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 and now the CR is sitting at nearly 11:1 . 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?

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1968 Dart 270. 225 Bored over .060, comp cam, head ported polished .080 off, SuperSix Carter BBD.

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

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'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

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

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

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!

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1968 Dart 270. 225 Bored over .060, comp cam, head ported polished .080 off, SuperSix Carter BBD.

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