<br>If you measure engine RPM you can calculate torque. And print some blue and red curves. <br>[/quote]<br><br>well, the dyno measures torque directly without knowing engine RPM, but your right in that it calculates a meaningful torque number using engine RPM. All it does is compare the rpm of the rollers with the rpm of the engine and, voila, you have flywheel torque, calculated from measured torque. And if you accurately measure engine rpm, then the numbers are more accurate.<br><br><br>the last part went right past me. Unless there is slippage or losses in the tire/roller interface, or in an slush box (automatic transmission) then the dyno won't care how fast anything spools up. my guess is that slippage is the cause of the weird numbers -- if you spin up too fast, the tires will break loose and you'll get lower torque numbers.

 

sorry I messed up on the quoting :P

 

The last opart looks like this- you won't see max power in first gear while driving because the truck will rev into the governor before having much boost. In OD or 5th or 6th gear you will have full power because the gear ratio is high enough to let you make boost before hitting the governor. If you use a dyno which regulates the brake so that you can accelerate from 30 to 60 mph within 3 seconds you'll see lower numbers than on the same dyno set to 10 seconds 30to60 mph time. On an inertia dyno you just have inertia as a brake. So if you'd measure in first gear the same thing as on the road would happen- you hit the governor almost instantly and therefore you don't accelerate anymore. Then you try the same thing in 5th gear and accelerating the same mass from 1-5 mph takes less time than from 10 to 50 (I know our gears are different) so you have more time to spin up the turbo, you get more boost, so more fueling is possible ( Either the AFC or ist software brother in the ECU don't want you to smoke). So using bigger tires gives you a longer overall ratio, and on an inertia dyno where the rollers are just right to simulate a Mustang or corvette, you will see lower power for a turbodiesel with a short ratio.<br>Easy way to determine this for yourself- drive up a mountain in the highest gear where you can sustain 1600 rpm - watch your boost. Then see whether you have the same boost @1600 rpm while on the dyno. <br>AlpineRAM

 

[quote author=AlpineRAM link=board=4;threadid=5599;start=15#54097 date=1034832334]<br>The last opart looks like this- you won't see max power in first gear while driving because the truck will rev into the governor before having much boost. <br>[/quote]<br>under normal driving conditions, certainly. under sufficient load, you'll see max power. I just don't know of many situations what will provide sufficient load in first gear! Thats because torque to the wheels is very very high -- near 10,000 ft lbs for a 6-speed! <br><br>well, thats just because you've found a way to load the engine sufficiently. Its not about gears necessarily, its about load, although certainly the lower gears are harder to load due to the tremendous force (torque) applied to the wheels.<br><br>ahh its becoming clear now. the dyno regulates the brake to accomodate certain acceleration goals. But without regard to that, the only reason you see lower numbers is becuase the dyno is not &quot;pushing back&quot; on the truck as much as the truck is pushing -- otherwise you wouldn't accelerate!<br><br>I see. so my question here is this: why not use a brake and load the truck to its own sweet spot for pulling? If the dyno could arbitrarily apply a constant load at some speed, then you could bring the truck up to wot fully loaded and topped out at its maximum rpm (sort of a stall speed for the truck). Are there any dynos that will do that? That would be one monster heat dissipation problem for the dyno! <br>

 

The Superflow dyno we used at the Diesel Dyno Stampede is a load dyno.. The brakes are applied in order to create a peak power number. Its used for highway tractors mainly and can bring a Signature 600 to a full stop in any gear LOL...<br><br>The way it works is not like the others. You go to full RPM (depending on your governor tweeks) and hold it there. Then the load is applied until the RPM begins to drop at a certain percentage to a low setpoint of say 2000 RPM. This gives you a curve and the HP numbers. With engine RPM the Torque is calculated.<br><br>The Superflow is the only way to go for guys like me with no wastegate and don't drag race. I have the time and ability to fully load the engine and bring it to its knees..LOL... The numbers are consistent and repeatable.<br><br>The guys &quot;up the road&quot; with their dyno from us never get the right #'s IMHO.<br><br>J-eh

 

