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10.5 to 1 pistons #705068 05/22/10 03:47 PM 05/22/10 03:47 PM
Joined: Jan 2003 Posts: 4,978 VA DAMOPARS OP master
DAMOPARS OP master Joined: Jan 2003 Posts: 4,978 VA	If you get 10.5 to 1 pistons. How do they figure this out? Stock deck height or zero deck? Thanks

Re: 10.5 to 1 pistons [Re: DAMOPARS] #705069 05/22/10 03:56 PM 05/22/10 03:56 PM
Joined: Oct 2003 Posts: 7,506 Az Crizila master
Crizila master Joined: Oct 2003 Posts: 7,506 Az	Numbers are based on stock or Mfg. deck height - which is almost never "0" and on some SB's as much as .060" down the hole. Fastest 300

Re: 10.5 to 1 pistons [Re: DAMOPARS] #705070 05/22/10 03:58 PM 05/22/10 03:58 PM
Joined: Jan 2003 Posts: 20,624 Eagle, Idaho Neil The Doctor is in.
Neil The Doctor is in. Joined: Jan 2003 Posts: 20,624 Eagle, Idaho	A piston is a piston until you know what it's surroundings are going to be. Cylinder deck height and the piston height relative to the top of the deck at the top of the stroke, combustion chamber volume, and head gasket thickness all determine what the mechanical compression ratio is.

Re: 10.5 to 1 pistons [Re: Crizila] #705071 05/22/10 03:58 PM 05/22/10 03:58 PM
Joined: Feb 2005 Posts: 28,312 Cincinnati, Ohio Challenger 1 Too Many Posts
Challenger 1 Too Many Posts Joined: Feb 2005 Posts: 28,312 Cincinnati, Ohio	Quote: Numbers are based on stock or Mfg. deck height - which is almost never "0" and on some SB's as much as .060" down the hole. SB 10 1/2 pistons are sticking out .025-030 or so.

Re: 10.5 to 1 pistons [Re: Challenger 1] #705072 05/22/10 04:48 PM 05/22/10 04:48 PM
Joined: Jan 2003 Posts: 9,826 las vegas 70AARcuda master
70AARcuda master Joined: Jan 2003 Posts: 9,826 las vegas	I have 10.5 compression and my pistons are down .017...on a 360 with .024 head gaskets and 63 cc heads... you need to know bore how much the piston is down or out of the bore...CC of the head...CC of the head gasket.. alot of 10.5 pistons end up as 9.5 even if they are out of the bore...unless the heads are CC ... the question is what are you trying to do...or what pistons are you looking at??? Tony 70 AARCuda Vitamin C 71 Dart Swinger 360 10.318 @ 128.22(10-04-14 Bakersfield) 71 Demon 360 10.666 @122.41 (01-29-17 @ Las Vegas) 71 Duster 408 (10.29 @ 127.86 3/16/19 Las Vegas)

Re: 10.5 to 1 pistons [Re: 70AARcuda] #705073 05/22/10 06:48 PM 05/22/10 06:48 PM
Joined: Jan 2003 Posts: 4,978 VA DAMOPARS OP master
DAMOPARS OP master Joined: Jan 2003 Posts: 4,978 VA	Thanks All

Re: 10.5 to 1 pistons [Re: DAMOPARS] #705074 05/22/10 06:51 PM 05/22/10 06:51 PM
Joined: Aug 2007 Posts: 902 Seattle, WA R rss super stock
rss super stock R Joined: Aug 2007 Posts: 902 Seattle, WA	Quote: If you get 10.5 to 1 pistons. How do they figure this out? Stock deck height or zero deck? Thanks If you are looking at different manufacturers sites or catalogs you will need to search around and figure out what assumptions they are making to calculate a specific compression ratio. For example, if you go to the KB site, they will tell you what compression ratio you will get depending on the combustion chamber volume of your heads. However,what you also need to know is that they are assuming you are using 0.030 overbore pistons and that the deck clearance (including gasket) is 0.040". So in the case of KB, if you are using a 0.040" thickness head gasket, then yes you would need zero deck clearance to get the same compressin ratio as they claim for some specific combustion chamber size. Clear as mud right? From what I have seen, there is not a standard for advertised compression ratios, so you'd have to check with the specific manufacturer to figure out what deck height and gasket thickness they are basing their numbers on.

