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Re: Cranking Compression?
[Re: MR_P_BODY]
#641594
03/16/10 11:20 AM
03/16/10 11:20 AM
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Joined: Mar 2003
Posts: 2,521
PA
moparacer
master
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master
Joined: Mar 2003
Posts: 2,521
PA
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Wallace has about every calculator you would ever need.
They have a dynamic and effective comp calculator.
Last edited by moparacer; 03/16/10 11:22 AM.
67 Barracuda street/bracket car 11.27-119
68 Dart 502 BB 8.70s-152
414 cid SB Dragster 7.65-174
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Re: Cranking Compression?
[Re: moparacer]
#641595
03/16/10 11:28 AM
03/16/10 11:28 AM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
moper
I Live Here
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I Live Here
Joined: Feb 2003
Posts: 12,675
Columbia, CT
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I use the KB site one. It's simple (aside from remembering the negative figure for dome volume/positive deck height) and is within 20psi of my results in most cases.
Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.
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Re: Cranking Compression?
[Re: mopar dave]
#641597
03/16/10 12:28 PM
03/16/10 12:28 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
OP
Master
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OP
Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Well with checking all the different calculators and doing a compression check MAYBE I dont have the compression I thought I had.... I cant believe I was that far off when I checked the measurements when I built it.... it comes up with a 9.5 compression ratio on just about all of them..... I did a leak down and that showed pretty decent, from 2% to 7%  ... no wonder I'm not making the power I figure it should 
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Re: Cranking Compression?
[Re: MR_P_BODY]
#641598
03/16/10 12:34 PM
03/16/10 12:34 PM
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Joined: Jul 2004
Posts: 19,318
State of confusion
Thumperdart
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I Live Here
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Posts: 19,318
State of confusion
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Too many variables..........just test it and you`ll know for sure. My experience shows that big duration cams w/lots of overlap generally show lower numbers for example: my 360 w/a dur. of 255@ .050 cranked bet 190-200 cold. My 470 w/275-280 dur.@.050 cranks bet 170-175 and my buddys low 8-sec chevy small block w/a BIG roller(don`t remember #`s) cranks at 155 or so. 
72 Dart 470 n/a BB stroker street car `THUMPER`...Check me out on FB Dominic Thumper for videos and lots of carb pics......760-900-3895.....
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Re: Cranking Compression?
[Re: mopar dave]
#641603
03/16/10 01:54 PM
03/16/10 01:54 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
OP
Master
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OP
Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Thats the one thing ... I dont have a degree at 0, my cam card only has .050 for the valve timing and my cam is a 276/284
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Re: Cranking Compression?
[Re: AndyF]
#641609
03/16/10 04:00 PM
03/16/10 04:00 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
OP
Master
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OP
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Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
I don't see how you can work backwards to CR from cranking compression. Put a 16V system on there and the cranking compression will go up due to the faster cranking speed. Pull all the plugs and pull the carb off the intake and the cranking compression will go up a bunch. Do it warm and the cranking compression will go up.
One of the calculators stated it for a 300 crank RPM
and I am assuming they do some magic calculations to
come up with a number
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Re: Cranking Compression?
[Re: MR_P_BODY]
#641610
03/16/10 04:13 PM
03/16/10 04:13 PM
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Joined: Mar 2003
Posts: 15,491
the boonies
aarcuda
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I Live Here
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Posts: 15,491
the boonies
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i used http://www.not2fast.com/turbo/compression/cranking_pressure.shtml for intake opening I only have .050 also. in the instructions it says to add 40 (thats 20 degrees x 2) to the duration at .050 so i did and it came out to 166. my cranking pressure is surprisingly 165
It's got a cop motor, a 440 cubic inch plant, it's got cop tires, cop suspensions, cop shocks. It's a model made before catalytic converters so it'll run good on regular gas.
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Remember to add in your cam advance cause it closes the intake earlier, the calc guys left that out 
