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Compression questions..

 
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NastyGbody
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Joined: 18 Jun 2011
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PostPosted: Sun Jun 19, 2011 2:37 pm    Post subject: Compression questions.. Reply with quote

I need help here. Im bulding a new motor for my car. It came with a sbc 350. I put a few bolt-ons to help it breath better... i.e. cam, intake, carb, headers and some other lil stuff.

Im tryin to figure out how to get it to be around 11.5:1 or 12:1...but someone i talked confused me with static compression and dynamic compression...please explain. Im tryin to learn to do a motor the right way the first time. Thank you!
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Paul P
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Location: Townsend, Mass.
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1971 Chevrolet Chevelle

PostPosted: Sun Jun 19, 2011 3:27 pm    Post subject: Reply with quote

To get a 350 to that high of a compression will take small combustion chambers and/or a domed piston. Pay for the calculators on this site it is worth the small amount of money for what they tell you.

Static is actual compression using the dimensions of the cylinder and combustion chamber volume.

Dynamic takes into account the static compression and camshaft overlap figures where some of the cylinder pressure is bled off.

If you don't know the static you can't figure out the dynamic anyway.

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2001 Focus 2.0 Zetec
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1971 - Chevelle 408 SBC N.A.
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NastyGbody
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PostPosted: Sun Jun 19, 2011 4:50 pm    Post subject: Reply with quote

Yea..the pistons will be domed. The head combustion chamber is 64cc. I have the basic idea to building a motor. Do you think gettin some "how to" books would help? Cuz i found a couple good ones on amazon. Im goin to as much of this build as i can..before i need to start need real hands on help or paying for shop labor.
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SMOKEmUP
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Joined: 30 May 2002
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1979 Chevrolet Camaro

PostPosted: Tue Jun 21, 2011 12:52 pm    Post subject: Reply with quote

Static compression is a ratio of the total cylinder volume to the compressed volume.

Dynamic compression is a ratio of the cylinder volume at the point where the intake valve closes to the compressed volume.

In other words, as the piston rises the intake valve is still open. When the intake valve closes this is where the cylinder volume is calculated to figure out DCR.

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NastyGbody
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PostPosted: Wed Jun 22, 2011 7:31 pm    Post subject: Reply with quote

I kinda have an idea of what your talking about. I was thinking about buying the programs you offer on here...im just not sure if i can use them all. For the price do they all come together?
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SMOKEmUP
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1979 Chevrolet Camaro

PostPosted: Thu Jun 23, 2011 5:39 pm    Post subject: Reply with quote

NastyGbody wrote:
I kinda have an idea of what your talking about. I was thinking about buying the programs you offer on here...im just not sure if i can use them all. For the price do they all come together?

Yep

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I challenge you to push yourself.
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NastyGbody
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PostPosted: Mon Jun 27, 2011 2:44 am    Post subject: Reply with quote

Thats good. Cuz i was looking at them and it would pricey if you had to pay for them separate!
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