Desktop dyno ~is it accurate???

[Dr. Righteous]

I have never tried any of the dyno simulation software that is out there. Have you guys tried any of them? Are they accurate? Has anyone got a reading from the simulation software, then actually had the engine dynoed?

[DusterDave]

I'm still building my Duster, but if Desktop Dyno is accurate, my 440 will crank out 605 hp.
A word of caution: Desktop Dyno was designed around Chevy engines, since they are the most common. DD won't allow you to input certain variables like cylinder head flow, so it's going to default to values typical to Chevy engines.
One hint to cheat it for more accuracy is to choose "roller" if you are running a true Chrysler solid lifter cam.
The more expensive programs, Like Engine Jr., will be more accurate. DD is fun to play with, though. I use it for comparing different cam profiles.

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www.mindspring.com/~dusterdave

[JANDJ]

THAT IS CORRECT THE DESK TOP DYNO PROGRAM IS MODELED AFTER CHEVY ENGINES. THERE IS A WAY TO ENTER HEADFLOW DATA ,IF YOU HAVE IT , THAT WILL MAKE THE PROGRAM MORE ACCURATE. I USE DESK TOP TO DO FIGURE OUT THINGS LIKE COMPRESSION RATIOS AND THINGS LIKE THAT. I USED DESK TOP DYNO AND DESK TOP DRAG TO FIGURE OUT MY CAR,IT PREDICTED 11.58 AND THE BEST MY CAR RAN THIS YEAR WAS 11.47,THATS NOT TO BAD, ALSO YOU CAN DO THINGS LIKE GEAR CHANGES, TIRE SIZES ETC.

[451Mopar]

The simulator programs are only as good as the information you put into them.

The old "original" desktop dyno was a bit optimistic on power output, and there was no easy way to figure which cylinder head to select (actually, small block wedge worked pretty good for both small and big blocks except Hemi's.)

The new Desktop Dyno 2000 allows you to enter headflow numbers into the program so it gives a more accurate result. Overall the program is more consertive. If you input the same engine combination in the old and new programs, the new program will show a bit less power.
The desktop dyno does not compensate for altitude or weather conditions (although the desktop drag strip program does.)

Rember that the numbers given in the simulation assume that the engine has the optimum spark and fuel, so unless you dyno tune the engine it may be off on power a bit.

The simulator results should be looked at like real dyno results, the outputs can be used to see changes in how the engine reacts to different parts.

One thing the desktop dyno dosen't do is tell you what octane fuel would be required, although it does display cylinder pressures.

[DusterDave]

I have the original Desktop Dyno. Another simulator I have is Dragstrip Plus. You can enter the whole car specs plus the engine, and it will tell you e.t., mph, and horsepower of the engine, and at the rear wheels. DD said 605 hp for my 440, and DP said 614.

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www.mindspring.com/~dusterdave

[451Mopar]

Cool webpage, Duster Dave!
Your 440 sounds really simular to my 451, 11:1 CR, 251 @ 0.050", 0.620" lift cam (roller), B-1 B/S heads, M1 single plane, 1,000+ CFM pro series carb (not a dominator.)
The engine simulators were putting my engine HP at about 600+ also, and almost 600 ft/lbs torque!

[Tim_K]

I tried to use Desktop Dyno about 2 years ago to get some numbers. It was not accurate. In only one case, after "building" a nice 9:1 318 smallblock with nice heads, wide variations in cam specs made very little change in the power output. I would not rely on it, and as a result, I am also skeptical of Desktop Dyno 2000.
The one program that I have heard that works well is Engine Analyzer. 340King used to be here and do power estimates for people, but I haven't seen him here lately.
Hey 340King, if you are here, let me know. I have some engine combos I'd like to get numbers on.

[451Mopar]

Tim, that was your combination?
I'll plug it in to Dyno 2000 and let you know what it gives me.

On one of the other topics I ran a simulation of a magazine buildup and the results were very close, I think 1 HP difference?

[T748]

My problem with the original desk top dyno;Take a bone stock 225 slant six and add a 1050 dominator.Big gains across the board.Add pocket porting 2.5" in. and 2" exhaust valves that wouldnt fit anyway and add .700 lift.All this and it makes alot more power without any bottom end losses.It seems pretty generous with hp numbers when you switch to a solid lifter from hydraulic also.

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1968 Dodge Dart GT 440ci.
1974 Dodge Charger 360ci.
1963 Dodge D-100 440ci.

[451Mopar]

If your going to use Desktop Dyno or any Dyno simulator I suggest you read the book "Desktop Dynos" by Larry Atherton (from S-A Design.)

