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scottc scottc is offline
Registered User
Join Date: Mar 2001
Location: mazama, washingtom
Posts: 126
Today I made another measurement of the various volumes using the Bruce Anderson method. I have nearly 100% confidence in the accuracy of this test and it yielded a compression ratio of 8.26:1.

I will talk to EBS about this. I too have bought a lot of stuff from them over the past 10 years and always found them to give great service. My piston and cylinder box has the correct part number so I am sure they are the correct part too.

My heads probably started out with 68ml combustion chambers but I didn't measure them before having machined this time and this engine had been apart once (at least) before I tore it down so the heads may have been machined in the past.

My combustion chambers are 66ml now and with the 10.6ml dome I can see no way to achieve the desired compression ratio of around 9-9.25:1. As you note it will take a substantial increase on dome volume to get to the advertised compression ratio with a 68ml combustion chamber. I calculate that it would require about a 13ml dome to get me to 8.5:1 with my 66ml chamber.

My head may have been cut in a previous rebuild but it sure looks like taking another .030" of the surface would bring me really close to the valves.

By my measurements and calculations each .010" cut on the heads will only reduce my combustion chamber volume by .36ml. Taking the full max cut of another .030" would only get me a reduction in chamber volume of 1.1ml. No where the 3ml I need to even get to the advertised 8.5:1.

I sure do appreciate the input you guys are giving. It is causing me to think more about this and spend more time on my measurements and calculations.
Thanks a lot,
73S sunroof coupe 68k second owner
73E driver/project
Old 09-15-2005, 08:27 PM
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