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Compression ratio? #1764716 02/27/15 09:51 PM 02/27/15 09:51 PM
Joined: Jan 2003 Posts: 1,787 Big Sky Country M MO_PA OP top fuel
MO_PA OP top fuel M Joined: Jan 2003 Posts: 1,787 Big Sky Country	.040 over bore 440, 906 heads, .020 head gasket, flat top pistons .120 in the hole. Estimates appreciated. Thanks!

Re: Compression ratio? [Re: MO_PA] #1764717 02/27/15 09:55 PM 02/27/15 09:55 PM
Joined: Oct 2003 Posts: 4,011 South Park, Pa. 68LAR master
68LAR master Joined: Oct 2003 Posts: 4,011 South Park, Pa.	With 89 cc heads, MAYBE 8:1 CR. No too good.. 4 speed street legal. Best time 10.99 @ 124 mph on 93 octane pump gas @ 3926# total weight

Re: Compression ratio? [Re: MO_PA] #1764718 02/28/15 12:09 AM 02/28/15 12:09 AM
Joined: Aug 2003 Posts: 43,129 Bend,OR USA C Cab_Burge I Win
Cab_Burge I Win C Joined: Aug 2003 Posts: 43,129 Bend,OR USA	Quote: .040 over bore 440, 906 heads, .020 head gasket, flat top pistons .120 in the hole. Estimates appreciated. Thanks! You really need to CC at least one chamber in each head to find out what CC heads your working with I've seen supposidly stock uncut 906 heads have 91.+ CC in them with the carbon removed I've also seen 4.3 CC varience in chamber sizes on the same head, same differences on the other head with the thickness within .003 on both heads on both ends of those heads Once you get a idea on the CC size you have go to United Machines web site , AKA KB Pistons, Silvolite and click on there calculator tab and go to the compression ratio calculator and plug in your numbers to get a idea what you have on the compression ratio with your pistons and the specs. you put on here Let us know your results Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

Re: Compression ratio? [Re: Cab_Burge] #1764719 02/28/15 12:24 AM 02/28/15 12:24 AM
Joined: Jan 2003 Posts: 1,787 Big Sky Country M MO_PA OP top fuel
MO_PA OP top fuel M Joined: Jan 2003 Posts: 1,787 Big Sky Country	United Engine Machine calculator comes up with 8.75 using 89cc head. this should power a grocery getter 62 Sport Fury

Re: Compression ratio? [Re: MO_PA] #1764720 02/28/15 10:54 AM 02/28/15 10:54 AM
Joined: Feb 2005 Posts: 4,311 Prospect, PA BSB67 master
BSB67 master Joined: Feb 2005 Posts: 4,311 Prospect, PA	It is about 8.4:1. You don't need to measure anything in my opinion, you have enough information. 86cc to 94 cc is 8.2:1 to 8.6:1, i.e. it really does not matter much.

Re: Compression ratio? [Re: BSB67] #1764721 02/28/15 01:12 PM 02/28/15 01:12 PM
Joined: Jan 2003 Posts: 16,376 D dogdays I Live Here
dogdays I Live Here D Joined: Jan 2003 Posts: 16,376	With a 90cc head the comp ratio calculates to 8.35:1. With a 93cc head the comp ratio calculates to 8.18:1. To get to 9:1 you need to lose 13cc of volume above the piston, meaning cut 0.053 off the deck or heads or move the piston tops up the same amount. Key calculation, the 440 + 0.040 has a per cylinder swept volume of 918cc R.

Re: Compression ratio? [Re: MO_PA] #1764722 02/28/15 01:52 PM 02/28/15 01:52 PM
Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska R RapidRobert Circle Track
RapidRobert Circle Track R Joined: Nov 2003 Posts: 36,040 Lincoln Nebraska	Quote: .040 over bore 440, 906 heads, .020 head gasket, flat top pistons .120 in the hole. Estimates appreciated. Thanks! I'm assuming it is all together. What cam? Advancing it might build some psi. definitely dial in the dist subsystems (in order) when the time comes live every 24 hour block of time like it's your last day on earth

Re: Compression ratio? [Re: dogdays] #1764723 02/28/15 01:54 PM 02/28/15 01:54 PM
Joined: Feb 2005 Posts: 4,311 Prospect, PA BSB67 master
BSB67 master Joined: Feb 2005 Posts: 4,311 Prospect, PA	That is why I said "about". Three significant figures is a bit of a push even if you are trying to equalize combustion volumes at the typical amateur/hobbyist budget level.

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