 509 cam 456 gear,68 fury1 318 3spd on the tree,50 merc flathead 3x2 3spd w/overdrive
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