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Old 06-13-2010, 09:33 AM
stoney 81ta's Avatar
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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

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Last edited by stoney 81ta; 06-13-2010 at 09:43 AM.
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Old 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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Old 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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Old 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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