Re: Calculating compression ratio?
[Re: ireland383]
#465504
09/11/09 09:45 AM
09/11/09 09:45 AM
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Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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click tech info at the top of the site then click calculators & you'll access the CR calculator to plug your specs into.
live every 24 hour block of time like it's your last day on earth
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Re: Calculating compression ratio?
[Re: JohnRR]
#465511
09/11/09 02:15 PM
09/11/09 02:15 PM
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Joined: Apr 2007
Posts: 871
WA 98043
thecarfarmer
super stock
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super stock
Joined: Apr 2007
Posts: 871
WA 98043
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Theoretically, your engine should assemble with the pistons .024 down the bore... if you got the mythical 'perfect' block Jonahah was referring to.
How much farther down - who knows?
Also, these decks aren't always level to the crank center; sometimes one end of the deck is higher than the other. My block was so out-of-square that the machinist ended up cutting enough off that I ended up with pistons ABOVE the deck a few thou (longer rods, stroker crank).
Also, I've read here from guys that CC'd their Sourcerer heads (I didn't bother w/ mine, 'cause they'll be coming back off for porting anyway) that they actually run between 84 and 86 CC's.
Plugging all that into my handy-dandy spreadsheet (that moparts member Schwep designed), your CR calculates out to 9.56:1 with 'perfect' deck and 84 CC chambers, and a marginal .062" quench distance.
With 86 CC chambers, and .015" extra on the deck (I pulled that out of my hat as a 'bad case'), your CR drops to 9.08 and the quench distance grows to a poor .077".
FWIW, you're into the $$$ for pistons, heads, etc; I'd think strongly about checking the deck height, see where you're at, and get that quench down to the .035-.045 range.
-Bill
Seduce the attractive, and charm the rest.
******
489 C.I.D., roller cam, aftermarket heads, tunnel ram, stock '54 Dodge rear axle assembly: which of these doesn't belong?
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Re: Calculating compression ratio?
[Re: thecarfarmer]
#465513
09/11/09 05:38 PM
09/11/09 05:38 PM
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Joined: Jan 2003
Posts: 74,970
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 74,970
U.S.S.A.
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Quote:
Theoretically, your engine should assemble with the pistons .024 down the bore... if you got the mythical 'perfect' block Jonahah was referring to.
How much farther down - who knows?
Also, these decks aren't always level to the crank center; sometimes one end of the deck is higher than the other. My block was so out-of-square that the machinist ended up cutting enough off that I ended up with pistons ABOVE the deck a few thou (longer rods, stroker crank).
Also, I've read here from guys that CC'd their Sourcerer heads (I didn't bother w/ mine, 'cause they'll be coming back off for porting anyway) that they actually run between 84 and 86 CC's.
Plugging all that into my handy-dandy spreadsheet (that moparts member Schwep designed), your CR calculates out to 9.56:1 with 'perfect' deck and 84 CC chambers, and a marginal .062" quench distance.
With 86 CC chambers, and .015" extra on the deck (I pulled that out of my hat as a 'bad case'), your CR drops to 9.08 and the quench distance grows to a poor .077".
FWIW, you're into the $$$ for pistons, heads, etc; I'd think strongly about checking the deck height, see where you're at, and get that quench down to the .035-.045 range.
-Bill
Bill the MYTHICAL blocks I speak of are the ones that are TALLER than stock .
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Re: Calculating compression ratio?
[Re: JohnRR]
#465514
09/11/09 06:15 PM
09/11/09 06:15 PM
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Joined: Apr 2007
Posts: 871
WA 98043
thecarfarmer
super stock
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super stock
Joined: Apr 2007
Posts: 871
WA 98043
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Oh, my bad.
I thought the 'hens teeth' were the ones that were a) blueprint spec height, and b) the same front-to-back and side-to-side.
Of course, there must have been something from Ma MoPar that got done 'on the money', but it never seems to have got traded for MY money...
FWIW, I'd just call the CR a nominal 9.2 and be done w/ it, unless I wanted to pull the heads off.
-Bill
Seduce the attractive, and charm the rest.
******
489 C.I.D., roller cam, aftermarket heads, tunnel ram, stock '54 Dodge rear axle assembly: which of these doesn't belong?
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Re: Calculating compression ratio?
[Re: ireland383]
#465516
09/12/09 11:06 AM
09/12/09 11:06 AM
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Joined: Jan 2003
Posts: 74,970
U.S.S.A.
JohnRR
I Win
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I Win
Joined: Jan 2003
Posts: 74,970
U.S.S.A.
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Quote:
Last ? on this topic is there a problem with running the kb400's with the stealths and flame travel?
The dome can be an issue with flame travel no matter what head it is , the best way to get the compression you want is to get a custom flat top piston made and cut the heads for a smaller chamber size.
Bill, the blocks, in my opinion, are different end to end and corner to corner, in part because the block has settled, been seasoned if you will, I really doubt the block was machined like that when new.
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