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By Butch Lawson - 7 Years Ago
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I guess I am being cheap, but I am trying to put a 312 together using what I already have and I need advice from somebody who is more knowledgeable than me. (which is just about everybody on here  The block has been zero decked and bored .040 and I am using ECZ-G heads, making my static compression ratio 10.3 if I am using the calculator right. The cam I have has an intake closing of 39 ABDC, making the dynamic compression ratio 8.8. My question is, how much can the cam be retarded to reduce the DCR to a livable level for a street engine and not kill its power? Should I bite the bullet and get another cam? If so, recommendations? The engine will be going in front of a Mustang 5 speed in a '46 Mercury coupe (about 3200 lbs). Cam specs: Lobe Center Line---Intake 106/Exhaust 110 Lobe Separation 108 Lift 454 with 1.53 rockers Duration 226/226 @ .050 ( 259/259 @ .020) Intake Open 7 BTDC Close39 ABDC Exhaust Open 43 ATDC Close 3 ATDC Thanks in advance for any help or advice. |
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By charliemccraney - 7 Years Ago
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I think you forgot the head gasket volume in the static compression calculation. Assuming 10cc for the head gasket, I come up with about 9.3:1. I'll let someone else answer the rest.
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By Butch Lawson - 7 Years Ago
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I didn't see any place to enter the head gasket cc's on any of the calculators I looked at Charlie. They asked for the head gasket thickness, and the head gasket bore diameter. I sure hope I have calculated wrong!!
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By charliemccraney - 7 Years Ago
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Something is wrong with that calculation, unless perhaps you had the heads milled to reduce the chamber volume. Gasket bore diameter also doesn't work with a Y because of the odd shape of the cylinder cutout in the gasket. If you used piston bore for that, then it would come out to a smaller volume, which will increase the compression calculation.
Ted has an article about head gaskets, and their volumes. Take a look at that: http://www.eatonbalancing.com/2012/06/30/head-gasket-volume-calculation/
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By Butch Lawson - 7 Years Ago
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Charlie, I went back to my calculator and added 10 cc's to my combustion chamber, and used a head gasket bore size of 4.040 (same as cylinder bore) and got a static compression of 9.250 and a dynamic of 7.926. If this is proper calculation, I am very happy.
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By charliemccraney - 7 Years Ago
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Cylinder bore is 3.840" I'm still not sure if that will work out. It seems like it would effectively double up the head gasket volume, although static compression does seem about right.
Is the calculator you are using online and do you have the link?
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By Butch Lawson - 7 Years Ago
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You're right Charlie. Bore was a mistype. Was thinking about a Windsor I am building too. I read the article by Ted and refigured and got a static of 8.5 and a dynamic of 7.3. Sounds more streetable. I guess I messed up my calculations and got my numbers all wrong. I think I got it now. Thanks for helping me get myself all sorted out.
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By Ted - 7 Years Ago
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Butch. In looking at your open/close specs, they are for the cam timing as measured at 0.050” lobe lifts and not at 0.020”. In running the calculation for the intake closing at 0.020” with a 259° advertised duration, I get 53½° ABDC. That’s with the camshaft installed 4° advanced. With the camshaft installed straight up or at 108° intake lobe centerline, I get the intake closing event occurring at 57½° ABDC.
Here are the SCR and DCR values with your camshaft with the lash set at 0.020” and assuming the heads have 69cc combustion chambers. Both the 4° advance and straight up numbers are posted to give you an idea of what happens with the DCR as the camshaft is moved around.
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By Butch Lawson - 7 Years Ago
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Thanks Ted and Charlie for your help. I'm hoping this makes a good torquey, pump gas friendly, engine.
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