'Puter Dyno Programs

[JackD]

" Theoretical records are set by theoretical bikes."
 Denis is where I heard it.

[k.h.]

"In theory, there is no difference between theory and practice, but in practice there is."
 
 Jan L. A. Van de Snepscheut, Holland

[ddahlgren]

There is a little problem with most of these programs. First anyone that is smart enough to write the definative answer type of program already has a good job and would not want to be troubled by farting arout with this sort of project. They can make more money by accident on their real job. It is the same problem with aftermarket EFI for the most part. A good example is, I have a customer in his late 20's early 30's. he has a hotrod import turbo car he plays with when he can find the time. he is a computer programer and we were talking about building something that was not offered in the aftermarket EFI world. he thought it an interesting project but also has a better job than that now working for United Technology to the point he would not take the time to do one for himself let alone a commercial venture.
 
 Ok the Dynamic compression ratio calc program.
 out of curiuosity i downloaded it and played with it. Built a SBC 355 with a 6 in rod 3.5 stroke and a static CR just over 13.5
 Put a cam in 272/282 108 Lobe separation and installed at 106 IC.. Pretty common engine. It come up with a dynamic CR of just under 11.0/1 so far all interesting numbers.. Now with said engine if the seal was perfect and we just take 11 X 14.7 psi for 1 atmosphere the cranking compression ought to be 11X 14.7=162 psi more or less. Well if i have built this engine and found this cranking compression i would wonder what was broken as i have never had this low a number on an engine like this . more typical is 200 to 210 psi.. Soooo I fear that program is just another arcade game.. most all of the engine simulation software I have seen is an ill fated attempt at something that is not well understood by the person writing the software. I am sure for the 50 to 100k range this is available and probably used by many engineering firms and departments. But to work correctly I would think it would need a 3d model of the intake and exhaust and chamber/piston top. Along with the ability to do CFD on said parts.
 
 A long time ago i wrote a program for MSD to size injectors and other things like intercoolers etc. I forced the operator to input VE and BSFC along with target A/F ratio. This did give a realistic output when sensible numbers were plugged in. In the process it offloaded the things other software pretend to calculate to the operator as input rather than make them output. A big difference in concept, if you used your head the numbers were surprisingly accurate.
 
 Dave
 
  <small>[ February 20, 2005, 07:13 AM: Message edited by: Dave Dahlgren ]</small>

[ddahlgren]

Originally posted by John Beckett:
  Dave
 
 On a blown motor you need to reduce the overlap as I guess you would force too much air/fuel out the exhaust. Drag cams seem to run lobe centers in the 106 range on a small block. So… on an NA motor for Bonneville what would be the ideal lobe center to run five miles?
 
 John

What makes you unhappy with 106? A blown(supercharged) engine generally needs some overlap to cool the piston down and an exhaust lobe larger than the intake.
 A turbo engine is an NA engine running at a different altitude..
 Dave

[panic]

"and we just take 11 X 14.7 psi for 1 atmosphere the cranking compression ought to be 11X 14.7=162 psi more or less"
 
 1. DCR tells you nothing at all about your compression during power range.
 2. CR X ATM will never give you an answer in psi.

[panic]

My point with the V/P numbers was to give a rough idea of how much better/worse a new cam or CR would be in terms of off-idle power, stall speed prediction and general flexibility for street purposes. It has almost no effect on actual power production, neither does DCR.

[Sumner]

Soooo I fear that program is just another arcade game.. most all of the engine simulation software I have seen is an ill fated attempt at something that is not well understood by the person writing the software.

You know Dave I can see you are a very knowledgable guy and I'll probably never have the knowledge you have, yet I try to stay open minded to new things and try to find some part of them that I can use.
 
 I've build 3 houses a store and a pretty nice truck using tools that weren't perfect or maybe best suited for the job, but they somehow got the job done.  Sure a lot of the Dyno programs out there and other programs like the one to figure DCR might not be perfect, but they are tools that some of us can use and afford. I'm no where near a Dyno and if I was I wouldn't have the money to use it or buy all the different combination of heads, cams, etc. to make decisions on what might work best for me.  These programs at least will get me close.  They might be 20-40 hp off, but I'll still probably build a better motor than I would have 20 years ago just listening to my buddies. They at least give us some new knowledge and something else to consider and think about.  No different than reading books, tech papers and using other sources to develope new ideas.
 
 Personally I'm almost getting to the point where I feel if I post something on this board I'll just be put down about the post.  Not a good feeling and I would hate to think others are not contributing because they might feel the same way.
 
 c ya, Sum

[JackD]

Don't be discouraged.
 A lot of people are degreed graduates from The School of Hard Knocks.
 They include Arnett,Crower.White,Vesco.Teague,Force.Gartlets, and You.

[ddahlgren]

I was open minded did not dare say a word until i downloaded the software spent around 30 or 40 minutes trying what if combinations, compared them to what i knew to be true and wrote back here what i found both with this and other simulation software that i have tried and bought over the years. it is an honest opinion and not meant to be a put down. A put down in my mind is one of the one liners that is from someone that was not open minded enough to read everything try it out and compare it to real life experiences. sorry if it sounds that way just comparing to what i have seen over the 30 or so years..
 Dave

[k.h.]

Re: LSR & other motorsports
 
 www.rbracing.rsr.com/secrets.htm