Re: Piston massaging
[Re: fast68plymouth]
#3147818
05/31/23 01:22 PM
05/31/23 01:22 PM
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Joined: Jan 2003
Posts: 4,760 Moved to N.E. Tennessee
GomangoCuda
master
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master
Joined: Jan 2003
Posts: 4,760
Moved to N.E. Tennessee
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The pistons may actually be installed "correctly". The arrow pointing "front" does appear to be pointing to the front of the engine, if that's the engine stand I see on the right side of the pic. Someone modified those L2355 "six pack" pistons by milling a dish in them...they are normally a 4 valve relief design. I've never seen a dish like that on the "top" side of the piston before, that would ruin any quench you may have had. It's possible whoever machined the pistons put the dish on the wrong side of 4 of them. It really won't hurt anything, just not the normal way of doing it. The pistons can be swapped side to side, which will properly orient the dish and quench areas so there could actually be some benefit when swapping to closed chamber heads. The arrow would then be pointing towards the rear........ which some claim is beneficial as well. This ^^^^^ Does that trw piston have an offset pin? It's been decades since I looked at one but i don't think it is offset. I would put them with the dish facing the chamber and call it done. I don't know what the compression might be without knowing the deck ht. and the volumes of the dish, chamber and head gasket.
In theory, there is no difference between theory and practice. In practice, there is.
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Re: Piston massaging
[Re: lewtot184]
#3147838
05/31/23 02:10 PM
05/31/23 02:10 PM
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Joined: Oct 2007
Posts: 4,213 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,213
New York
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The valve relief depth show the valve stems inclined toward the exhaust side: wrong.
Boffin Emeritus
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Re: Piston massaging
[Re: polyspheric]
#3147840
05/31/23 02:20 PM
05/31/23 02:20 PM
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Joined: Jan 2003
Posts: 13,404 Marion, South Carolina [><]
an8sec70cuda
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 13,404
Marion, South Carolina [><]
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The valve relief depth show the valve stems inclined toward the exhaust side: wrong. The dish was machined in those pistons after they were bought. When new, those pistons are flattops w/ 4 valve reliefs allowing them to be installed on either bank. You can see the remnants of the other two reliefs on the dished side. If all 8 pistons had the dish cut the same way, then 4 of them will appear to be installed incorrectly if the directional arrow is pointing to the front. The other bank may have the dish in the correct orientation.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Piston massaging
[Re: jwb123]
#3147858
05/31/23 04:23 PM
05/31/23 04:23 PM
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Joined: Dec 2005
Posts: 11,739 Fulton County, PA
CMcAllister
Mr. Helpful
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Mr. Helpful
Joined: Dec 2005
Posts: 11,739
Fulton County, PA
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I always soften sharp edges. Smoother is better. Eliminate potential hot spots. Verify the extended tip plug isn't crowded.
If the results don't match the theory, change the theory.
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Re: Piston massaging
[Re: Cudatali]
#3147914
05/31/23 10:52 PM
05/31/23 10:52 PM
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Joined: Oct 2007
Posts: 4,213 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,213
New York
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If the cam, and especially the overlap window area, is smaller than optimum, radiusing & blending those sharp edges is helpful as it makes flow through the chamber more efficient. If the cam is too big: leave it along. Large chamber + low static CR: don't bother.
Boffin Emeritus
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Re: Piston massaging
[Re: Cudatali]
#3147988
06/01/23 01:28 PM
06/01/23 01:28 PM
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Joined: Jan 2005
Posts: 12,424 Kalispell Mt.
HotRodDave
I Live Here
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I Live Here
Joined: Jan 2005
Posts: 12,424
Kalispell Mt.
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[quote=LA360] The plan is to install some aluminum heads, get compression between 9.5-10.0. Install a 22X-23Xish cam and a 6bbl setup. With that being said, Would CR close to 10:1 . I shoot for between 10.530 to 10.80 to 1 compression ratio on my non ethanol 91/93 octane pump gas BB builds with aluminum heads, that has work very well for me and my customers Thanks for the advice unfortunately I have no access to non ethanol in my area. Ethanol in the fuel makes the fuel act like it has higher octane than it really does, compression can go higher with ethanol, the only concern could be fuel system corrosion but in nearly 20 years I have never had an issue running old fuel system components even my experiment with a bunch of parts and pieces in a sealed up peanut butter jar has not shown any degradation of the parts. It needs access to the atmosphere for extended periods of time to absorb moisture and that is what causes corrosion. As for messaging the pistons I always round off all the sharp edges, you never know when you might get a bad batch of fuel or maybe they are out of premium and you got to run low grade in a pinch or the fuel delivery guy acidently put some diesel fuel in the tank in the ground, maybe you decide later on down the road to put some smaller chamber heads on and the work is already done without disassembling the short block or... it is just cheap/free insurance.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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