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Re: How much compression is really enough?
[Re: DRDart]
#818103
09/30/10 10:15 PM
09/30/10 10:15 PM
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Joined: Jul 2008
Posts: 30,451
Florida STAYcation
dOoC
The village idiot's idiot
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The village idiot's idiot
Joined: Jul 2008
Posts: 30,451
Florida STAYcation
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Quote:
16-1 Might be too much 
NOT running E85 and a big gear and open headers !!
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Re: How much compression is really enough?
[Re: frank]
#818108
10/01/10 12:43 AM
10/01/10 12:43 AM
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Joined: Aug 2003
Posts: 43,223
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,223
Bend,OR USA
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I forgot to mention, besides I had rambled on long enough on that post, that when I hopped my 512 up three years later I had switch cylinders heads from the big valve ported iron 906 heads (OEM productions ones) to a set of Eddy RPM CNC ported by Jeff at MCH and I swapped the crank out from the Ohoi Crankshaft CO. crank 4.25 stroke  to a Chinese imported 6 bolt 4.150 440 crank that I had offset ground to 4.300 stroke(+.050  ) and modified to match the balance and clear in my motor by the same shop that had prepared the 4.25 origunally. It bolted right in with no hassles at all  That moved the 22.0 cc dihed piston from -.025 in the cylinders to zero deck bumping the compression from 9.25 to to 10.29 to 1, it also increased the C.I. from 512 to 518. I reused the same rings, bearings, rods and pistons and the head gaskets No other changes other than the crankshaft and cylinder heads. I had swapped the cylinder heads onto the motor the previuos winter  Those heads pick the cars ET and MPH up by about .3 ET and almost three MPH I dyno tested the motor here in Oregon during the winter of 2006- 2007 on the local Studka engine dyno using Oregon 92 octane pump gas bought at a local Chevron station, nothing special The motor made a best of 718 to 720 HP at 5800 RPM on two different days and 644 FT lbs at 4700 RPM several times This is the same Comp Cams solid roller as before, 260 degrees at .050 intake ground on 108 LSA with .710 net lift at the retainers using the Harland Sharp 1.6 ratio rockers( which measured out to be 1.65 net actual ratios ) Put the biggest street and strip shelf cam you can get or contact me if you want a really good custom ground hydraulic roller cam made
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: How much compression is really enough?
[Re: frank]
#818110
10/01/10 12:26 PM
10/01/10 12:26 PM
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Joined: Jan 2003
Posts: 16,928
NC
440Jim
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 16,928
NC
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Quote:
Thank you for your replies. The cam I was looking at is a Comp hyd roller
549/544 lift
242I 248E duration at .050
Again thanks
That will be real mild in a 500 inch motor. They like to eat duration for breakfast. IMO, cam duration and compression ratio depend on each other. Also remember aluminum heads will tolerate CR (octane need) better than iron heads. And I think your altitude will tolerate a bit more CR than sea level also. Also, when comparing duration of a solid lifter cam to a hydraulic, the lash of the solid lifter will make the duration "feel" smaller, maybe 5-7 degrees? So a solid 260 might feel more like a hydraulic 253.
My street car 440 has iron heads at sea level (80 ft), 257 deg solid lifter flat tappet cam, IRON heads, and 10.75 CR. Pump gas all the way.
For your application, 260ish duration at 0.050" solid lifter cam, 11.0 CR (10.5 is OK with the smaller cam). You could likely get away with even more CR, so I think this is conservative and will work great.
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Re: How much compression is really enough?
[Re: ademon]
#818112
10/01/10 01:52 PM
10/01/10 01:52 PM
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Joined: Mar 2007
Posts: 3,285
West Coast, USA
jbc426
master
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master
Joined: Mar 2007
Posts: 3,285
West Coast, USA
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Why straight pump gas in your hotrod? How many tankfuls of gas are you planning on burning through this thing a month? Go high compression and add some good gas to that pump piss!
1970 Plymouth 'Cuda #'s 440-6(block in storage)currently 493" 6 pack, Shaker, 5 speed Passon, 4.10's
1968 Plymouth Barracuda Convertible 408 Magnum EFI with 4 speed automatic overdrive, 3800 stall lock-up converter and 4.30's (closest thing to an automatic 5 speed going)
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