Dyno Question.
01-24-2003, 06:49 PM
#12
Registered User
[QUOTE]Originally posted by ultimate lurker
[B]For example, losses on most FWD, manual transmission, moderate to high hp engines will tend to land in the 25-30 hp range (on a dynojet).
[B]For example, losses on most FWD, manual transmission, moderate to high hp engines will tend to land in the 25-30 hp range (on a dynojet).
01-25-2003, 09:03 AM
#13
Originally posted by schwett
not that i would usually differ with a man who owns his own dyno, but the H series tends to show more like 35-40hp of loss, not 25-30. it is an extremely rare prelude that puts down 175whp stock... 160-165 is the norm out of an engine rated at 200. that's actually MORE than the s2000 - last time i checked the mass dyno poll/thread, the average was almost exactly 200whp, which is 17.5%.
not that i would usually differ with a man who owns his own dyno, but the H series tends to show more like 35-40hp of loss, not 25-30. it is an extremely rare prelude that puts down 175whp stock... 160-165 is the norm out of an engine rated at 200. that's actually MORE than the s2000 - last time i checked the mass dyno poll/thread, the average was almost exactly 200whp, which is 17.5%.
01-25-2003, 09:07 AM
#14
Originally posted by cdelena
Actually if you factor in the secondary reduction gear it may be 6th that is closest to 1:1 (and the secondary reduction design could be the reason for higher losses than other cars). I would think that wheel speed over a certain level may be undesirable on the dyno so lower gears are used.
Actually if you factor in the secondary reduction gear it may be 6th that is closest to 1:1 (and the secondary reduction design could be the reason for higher losses than other cars). I would think that wheel speed over a certain level may be undesirable on the dyno so lower gears are used.
01-26-2003, 07:54 AM
#15
Registered User
Turbo Pwr, by definition if you lose 20% hp (ignoring my issues with using percentages for a second :-) you must lose 20% torque as well. HP = Torque*(rpm/5252)
Actually, I've never dyno'd a Prelude on my Dynapack. But back in the day when the 5th gen Ludes were introduced, we were testing a lot at VTEC.net using Dynojets. Typical stock car put down right around 165, which with a 195 hp rating was right at the 30 hp mark.
In terms of gearing, I don't know where this 1:1 rumor came from, but I've been seeing it _everywhere_ and it's just misleading.
If you do a little research on gearing, you'll find that while power transmission efficiency does vary with gear ratio, the differences in efficiency are quite small. For example, for helical cut gears, you might find that a 1:1 ratio is 99% efficient, while a 3:1 ratio might be 98% efficient. Thus, the difference in power from just a change in ratios is minimal.
Where the change in power comes from is _the load time_. On a typical roller dyno, if you go in 3rd gear on an S2000, the load time from 2000-9000 rpm might be 9 seconds. If you go in 4th gear, it might be 12 seconds. In 5th gear it'll be 14-15 seconds (these are just estimates). I've found that for a typical street car, if you're getting load times under 10 seconds, or over 13-14 seconds, you'll start getting variation in the results for the reasons I've pointed out. I usually shoot for a load time of 10 seconds on most cars I test. But the difference is that I can control the load time, no matter what gear I choose to put the car in.
Now, this is where the thread hijacking _really_ begins :-)
You see, that's one potential disadvantage of a dynojet that I just realized yesterday. Let me give you an example. Let's say you just dyno tested your stock S2000 on a Dynojet. It shows 200.0 hp tested in 4th gear, starting the acceleration run at 3000 rpm. Now, you install an AEM CAI on the car and put it back on the dyno. All conditions are the same (not easily done, but let's assume). You run the test again and the Dynojet shows 207.0 hp corrected. You have a 7 hp gain, right? Wrong. You actually made more than 7 hp, but you have to look beyond the simple hp number. The key is the run time. In the first run, it might have taken the car 9.5 seconds to run from 3000 to 9000 rpm. Now, with the intake, it takes 8.9 seconds to make the run. So the car showed 7 hp more, but it was also accelerating faster, which means more energy was absorbed by the crank, flywheel etc. In the real world, if you were to simulate acceleration, you'd have to take into account the additional measured hp plus a factor for the faster acceleration. I'm not quite sure how you'd do this.
UL
Actually, I've never dyno'd a Prelude on my Dynapack. But back in the day when the 5th gen Ludes were introduced, we were testing a lot at VTEC.net using Dynojets. Typical stock car put down right around 165, which with a 195 hp rating was right at the 30 hp mark.
In terms of gearing, I don't know where this 1:1 rumor came from, but I've been seeing it _everywhere_ and it's just misleading.
If you do a little research on gearing, you'll find that while power transmission efficiency does vary with gear ratio, the differences in efficiency are quite small. For example, for helical cut gears, you might find that a 1:1 ratio is 99% efficient, while a 3:1 ratio might be 98% efficient. Thus, the difference in power from just a change in ratios is minimal.
