Reliable DCR Calculator?

Posted By: BPBP440

Reliable DCR Calculator? - 12/12/12 04:07 AM

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?

Attached picture 7499626-DCRWrong.jpg

Posted By: MR_P_BODY

Re: Reliable DCR Calculator? - 12/12/12 04:13 AM

Wallace has one

http://www.wallaceracing.com/Calculators.htm

Posted By: bobs66440

Re: Reliable DCR Calculator? - 12/12/12 04:45 AM

I've used this one with good results. The link for download is at the bottom of the page.

http://cochise.uia.net/pkelley2/DynamicCR.html

Posted By: BPBP440

Re: Reliable DCR Calculator? - 12/12/12 05:12 AM

Quote:

I've used this one with good results. The link for download is at the bottom of the page.

http://cochise.uia.net/pkelley2/DynamicCR.html

Thanks. I tried to download that one, but my work laptop wouldn't allow it. Will need to try it from my home computer.

Posted By: polyspheric

Re: Reliable DCR Calculator? - 12/12/12 05:33 AM

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.

Posted By: MR_P_BODY

Re: Reliable DCR Calculator? - 12/12/12 05:47 AM

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

Posted By: BPBP440

Re: Reliable DCR Calculator? - 12/12/12 06:12 AM

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.