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06-13-2010, 09:33 AM
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This may be a stupid question
I currently using a 305 sbc with 2102 edelbrock cam,2101 intake and 1406 carb though headers and dual exhaust in a 1981 trans.Now i did some desktop dynoes on the setup i have and notice that increasing the stock heads compression i will have some good gains from 8.0 compression to 9.50 compression.Now my question is if possible to do a head gasket change is it possible that it will raise the compression.Here is the dyno results form 8 to 9.50 compression.2000 122.232239 320.859619
2500 156.955475 329.606506 3000 191.165466 334.539551 3500 222.685989 334.028992 4000 242.980362 318.911713 4500 243.513763 284.099396 5000 226.300232 237.615250 5500 203.369583 194.125519 6000 166.980713 146.108124 6500 132.439270 106.970177 7000 87.705399 65.779053 7500 42.571686 29.800180 8000 0.000000 0.000000 8500 0.000000 0.000000 9000 0.000000 0.000000 9500 0.000000 0.000000 10000 0.000000 0.000000 10500 0.000000 0.000000 11000 0.000000 0.000000 these are the results at 8.0 compression. 2500 146.209290 307.039520 3000 177.418610 310.482574 3500 206.258270 309.387390 4000 222.595108 292.156067 4500 218.560974 254.987808 5000 199.563812 209.542007 5500 175.526459 167.547989 6000 138.810196 121.458923 6500 103.396904 83.512886 7000 57.704296 43.278221 7500 11.868833 8.308183 8000 0.000000 0.000000 8500 0.000000 0.000000 9000 0.000000 0.000000 Last edited by stoney 81ta; 06-13-2010 at 09:43 AM. 
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06-13-2010, 10:13 AM
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If you increase the cr of an engine 2 whole ratios (8.0:1 to 10.0:1) the power will increase by 6.5%.
Just switching the head gasket on a 305 with a thin one, alone won;t increase the cr that much. About .5 of a ratio if you replace a .041" gasket with a thinner .015" gasket. You would need to run higher octane fuel to avoid engine knock. Higher operating cost.
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06-13-2010, 10:36 AM
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Thanks for your input f-bird but i was hping to go from 8 to possibly 9-9.50 compression to keep in the lower octane gas.Is that doable and also how work is involved in doing the switch.
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06-13-2010, 10:53 AM
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To see such a cr increase on a 305 you would need to switch the gasket from say a .041" to a .015" shim gasket AND max flat mill the heads from 58cc to 51cc. (need to flat mill the heads to the max right down to the spark plug boss edge / intake valve seat edge)
It would be a real waste to pass up porting the heads to further increase power, while they are off the motor. The combined power increase of the cr jump and the max effort home head porting would make the job more worth while.
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