Well the small inertia dynos are good for simulating acceleration of a car. That's what counts for most users. A drag racer can't use 50000000HP if they are available 30minutes after the start. Since the inertia dynos have an inertia to simulate lets say a corvette or some less they will easyly read wrong for trucks. I don't know the superflow, but the Bosch dyno uses either a magnetic brake or a hydraulic brake to load the engine. Usually we ran the tests upwards. So you start at some RPM, typical 1500 for passenger cars, go to WOT and let the dyno apply the brake till it holds the RPM. Then you let RPM climb very slowly- something like 10secs per 100 RPM or even slower depending on the vehicle. <br>Heat dissipation is a problem that occurs for the dyno- our LPS dyno had a water cooling with 3 cubic meters of reservoir and some massive coolers. <br>Sorry for any spelling errors, its past midnight over here..<br><br>AlpineRAM

 

guys, thanks for the primers on dynos. I was approaching the issue from the standpoint of pulling. not knowing how actual dynos are made, I assumed that the natural thing to do would be to apply a break and dissipate the heat. I can see that inertia dynos are cool for accleration, but really if you want to do that, you can get one of those $150 devices with an electronic accelerometer and accomplish the same thing!<br><br>well, almost. electronic, semiconductor accelerometers are very accurate, and the physics/mathematical proofs of accuracy are solid and robust. The idea is that the accelerometer itsef measures accleration directly and provides an electrical signal that can be processed. well, voila! a little mathematical hand waving (electronic processing) and you have a hand-held inertial dynomometer. Only problem is that electronic accelerometers are only good to about 0-60 in 7 seconds. they're not capable of measuring faster accelerations, so these devices are not so great for funny cars, but great for trucks :-)<br><br>But a good, stout break dyno is arguably the best bet for truck pulls :-).

 

Manual tranny guys should be using 4th gear (direct drive - not overdrive, and not underdrive) for minimal frictional losses through the trans. 4th gear is that gear in the NV4500s. I am not sure about 5600s - can someone confirm?<br><br>At least that's how they have us do it in Omaha... seemed to make sense to me.<br><br>-scott

 

I didn't think altitude would be as big a factor on a Turbo Diesel as on a naturally aspirrated gasser.<br><br>Sure, there's less air for the turbo to compress, but compressed is still compressed.<br>Might take it a bit longer to get the boost up, but once it's up there it is.<br><br><br>phox<br><br>

 

[quote author=dieselgeek link=board=4;threadid=5599;start=15#54510 date=1034908881]<br>Manual tranny guys should be using 4th gear (direct drive - not overdrive, and not underdrive) for minimal frictional losses through the trans. 4th gear is that gear in the NV4500s. I am not sure about 5600s - can someone confirm?<br><br>At least that's how they have us do it in Omaha... seemed to make sense to me.<br><br>-scott<br>[/quote]<br><br>for the 6-speed, this is 5th. But why does that minimize frictional losses through the tranny? in other words, why does the number of teeth on a gear matter? -- or is the gearing itself simpler (fewer frictional parts)? Makes sense if using the 1:1 gear ratio actually eliminates a gear in the drivetrain, though. other than that, it shouldn't make any difference.

 

Doug- direct gear usually is just a dog clutch between input and output shaft. So there are no gears involved.Nor is the countershaft turning. This reduces friction losses.
We usually measured for friction losses in the racecars. You win or loose with the power on the wheels. For the daily driver friction losses can be very interesting.All those beautiful horsepowers used for heating tranny oil or grinding away some expensive parts...

AlpineRAM

 

Lawrence from DD used to work for Dynojet before starting in business for himself. He's logged thousands of hours of dyno time and is probably THE formost expert on Dynojets, and possibly dynos in general, in the country. Once he even spent over 2 weeks dyno testing different rear end gear lash settings for optimal power, for a NASCAR team. DD uses overdrive on its dyno runs to help with turbo spoolup. <br><br>This method doesn't necessarily work on other dynos, such as a Mustang for example, because of the high roller speeds involved. Direct drive works better on those dynos.

 

at my work we have a rule of thumb thatyou lose 1% power for every 1000' of elevation for turbo charged engines and 3% for naturally aspirated. ever heard of this?

 

Anyone who thinks that altitude does not affect a diesel needs to take a Detroit 238 (6-71) grossing 80,000 up a pass over 7,000 feet. What is neat is the old locomotive effect with the smoke trail that you can see for the last 10 miles or so back down the road. And then there was the B-61, naa I won't even go there. Modern engines have enough power to mask the loss to a great extent. I put over 1,000,000 miles on the old 238 years ago. Of course that was when a 318 was a big motor ;D