The book explains that when choosing the carburator, the simulator just looks at the size of the carb as an air restriction, and the simulator alaways assumes the correct air-fuel ratio. So yes a larger carb/throttle body should make more power accross the RPM range as long as it can supply the correct air/fuel mixture. The problem is a large carb on a small engine does not get a good booster signal at low rpm, so the air/fuel mixture is not correct and you loose low end power. This is why fairly stock 350 chevy can run a 1,000 CFM throttle body. The Fuel Injection maintains the correct air/fuel mixture.

As for the valve sizes and lift, yes you can simulate combinations where the actual parts will not fit, but if you want to simulate the engine and provide it with real data, the simulator does do a good job of estimating power and torque.

[T748]

Your right on all counts 451Mopar and I do have the book.$18.95 and not an very easy book too read.They spend most of it patting themselves on the back for making such a wonderfull program.Hidden in the middle is the good stuff like why a 440 has smallblock heads.The reason for my rant is that alot of people are using this program to help decide what parts to use.I just think its too easy to be led into making bad choises and come up with overly optimistic power.It's cool for simulating a motor thats already built and proven.BTW if those pocket porting estimates are true,I must be doin' something wrong with the die grinder.

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1968 Dodge Dart GT 440ci.
1974 Dodge Charger 360ci.
1963 Dodge D-100 440ci.

[Dr. Righteous]

Has anyone tried getting ahold of the software company and pointing out how badly their program works with MoPars. How their 'one size fits all' approach doesn't work.

[340king]

Hi Doc, I did try to consult the makers of the programs that I use. They are Engine Pro from Patrick Hale and Engine Analyzer 2.51 from Performance Trends. The area of interest or concern for me was the intake port size. On EA 2.51, a change in intake port volume could lead to very substantial HP gains. This was especially true with long stroke engines. I was very skeptical and still am. We, my machinist and I, have not been able to back up the predicted gains with real numbers. It doesn't help that the engine spit the bit twice during this process. Once it chucked the balancer and the other time it ate the rod bearings. Neither time did it come close to the predicted performance before failure.

On the other hand, I used the Engine Jr. program as a baseline. We never failed to exceed the predicted HP. The torque numbers were closer at peak with Engine Jr. We have been able to nearly duplicate the predictions with EA 2.51 on well tuned engines. Two cases in point are the 360 in my Mod and the 355 dyno mule in Monty's Camaro. The program predicted 511 HP for my 360 @ 6,000 rpm. It made 500. The program predicted 461 HP for Monty's 355 and it made 465. The 355 spent about two weeks on the dyno to get to the predicted performance, while the Mopar hit the numbers out of the box with only a jet change.

Some things I have seen with the little experience that I have had with a dyno. Accuracy in the process is as important with the dyno as it is with the simulators. It is easy to miss the correct combination on the dyno. Only experience and a little luck can beat the clock when flogging on the dyno. Some odd things work when they are compared under a microscope(dyno).

I use Engine Pro to size the cams. It is very quick with only 12 required inputs. I also use it as a baseline. Engine Pro is closer to EA 2.51 in performance prediciton than Engine Jr. Some combinations are within a few HP on both programs.

I use EA 2.51 to play with lobe seperation, exhaust, cam timing etc. It has been a valuable tool.

One last plug for the programs. On another buddy's baja truck, the program(EA 2.5) predicted a 30 HP increase by placing a Victor Jr. on his 355. He later claimed that it was wrong. It was more like 50 HP! He was running a Performer RPM prior to that and I would not have thought a single plane intake could outperform a dual plane in that application. I was proven wrong. I am a believer, with a little skepticism.

Tim, I am still alive. I was/am very busy through the summer. I should start to get a little more time now. E-mail me with your questions.

[BillyBob]

340 King,

There is now an updated version of Engine Analyzer.......3.0 available at www.performancetrends.com

Other sources for software are: www.auto-ware.com/software/ea/ea.htm www.wsu.edu/~moparman/tech/sims.html

[Keith]

Anyone interested in a collaboration in making an open source all mopar specific simulator? I would help a bit, or maybe even organize if there was enough interest. Could be a good way to really get to know mopar engines and theory.

