compression ratio - calculatons
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From: Quaker Hill ,CT U.S.A.
compression ratio - calculatons
Is there any way to determine the compression ration of an engine by the CRANKING compression psi?
lets say I have a 360 that has 120 psi on every cylinder and a 410 that has 170 on every cylinder .
does this make any sence to anyone .
lets say I have a 360 that has 120 psi on every cylinder and a 410 that has 170 on every cylinder .
does this make any sence to anyone .
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From: Quaker Hill ,CT U.S.A.
that is what I was thinking - I dont have any books that list the compression ratio for my engines I am thinking that the 410 is somewhere in the neighborhood of 10.0 to 1 but I really dont know for sure .
the problem is the gasoline around here stinks and ( with the stock advance curve in the dizzy .) the 410 pings bad I have played with it a lot and basically to get it not to ping I have to tune to to be pretty pigged out . I am running 93 octane .
My 1975 100 with the 360 will run on regular - 87 octane but likes 89 better .
ONe other thing I would like ot point out is that my owners manula for the 1975 says that you should run at LEAST 91 octane in the truck . does anyone know if they rated the octanes differently back then ?
The manual also says that the engine will run on leaded , low leaded and unleaded - does that make a difference in octane?
the problem is the gasoline around here stinks and ( with the stock advance curve in the dizzy .) the 410 pings bad I have played with it a lot and basically to get it not to ping I have to tune to to be pretty pigged out . I am running 93 octane .
My 1975 100 with the 360 will run on regular - 87 octane but likes 89 better .
ONe other thing I would like ot point out is that my owners manula for the 1975 says that you should run at LEAST 91 octane in the truck . does anyone know if they rated the octanes differently back then ?
The manual also says that the engine will run on leaded , low leaded and unleaded - does that make a difference in octane?
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From: Evanston, WY
I had the very same question years ago, and unfortunately the answer is no. At first glance it seems like you should be able to compare the cranking compression to the atmospheric pressure at the time of the test and come out with a static compression ratio. But, alas, this is not to be. The reason is the cam. Both overlap and the intake valve closing event timing have an effect on how much compression is seen at low RPM. If you take the same engine with the same compression, and test the cranking pressure with two different cams you will get two different pressures, therefore, no direct relationship to the static compression ratio.
-Scouder
-Scouder
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From: Quaker Hill ,CT U.S.A.
I thought that was the case so basically the only way to get the 410 not to ping is to do a cam swap with a cam that has more "bleed off" on cranking and then play with the advance .
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From: iowa
10.5 for the 410 and hell my 390 loves 92 compared to 89. I can't believe the difference but its worth the extra 20 cents a gallon to me. Those octane boosters are junk. They barely raise crap. I have tripled the concentration and it still sucks.
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From: Evanston, WY
Originally posted by Chas1234
I thought that was the case so basically the only way to get the 410 not to ping is to do a cam swap with a cam that has more "bleed off" on cranking and then play with the advance .
I thought that was the case so basically the only way to get the 410 not to ping is to do a cam swap with a cam that has more "bleed off" on cranking and then play with the advance .
You can also retard the cam you have. This has the same effect with compression (lowering it), but will also reduce some of your low end grunt and make her run harder up top.
Other than that, the only things I can think of are to reduce timing, like you said, and run your fuel mixture on the rich side.
-Scouder
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From: Quaker Hill ,CT U.S.A.
I would like to actually advance the cam for more low end punch .
So I guess I am going to have to find a different cam - hey I like what you are doing to your truck BUT if you decide to change your mind for some reason I would love to put your 427 monster in my 65' galaxie that ol 352 is tired
- thanks for your help !
So I guess I am going to have to find a different cam - hey I like what you are doing to your truck BUT if you decide to change your mind for some reason I would love to put your 427 monster in my 65' galaxie that ol 352 is tired
- thanks for your help !
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