Re: 10.5 to 1 pistons [Re: rss] #705075 05/22/10 07:22 PM 05/22/10 07:22 PM
Joined: Jan 2003 Posts: 15,976 Chilliwack B.C. Canada R RUNCHARGER I Live Here
RUNCHARGER I Live Here R Joined: Jan 2003 Posts: 15,976 Chilliwack B.C. Canada	Typically the stock Chrysler pistons and aftermarket pistons of the 70's era came out at .75-1 point under advertised. 10-1 advertised were typically 9-1 or 9.25-1 with the original machining of deck heights and chamber volumes. Sheldon

Re: 10.5 to 1 pistons [Re: RUNCHARGER] #705076 05/22/10 09:32 PM 05/22/10 09:32 PM
Joined: Jan 2003 Posts: 24,562 Brookeville, Md Mr.Yuck Not enough dumb comments...yet
Mr.Yuck Not enough dumb comments...yet Joined: Jan 2003 Posts: 24,562 Brookeville, Md	20 thou in the hole w/ a steel shim gasket and 84cc heads should net you approx 10:1 [IMG]http://i66.tinypic.com/pui5j.jpg[/IMG] Coming soon!!!!

Re: 10.5 to 1 pistons [Re: rss] #705077 05/22/10 09:37 PM 05/22/10 09:37 PM
Joined: Feb 2003 Posts: 21,318 Manitoba, Canada DaytonaTurbo Too Many Posts
DaytonaTurbo Too Many Posts Joined: Feb 2003 Posts: 21,318 Manitoba, Canada	Quote: From what I have seen, there is not a standard for advertised compression ratios, so you'd have to check with the specific manufacturer to figure out what deck height and gasket thickness they are basing their numbers on. That's why the piston manufacturers publish piston compression height. This way you can do the calculations yourself: block deck height - (piston compression height + rod length + (stroke/2)) will give you how far in the hole your pistons are. However you are still making assumptions about machining variances in the rods/crank/pistons as well as you are assuming to KNOW what your block deck height is. Can't accurately just take the factory published # because the factory blocks do vary in deck height.

383man [Re: DaytonaTurbo] #705078 05/22/10 11:57 PM 05/22/10 11:57 PM
Joined: Jan 2003 Posts: 27,421 Balt. Md 3 383man Too Many Posts
383man Too Many Posts 3 Joined: Jan 2003 Posts: 27,421 Balt. Md	Piston manufactors give advertised comp ratio on the assumption of all stock specs. And of course on the BB Mopar the year and head will need to be known. I always figure I will have to do final machine work to get the comp I want with any piston. I always like to cc my heads and know my deck height before I get pistons but no matter how you figure it you always have to assemble the pistons in the shortblock and take final measurements to get the exact comp you are after. Ron Last edited by 383man; 05/22/10 11:59 PM.

Re: 383man [Re: 383man] #705079 05/23/10 01:32 AM 05/23/10 01:32 AM
Joined: Aug 2007 Posts: 902 Seattle, WA R rss super stock
rss super stock R Joined: Aug 2007 Posts: 902 Seattle, WA	Quote: Piston manufactors give advertised comp ratio on the assumption of all stock specs. Not necessarily true. For example, For KB, advertised compression ratios are based on 0.030 overbore and combined deck height/gasket thickness of 0.040". http://www.kb-silvolite.com/article.php?action=read&A_id=15 For Diamond flat tops for a 440 piston, they use 0.012" deck height and 0.040" gasket thickness (9.9 CCs). http://www.mopartsracing.com/parts/diamond.html 0.012" difference would result in about 0.2 compression points difference. Last edited by rss; 05/23/10 01:37 AM.

