'Puter Dyno Programs

[John Beckett]

Just bought the "Dyno Sim" dyno-test simulation software. Got it up and running with no trouble. Plugged in the info for a 23 degree Chevy 302" motor for Bonneville. And to my surprise it made 675 HP at 8500 RPM. Sorta blew my faith in this sort of 'puter dyno programming. A lot of money for untrustworthy results.
 
 Also have an old Performance Trends, Engine Analyzer. A lot more info to enter in the first place, but way more realistic results. About a hundred HP less than the ?Dyno Sim? in this case.
 
 Anyone else have any experience with this stuff?
 
 JB

[Sumner]

Sounds like to me it is a good way to make more HP cheap   .
 
 I have Dyno 2000 and it seems to give some trends, but I don't take a whole lot of faith in it.  It is pretty cheap.  It also seems to give roller cams a lot more HP than they probably deserve.
 
 c ya, Sum

[ddahlgren]

If you do not have to enter the cam lift curve and the head flow every 0.100 along with intake minimum restriction among other things they will always lie to you and make too much power. If they can not produce a realistic pressure- volume curve they are just guessing.
 Dave
 
  <small>[ February 15, 2005, 04:58 AM: Message edited by: Dave Dahlgren ]</small>

[panic]

Thanks - that confirms what I suspected; their own "plug-in" data is too optimistic.

[John Beckett]

The Dyno Sim program does allow you to put in all the proper cam timing inputs as well as head flow every .100". Limited input for intake manifolds, exhaust, and friction losses etc. Results are still way to high.
 
 Engine Analyzer has most cam info and allows for head flow at one point along with port volume and flow efficiency. Much greater detail on intake manifolds, exhaust, and friction losses. Results are closer to reality, but wish it also had more cam and head flow inputs.
 
 JB

[John Beckett]

Another interesting thing on the Dyno Sim the program can try and pick the prefect cam timing. So when I try this the lobe centerline always seems to come up in the 112 to 116 degree range. Why so little overlap?
 
 JB

[John Beckett]

Dave
 
 Is there a program out there that will produce realistic results??
 
 JB

[panic]

Just a guess: where a program predicts wide LSA (not less cam) 2 things I'd look at are static CR too high, and high chamber efficiency at low lift (making OL flow better than needed)

[ddahlgren]

Don't want to forget the wide lobe separation cams will not cool things down as much.. A little wasted intake charge can be a good thing at the 5 mile mark.. the trouble with going 200 is you have to go 190 first and you have to have the engine alive at the 5.. Don't ask how I know it is a long story but trust me it is real.
 Dave

[John Beckett]

Panic
 
 The program doesn?t recommend much of a change in cam timing but a big change in LC (108 to 116 in one case). With this motor the CR was 10.7 to 1. and the chamber was a standard wedge. According to the program the motor picks up about 30+ HP with LC change.
 
 Put the same cam in my other dyno program and it doesn?t help much if at all. Backing it off some HP may be a little better in the 109 to 110 range.
 
 Nice idea to have a file of cam profiles that the ?puter can play with to see which is making the most HP, but the Dyno Sim program just seems to be extremely unreliable.
 
 John

[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

[Sumner]

The program doesn?t recommend much of a change in cam timing but a big change in LC (108 to 116 in one case). With this motor the CR was 10.7 to 1. and the chamber was a standard wedge. According to the program the motor picks up about 30+ HP with LC change.
   

I could see where going from the 108 to 116 would give you a hp increase as it would up the dynamic compression even more and with the 10.7 to 1 static it would be a lot more compression.  Now you would also have to have the right gas to let you get away with that.
 
 On the street putting the 108 in the 10.7 motor would help bleed off some of the compression and might let the motor live on pump gas.  Of course you now might also be giving up HP.
 
 If you download the:
 
 Dynamic Compression Ratio
 Information and Calculator Download Page
 
 on this site:
 
 http://cochise.uia.net/pkelley2/
 
 It will let you figure the dynamic compression on a motor with different cams, strokes, etc..
 
 I like it, but I'm not smart enough to know if all of the guy's math is accurate or not.  
 
 I use to think compression ratio was compression ratio, but now I can see that the cam and some other varibles are going to really come into the picture and it is not as easy as saying "I want to build a 12 to 1 motor".  The more you learn the more you find out there is to learn   .
 
 c ya, Sum

[panic]

Narrower LCA means earlier intake closing - this will increase DCR (unless the cam is installed retarded).
 I would guess the added power from 116 is intake ramming (inertia fill ABDC).
 IMHO DCR has some flaws, I've written some stuff on it, take a look:
 http://victorylibrary.com/mopar/cam-tech-c.htm#DCR

[Sumner]

Sorry, I mis-read the post and was thinking LSA.
 
 I read your paper.  Very interesting.  I just read it once so far, so a lot of it is still over my head.
 
 I've been working on what I want in the next motor for my GMC.  For the street and not the salt.  Due to the number of miles I drive and  the cost of gas I want it to use 86-87 oct. gas like the current motor.  I'm thinking a 383 or a 350 with a roller cam.  I've been using the DCR calculator to help pick out heads (chamber size), pistons and a cam that would work with the low octane gas, yet give me as much torque as possible.
 
 I'd like to also use your V/P Index if I could figure out what kind of numbers I'm trying to achive for what I want to do.  With the DCR I can take my current motor and look for similar numbers with the new one and hope for the same results.  Should I plug my current numbers into the V/P Index formula and try and do the same?
 
 Thanks,  Sum

[ack]

There is a reason computer games are called fantasy games.
 
 fan?ta?sy  (P) Pronunciation Key (fnt-s,-z)
 1. An imagined event or sequence of mental images, such as a daydream, usually fulfilling a wish or psychological need.
 2. An unrealistic or improbable supposition.