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Piston to Deck Calculations #1303061 09/12/12 07:50 PM 09/12/12 07:50 PM
Joined: Mar 2008 Posts: 293 salem, oregon. usa E elmor OP enthusiast
elmor OP enthusiast E Joined: Mar 2008 Posts: 293 salem, oregon. usa	If you know the deck height of your block, stroke, rod length and compression height of your piston, can you effectively calculate how far the top of the piston will be from the deck?

Re: Piston to Deck Calculations [Re: elmor] #1303062 09/12/12 08:34 PM 09/12/12 08:34 PM
Joined: Jan 2007 Posts: 7,664 IN A ahy master
ahy master A Joined: Jan 2007 Posts: 7,664 IN	Piston height= 1/2*stroke+rod length+piston height. Compare to deck height to determine where the piston will land at TDC. Deck height is measured from the center of the main bearing bore to deck top. Its best to measure deckheight at the front and back of both banks, especially if the deckl hasn't been squared. Piston height is from the center of the pin to piston top.

Re: Piston to Deck Calculations [Re: elmor] #1303063 09/12/12 08:42 PM 09/12/12 08:42 PM
Joined: Mar 2008 Posts: 5,746 Ontario, Canada Dodgem master
Dodgem master Joined: Mar 2008 Posts: 5,746 Ontario, Canada	Yes block height - compression height - Rod length - 1/2 stroke = - number will be positive deck so 10.725 - 2.060 - 6.768 - 1.875(1/2 3.75) = .022 Last edited by Dodgem; 09/12/12 08:43 PM.

Re: Piston to Deck Calculations [Re: elmor] #1303064 09/12/12 09:03 PM 09/12/12 09:03 PM
Joined: Jan 2006 Posts: 8,162 USA 3 360view Moparts resident spammer
360view Moparts resident spammer 3 Joined: Jan 2006 Posts: 8,162 USA	In the real world It is also worth keeping in mind "piston rocking" or the amount that the rings and bore clearance will allow the piston crown top outer edges to be on a slant with one side high. (Piston Pin offset from true center slightly affects this too) On the exhaust stroke it is also worth keeping in mind that upward momentum will "throw" the piston crown a bit further upward by the sum total amount of The clearance in the bearings And The stretch of the crank throws plus stretch of connecting rod, plus slack in piston pin Bore plus stretch of piston lengthwise The higher the RPM the more the total stretch during the top of the exhaust stroke The hotter the combustion the more the expansion of the crank throw, connecting rod length, piston height BUT The hotter the block walls the more it expands in the stroke direction giving a wee bit more length there There have been numerous prior discussions here about whether 0.026 inch up to 0.060 inch of clearance Is the practical limit The original Honda Vtech piston top to cylinder head clearance in their SAE technical paper called for 0.75 millimeter when cold and mentioned that was important, which works out to 0.0295 inches

Re: Piston to Deck Calculations [Re: elmor] #1303065 09/12/12 10:03 PM 09/12/12 10:03 PM
Joined: Aug 2003 Posts: 43,237 Bend,OR USA C Cab_Burge I Win
Cab_Burge I Win C Joined: Aug 2003 Posts: 43,237 Bend,OR USA	Quote: If you know the deck height of your block, stroke, rod length and compression height of your piston, can you effectively calculate how far the top of the piston will be from the deck? Yes you can calculate it, will it be accurate, probally not do to variences in prodution parts I've seen as much as .017 differences in one motor from the tallest to the shortest deck hieghts, alway check all eight pistons and rock them back and forth and check them at the cam side and the outside edge of the block side on the piston tops if they are close to zero deck hieght, don't ask why I suggest that I've had way to many things like that show up later on a tear down, luckily so far no major parts failures yet due to close of tolerances on that Always check everything More clearances are way better than a tiny bit to close or to tight Last edited by Cab_Burge; 09/13/12 01:28 AM. Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

Re: Piston to Deck Calculations [Re: Cab_Burge] #1303066 09/13/12 12:44 AM 09/13/12 12:44 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	Myself no matter how many times I do the math I am never satisfied until I assemble the shortblock and check it. And it makes you feel smart when you got it right. Ron Last edited by 383man; 09/13/12 12:44 AM.

