Quench distance
Thread Starter
Intermediate
Joined: Jul 2005
Posts: 37
Likes: 0
Quench distance
Hi all
im building a 396 and opt for a compression abput 10.5:1
im using 66cc AFR heads, and came up with a Quench distance of .055 to achieve about 10.56 to 1
is this safe?
this is the block height - 0.010 milling + .040 head gasket
regards
im building a 396 and opt for a compression abput 10.5:1
im using 66cc AFR heads, and came up with a Quench distance of .055 to achieve about 10.56 to 1
is this safe?
this is the block height - 0.010 milling + .040 head gasket
regards
Racer
Joined: Oct 2001
Posts: 262
Likes: 0
From: Palos Hills IL
What is your deck height? The .010, is this off the heads? If so, that doesn't have anything to do with your quench. Quench is basically how far the piston is down in the bore and what thickness your head gasket will be.
Thread Starter
Intermediate
Joined: Jul 2005
Posts: 37
Likes: 0
Block height is 9.025, but i will have it milled to 9.015, so piston is 0.015 in the bore
heads wont be milled..
maybe its a bit to early to ask, since my heads aren´t here now, and i will have to cc my pistons also...
regards
pistons a SRP flat top w/ valve pockets
heads wont be milled..
maybe its a bit to early to ask, since my heads aren´t here now, and i will have to cc my pistons also...
regards
pistons a SRP flat top w/ valve pockets
Le Mans Master
Joined: Oct 2004
Posts: 5,841
Likes: 19
From: CLT, North Carolina
Compression Ratio and Piston Deck Height
Don't rely on math figures, check all 8 with a dial indicator when you have the shortblock together. Professional engine builders like to use a simple bridge with two 0-1" travel dial indicators for fast accurate checking. Technically speaking you should be OK with a zero deck (and the engine will run its best at zero, piston exactly at deck height at TDC, square in the bore) and a compressed gasket thickness of .040 but that would also depend on how much the piston rocks in the bore (side to side) due to skirt design. You should be OK if it does not rock out more than .015 over the deck. You will have your most efficient combustion chamber when you limit crevice volumes and end gases which is what excess minus deck height would translate into. This would be more of a consideration for an all-out engine and not so important for the street but your target compression ratio should be derived from the combustion chamber volume rather than adjusting piston deck height.
Regards, Greg
Regards, Greg
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
See if my spreadsheet helps you any. There is a compression ratio calculator on the lower right that also calculates quench height.
http://www.wku.edu/~nathan.plemons/calc.xls
http://www.wku.edu/~nathan.plemons/calc.xls
Burning Brakes
Joined: Nov 2000
Posts: 810
Likes: 3
From: Austria
hi all
thank you for your replys, and Nathan, your spreadsheet is very helpful!
here is my combo
396 with eagle forged stroker kit, SRP Flattop Pistons with 7cc Valve Pockets, AFR heads with 66cc Chambers
anyways, im ending up with 10.9 to 1 with 0 deck height and 0.040 gasket
the cam i use is a 224/230 .605 .622 113LSA 110ICL
this ends to a Dynamic C/R of 8.57 to 1
a forum member runs his 396 with the very same cam on 93 octane gas...
here in Austria, 98 and 100 octane gas is available, which should be 95 to 96 in your (american) numbers..
i´m open for any Inputs!!!
thank you for your replys, and Nathan, your spreadsheet is very helpful!
here is my combo
396 with eagle forged stroker kit, SRP Flattop Pistons with 7cc Valve Pockets, AFR heads with 66cc Chambers
anyways, im ending up with 10.9 to 1 with 0 deck height and 0.040 gasket
the cam i use is a 224/230 .605 .622 113LSA 110ICL
this ends to a Dynamic C/R of 8.57 to 1
a forum member runs his 396 with the very same cam on 93 octane gas...
here in Austria, 98 and 100 octane gas is available, which should be 95 to 96 in your (american) numbers..
i´m open for any Inputs!!!
Last edited by corvette90; Sep 20, 2005 at 02:03 PM.
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Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by corvette90
this ends to a Dynamic C/R of 8.57 to 1
RACE ON!!!
Burning Brakes
Joined: Aug 2000
Posts: 1,146
Likes: 2
From: Albuquerque NM
Originally Posted by corvette90-1
Hi all
im building a 396 and opt for a compression abput 10.5:1
im using 66cc AFR heads, and came up with a Quench distance of .055 to achieve about 10.56 to 1
is this safe?
this is the block height - 0.010 milling + .040 head gasket
regards
im building a 396 and opt for a compression abput 10.5:1
im using 66cc AFR heads, and came up with a Quench distance of .055 to achieve about 10.56 to 1
is this safe?
this is the block height - 0.010 milling + .040 head gasket
regards
Thread Starter
Intermediate
Joined: Jul 2005
Posts: 37
Likes: 0
Originally Posted by CFI-EFI
First, I see nothing wrong with that parts combination. But your dynamic compression ratio is too high for the engine to live. Also, intuitively, it just looks too high for the rest of your combination. Something is wrong, here. Did you use the .050" lift duration (224°) when you figured the dynamic CR? Compression can't start to build in the cylinder until the intake valve is on it's seat.
RACE ON!!!
RACE ON!!!
No, i used the advertised duration, thats 275°
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
And you used the advertised duration intake valve closing point in the calculation? Your dynamic CR is higher than in the 11.5:1 static CR engine I'm building. I really think there is something wrong with those numbers.
RACE ON!!!
RACE ON!!!
Thread Starter
Intermediate
Joined: Jul 2005
Posts: 37
Likes: 0
hi
the intake closing point is 67,5° ABDC...
i know, with the 66cc chamber i was getting 8.57 to 1 DCR
BUT
called AFR yesterday, and they was able to change the chambers, since the heads was not casted yet!!!!
with the new bigger chambers, i will get about 8:1 DCR which sounds fine to me!!
Their customer service works!!!!
the intake closing point is 67,5° ABDC...
i know, with the 66cc chamber i was getting 8.57 to 1 DCR
BUT
called AFR yesterday, and they was able to change the chambers, since the heads was not casted yet!!!!
with the new bigger chambers, i will get about 8:1 DCR which sounds fine to me!!
Their customer service works!!!!
Le Mans Master
Joined: Mar 2002
Posts: 5,889
Likes: 2
From: Castro Valley Calif.
St. Jude Donor '03 thru '26
Here's a real good tool to help figure out your DCR. You can enter your valve events "straight up", and compare that to 4* advance/retard, etc. 
http://cochise.uia.net/pkelley2/dcrvb6.zip
http://cochise.uia.net/pkelley2/dcrvb6.zip