Increasing compression ratio
#979938
04/24/11 10:58 PM
04/24/11 10:58 PM
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Joined: Jan 2011
Posts: 492 Kansas
BEINGmeISaCRIME
OP
mopar
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OP
mopar
Joined: Jan 2011
Posts: 492
Kansas
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I'm sure some have read my posts from a few weeks ago about me getting a 440 and what I have planned for the future and whatnot. At the same time some of ya might be getting tired of all my lame engine questions but anyways... So, its a 1974 440, forged crank, out of a motorhome. It has the 213 heads which I plan on replacing. I removed one of the heads and calculated a CR of about 7.8:1. I wasn't expecting to be at that low of number being a steel crank, but the pistons are .150" in the hole I'd like to shoot for somewhere near 9:1 CR without doing a rebuild of the bottom end. As it sits, there is barely any cylinder ridge, so the bottom end in theory is good. When I calculated the CR I guessed the 213 heads to be about 90cc being open chambered. If I were to put on a pair of 915 heads, being about a 74 cc or so combustion chamber, that should raise me to around 8.8 CR which would be close enough. Would that be the easiest way to get me up in compression or is there something else that could be done?
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Re: Increasing compression ratio
[Re: dOrk !]
#979940
04/24/11 11:48 PM
04/24/11 11:48 PM
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Joined: Jan 2011
Posts: 492 Kansas
BEINGmeISaCRIME
OP
mopar
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OP
mopar
Joined: Jan 2011
Posts: 492
Kansas
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Quote:
915's are a good add-on .. but I would even cut-those another 60.
I guess I don't understand. Cut what exactly?
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Re: Increasing compression ratio
[Re: BEINGmeISaCRIME]
#979941
04/25/11 12:16 AM
04/25/11 12:16 AM
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Joined: Jan 2004
Posts: 27,347 Today? Who Knows?
1_WILD_RT
Management Trainee
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Management Trainee
Joined: Jan 2004
Posts: 27,347
Today? Who Knows?
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The head gasket surface... Cutting it reduces chamber volume... But cutting .060 may require shorter pushrods I believe on the closed chamber heads 1cc = .006 so cutting .060 will reduce chamber volume by 10cc...
"The Armies of our ancestors were lucky, in that they were not trailed by a second army of pencil pushers."
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Re: Increasing compression ratio
[Re: BEINGmeISaCRIME]
#979946
04/25/11 02:14 PM
04/25/11 02:14 PM
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Joined: Aug 2007
Posts: 6,095 Valencia, España
NachoRT74
master
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master
Joined: Aug 2007
Posts: 6,095
Valencia, España
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get new pistons what will get 0.10-0.20 down the hole and done... then if you want, get closed chambers heads or cut your actual ones.
even earlier stock replacement pistons will be good enough and cheaper, and will get you around 050-070 down the hole
THE BIG DEAL on post 72 engines is JUST THE PISTON COMPRESION HEIGHT, period.
With a Charger born in Chrysler assembly plant in Valencia, Venezuela
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Re: Increasing compression ratio
[Re: NachoRT74]
#979948
04/25/11 02:24 PM
04/25/11 02:24 PM
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Joined: Aug 2007
Posts: 6,095 Valencia, España
NachoRT74
master
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master
Joined: Aug 2007
Posts: 6,095
Valencia, España
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whats the bore on the engine ?
type Mopar 440 pistons on the ebay and you'll find several GOOD AND CHEAP options for good used ones. In the long ( and also short ) even with some mechanic shop job if you can't, will be less headache try to get the right pistons than mill, heads and still be that DOWN IN THE HOLE. VERY DISSAPOINTING IF YOU ASK ME spend that money and still not get what you want
easier and cheaper get the .100-.150 piston raised AT ONCE keeping 90 cc heads, than be able to cut .060 from heads to get around 82cc and still will be .150 down
With a Charger born in Chrysler assembly plant in Valencia, Venezuela
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Re: Increasing compression ratio
[Re: BEINGmeISaCRIME]
#979950
04/25/11 07:45 PM
04/25/11 07:45 PM
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Joined: Feb 2005
Posts: 5,221 Branson, Mo.
joedust451
super gas
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super gas
Joined: Feb 2005
Posts: 5,221
Branson, Mo.
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Your best bet is rebuild it, otherwise it will be doggy trust me, I'd get the TRW forged 2355 sixpack pistons, with a thin head gasket & those 91cc heads, you'll be closer to 10.1, more or less around 9.7.1, it'll run very good with a nice cam & bolt-ons.
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Re: Increasing compression ratio
[Re: BEINGmeISaCRIME]
#979952
04/26/11 01:48 AM
04/26/11 01:48 AM
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Joined: Feb 2005
Posts: 5,221 Branson, Mo.
joedust451
super gas
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super gas
Joined: Feb 2005
Posts: 5,221
Branson, Mo.
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Quote:
By doing that, I would need to have the rotating assembly rebalanced, correct?
It wouldn't hurt, but the nice thing about those TRWs is, there about the same weight as the factory pistons, there were many back in the day that never had them balanced, But that was then, its really a good idea to spend the extra say 150.00 or so bucks, they will/should make sure the rods are all the same weight, then the pistons, then balance the rotating assemble, very simple straight forward balance job.
Back in the day, guys with this build ran mid 12s (with ease) in fully dressed Chargers with a 509 stick, 4.10 gears, 3500 stall, 850dp, Holley street dom. intake at or about sea level, in an A body, you'll have a 11 second ride garuanteed.
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