Re: Piston to Deck Calculations [Re: 383man] #1303067 09/13/12 03:03 AM 09/13/12 03:03 AM
Joined: Mar 2008 Posts: 293 salem, oregon. usa E elmor OP enthusiast
elmor OP enthusiast E Joined: Mar 2008 Posts: 293 salem, oregon. usa	I'm asking because I want to gather some info to help me decide on pistons and heads to use. I'm going to build a mid 70's 360. I want to get 9.5 or maybe 10 to 1 compression. I was leaning towards KB 107's, my machinist is saying Sealed Power H116CP. It's going in an A-body, 727, 3.91 gears. I am looking to get 400 HP out of it and I know it can be done with the right parts fairly easily.

Re: Piston to Deck Calculations [Re: elmor] #1303068 09/13/12 07:00 AM 09/13/12 07:00 AM
Joined: Feb 2005 Posts: 4,318 Prospect, PA BSB67 master
BSB67 master Joined: Feb 2005 Posts: 4,318 Prospect, PA	Quote: I'm asking because I want to gather some info to help me decide on pistons and heads to use. I'm going to build a mid 70's 360. I want to get 9.5 or maybe 10 to 1 compression. I was leaning towards KB 107's, my machinist is saying Sealed Power H116CP. It's going in an A-body, 727, 3.91 gears. I am looking to get 400 HP out of it and I know it can be done with the right parts fairly easily. Sounds like you are asking the right questions at the right time.

Re: Piston to Deck Calculations [Re: elmor] #1303069 09/13/12 11:38 AM 09/13/12 11:38 AM
Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska	Quote: I was leaning towards KB 107's, my machinist is saying Sealed Power H116CP. the compression height is 1.670" on the SP's and 1.675" on the KB's so virtually identical on that dimention live every 24 hour block of time like it's your last day on earth

Re: Piston to Deck Calculations [Re: elmor] #1303070 09/13/12 06:31 PM 09/13/12 06:31 PM
Joined: Aug 2003 Posts: 43,237 Bend,OR USA C Cab_Burge I Win
Cab_Burge I Win C Joined: Aug 2003 Posts: 43,237 Bend,OR USA	If your going to use a set of iron heads make (on Oregon 10 or 15% pump gas) your compression ratio under 9.5 to 1 If aluminum shoot for max of 10.5 to 1 Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

Re: Piston to Deck Calculations [Re: Cab_Burge] #1303071 09/13/12 08:32 PM 09/13/12 08:32 PM
Joined: Apr 2008 Posts: 1,285 Pacific NW USA CompSyn pro stock
CompSyn pro stock Joined: Apr 2008 Posts: 1,285 Pacific NW USA	Quote: If your going to use a set of iron heads make (on Oregon 10 or 15% pump gas) your compression ratio under 9.5 to 1 If aluminum shoot for max of 10.5 to 1 Right across the border in Idaho several of our local gas stations have been offering Ethanol-FREE super unleaded. It's fairly popular with the powersports crowd so I hope they keep it around for a while

Re: Piston to Deck Calculations [Re: elmor] #1303072 09/13/12 09:47 PM 09/13/12 09:47 PM
Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,041 Lincoln Nebraska	Quote: I'm asking because I want to gather some info to help me decide on pistons and heads to use. I'm going to build a mid 70's 360. I want to get 9.5 or maybe 10 to 1 compression. I am looking to get 400 HP out of it. I'd have the crank turned & get your bearings and bore/hone and square deck it then mockup a rod/piston & see what you're deck height is. May need decking again or the correct or custom $Cometic$ head gaskets. I would absolutely shoot for .040" quench on every hole. Alot of work/expense but right is right and you're after some good power and fuel is so poor these days. (1) decide on the octane you will be using (2) decide how much cam you are willing to tolerate. (3) set the SCR to match (1) and (2) & leave room to run a fast dist curve. You could check heights in all 4 corners then deck to square the appropriate amt all in 1 shot but I prefer to have everything square/parallel/plumb before I start measureing especially since I want my quench perfect in each hole & less chance for measuring errors anywhere else along the way. EDIT Magnum heads Last edited by RapidRobert; 09/13/12 09:48 PM. live every 24 hour block of time like it's your last day on earth

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