Piston/wrist pin height - Chevelle Tech
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  #1  
Old Nov 12th, 02, 9:06 PM
JIM JIM is offline
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Considering a standard 9.8" block height and a standard 6.135" rod, what is the stock measurement for the piston deck/wrist pin height (also referred as compression height)for a standard 396/427 piston vs a 454 piston. I am trying to figure something out and my info is at home.
Thanks



------------------
Jim
My 70 Chevelle
427 + (.125")
4-speed
Best ET 12.53@110.3
BSE Power
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  #2  
Old Nov 13th, 02, 8:01 AM
Wally Wally is offline
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427 is a nominal 1.765 and the 454 is 1.640.

Some pistons makers have their own idea about what the compression height should be, my 427 pistons have a compression height if 1.785, just enough to hang the piston out of the bore by .020. Not bad, made wrong for $650, I just love it.

------------------
www.muncie4speed.com
Gold 67
1967 Malibu, 2nd owner.
1971 Malibu, new rat motor going in.
There is nothing like rowing through the gears at 7500. Stick cars are so much fun they should be a controlled substance!
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  #3  
Old Nov 13th, 02, 8:33 AM
JIM JIM is offline
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Wally, Thanks for the reply.
Why would 1.785" be bad??
9.8-(6.135+1.88) = 1.785. Wouldn't that put the piston at a zero deck height? In any case, the difference between the two pistons is .125"?? That is what I am trying to figure out. My motor has a deck height of .080" and I am trying to figure out how that happened?

------------------
Jim
My 70 Chevelle
427 + (.125")
4-speed
Best ET 12.53@110.3
BSE Power
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  #4  
Old Nov 13th, 02, 8:46 AM
Wally Wally is offline
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I like to be the one who makes the decisions about total deck, not the piston maker. It should have been the stock pin height, then I would have been right on 0 deck, now it is plus on deck.

------------------
www.muncie4speed.com
Gold 67
1967 Malibu, 2nd owner.
1971 Malibu, new rat motor going in.
There is nothing like rowing through the gears at 7500. Stick cars are so much fun they should be a controlled substance!
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  #5  
Old Nov 13th, 02, 12:54 PM
Tom Mobley Tom Mobley is offline
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Jim,

You have to be a little careful about pistons these days. Many of the manufactureres are making what might be best called "universal rebuilder" pistons. They're usually short on the deck height, some of them quite a bit short. In the specs for the piston it should give the compression height, from center of wrist pin bore to deck of piston. I had to look around a bit to find full-height pistons for my 406.

Wally, those slugs you got are probably meant to give a zero deck on a unmachined block, what brand are they, mind if I ask? I'd like know who is doing this? Forewarned is forearmed... Was your block already decked to nominal zero?

Tom

[This message has been edited by Tom Mobley (edited 11-13-2002).]
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Old Nov 14th, 02, 12:25 AM
JIM JIM is offline
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Good point Tom. My problem is from when I first got this motor as a pile of pieces 18 years ago. I knew absolutely nothing about deck height, quench, cc's compression ratio back then. I didn't purchase the parts, they came with the car. If I only knew then what I know now It was just recently when changing cams and finding TDC that I realized I had a .080" deck height (80 thousandths in the hole!!). The pistons are .125 over Arias forged with 1" bushed full floating small ends, not the standard .990's. At first I was thinking they were 454 pistons on there, but that would put me .125" down the hole. I can't imagine the blocked was decked .045", could it be??

------------------
Jim
My 70 Chevelle
427 + (.125")
4-speed
Best ET 12.53@110.3
BSE Power
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  #7  
Old Nov 14th, 02, 1:15 AM
Tom Mobley Tom Mobley is offline
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Duuuhhh, I don't understand that last question. If the block was decked .045 you would have pistons sticking out of deck at TDC?

(later) OIC, you mean 454 piston and decked .045? I doubt it, you wouldn't be able to get a manifold on it. I bet somebody ordered a set of Arias for a would-be blower motor, that used to be the way they did the low compression thing. That would also account for the oversize wrist pins.

They didn't have all this fancy computer operated CAD driven automatic mill stuff, making a D-shaped dish in a piston was not easy. Next time you have it out all this can be corrected and brought up to date. I wouldn't get in a sweat about it now if the engine is doing all right otherwise. Unless of course, that wallet is just so overloaded and needs lightening up a little.

Tom
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  #8  
Old Nov 14th, 02, 7:59 AM
Wally Wally is offline
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BRC. I had pistons made for my 427 with the open chambered 049 heads. Nice pistons but having them sticking out of the block .020 was kind of ugly. When BillK did the block we took a cleanup cut off the deck, about .004. Most rats need way more than that to come into sharp focus. They added the .020 to the pin height and screwed me to the wall. Now I have a .052 thick gasket and not a lot wiggle room.

------------------
www.muncie4speed.com
Gold 67
1967 Malibu, 2nd owner.
1971 Malibu, new rat motor going in.
There is nothing like rowing through the gears at 7500. Stick cars are so much fun they should be a controlled substance!

[This message has been edited by Wally (edited 11-14-2002).]
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  #9  
Old Nov 14th, 02, 8:11 AM
JIM JIM is offline
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Tom,
Right, the only way to know for sure is to pull it and measure. Still running pretty good after all of these years though. So thatwill have to wait and remain a mystery. Blower pistons....no these have huge domes measuring 42cc's so who knows what is going on.

Wally,
I see your point and it is well noted. Next time I order a set of pistons, I will do the math first and tell them what I am looking for.

------------------
Jim
My 70 Chevelle
427 + (.125")
4-speed
Best ET 12.53@110.3
BSE Power
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  #10  
Old Nov 15th, 02, 11:45 AM
ChevelleTodd ChevelleTodd is offline
 
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I have a two bolt 454 70's era block with stock cast crank and rods with federal mogul hyperutectic cast (speed pro) pistons with the stock compression height listed above. my piston decks are also out of the hole by about .007 to .010. I know that the block deck is stock and the mains have not been bored or honed. So this leads me to belive that there is some mistake or miscommunication with the piston manufacturers data because they list this piston as being 20-25 in the hole. Or could the stock deck heights be out of spec by this much? The motor runs great with a .040 gasket with no detination etc.
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