cranking compression
#1377566
01/28/13 03:08 PM
01/28/13 03:08 PM
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Joined: Sep 2006
Posts: 1,139
West Tennessee
rbstroker
OP
super stock
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OP
super stock
Joined: Sep 2006
Posts: 1,139
West Tennessee
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I've asked this question before on another forum, but never got an answer. I know that the dynamic compression ratio is what determines what grade fuel is necessary, but what should the DCR and cranking compression be for the different grades of today's gasoline (87, 89, 91 octane)?
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Re: cranking compression
[Re: rbstroker]
#1377569
01/28/13 04:55 PM
01/28/13 04:55 PM
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Joined: Aug 2011
Posts: 2,855
Pattison Texas
CSK
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master
Joined: Aug 2011
Posts: 2,855
Pattison Texas
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the gear ratio,converter,weight of car,& the comp ratio also play a role in your question.
1968 Charger COLD A/C Hilborn EFI
512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim
2020 T/A 392 Stock 11.79 @ 114.5
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Re: cranking compression
[Re: CSK]
#1377570
01/28/13 04:57 PM
01/28/13 04:57 PM
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Joined: Jun 2008
Posts: 3,916
usa
lewtot184
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Posts: 3,916
usa
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Re: cranking compression
[Re: lewtot184]
#1377571
01/28/13 09:28 PM
01/28/13 09:28 PM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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Is the long block together or are you still in the planning stages? If together what SCR did you measure?
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Re: cranking compression
[Re: rbstroker]
#1377574
01/29/13 11:58 AM
01/29/13 11:58 AM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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unfortunately I am not a cam guy so I dont have a specific recommendation but with 7.31 dynamic I sure think you could go milder for more bottom end. I'm not sure the 528 would be a good choice. What was the SCR? & what calculator did you use to get the DCR? You mentioned the .050 lift & reportedly the calculators such as the ones at Wallace racing use lift @ .005 which gives a more accurate DCR figure. Sorry no help but here's a BTT. EDIT just reread & saw the 3.23's & I'll emphatically say avoid the 528 (& I'm not a cam guy)
Last edited by RapidRobert; 01/29/13 01:57 PM.
live every 24 hour block of time like it's your last day on earth
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Re: cranking compression
[Re: RapidRobert]
#1377575
01/29/13 02:08 PM
01/29/13 02:08 PM
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Joined: Feb 2003
Posts: 12,675
Columbia, CT
moper
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I Live Here
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Columbia, CT
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Please be detailed and tell us what your engine is now. Piston choice? deck height? head gasket used? head type (p/n)?
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: rbstroker]
#1377576
01/29/13 03:22 PM
01/29/13 03:22 PM
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Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
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master
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
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So your saying you have stock stroke 440 with 8.3 to 1 compression giving a dynamic of 7.3 to 1 and 140 cranking with aluminum heads?? I would like to see the total workup on the engine, heads, exhaust and torque converter?  Can't see where a .528 would perform much different maybe a few more ponies but even less bottom end but mostly the same. If you want more bottom end assuming the racer brown cam is 108 LSA advance the install to 102 
Last edited by Dodgem; 01/29/13 03:28 PM.
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Re: cranking compression
[Re: rbstroker]
#1377577
01/29/13 03:43 PM
01/29/13 03:43 PM
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Joined: Oct 2006
Posts: 3,054
USA
b54406barrel
master
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master
Joined: Oct 2006
Posts: 3,054
USA
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When gas got spendy in the 80's, I rebuilt my 440-6 engine to pretty much stock except with a set of low compression pistons. I measured it up & it was in the 8.5-6 range. I finally used a hughes cam with these specs, after running a tp-238 (230 @.050/480) for several years ;
Camshaft Technical Details
Intake Valve Lift 1.5 .470"
Exhaust Valve Lift 1.5 .506"
Intake Duration at .050" 215°
Exhaust Duration at .050" 223°
Lobe Separation Angle 112º
Intake Opening at .050" -1.5° BTC
Exhaust Opening at .050" 46.5° BBC
Intake Closing at .050" 36.5° ABC
Exhaust Closing at .050" -3.5° ATC
Cranking compression was 150 or so, with the second cam. Runs just fine on 87, total mechanical advance of about 34-6%.
Whoops, I didn't mean spendy in the 80's, I meant crappy!
Last edited by b54406barrel; 01/30/13 07:01 PM.
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Re: cranking compression
[Re: rbstroker]
#1377579
01/30/13 12:14 AM
01/30/13 12:14 AM
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Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
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Joined: Mar 2008
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Ontario, Canada
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well the .528 is 112 LSA and 241 @ .050
that racer brown with 238 duration should be fine but with that compression, 4 speed and gear and a 493 inch I would maybe advance it 102 but 105 should work real nice with 89 maybe even 87.
Last edited by Dodgem; 01/30/13 12:20 AM.
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Re: cranking compression
[Re: rbstroker]
#1377580
01/30/13 05:00 PM
01/30/13 05:00 PM
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Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
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master
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
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On running numbers on My EA dyno I would leave the Racer brown installed where it is on a 383 or 440 maybe more advance but not on a 493. Should give you 450 foot lb @ 2500 and peak torque 540 @ 3500. Peak hp at 5000 so a 5500 all out shift point?? the solid .528 would give about 3 to 4 more hp and about the same more in torque not sure the switch to solid would be worth it??
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