V/P Index

[Kevin Shasteen]

In the Dynamic Compression Ratio thread, in this same forum Pete P. recently brought to my attention the V/P Index site that I had forgotten.

 

The purpose for mentioning that site was to concentrate on Cylinder Pressures: specifically the CP = CRE^1.2 * AP. I understand this forumula & appreciate Pete bringing that to my attention.

 

My problem is w/the V/P Index itself...has anyone else been able to come up w/the same numbers this site's author presents? He throws out his first example and then gives two/three others as comparisons...unfortunately I cant seem to come up w/the same numbers to the first example.

 

Go to http://www.victorylibrary.com/mopar/cam-tech-c.htm

 

Then scroll down till you come to the V/P Index Chart. Just underneath this chart you will find his "340 Calculation" where he "hap-hazzardly" walks the reader thru the process. I have tried & tried to come up w/the same [269] V/P Index that he has come with but for some unknown reason my numbers dont jive w/his.

 

In his "340 Calculation" he firs offers:

1) 340 cu.in Mopar V8

2) BxS = 4.04 x 3.310

3) 10.0:1 SCR = 77.4cc Ttl.Chamber Volume

4) Cam w/IVC @ 66*

5) Leaves an Effective Stroke of 2.52"

6) #5 gives an Effective Volume after IVC of 258.4cu.in

Ex: B^2 x S x .7854 x 8 = 258.4cu.in

7) This gives us a DCR (Effective Compression Ratio) of 7.84:1

8) Cyl.Pressure = DCR^1.2 x AP

Ex: 7.84^1.2 x 14.7 = 173.9 psi

 

Now, this V/P Index formula is as follows:

 

V/P = CP x VE x N x .003

 

Therefore, the V/P equation, using his data, would look like this:

 

V/P = 173.9 x 32.30 x 8 x .003

 

Now, in case you have not worked that equation out, let me walk you thru this.

 

173.9 x 32.30 = 5616.97

5616.97 x 8 = 44935.76

44935.76 x .003 = 134.80.............NOT 269!!!

 

I have worked this every possible way I could think of, could someone please tell me what I am doing wrong. I figure either I am doing something wrong or the author of this V/P Index site has left out a very important step...please advise before I go crazy...thank you.

 

Kevin,

(Yea,Still an Inliner)

[Kevin Shasteen]

..' date=' has anyone else been able to come up w/the same numbers this site's author presents.., the V/P equation, using his data, would look like this: V/P = 173.9 x 32.30 x 8 x .003

 

173.9 x 32.30 = 5616.97

5616.97 x 8 = 44935.76

44935.76 x .003 = 134.80.............NOT 269!!!

 

I figure either I am doing something wrong or the author of this V/P Index site has left out a very important step.., [/quote']

 

OK Everyone,

 

I have prooven once again I am not crazy...at least not for the reason this thread initially suggested. I believe I have figured out the VP Index problem. Turns out there was a step left out. If you will notice the 134.80 number: now multiply it by two what'dya get..such as,

 

134.80 x 2 = 269.6

 

I cant believe the site's author left out "THIS VERY IMPORTANT STEP ...this VP Index has perplexed me for three years now: ever since it was first posted by someone-I coulndt get it to work then & only now do I know why.

 

Ooooh, I hate it when these things happen. Anyway, for anyone attempting to use the VP Index just remember to multiply your answer by 2.

 

Kevin,

(Yea,Still an Inliner)