i have tried to mess around with desktop dyno to get close to stock specs. and i even searched around this site for some. and i have found one that is close, but there are a few things that are weird about it. its posted below. does anyone have anything closer to the 88 L98? thanks.

 

Check out http://www.prestage.com/carmath/DesktopDyno.asp

They have a load of cam and head files.

 

yup, except the stock cam. and when i try to put the cam specs in with .05" lift it always give me like crazy results..

 

That is because DD2000 is designed to use "Seat to Seat" numbers in order to give proper results. It is the ONLY way to get the right numbers, so have at her! That's in the instruction manual.

 

yes me too i'm having a hard time getting the numbers for my LG4
it should be around 150HP and 240torque but i get high numbers... i do have a file for cam & heads that say "stock" but stock for wich car?? anyway, it's not the good files for sure...

 

hmm well the problem with that is i don't know the seat to seat specs for the stock L98 cam. im not sure if the one i have in that is correct. also, is seat to seat the same thing as advertised duration?

 

You guys have to remember too, DD2000 is exactly accurate.

 

Since there is no technical support for Desktop Dyno, and repeated calls to them netted me ZERO results, my enthusiasm for DD2000 as a development tool has diminished. They say they are accurate, but I wanted to know if they had ever deviated from their established models and re-tested the software. No reponse from their software developers.

So, since DD2000 is predicting a 525 ft.lb, 510 horsepower response for my fuel injected 385, I'm going to be posting my results when I finally finish the minirammed 385 project. Hopefully in the middle of the summer 2003. The project is behind schedule due to unanticipated expenses and unanticipated drop in income.

--drb

 

I believe so. All of the cam files that DD 2000 supply are seat to seat.

I found the "Seat to Seat" info in their Operator's Manual pdf file, available on their website.

 

if your numbers are ridiculkously high your inputing the wrong info. make sure each and every little peice of info is correct and it will give a good number thats actually attainable.

 

I'll tell you what: I have a DD2000 file here that uses real flow numbers from a real cylinder head, and a real cam profile based on valve lift at .050". Desktop Dyno will indeed let you specify a lobe duration based on a .050" lift. It is an option in the software that you can find in the camshaft sub-menu. The option reads "Camshaft specs @" and you can choose between seat-to-seat and .050" lift.

My cylinder head flow numbers come directly from Tim Siford's (Traxion) flow test data, and the cam is a custom grind based on the Comp Cam Xtreme Energy roller retrofit contours. That very cam (230/236 @ .050", 112 LSA) is now mounted in the short block on a 108 degree intake centerline. DD2000 claims optimal power will be made on a 112 intake centerline. Comp Cams claims a 106 ICL is best. (I'll be trying 108 versus 112 in the upcoming dyno test sessions to see who is right.)

The 58mm (1050 cfm) throttle bodied Miniram with three-inch runners is modeled as a 900 cfm sequential fire injection system per DD2000 manual recommendations.

I can email you the DD2000 file if you want to look at it. When I am done getting my cylinder heads ported, I'll be revising the model to reflect the new port flow numbers. After that, it's assembly time.

The motor will be initially tuned on a water brake dyno stand with wide-band oxygen sensor and exhaust temperature thermocouples. I'm going to be investing $500 in dyno time and whomever is available to help me tune a #730 speed-density ECM is welcome to attend. It'll be interesting to see what kinds of numbers we get. I am just a little skeptical of the DD2000 numbers though - They make so many assumptions, especially about stuff like:

- Cam lobe profiles
- Ignition & spark advance
- Intake runner length
- Exhaust tube diameter & configuration
- Engine operating temperature
- Intake air temperature and altitude
- Connecting rod length

With assumtions of the above variables, I cannot see how DD2000 can get any closer than 10% of the real-world. Therefore, any fiddling with cam profiles, intake centerlines, etcetera seems somewhat misleading, especially if it only makes a difference of a few percent.

Ten percent of 460 ft.lbs is +-46 ft.lbs. That seems to be a pretty broad brush. I want a simulation that is within two percent of the real world.

Then again, DD2000 shows me getting 525 ft.lbs @ 4000 RPM and 509 HP at 6000 RPM, with Tim Siford's ported AFR190 flow numbers, and my cam dialed in at a 112 intake centerline. If I get within two percent on the dyno, I'll most certainly bow to the DD2000 designers!

 

Daniel,

On page 103 of the pdf file it states the following:


Question: The horsepower produced when I enter the seat-to-seat timing on my
cam card does not match the horsepower when I enter the 0.050-inch timing
figures for the same camshaft. Why are there differences?

Answer: The Dyno2000 uses the timing specs found on your cam card, and in
cam manufacturer’s catalogs, to develop a valve-motion curve (and from this
curve it develops the instantaneous airflow for each port at each degree of crank
rotation). Neither the seat-to-seat nor 0.050-inch timing figures precisely describe
actual valve motion; you would need to measure valve position at each
degree of crank rotation to come close to developing an exact valve-motion
diagram! Lacking this, the Dyno2000 “creates” its own seat-to-seat, valve-motion
diagram for use in later calculations of power and torque. A lot can happen
in induction airflow between the time the valve rests on the seat and when it
reaches 0.050-inch of lifter rise. When in doubt, use seat-to-seat timing figures.
They provide the Dyno2000 more information about valve motion at low lifts,
and are more likely to produce accurate simulated power levels.


Hopefully that helps you in figuring what is going on. DD2000 does have some idiosyncracies. For instance, when you choose Dual Plane as the intake type it seems to assign the power you find from a really top flight intake, like a Performer RPM Air Gap, instead of the generic factory manifold. Thus I knock 20 hp right off the top of any figures it provides me, as I have a simple Performer intake.

Also, the hp and torque numbers DD2000 comes up with are Gross HP and Torque, as in the engine on a stand with NO accessories attached, not even a water pump. For a GM-style SAE number you should maybe slice 30 hp off what it says, to account for the accessories. And an additional 20% for rear wheel hp numbers, if you are running an automatic tranny.

 

Breathment,

I couldn't find you other post looking for a good cam selection.

I've decided upon my buildup and I'm definitely going roller cam. Now these programs tend to be rather screwy, so these numbers may be way off, but for what it's worth.........

Comp Cams XR264HR cam...... 487 intake 495 exhaust 264 in duration and 270 exhaust

Here's a little comparision between 3 cams I looked at:


264 peaks are: Horsepower 455 @6000 rpm
Torque 458 @ 4000 & 4500 rpm

270 peaks are: Horsepower 463 @ 6000 rpm
Torque 456 @ 4500 rpm

ZZ4 peaks are: 469 horsepower @ 6500
441 Torque @ 5000

XR264HR XR270HR ZZ4
RPM hp/tq hp/tq hp/tq
2000 157/413 150/395 143/374
3000 249/437 240/420 224/392
4000 349/458 344/451 327/429
5000 428/449 428/449 420/441
6000 455/398 463/405 468/409


They're all pretty close, but the torque curve of the 264 is pretty impressive if you ask me.

 

i always thought that it was more accurate to specify duration at .05" then using seat to seat. thats why u look at .05" duration when picking out a cam. at least that is always what i have been told. so why would Dektop Dyno actualy choose a less accurate method?

 

Simply because it was easier for them to code. And it isn't any less accurate, as far as software measurement goes, it just depends on how the software programer decided to measure things. In this instance it was apparently easier to do it seat to seat.