[Tim_K]

Ok 340king, thanks for helping. Here is an engine combination I'm going to build for my '71 Valiant daily driver. I hope you can give me a good idea of what kind of hp and torque numbers to expect. And at what rpm's.
225 Slant Six engine, standard bore.
8.5 compression ratio, maybe 8.3 or 8.0 compression. I know more compression makes more power, but I want the daily driver to run on 87 octane. I'll give up 3% hp to get it.
Bottom end of the motor pretty much stock, tri-metal bearings and such. A MP 268 degree 0.460" lift cam. Probably installed 4 degrees advanced to make up for the 106 degree lobe seperation.
The low compression will allow me to run a full advance curve. 30-35 degrees between initial and mechanical, one light factory spring on one of the weights.
Exhaust is (and will be) Clifford Street Rod 1-1/2" headers to a 2-1/2" single exhaust with a Flowmaster 40 series 3 chamber delta flow muffler.
Induction is currently a factory 2 bbl. intake manifold with a 318 BBD. Would like to switch to a Clifford 4 bbl. (not Hyper-Pak) and either a 390 or 465 or 600 Holley vacuum secondary with the primaries pointed towards the cylinder head.
The cylinder head will be ported, and 440 1.81" exhaust valves for my intake valves and 1.65" cut down to 1.50" 361 exhaust valves will be put in.
Flow numbers? I don't know yet. Maybe you could try several numbers and let me know on all of them. 180 cfm? 200? 220?
The converter in the car now stalls at 1750 and is junk. It bogs the engine way down. I'm going to get one that stalls at more like 2300-2500. That should fix that. The car already has a rebuilt 904 with 4 disc clutches and the wide ratio planetaries. 3.23 rear gears.
Hopefully, this is enough information for you to get me some accurate numbers. If you need more, just let me know. Thanks.

[451Mopar]

Tim_K, I plugged your combination into Desktop Dyno 2000 with these specs:
Stock 225 bore and stroke,
Stock 8.4:1 Compression Ratio
Your valve sizes of 1.81"/1.50"
Heads / intake ported for the new valves.
Headers with muflers,
Mopar 268 duration 0.460" cam installed at 104 per Mopar spec.

I tryed different sized carbs and this is the results: Note peak torque was around 4,500 RPM, and Peak Power at 5,500 RPM reguardless of carb size. (with unported heads peaks were about 500 RPM less, and power was about 10% lower.)

390 CFM 2-bbl: HP=234, TQ=247
500 CFM 2-bbl: HP=242, TQ=252
390 CFM 4-bbl: HP=245, TQ=254
500 CFM 4-bbl: HP=250, TQ=256
600 CFM 4-bbl: HP=252, TQ=258

It looks like the 500 CFM 4-bbl would probbly work good, as going to the 600 made only a small difference, but the dyno won't show losses caused by poor air/fuel metering signals with the 600 CFM carb.

[Tim_K]

Thanks 451Mopar, those numbers seem to be pretty good, although the torque peak is at a higher rpm than what I hoped it would be. Can you give me more numbers on what the power levels would be at 8.0 compression? And what the HP and Torque numbers are at lower rpm's, like 2500 and 3500? Thanks again.

[451Mopar]

Why 8:1 compression? Plan to run Kerosene

Here is the modified /6 file with 500 cfm 4-bbl numbers at 8.4:1 CR:
RPM HP TQ @8:1 HP TQ
2000 79 208 ---- 78 204
2500 104 218 ---- 101 213
3000 131 229 ---- 128 224
3500 162 244 ---- 159 239
4000 193 253 ---- 189 248
4500 220 256 ---- 215 251
5000 241 253 ---- 236 248
5500 250 238 ---- 243 232
6000 248 217 ---- 240 210
6500 236 191 ---- 228 184
7000 212 159 ---- 203 153

From other engines I have, the simulator does OK on the power, but I usually see the power curve at a slightly lower RPM than what the simulator shows. This my be because of the long rods Mopars use?
I think at 8.0:1 you may loose more low end than shown on the simulation because the carb won't get as strong a signal so, again, Air/Furl ratios may be harder to maintain at the lower compression ratio.

[Tim_K]

Thanks again 451Mopar.
Like I said before, I want to run 87 octane AND have the compression low enough to be able to use a full advance curve in the distributor. I think it's more driveable on the street, at least for me it is.
When I rebuilt the 360 in my '79 Aspen R/T, I went from the 268/272 degree .450"/.455" cam to some junk aftermarket cam that had 268 degrees but only .410" lift. Cash was short, and I needed some kind of cam to put in it. It will be replaced this winter. Anyhow, between the cam and installing 0.040" Fel-Pro head gaskets, which lowered compression to 7.92 to 1 (accurately measured) and using a full fast timing curve in the distributor, the car picked up 4 tenths and 1-1/2 mph in the 1/4 mile, and does it with no pinging on 87 octane! I tried advancing the timing another 5 degrees for a test and it still didn't ping!