383man [Re: rss] #705080 05/23/10 02:42 AM 05/23/10 02:42 AM
Joined: Jan 2003 Posts: 27,421 Balt. Md 3 383man Too Many Posts
383man Too Many Posts 3 Joined: Jan 2003 Posts: 27,421 Balt. Md	Quote: Quote: Piston manufactors give advertised comp ratio on the assumption of all stock specs. Not necessarily true. For example, For KB, advertised compression ratios are based on 0.030 overbore and combined deck height/gasket thickness of 0.040". http://www.kb-silvolite.com/article.php?action=read&A_id=15 For Diamond flat tops for a 440 piston, they use 0.012" deck height and 0.040" gasket thickness (9.9 CCs). http://www.mopartsracing.com/parts/diamond.html 0.012" difference would result in about 0.2 compression points difference. I see what you mean. I guess I was thinking more on the line of stock replacement type pistons and not so much of race or higher comp pistons. You know when you would see a Speed Pro piston for a 68 to 71 340 with 10.5 comp I would say they are talking stock pistons for stock specs. Or Speed Pro 11.0 pistons for a 68 to 70 440 hp. My assumption would be they are based on a 906 head stock spec 440 eng. But you are correct for most hi performance pistons of today are based on comp hieght specs and so on. And the more I think about it most pistons really cant be sold with an eng comp ratio listing because they dont know what heads are going to be used so unless they are a stock replacement piston I guess they have to go on comp height ? Ron Last edited by 383man; 05/23/10 02:48 AM.

Re: 10.5 to 1 pistons [Re: DAMOPARS] #705081 05/23/10 08:16 AM 05/23/10 08:16 AM
Joined: Jan 2003 Posts: 75,043 U.S.S.A. JohnRR I Win
JohnRR I Win Joined: Jan 2003 Posts: 75,043 U.S.S.A.	Quote: If you get 10.5 to 1 pistons. How do they figure this out? Stock deck height or zero deck? Thanks I'll ask the STUPID question ... WHAT ENGINE are you talking about ? There are a lot of ASSumptions in this thread without knowing the engine size.

Re: 10.5 to 1 pistons [Re: JohnRR] #705082 05/23/10 04:25 PM 05/23/10 04:25 PM
Joined: Jan 2003 Posts: 4,978 VA DAMOPARS OP master
DAMOPARS OP master Joined: Jan 2003 Posts: 4,978 VA	Why does it matter what engine it is? 10.5 pistons are sold for SB and BB right? If you want to go with mine it is a 400 - 440 crank 4.375 bore .035 over 3.750 stroke 6.768 rods 1.320 CH -6cc pistons 80 cc heads I was just curious

Re: 10.5 to 1 pistons [Re: DAMOPARS] #705083 05/23/10 07:11 PM 05/23/10 07:11 PM
Joined: Jan 2003 Posts: 75,043 U.S.S.A. JohnRR I Win
JohnRR I Win Joined: Jan 2003 Posts: 75,043 U.S.S.A.	Actually, NO, 10.5 pistons aren't sold for every engine and there are many factors involed to come up with a compression ratio. As far as Chrysler engines go the factroy OVERRATED the compression of many engines and the replacement pistons available don't match , except for a very few, what the factory installed.

Re: 10.5 to 1 pistons [Re: JohnRR] #705084 05/23/10 09:47 PM 05/23/10 09:47 PM
Joined: Feb 2009 Posts: 1,274 Ontario.Canada C can.al pro stock
can.al pro stock C Joined: Feb 2009 Posts: 1,274 Ontario.Canada	..i think the factory rating was for NHRA blueprint specs. a '69 340 would be 10.5 if built to the legal NHRA specs which allowed 63 cc heads etc. a stock head is 70 -72 cc and will probably yield about 9.0 : 1 or so. ...but you really have to do the math.

Re: 10.5 to 1 pistons [Re: can.al] #705085 05/23/10 10:02 PM 05/23/10 10:02 PM
Joined: Jan 2003 Posts: 9,826 las vegas 70AARcuda master
70AARcuda master Joined: Jan 2003 Posts: 9,826 las vegas	Quote: ..i think the factory rating was for NHRA blueprint specs. a '69 340 would be 10.5 if built to the legal NHRA specs which allowed 63 cc heads etc. a stock head is 70 -72 cc and will probably yield about 9.0 : 1 or so. ...but you really have to do the math. 69 340 nhra specs...allows 63.3 head cc ...piston is .045 above deck...head gasket is .035 I bet the compression is higher then 10.5 to 1... Tony 70 AARCuda Vitamin C 71 Dart Swinger 360 10.318 @ 128.22(10-04-14 Bakersfield) 71 Demon 360 10.666 @122.41 (01-29-17 @ Las Vegas) 71 Duster 408 (10.29 @ 127.86 3/16/19 Las Vegas)

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