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Re: 572 Hemi: Pump gas compression with no squish/quench [Re: hemienvy] #2630993
03/10/19 08:02 AM
03/10/19 08:02 AM
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Originally Posted by hemienvy
Thanks All.

I don't think I'm being nit-picky on the compression issue,
just cautious.

Here's a lttle more info. I don't want to take the motor
over about 6000. This should assure some good low RPM street
manners. In view of this, I won't need huge intake ports,
manifold, or carb. So all that limits cam duration to something
maybe around 250 degrees ? Less ?

That is not a big cam, so what can I get away with for
compression with aluminum heads, polished chambers and
piston tops, and zero quench ?


I am not an expert on Hemi's but do street drive a warm wedge with manual transmission. Compression that is OK for a short blast on the strip may not work for extended street driving. Heat builds up cruising and a manual transmission can let the engine lug under load. I was conservative by standards of the board with 10.2 CR and tight quench on 496 wedge. 243 @.050 fast mechanical cam. The car also has a stout cooling system that keeps temps right on the 180 stat when rolling... even driven hard. With the conservative CR I still have to watch timing. Transition from light cruise (50 deg) to WOT (34 deg) needed some care to prevent rattle. I have gradual timing curve vs RPM at WOT to prevent rattle coming out of the corners when hot lapping the road course.

First time I noticed the cruise rattle was on I8 along the Mexican border. Cruising at sea level in OD, about 95 degrees F and just starting to climb the coastal mountains. I pressed the pedal a little more and that cleared it up... I also enjoyed a fast trip to ~4,000'. When I got home I took 2 degrees timing out in that transition area.

Point is, cruising (and road racing) needs a little bit conservative CR and tune.

Re: 572 Hemi: Pump gas compression with no squish/quench [Re: ahy] #2631024
03/10/19 10:44 AM
03/10/19 10:44 AM
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polyspheric Offline
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Heat builds up cruising
... until the thermostat opens


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Re: 572 Hemi: Pump gas compression with no squish/quench [Re: polyspheric] #2631102
03/10/19 02:17 PM
03/10/19 02:17 PM
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Cylinder head temp and intake air temp have a big effect on detonation. Even with water temp well controlled, metal of the head and intake air can get hot after a long period of running.

Re: 572 Hemi: Pump gas compression with no squish/quench [Re: hemicar1971] #2631107
03/10/19 02:23 PM
03/10/19 02:23 PM
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hemienvy Offline OP
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Good Morning Hemicar,
I just logged on after a few days and saw all your PM's so I sent you one.

Re: 572 Hemi: Pump gas compression with no squish/quench [Re: hemienvy] #2631109
03/10/19 02:28 PM
03/10/19 02:28 PM
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hemienvy Offline OP
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Thanks to all who posted here, there's a lot of good info. Can only talk about it so much,
I need to get with a builder. I think I'm in the ballpark at least.

Re: 572 Hemi: Pump gas compression with no squish/quench [Re: ahy] #2631126
03/10/19 03:33 PM
03/10/19 03:33 PM
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polyspheric Offline
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Repeating it doesn't change the laws of physics. Heat doesn't "build up".


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