 Calculating compression ratio..., on a 1.7 with popups. |
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| BMXerror |
 Apr 13 2008, 09:14 PM
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#1
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Senior Member  Group: Members Posts: 1,705 Joined: 8-April 06 From: Hesperia Ca Member No.: 5,842  |
Anyone know the CCs of 1.7 heads and the bump on the Euro pistons? I am coming down to the wire on my build and need to know if the deck height needs to be changed at all. This info or any related info would be great. Thanks guys.
Mark D. |
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| JoeSharp |
Apr 14 2008, 09:03 AM
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In Irvine, Ca. May 15-18 Group: Members Posts: 3,947 Joined: 9-July 03 From: DeLand, Florida Member No.: 898 Region Association: South East States |
Mark, how many times have the heads been milled? I just had to do this on a T-1. I weighed 50cc's of water 3 times on a tripple beam and came out with an avarge weight of 54.2 gr. My heads on the type 1 are 51 cc's.
Remember that for every shim you add to the base you need to add that volume to the combustion chamber. That drops your C/R fast. |
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| Dave_Darling |
Apr 14 2008, 09:39 AM
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#3
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914 Idiot Group: Members Posts: 14,991 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California 
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Small changes to the head CCs or the dome/dish CCs result in relatively large changes to the overall compression ratio. That's why there's no substitute for actually measuring the parts yourself.
--DD |
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| Mark Henry |
Apr 14 2008, 09:58 AM
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#4
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
What Dave said....
To figure out the dome use modeling clay, make an impression and measure. |
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| toon1 |
Apr 14 2008, 10:01 AM
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#5
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Senior Member Group: Members Posts: 1,849 Joined: 29-October 05 From: tracy,ca Member No.: 5,022 |
I have the same combo.
If memory serves, the heads where 56cc, DH was .038, compression was 8.2:1 The bump on the piston is 3cc basically this is a euro spec motor, the US engine( 3cc dish) was 7.1 euro spec( raised to pistons) 8.1 What cam are you using? BTW- you will notice a big difference with the higher comp. pistons Keith |
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