Determining Compression ratio??

[scgamecock]

How does a diy'er determine compression ratio and what is considered "good" for the street while designing a build?

I plan on building a 460 stroked to a 512.  I found a used rotating assembly that I plan on buying that comes with "dished" pistons and have a CHET HERBERT solid roller cam.  I am trying to make good HP but mainly have a torque monster.  Her is the planned engine setup.

  -460 block bored .080

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  -DOVE iron heads with basic gasket matching and port\polish, stainless steel 1 piece valves

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  -JE "dished" pistons  (Used)

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  -H beam rods (Used)

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  -Steele OEM crank

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  -Chet HERBERT solid roller (part # H6H) 685/683 258/270  108 lobe center (Used)

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  -WEIEND stealth intake or similar

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  -650 dble pump

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I'm hoping for a compression ratio of 10:1 or lower.  What would I need in terms of deck height, gasket thickness and head surfacing? Is that achievable with this setup?  

One thing to mention is that the rotating assembly is $300 and the cam was free so I want to use all of this since it dramatically reduces the cost of the build compared to buying new.  So this is a goal.

Thanks!

wade

 

[c9zx]

You will need to do some research to determine the numeric values required to accurately calculate compression ratio. Use this calculator when you have the answer to all the questions the calculator asks. http://www.diamondracing.net/tools/  Chuck

 

[scgamecock]

You will need to do some research to determine the numeric values required to accurately calculate compression ratio. Use this calculator when you have the answer to all the questions the calculator asks. http://www.diamondracing.net/tools/  Chuck

Ouch!  there is a lot of info needed that sounds like it cant be calculated till after all machining is done.  I was hoping to get a ball park number to ensure I stayed at or below 10:1 preferably below.  

About all I know right now is:

71 DOVE heads I think stock they are 260-270 CC

4.15 stroke

.080 over Dish JE pistons. 

6.8 H-beam rods

solid roller (part # H6H) 685/683 258/270  108 lobe center

I've asked the seller of the rotating assembly what the piston part number is as well as some details of what the assembly came out of.  I have not heard back yet.

 

[Don C]

You will also need to calculate your dynamic compression ratio, it will give you a better indication of how your engine will perform and fuel requirements than the static compression ratio.

https://www.7173mustangs.com/thread-engine-and-compression-calculations?pid=199290#pid199290

 

[c9zx]

I have no idea what the dish volume of your pistons are so you will need to have one cc ed. The screen shot attached gives some generic values that will get you started. Chuck

 

[TommyK]

JE makes an .080 over -28cc inverted dome shelf piston for this combo. Assuming that is what you have your compression ratio with uncut D0VE heads should be just under 10:1 depending on the exact measured values of the rest of the components. As Chuck suggested you need to measure everything you have to get the right number.

 

[rotorr22]

Go to the Summit Racing website and enter "Pistons" in the search function. Click on any piston to bring up the "Overview" tab. Scroll down past the piston specifications and you will see a compression ratio calculator. Enter your data to get a rough idea of your static CR. In regard to head gaskets, most OEM stuff tends to be in the .045" +or - .003" compressed if you need something for that field,

Just for grins, you can enter different numbers for stroke, chamber volume, deck height etc. to see how those variables change the CR.

Sample

Compression Calculator

Get accurate compression without the guesswork!

Get your engine's optimal compression ratio and total displacement in no time flat! Just complete your engine setup, click calculate, and you’re on your way to maximum performance.

Bore: (diameter)

Stroke:

Cylinder Head Volume:

Effective Dome Volume:

Use (-) for Dome and (+) for Dish.

Deck Clearance:

Compressed Gasket Thickness:

Number of Cylinders:

Compression Ratio :

Total Displacement (in.3) :

Total Displacement cc's :

.