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Decompressed pistons

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bill

04-01-2003 18:07:30

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whats the deal with decompressed pistons? some people say its the way to go but i always thought that a lot of compression meant a lot of power? is there some advantage or what? any insight on the subject would be appreciated

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REDMAN

04-12-2003 21:49:46

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Re: decompressed pistons in reply to bill, 04-01-2003 18:07:30

you decompress the pistons on a turbo diesel
to lower the amont of heat in the cyl. during
the 10 seconds that they run.If you don't,the heat
build up causes the engine to loss lugging power
at the end of the run.Atleast that is what my man
Max says over there in Charlotte MI.

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Farmall Boy

04-02-2003 14:18:51

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Re: decompressed pistons in reply to bill, 04-01-2003 18:07:30

Some gas pistons are done that way even when not adding a turbo, if your making a stroker some are made to give room for the valves to move

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ZR-1 PULLER

04-02-2003 16:00:59

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Re: Re: decompressed pistons in reply to Farmall Boy, 04-02-2003 14:18:51

WHAT the Dell are you saying!?!?!?
DID you read what you posted?,you don't make any sents!

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G-MAN

04-03-2003 11:01:00

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Re: Re: Re: decompressed pistons in reply to ZR-1 PULLER, 04-02-2003 16:00:59

It makes perfect sense. If you dramatically increase your stroke, sometimes you have to cut down the tops of the pistons to avoid gettting too high of a compression ratio, due to the decreased volume above the pistons. "Decompressed" pistons also don't give you any more displacement. What you add when the piston is at the bottom of the stroke, you also lose when the piston is at the top of the stroke. The only way to increase cubic inches is to increase bore and/or stroke. Supercharged engines and ones using nitrous commonly run lower compression ratios (decompressed pistons) to avoid getting into super-high cylinder pressure situations and detonation/pinging problems.

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dean

04-02-2003 16:52:13

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Re: Re: Re: decompressed pistons in reply to ZR-1 PULLER, 04-02-2003 16:00:59

i think hes referring to the pistons with the fly cuts or "eyebrows" for valve clearance...not necessarily dished or decompressed per say but versus a flattop would technically be decompressed

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Farmall Boy

04-03-2003 13:00:48

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Re: Re: Re: Re: decompressed pistons in reply to dean, 04-02-2003 16:52:13

thanx for haveing my back on that one g-man and dean...i know thats how it works in stroker car motors

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G-MAN

04-03-2003 16:29:12

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Re: Re: Re: Re: Re: decompressed pistons in reply to Farmall Boy, 04-03-2003 13:00:48

No problem, Farmall Boy. I think some people don't realize the difference between compression ratio and displacement. You can put as tall or as short of a piston as you want in an engine, and you haven't changed the displacement a lick until you change the bore or stroke. Same goes for lengthened or shortened rods. Changing the volume of the combustion chamber, dishing pistons and so forth also doesn't change displacement. Displacement is the swept volume of the cylinder. Compression ratio is the ratio between the volume above the piston at BDC and the volume above the piston at TDC. I'm sure you're aware of those things. I just threw that in for anyone that wasn't sure what is what.

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Farmall Boy

04-03-2003 17:24:10

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Re: Re: Re: Re: Re: Re: decompressed pistons in reply to G-MAN, 04-03-2003 16:29:12

hmmmmm ....you sound like a very educated
guy...even if you got the wrong color
.....hehehehe...thanx we were deciding between
stroking and high comp. pistons the info really
helps Appreciated fb

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Farmall Boy

04-03-2003 13:00:25

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Re: Re: Re: Re: decompressed pistons in reply to dean, 04-02-2003 16:52:13

thanx fpor haveing my back on that one g-man and dean...i know thats how it works in stroker car motors

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ZR-1PULLER

04-01-2003 19:47:53

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Re: decompressed pistons in reply to bill, 04-01-2003 18:07:30

Decomp. pistons or dish pistons are used in turbocharged motors becaused the turbo is "PACKING" the bore with air/fuel if the comp. is To high it will melt down the piston,now,here comes the "BIG" turbos that "PACK" in more air/fuel inorder to keep from melting down the pistons this way you will use WATER injected in the chamber to 'cool' down the burn,thus preventing meltdown.DISH pistons have no benefit in a GAS motor other than lowering compression.

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E J

04-01-2003 19:13:10

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Re: decompressed pistons in reply to bill, 04-01-2003 18:07:30

Used in the big smokers for more cylinder volume.Start with starting fluid to make them fire and run.

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oliverman

04-01-2003 19:12:46

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Re: decompressed pistons in reply to bill, 04-01-2003 18:07:30

i've heard of guy's decompressing there engines but i've only heard some guy's doing this when they are adding a Turbo! I guess they would do that to get more valume!!

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