Fun with Desktop Dyno

[Dr.Jass]

Anyone ever really mess with this program?

I've been having a lot of fun with it lately... I know some folks say it's not accurate, it's overly optimistic, etc. but I ran Car Craft's old W2 Stroker engine build and came within 2HP of their actual dyno run peak HP. The graphs were quite close, too, so I think it's a matter of being very susceptible to GIGO (garbage in, garbage out).

Well, one aspect of the program I hadn't messed with previously was the Iterator--now that is a cool thing with which to play... you can put in a range of camshaft specs, compression ratios, even bore/stroke combinations on your current engine, and it will pick out the best combination(s)--up to 10--based on whether you want max HP or max torque. Obviously, the more variables you choose, the longer it's going to take to work out every possible combo... but if you have a fast PC it's not so bad (it'll warn you when you get ridiculous).

Anyhow, I ran my 318 through it using realistic head-flow numbers from ported "J" castings (actual flow numbers, though not from mine), the 276/.490" solid MP cam I'm running, and a TQ atop a single-plane intake, with 9.2:1 compression... I think I need a better crank. I didn't do any iterations on it, other than what would happen with 1.6:1 rockers (not a hell of a lot, actually) but this is my combo as it stands.

Even if it's off by 10-15%, it's still a relatively-stout pump-gas grocery motor... for aboot $1700. [smilie=e:

 

[dodgechargerfan]

Where does one acquire said program?

 

[beeper*71]

Barney has spent a lot of time with that program jass. He used it to build the wicked mill in the S-10. It is a good tool IMHO and I think not to far of from real world numbers.He will be back on here soon, perhaps he could contribute what he has learned.

That 318 is putting down some sweet numbers!

 

[firefighter3931]

Desktop dyno is a neat toy but is usually generous in it's predictions, particularly with chrysler motors. The problem with the program is that it's based on a chevy head which by comparison to a mopar head is much bigger in terms of port volume and flow #'s. Some aftermarket chevy sb heads have bigger port volumes than BB mopar heads, fwiw. The chevy rod ratio is also quite different from a mopar rod ratio as we all know so the motors will react differently when using the same software package....

This was the explanation given to me by the builder who ported the edelbrocks and specced out the solid cam for my motor. He has dynoed hundreds of motors of all brands....chevy sb/bb, pontiac, olds etc....and these are his own observations when comparing DD to actual dyno results. I saw this when i plugged in my own combo into the DD software package which predicted ~600hp but it ended up making 535hp on his dyno.

I would think the combo that's been outlined above would realisticly make in the 350-375hp range at the crank...which would be pretty descent for a mild 9:1 iron headed 318 combo with a small solid cam. My .02

Ron

 

[Dr.Jass]

It's not based on any head, though... you have to plug in the numbers unless you use their "mildly ported blah blah" which I didn't. I plugged in actual flow numbers & valve sizes from a Chrysler J head... it wasn't based on anything supplied with the program.

I expect it's a bit optimistic, though as I said it was nearly dead-on with the W2 stroker Car Craft built... 2HP at 600+ is only a .003% margin of error. The graphs were eerily similar, too. I know later versions of the program are far more accurate than the earlier ones. I'm using v3.10 at the moment.

Hot Rod did a 318 last year (oops--two years ago now) that made slightly over 400HP with the wildly-overrated, gar-bosh 302 castings. Those heads had about $1500 worth of porting on them to make them flow almost as well as a stock 2.02" J-head (they got a whopping 215CFM @ .500"), so I'm fairly certain I'm making at least similar power to their combo... their engine had more compression, but I believe the far-better flow (~30 CFM on the intake port @ .500" lift) more than makes up for the loss of squeeze... plus, I'm using a slightly-hotter grind, which is solid to their hydraulic. Plugging in their Comp Xtreme 268H grind drops 39HP from my peak number. [smilie=e:

As beeper said, if nothing else, it's an interesting tool... and that iterator is a real hoot if you let it go wild (and have some time to let it run). On the 474 I'm considering building, it found about 25HP and 40lb/ft by mangling my cam specs... again, maybe not perfect, but I bet real-world testing would show somewhat similar results, if not at the same level. Obviously, it's also assuming perfect weather/climate conditions and God's own jetting, so it's not like I'm going to run around telling people the engine has a proven 440HP... unless I get a real-live dyno slip or a corroborating timeslip, it's just fun for experimentation.

I got my copy bootleg, DCF. [smilie=e:

 

[firefighter3931]

As beeper said, if nothing else, it's an interesting tool... and that iterator is a real hoot if you let it go wild (and have some time to let it run). On the 474 I'm considering building, it found about 25HP and 40lb/ft by mangling my cam specs... again, maybe not perfect, but I bet real-world testing would show somewhat similar results, if not at the same level.

I agree, DD is good for predicting "trends" with camshaft profile changes although i'm sceptical of the power #'s that it predicts. Headflow #'s are good but the software can't measure velocity. Big flow #'s with small runner volumes will make a more efficient combo, everytime. The 440 with it's 1.80 rod ratio and smallish port volume/high velocity heads is a good example of this....A chevy motor by comparison has a less desirable rod ratio and bigger port/lower velocity head that will make good hp#'s but average tq#'s.....at least compared to a mopar motor of the same displacement.

I'll take a flat broad tq curve over a peaky high hp combo on a streetcar any day of the week....

Ron

 

[Dr.Jass]

I'll take a flat broad tq curve over a peaky high hp combo on a streetcar any day of the week....

Agreed, but this whole build started as a "tech article"-type deal, where maximum power on minimum buck was the goal... and let's be honest: max power from a given combo will generally end up being a peaky bitch. This one is peaky, though certainly not the worst case I've seen. Realistically, the torque curve is pretty flat from 3000-6500... it's just high on the RPM scale. [smilie=e:

I have another, more-expensive engine--a 474 low-deck--in the works for a different project, and I'd like nothing better than to have a torque curve like a plateau... it's to be a street-only engine, although it might see a pass or two just to see how well the combo works.