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11.3:1 compression ratio?

Old 12-01-2005, 11:52 PM
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Default RE: 11.3:1 compression ratio?

Well first of all you would need to know the exact measurements of each cylinder in the areas that pertain to calculating of thier respective static compression ratio's. However its really not neccessary as they very ever so slightly that it doesnt matter for anything less than a full competition engine and even then its still not a regular practice.

As far as the original question about the 11.3:1 compression ratio, it depends on many variables. The camshaft, type of heads, quality and octane of the fuel, and intended use of the engine. In your case I would say its too high for street/strip use and will require a higher octane fuel then premium pump gas. I say this because it takes a rather large cam even with aluminum heads and a ultra efficient cooling system to allow you to run a 11.3:1 compression ratio on premium pump gas. The other altertrnative would be to retard your timing and that would cause a loss of more power then would be gained by the compression increase. When calculating octane versus compression you must use the dynamic compression ratio. Doing it that way takes into account the spec's of the cam your using. Using the Dynamic Compression ratio is the best and safest way to figure out the octane requirements of an engine. Even with that you should always adjust your Dynamic compression ratio on the low side as maxing it out doesnt allow for changes in the weather and the varying quality of the gas you get at your local gas station. If you want to push it to the max allowable then I'd recommend runniong octane boost with every tankful.

Adjusting your compression ratio for the Altitude is fine if the car is never driven to any place with a lower Altitude. Thier are other much better ways to tune a car for high altitude than raising the static compression, which doesnt allow for adjustment for other altitudes. This sort of thinking works fine with a boosted car where your base compression ratio is rather low and you can increase and decrease the boost pressure to compensate for the air density of the altitude your driving in at the time.

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Old 12-02-2005, 01:08 AM
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Default RE: 11.3:1 compression ratio?

i would try to get back in ford range like 10.5:1 max....your in gm territory that high.

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Old 12-02-2005, 01:44 AM
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Default RE: 11.3:1 compression ratio?

thanks again for all the help. ill keep it right around 10:1.
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Old 12-02-2005, 06:47 PM
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Default RE: 11.3:1 compression ratio?

That was Hot Rod Magizine, 8/5 issue.
Got Dukes of Hazard on the cover.
Read the story and study it about 'pump gas race motors'. Interesting about the idea of 'quenc' chambers, Mopar racers have been doing this for years due due POS head castings......
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