Re: Milling pockets in pistons
[Re: mopfried]
#2457623
02/25/18 11:50 PM
02/25/18 11:50 PM
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Joined: Apr 2007
Posts: 289 Lowes
steve660
enthusiast
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enthusiast
Joined: Apr 2007
Posts: 289
Lowes
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Dont know how much of a decrease in comp your wanting but maybe you can try thicker head gasket. Cometic can make just about any thickness you need.
PSO headed 632 from MM. Cracked cylinder, loose valve seats, low oil pressure, low cylinder pressure. ..... Now its a door stop....
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Re: Milling pockets in pistons
[Re: mopfried]
#2457639
02/26/18 12:13 AM
02/26/18 12:13 AM
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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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Before you consider a hick gasket, what's your quench distance now? If it's at .060", you lose it completely with a thicker gasket. If you have .035-40", it will be less effective but still active. Your bob weight will change by 50% of the weight change.
Boffin Emeritus
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Re: Milling pockets in pistons
[Re: 440_Offroader]
#2457675
02/26/18 01:13 AM
02/26/18 01:13 AM
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Joined: Jan 2003
Posts: 6,591 Canton, Ohio
Sport440
master
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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Just throwing this out there. What about increasing your cylinder head cc, like deshrouding the intake valve. Not sure what heads you have if it's feasible or not. This is what I would do before messing with the pistons, that and maybe more thickness of the head gasket if you don't lose quench.
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Re: Milling pockets in pistons
[Re: mopfried]
#2457687
02/26/18 01:25 AM
02/26/18 01:25 AM
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Joined: Sep 2014
Posts: 4,457 Washington
madscientist
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master
Joined: Sep 2014
Posts: 4,457
Washington
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How much compression do you have?
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Milling pockets in pistons
[Re: mopfried]
#2457728
02/26/18 03:10 AM
02/26/18 03:10 AM
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Joined: Oct 2007
Posts: 4,213 New York
polyspheric
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master
Joined: Oct 2007
Posts: 4,213
New York
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I'd certainly look at unshrouding the valves. It's a lot of work (and should all be really close) but where and how much depends on the shape now, valve lift, stem angle, blah. Sometimes too open is a mistake, the flow leaving the seat wants to expand gradually and in the right direction, not turned loose all at once (like a vertical valve). I wrote some stuff on the subject, some of it may be relevant: http://victorylibrary.com/mopar/chamber-tech.htmGot a picture of a chamber?
Boffin Emeritus
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Re: Milling pockets in pistons
[Re: mopfried]
#2458183
02/26/18 11:53 PM
02/26/18 11:53 PM
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Joined: Jan 2003
Posts: 6,591 Canton, Ohio
Sport440
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master
Joined: Jan 2003
Posts: 6,591
Canton, Ohio
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I re-checked my calculations. I am right a 10.13 with a 70 cc head and no quench (.080). That is with a .027 thick gasket. If I mill .050 off the head the compression will go up 1 point. I believe that is too much for a iron head on pump gas. I read the info Polyspheric posted..... good info. I will buy a head gasket and see what I can come up with. Playing with the numbers I need roughly 10-11 cc less than I have if I mill the head to be closed chambered and have .033-.035" quench. Where did you think you were? Iron heads, 9.5 comp is the safe rule of thumb. If it were me , id go for quench, mill .030/.040 and then deshroud the head. I haven't done any of the math except the quench, trusting you on the comp figure. But quench is always better if its in range and you can figure out how to get it.
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Re: Milling pockets in pistons
[Re: mopfried]
#2458546
02/27/18 07:47 PM
02/27/18 07:47 PM
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Joined: Oct 2003
Posts: 3,698 NE Oklahoma
Von
master
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master
Joined: Oct 2003
Posts: 3,698
NE Oklahoma
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Call rebco machine, think he is Wichita. He cut deeper pockets in two sets of my pistons. He does great work.
72 RR, Pump gas 440, 452s, 3800 lbs, Corked, ET Radials,. 11.33@117.72.
Same car, bone stock 346s, 9.5 comp, baby solid. 12.24@110.
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