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  #151  
Old 23 Hours Ago
260Alpine 260Alpine is offline
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Mike, Does the 2.9 crank put the piston at zero deck without decking the block? The longer stroke will change the Dynamic number. The calculations were done with a 2.8 crank stroke. Are you sure you only have 9.3 compression? I'll run the 2.9 stroke to see the difference.
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  #152  
Old 23 Hours Ago
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MikeH MikeH is offline
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Originally Posted by 260Alpine View Post
Mike, Does the 2.9 crank put the piston at zero deck without decking the block? The longer stroke will change the Dynamic number. The calculations were done with a 2.8 crank stroke. Are you sure you only have 9.3 compression? I'll run the 2.9 stroke to see the difference.
This is planned without decking the block. I want to just square it up. I found that the '74 pistons have a different pin placement that gets it close to 0 with the 2.9 crank. Rods are the same.
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  #153  
Old 22 Hours Ago
260Alpine 260Alpine is offline
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Mike, I like to zero deck when possible also. My question is, if .090 down is stock and 8.5 to 1. I think you would be at least 10 to 1 at zero deck. Which would be fine with the Jose grind cam. I'll run simulations with 9.3 and 10.
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  #154  
Old 22 Hours Ago
260Alpine 260Alpine is offline
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Mike, Even with 5 degrees advance at 9.3 to 1 the Dynamic compression is only 6.8. At 10 to 1 it is perfect at 7.3.
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  #155  
Old 14 Hours Ago
RootesRacer RootesRacer is offline
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Originally Posted by MikeH View Post
So with my build plans; 2.9 crank,2.9 valves, .030 over bore, 0 deck height, and rough calculations show 9.3:1 CR, offy intake, Holley 390, it looks like I would need to run one tooth advanced on the cam.
You sure 1 tooth is gonna be 8 degrees?

Remember that cam degrees double the crank degrees (which is what the engine simulator uses).

You want 4 degrees at the cam to make 8 at the crank. You may be able to get there with an offset key. Otherwise you may need to make a timing adjustable cam drive or a custom cam gear.
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  #156  
Old 13 Hours Ago
260Alpine 260Alpine is offline
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One cam tooth=5.3 degrees.
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  #157  
Old 12 Hours Ago
RootesRacer RootesRacer is offline
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Originally Posted by 260Alpine View Post
One cam tooth=5.3 degrees.
So then if there are 68 teeth on the cam gear, one tooth is 10.6 degrees.
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  #158  
Old 12 Hours Ago
260Alpine 260Alpine is offline
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Yes, I see what you are saying, in crank degrees. Most chain setups have 4 crank degrees on the crank sprocket so would only move the cam 2 degrees. 10 crank degrees is a bit much and changes every thing. You would have to check piston to valve clearance for that much and the Dynamic numbers and cam specs would be way different. I would suggest an offset key or another keyway in the cam or crank gear at 4 crank degrees advanced. Thanks, RootesRacer for opening my eyes. Seems nothing is easy.
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Last edited by 260Alpine : 6 Hours Ago at 01:18 AM.
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  #159  
Old 8 Hours Ago
todd reid todd reid is offline
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Jim,

I am following this discussion with interest - very educational. So the take away from the previous exchange with RootesRacer is that previous references to advancing/retarding a cam by 4 cam degrees should really be 2 cam degrees (and 4 crank degrees)?

Is there any point to crunching the numbers on a basically stock engine, or in your experience have the factory engineers already got it right?

Thanks in advance!

TR
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  #160  
Old 7 Hours Ago
260Alpine 260Alpine is offline
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Todd, Yes, Cut another keyway in cam or crank gear or use offset key. The picture with 3 keyways on cam gear earlier in this thread. I could run the numbers for a stock cam if I knew the specs like in the Jose cam. Mustang II or Ranger? Or both. The factory engines use tame specs , compromise for emissions and economy. That last mild cam simulation is a good midrange cam.
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Last edited by 260Alpine : 7 Hours Ago at 11:56 PM.
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