Piston to head minimum?
#2895200
03/03/21 01:27 PM
03/03/21 01:27 PM
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Joined: Jan 2003
Posts: 10,016 Frostbitefalls MN (Rocky&Bullw...
gregsdart
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OP
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Frostbitefalls MN (Rocky&Bullw...
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Looking for input on where i should set piston to head clearance. 440-1 heads, molnar 7.1 h beams, Gibtech custom pistons line2line coated, stroke 4.315, bore 4.500. Power should be 925 hp, shift at 7400 max rpm 7600 rpm limit, trap rpm 7500 max. Digital 7 MSD for a rev limiter. What have you run at 4.5 bore and 7500 rpm?
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Piston to head minimum?
[Re: Cab_Burge]
#2895322
03/03/21 06:35 PM
03/03/21 06:35 PM
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Joined: Jan 2003
Posts: 10,016 Frostbitefalls MN (Rocky&Bullw...
gregsdart
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Cab due to the large bore i am guessing .040 may or may not be safe. I was running .045 with the iron block. I assume i can go .040 cold with the aluminum block? Never run one before.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: Piston to head minimum?
[Re: gregsdart]
#2895372
03/03/21 07:54 PM
03/03/21 07:54 PM
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Joined: Aug 2003
Posts: 43,285 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,285
Bend,OR USA
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On my deal I would rock the pistons over both ways to get the piston edges up as high as they would go at TDC use that for making .035 and .040. I've never warmed up a aluminum block enough to see how much the deck of the block grows in height in relation to the sleeves, rods and pistons at TDC from room temps to above 160 F
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: Piston to head minimum?
[Re: gregsdart]
#2895410
03/03/21 09:42 PM
03/03/21 09:42 PM
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Joined: May 2006
Posts: 740 WA
JD Dart
super stock
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super stock
Joined: May 2006
Posts: 740
WA
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II run .040 with 4.5 bore Indy block no witness marks. Thru the traps at 7700
Last edited by JD Dart; 03/03/21 09:44 PM.
best so far 8.53 @ 158.59 MPH 60'1.240
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Re: Piston to head minimum?
[Re: gregsdart]
#2895423
03/03/21 10:49 PM
03/03/21 10:49 PM
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Joined: Nov 2015
Posts: 883 Missouri
jwb123
super stock
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super stock
Joined: Nov 2015
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Missouri
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I think the rule that with steel rods, .040 is ideal and .060 for aluminum rods is pretty much spot on, first from my personal experience. And a few years ago I built a 512, with a world products aluminum block, aluminum rods, and aluminum heads. I knew the .060 rule for those rods, but I pondered about the aluminum block and it's affect on the clearance. WELL, my son is a mechanical engineer and I called him and asked him to calculate the required clearance, he said he needed the aluminum alloy numbers, and some other measurements, after he did the calculations, he came up with .058 for my engine. So I just figure the .060 is a pretty iron clad result.
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Re: Piston to head minimum?
[Re: JD Dart]
#2895576
03/04/21 11:41 AM
03/04/21 11:41 AM
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Joined: Jan 2003
Posts: 19,382 Las Vegas
Al_Alguire
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The consensus on what is a safe number is going to be .050" for an aluminum rod and .040" for a steel rod. The reason being is you need to have some "wiggle" room. Things many don't account for is skirt design, and piston to wall, as well as ensuring the stroke is equal on all cylinders and the type of material used for the rods etc. So I think you will find those to be the most common numbers thrown around out there.
I have run as little as .040" aluminum block aluminum rod with no issues on my sruff. We run the Vette even tighter at .033" with an aluminum block and rods too at 10,000rpm. But alot of things have to be perfect to get away with that tight of a clearance. When trying to get to 18-1 compression you have little choice but to push things a bit.
"I am not ashamed to confess I am ignorant of what I do not know."
"It's never wrong to do the right thing"
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Re: Piston to head minimum?
[Re: gregsdart]
#2895661
03/04/21 02:24 PM
03/04/21 02:24 PM
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Joined: May 2006
Posts: 740 WA
JD Dart
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super stock
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WA
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Aluminum block Molnar steel rods 4.250 stroke
best so far 8.53 @ 158.59 MPH 60'1.240
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Re: Piston to head minimum?
[Re: JD Dart]
#2897152
03/08/21 04:12 PM
03/08/21 04:12 PM
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Joined: Jan 2005
Posts: 12,423 Kalispell Mt.
HotRodDave
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Kalispell Mt.
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I have run as low as .028 in a SB with no contact. That being said, it's gonna depend on bore size, and bore clearance, bearing clearance, rod material and RPM. Also remember on an aluminum block the clearance with steel rods will grow as it warms up, aluminum rods should grow at a similar rate and keep clearance about the same.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Piston to head minimum?
[Re: HotRodDave]
#2897213
03/08/21 08:28 PM
03/08/21 08:28 PM
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Joined: Oct 2007
Posts: 4,210 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,210
New York
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The lightest contact (-.001") won't even leave witness marks. It may slightly collapse the normal .006" ring to groove vertical clearance and reduce ring seal. If it continues the land will fracture.
There are too many variables to have more than a range. A 2" long skirt, .001" wall clearance, 2:1 rod ratio, and 3.50" bore with pin offset can run tighter than 1" long skirt, .005" wall clearance, 1.5:1 rod ratio, and 4.60" bore with centered pin.
Boffin Emeritus
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Re: Piston to head minimum?
[Re: quickd100]
#2897584
03/09/21 11:31 PM
03/09/21 11:31 PM
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Joined: Feb 2006
Posts: 474 Alberta, Canada
451Guy
mopar
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mopar
Joined: Feb 2006
Posts: 474
Alberta, Canada
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With a .039 head gasket I like to put the piston .003 - .005 in the hole. .000 deck with a .045 gasket.
Thanx 451 Guy
512 cu in 71 Demon Super Street Car - NO LONGER - Broke Crank Best ET 9.57 @ 139.96
451 cu in Pump Gas - 71 Demon Super Street Car Best ET 9.99 @ 136.80
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