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Compression ratio screw up
https://www.slantsix.org/forum/viewtopic.php?t=22142		 Page 1 of 1
Author:  6>8 [ Tue Mar 06, 2007 11:42 pm ]
Post subject:  Compression ratio screw up
When I had my new slant built, I used a head that someone told me had .080 planed off, and I bored the engine .060 over. I was thinking I'd get somewhere around 9.8:1 or so compression range. Well, I just took his word for it and didn't actually measure the heads :oops: and now the CR is sitting at nearly 11:1 :shock: . The Cam has 435 lift and 252 duration. Right now I have the timing set to 0* advance and of course running premium 91 but it's California blend. I plan on getting a water/methanol injection so I can run pump gas, but until then am I in danger of destroying my engine?
Author:  bwhitejr [ Wed Mar 07, 2007 3:54 am ]
Post subject:  Cr?
I don't know how you got there with only 0.080 off of the head and 0.060 over pistons. How are you measuring the new CR with out CC'ing the heads? Cylinder pressures don't work for calculating CR.

bwhitejr
Author:  Charrlie_S [ Wed Mar 07, 2007 4:55 am ]
Post subject: 
How many CC's are the combustion chambers? How thick is the head gasket? How far down from the top of the block is the top of the piston? Without these measurements, along with the bore and stroke, there is no way to determine compression ratio. You are just guesing. I have seen the CC's of a slant head vary by 10 CC's between different stock heads
Author:  6>8 [ Wed Mar 07, 2007 8:03 am ]
Post subject: 
Ah, that'd be my ignorance coming in to play. Yeah, I tried to use cranking pressure to find the compression. Life is always finding new and inventive ways to remind me of how much I don't know. I bought this car to learn how to work on (i've never worked on a car before in my life) and dove in with a haynes manual and the forums. Thanks for your help!
Author:  Doc [ Wed Mar 07, 2007 8:15 am ]
Post subject: 
What are the cranking compression test readings you are getting?
Are your getting a lot of spark knock?
How does the engine run otherwise?
DD
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