Where the change in power comes from is _the load time_. On a typical roller dyno, if you go in 3rd gear on an S2000, the load time from 2000-9000 rpm might be 9 seconds. If you go in 4th gear, it might be 12 seconds. In 5th gear it'll be 14-15 seconds (these are just estimates). I've found that for a typical street car, if you're getting load times under 10 seconds, or over 13-14 seconds, you'll start getting variation in the results for the reasons I've pointed out. I usually shoot for a load time of 10 seconds on most cars I test. But the difference is that I can control the load time, no matter what gear I choose to put the car in.
Now, this is where the thread hijacking _really_ begins :-)
You see, that's one potential disadvantage of a dynojet that I just realized yesterday. Let me give you an example. Let's say you just dyno tested your stock S2000 on a Dynojet. It shows 200.0 hp tested in 4th gear, starting the acceleration run at 3000 rpm. Now, you install an AEM CAI on the car and put it back on the dyno. All conditions are the same (not easily done, but let's assume). You run the test again and the Dynojet shows 207.0 hp corrected. You have a 7 hp gain, right? Wrong. You actually made more than 7 hp, but you have to look beyond the simple hp number. The key is the run time. In the first run, it might have taken the car 9.5 seconds to run from 3000 to 9000 rpm. Now, with the intake, it takes 8.9 seconds to make the run. So the car showed 7 hp more, but it was also accelerating faster, which means more energy was absorbed by the crank, flywheel etc. In the real world, if you were to simulate acceleration, you'd have to take into account the additional measured hp plus a factor for the faster acceleration. I'm not quite sure how you'd do this.
UL
01-26-2003, 08:26 AM
#16
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Sorry, I am trying to understand things more. So now changing gears in the s2000 with the J's 4.44 final gear. Does that effect the way the dyno numbers come out? If so, what can you do to correct that?
UL thanks for answering my first question that's the answer I was looking for.
UL thanks for answering my first question that's the answer I was looking for.
01-26-2003, 09:01 AM
#17
Registered User
From an actual drivetrain loss perspective, there really shouldn't be any measurable change in power.
However, since the final drive change means you're putting more torque to the wheels, you'll be accelerating faster. This means your run time (load time) will be shorter. This could mean that you might actually show a little less power on a dynojet.
UL
However, since the final drive change means you're putting more torque to the wheels, you'll be accelerating faster. This means your run time (load time) will be shorter. This could mean that you might actually show a little less power on a dynojet.
UL
01-27-2003, 02:41 PM
#18
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Let's clear up turbo pwr's question. Hp loss and Torque loss on the dyno are not always going to be the %. What ultimate lurker did not explain is how a dynojet works. It takes the weight of the roller, the engine rpm and the time it take to spin the roller to a certain rpm(or run time has ult. lurker puts) to calc. Hp and torque. So if you have a engine that produces more Hp than Torque, it will show more torque loss than Hp on a dynojet due to the fact that torque will be eatin up during the spin up of the rollers weight, and that the Hp comes very late when the rollers are already rolling at a much faster rate. If any one has dyno'd on a dynojet they will notice that at the begineing of the run the engine accel's a lot slower than at the end of the run. You never know the total Hp gain at the crank unless you pull the engine and test it on a engine dyno. Gernby question of what gear to test in. What ever gear puts 1:1 to the gound, lets not forget that you a testing power to the ground. So the wheel Rpm and the engine Rpm need to match has close has possible so the computer can calc. the Hp and torque correctly.
01-27-2003, 02:48 PM
#19
Registered User
A dynojet has an rpm pickup, so you don't have to worry about engine rpm and wheel rpm being close. Don't forget that virtually every Honda out there is running a very steep differential gear - in the 4:1 range or higher. Even in 5th gear on most Hondas you're overall gear reduction will still be well above 2:1. On an S2000 in 6th its closer to 4:1!!
Don't forget that a dynojet measures instantaneous acceleration of the rollers in very small time increments (tenths of a second or less). The energy required to accelerate the roller from any start rpm (roller) to any finish rpm is a known factor and is all part of the calculation of power that the dynojet computer undertakes to provide a readout.
UL
Don't forget that a dynojet measures instantaneous acceleration of the rollers in very small time increments (tenths of a second or less). The energy required to accelerate the roller from any start rpm (roller) to any finish rpm is a known factor and is all part of the calculation of power that the dynojet computer undertakes to provide a readout.
UL
01-27-2003, 03:00 PM
#20
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I was looking at some photographs of the Amuse shop. Apparently they use the Dynapack like UL. It would be interesting to see what dyno's the other aftermarket tuners use to come up with the HP gains for different mods.