Reliable DCR Calculator?
#1349971
12/12/12 12:07 AM
12/12/12 12:07 AM
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Joined: Nov 2012
Posts: 264
Farmington Hills, MI
BPBP440
OP
enthusiast
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OP
enthusiast
Joined: Nov 2012
Posts: 264
Farmington Hills, MI
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I ran the DCR calculator from www.kb-silvolite.com only to get a result that differed from the advice I had received on the boards previously, which put it in question. So I checked another calculator on www.jeepstrokers.com/calculator/ and got much closer to what I have been told here. 9.58:1 static compression on a stock stroke 440 with an Intake valve closing 61 degrees ABDC is 7.83:1 DCR. Wallace racing closely confirmed this. A far cry from the www.kb-silvolite.com calculated DCR of 6.90:1.  Looks like the difference is that KB has you add 15 degrees to the Intake closing ABDC value. So, what calculator do you guys use and trust?
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Re: Reliable DCR Calculator?
[Re: BPBP440]
#1349975
12/12/12 01:33 AM
12/12/12 01:33 AM
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Joined: Oct 2007
Posts: 4,206
New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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There are 2 major differences:
1. you have to know the nominal intake closing point. The .020" and .050" are useless, and the K-B correction is a vague guess (based on Vizard's estimate of 30° effective duration diff between lashed and .050").
2. the ratio of variable heats (the exponent in th formula) will vary all over the place between about 1.2 and 1.4 depending on water jacket temperature, compression ratio, EVO point etc. No engine you can buy runs 1.4, the best guesses are 1.25 to 1.3.
BTW: DCR is now a buzzword (yes, that 15 year old at the magazine rack uses it), but it does very little of practical value.
Boffin Emeritus
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Re: Reliable DCR Calculator?
[Re: polyspheric]
#1349976
12/12/12 01:47 AM
12/12/12 01:47 AM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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Quote:
There are 2 major differences:
1. you have to know the nominal intake closing point. The .020" and .050" are useless, and the K-B correction is a vague guess (based on Vizard's estimate of 30° effective duration diff between lashed and .050").
2. the ratio of variable heats (the exponent in th formula) will vary all over the place between about 1.2 and 1.4 depending on water jacket temperature, compression ratio, EVO point etc. No engine you can buy runs 1.4, the best guesses are 1.25 to 1.3.
BTW: DCR is now a buzzword (yes, that 15 year old at the magazine rack uses it), but it does very little of practical value.
The one posted by the OP uses a 15* based on the .050
so there are some variables out there
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Re: Reliable DCR Calculator?
[Re: polyspheric]
#1349977
12/12/12 02:12 AM
12/12/12 02:12 AM
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Joined: Nov 2012
Posts: 264
Farmington Hills, MI
BPBP440
OP
enthusiast
|
OP
enthusiast
Joined: Nov 2012
Posts: 264
Farmington Hills, MI
|
Quote:
There are 2 major differences:
1. you have to know the nominal intake closing point. The .020" and .050" are useless, and the K-B correction is a vague guess (based on Vizard's estimate of 30° effective duration diff between lashed and .050").
2. the ratio of variable heats (the exponent in th formula) will vary all over the place between about 1.2 and 1.4 depending on water jacket temperature, compression ratio, EVO point etc. No engine you can buy runs 1.4, the best guesses are 1.25 to 1.3.
BTW: DCR is now a buzzword (yes, that 15 year old at the magazine rack uses it), but it does very little of practical value.
Sure, a simplified calc is never a substitute for a full blown combustion model. Indicated mean effective pressure, kernel formation, flame propagation, mass fraction curve, etc. are all thrilling topics, but when I go talkin that talk to the 15 year olds at the magazine rack, they just look at me funny. 
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