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Re: Cranking Compression?
[Re: roadhazard]
#641578
03/16/10 09:42 AM
03/16/10 09:42 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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OP
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Posts: 52,972
Romeo MI
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If anyone knows their cranking compression and can test that calculator PLEASE let me know if its even close 
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Re: Cranking Compression?
[Re: cl440]
#641580
03/16/10 09:51 AM
03/16/10 09:51 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Quote:
It is a bit confusing to me? For stroke it says "Same units as rod length" and for Rod length it says "Same units as stroke" so do I enter rod length for stroke and stroke for rod length? 
I was thinking they meant metric or american 
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Re: Cranking Compression?
[Re: MR_P_BODY]
#641581
03/16/10 10:00 AM
03/16/10 10:00 AM
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Joined: Feb 2003
Posts: 2,563
S.E. Michigan
cl440
master
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master
Joined: Feb 2003
Posts: 2,563
S.E. Michigan
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Quote:
Quote:
It is a bit confusing to me? For stroke it says "Same units as rod length" and for Rod length it says "Same units as stroke" so do I enter rod length for stroke and stroke for rod length?
I was thinking they meant metric or american
You may be correct?
I can say that our 528 Aluminum block has 155# of cranking pressure with the engine warm. This is with a tight lash long duration (290 @ .050) .650 lift solid cam and 13:1 compression and 440-1 heads. Is that where it is supposed to be???? I dont know for sure but we were happy with its performance and it made its fastest pass of the season at the last race last year. 
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Re: Cranking Compression?
[Re: MR_P_BODY]
#641582
03/16/10 10:04 AM
03/16/10 10:04 AM
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Joined: Feb 2004
Posts: 1,093
Long Beach, CA
Mike Swann
super stock
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super stock
Joined: Feb 2004
Posts: 1,093
Long Beach, CA
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Mike,
If you can use an excell spead sheet, pm me your private email address and I will send you a file that will do this.
8.30's @3400 lbs
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Re: Cranking Compression?
[Re: cl440]
#641583
03/16/10 10:09 AM
03/16/10 10:09 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Well it says for mine I should be seeing 307 psi cranking pressure(no way) I just did a compression test and its 150 in 1 cyl and as high as 175 in another with a average of 165 and based on the cranking pressure I would have 9.4 compression ratio.... I'm going to do a leak down in a little bit also... I know when I built the engine I had a leak rate of just under 3% (between 2.5 to 2.8 percent)
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Re: Cranking Compression?
[Re: Mike Swann]
#641584
03/16/10 10:10 AM
03/16/10 10:10 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Quote:
Mike,
If you can use an excell spead sheet, pm me your private email address and I will send you a file that will do this.
Thanks Mike
mracerraff@aol.com
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Re: Cranking Compression?
[Re: cudadon]
#641586
03/16/10 10:15 AM
03/16/10 10:15 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Quote:
mike compr. is a relative test. cam timing / bleed off has a lot to do with it. if the cyls are within 10-15% thats ok. leak down will tell if the cylinder/valves are sealing good. Don
That I know and thats why I dont want to go by that
calculator above... it doesnt ask the IVC point which
is a must know
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Re: Cranking Compression?
[Re: cudadon]
#641587
03/16/10 10:18 AM
03/16/10 10:18 AM
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Joined: Jan 2003
Posts: 2,930
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,930
A shed in England
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I don't know how it did it  On the gauge we had around 125 psi (cam installed as per card) the calculator showed 126psi
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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Re: Cranking Compression?
[Re: Dodgem]
#641589
03/16/10 10:28 AM
03/16/10 10:28 AM
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Joined: Jan 2003
Posts: 2,930
A shed in England
Tig
master
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master
Joined: Jan 2003
Posts: 2,930
A shed in England
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Quote:
This one seems to be real close
http://www.rbracing-rsr.com/comprAdvHD.htm
30+ psi off with that one I'm scratching my head now 
'74 Challenger..9.46 @ 145.9 1/4, 6.001 @ 118 1/8 so far. 4023lb !!! # N/A, Marsh performance 655ci, Indy Maxx, T/R, Indy 600-13 X's, Street legal, pump gas, full interior, Cal-Tracs, mufflers, 3:73's and real 10.5 radials.
9.51 @ 142.4 1/4, 6.003 @ 114 1/8 with our old mule KB, 572-13, 580 wedge.
RHD '68 Barracuda Fastback 323ci street/strip. Best ET 13.88 @ 99.03
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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: 2,516
PA
moparacer
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master
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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
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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
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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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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
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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
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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
I Live Here
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I Live Here
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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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Re: Cranking Compression?
[Re: MR_P_BODY]
#641613
03/16/10 07:29 PM
03/16/10 07:29 PM
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Joined: Nov 2009
Posts: 3,410
Belpre,Ohio
CHAPPER
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master
Joined: Nov 2009
Posts: 3,410
Belpre,Ohio
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I don't understand any of this stuff you all are WORRYING about. If the engine was put together and you KNOW what the static compression is/was/should be,,,you are not going to change that figure with all these 'calculations'. A leak-down test will show you if there is a problem in the valves/rings/headgaskets etc. Why worry and ask questions about your engine? If the leakage is high,,you have a problem in that cylinder.....simple enough I think.
If you like drag racing, support your local track.
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Re: Cranking Compression?
[Re: CHAPPER]
#641615
03/16/10 08:12 PM
03/16/10 08:12 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Quote:
I don't understand any of this stuff you all are WORRYING about. If the engine was put together and you KNOW what the static compression is/was/should be,,,you are not going to change that figure with all these 'calculations'. A leak-down test will show you if there is a problem in the valves/rings/headgaskets etc. Why worry and ask questions about your engine? If the leakage is high,,you have a problem in that cylinder.....simple enough I think.
Pretty simple really.... I was going to do a compression
test and wanted to know what it should be... thats
all, I wanted to do the compression test before I
pulled the rockers to do the leak down
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Re: Cranking Compression?
[Re: emarine01]
#641617
03/16/10 08:52 PM
03/16/10 08:52 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
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Quote:
I think once you have your intake closing point close for the calc it should fall with in 10 psi of your gauge reading, the calcs are a little confusing on the duration methods 
It came real close once I added the 40* (which I didnt
read before)... I guess you need to read the directions...LOL
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Re: Cranking Compression?
[Re: mopar dave]
#641620
03/17/10 01:38 AM
03/17/10 01:38 AM
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Joined: Oct 2007
Posts: 4,209
New York
polyspheric
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master
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Posts: 4,209
New York
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whats the volume to pressure index representing or what does it mean?
That's so kewl!
They "borrowed" it from my (copyright-protected) site.
It's the DCR times the actual trapped cylinder volume times a .6% correction factor to approximate low speed torque for converter stall purposes,etc.
Boffin Emeritus
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