seat to seat vs. @ 0.050\" cam info power ratings

Playing around with the Desktop Dyno stuff, just trying to narrow down my choices on cams.
If I put in the information for the same cam, one setup with cam timing at 0.050" vs the same cam but at seat to seat timing the results are very different, for instance

seat to seat info gives
RPM HP TQ
3000 250 438
3500 307 460
4000 362 475
4500 412 480
5000 449 471
6000 459

and with cam timing at 0.050 I get

RPM HP TQ
3000 267 467
3500 321 481
4000 370 486
4500 414 483
5000 439 460
6000 414

All the cam info came straight from the manufacturer, and every cam I've compared like this ends up with a pretty big difference between seat to seat vs. @ 0.050".

Does the timing @ 0.050 give more accurate results?

With the setup I've got in the program I'm sure it won't reach 459 HP, even 439 is questionable but I'd like to compare different cams, but I can't find seat to seat timing and @ 0.050 timing for all the cams, and now I can't compare cam A @ 0.050 vs cam B with seat to seat timing right-

I believe the seat timing is more accurate since it tells when the valve is actually starting to open. You should be using the data right off the cam card if possible.

The info is straight from the makers info, when they give the specs seat to seat & @ 0.050 I put them both in just to see what happens, big difference.
Not taking the output to seriously, just trying to compare one cam to another.

On Desktop Dyno use seat to seat. It gives the computer a more accurate model. If you use .050" timing, it has to 'guess' where the advertised duration falls based on the lifter type (and thus cam lobe profile), then model off that. It doesn't actually use the .050" for timing purposes.

All .050" numbers do is give you, me, and the average cam purchaser a rough idea how aggressive a given lobe is or is not. For example I'm using a 286-296 advertised solid roller in my 347 with 246-256 at .050". Another guy might have a 286-296 hydro roller, with 234-244 at .050". My lobe is obviously more aggressive. This is of course other than the valuable cam degreeing purposes =).

Cris

<font size=-1>[ This Message was edited by: Is1BadFord on 10/4/06 12:01pm ]</font>

DD is off in comparison to real world measurements. I own it. I have dyno'd my engines against it and it's plain wrong.

I would coach you to use another program as it was off only by 4HP on the same combo that I dyno'd.

I noticed that DD was always optimistic so I would use the smaller HP numbers which look like the .050" lift numbers. Use DD to help you feel out how one cam performs over another or how advancing/retarding helps. Look for the gains.
[addsig]

if you read the instructions it will tell you to use duration@ .050 , its closer than seat to seat.
save yourself time and money, get the performance trends dyno software and drag simulator.
Mike S

Dyon is fun to play with but don't bet your house on it !!
[addsig]

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On 2006-10-17 21:42, allenman85 wrote:
DD is off in comparison to real world measurements. I own it. I have dyno'd my engines against it and it's plain wrong.

I would coach you to use another program as it was off only by 4HP on the same combo that I dyno'd.

I noticed that DD was always optimistic so I would use the smaller HP numbers which look like the .050" lift numbers. Use DD to help you feel out how one cam performs over another or how advancing/retarding helps. Look for the gains.

</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

Agree completely. And I also agree Perf Trends is a BUNCH more accurate...however it's also a hell of a lot more complicated =). I've built a motor or three in my time, and know quite a bit about engine theory...and...based on their format, I can't figure out if I'm coming or going regarding their flow coeffecients, and how they actually apply to a real motor lol. Using their Victor Jr model head for real power numbers is pretty unbalanced in favor of the heads as just one example.

But all in all, allenman85 is right. Dyno 2000 is a toy, and if anything should be used to get in the ballpark of the right cam. Also, NEVER take their low end torque numbers for gospel...the program does not take port air speed into consideration at ALL!

Cris