OK, I think we are getting to the part where you are unclear. It measures the amount of force applied to the drum by comparing the amount of drum acceleration vs the time it took to accelerate.
Ya you kinda oversimplify things, it can’t simply measure the accelration due to a small thing called momentum.
Therefore the dyno measues the acceleration, from one rotation to the next, then uses a bunch of factors to try and remove the momentum of the drums from the equation, and give you a reading of the actual force you are applying.
This isn’t a perfect process, dyno’s use a bunch of hardcoded variables to produce their end result, an estimate of your power.
I don’t build or design dyno’s so I can’t tell you why it’s results are affected by the gear ratio, but they are.
Therefore the dyno measues the acceleration, from one rotation to the next, then uses a bunch of factors to try and remove the momentum of the drums from the equation, and give you a reading of the actual force you are applying.
Put simply:
Objects in motion tend to stay in motion. Objects at rest tend to stay at rest.
This isn’t a perfect process, dyno’s use a bunch of hardcoded variables to produce their end result, an estimate of your power.
I don’t build or design dyno’s so I can’t tell you why it’s results are affected by the gear ratio, but they are.
No, a dyno measures acceleration amount vs time. You can apply correction factors afterwards to account for elevation, humidity, and temp, but the raw data is acceleration vs time. And this raw data is basically as close to perfect as you can get. It shows how much your car was able to accelerate a known weight in a known amount of time. Now, depending on a slew of factors that data can change. However, the change of a gear ratio alone isn’t one of those factors. A ratio change can help intake/exhaust resonance, or be a more effecient power path, but taken alone, there is no difference in power.
Removing momentum from the equation basically means that you don’t measure the force needed to overcome the “momentum” of the drum. And, seeing as only force applied to the drum can cause it to accelerate/decelerate, it would make it pretty hard to get any reading at all given your assumption of how a dyno works.
Put simply:
Objects in motion tend to stay in motion. Objects at rest tend to stay at rest.
This isn’t a perfect process, dyno’s use a bunch of hardcoded variables to produce their end result, an estimate of your power.
No, a common chassis dyno measures acceleration amount vs time. You can apply correction factors afterwards to account for elevation, humidity, and temp, but the raw data is acceleration vs time. You can blame a selectively or improperly applied correction factor to explain your power difference if you like. That I can agree with. But, like I said, this is the perfect example of the intervening variable I mentioned repeatedly earlier.
I don’t build or design dyno’s so I can’t tell you why it’s results are affected by the gear ratio, but they are.
So you don’t know how a dyno works, and you refuse to admit that parasitic or engine variables can make a big enough difference. I agree it seems like a big difference, and without taking things apart or seeing data logs, there is no way for me to credibly explain it. However I think there is an explanation of the power difference. It could be 1 15 year old engine sensor giving a different reading, or it could be a multitude of things, but gear ratio alone isn’t it.
Also: Seeing as you now have said you don’t know how a dyno works, just keep arguing with me. :shrug:
I know its nt going to help by more people chiming in, but I think taht both of you are right and that you aren’t truly arguing the same concepts here.
Yes you realized an increase in power due to gear changes and yes a tranny/gear change will not produce more power. Why is this so?
Well you were probably on a dynojet (more common, not as complex as dynamometer) which measure power by the rate at which rollers get up to speed. Well since we know that you can drive at 50 mph in 4th gear and 3rd gear, you can be in 2 gears at th esame speed. If you meausre a 3k-redline pull in 3rd gear and end up at say 78mph and it takes you 4 seconds you will get one reading of power. If you do another pull in 4th gear (same tranny, same everything) from 3k- redline and it takes you 6.5 seconds then this is so because you are putting down less torque (which the dyno measures) and you will get a lower reading in both. This only happens because this is not a newer more advanced dynamometer which uses load to measure torque whereas these take the same amount of load to turn the rollers regardless.
These dynos measure power by applying load to your motor and seeing what it takes to maintain this load. These dynos will see no changes due to gearing/tranny’s at all. However these are very expensive and not very common.
There is a LOT of good information in this thread however. And the results that you all are seeing because of tranny swaps/gear changes are valid simply because of the TYPE of dyno that is being used.
Not exactly. Originally, Scooby and the other guy were arguing that deeper gears = higher power readings. They have now abandoned that platform, largely because I think they realized they are wrong. Now they have moved to a “ratios still effect readings” but seem to beleive that the it is the ratios themselves and not other factors like parasitic loss or engine variables that account for the change. Personally, I think they are attempting to basically jump to a different arguement/platform that can hopefully result in a drawn out tie position, instead of just admitting they were wrong earlier. The smokescreen does help maintain some vestige of credibility.
My point can be summed up in 10 words: Gear ratio alone has no effect on dyno power readings.
If I can finally just see “OK, I get that ratios alone make no difference to measured power” I’d be a happy camper and deam the matter settled.
The mere fact the internals are different can lead someone to infer that frictional losses are different depending on the transmission. Having said that, you may argue that the difference is not as dramatic as 7% from one transmission to the next.
I personally have not used a dyno before, but I have friends who have. They have seen variations as much as 3-5% on the SAME dyno with the SAME car using the SAME gear in an single day’s worth of dyno runs.
Now, that 7% variation from different transmissions seems a little more plausible. Also don’t forget that environmental factors could also play a role in skewing dyno results. The humidity, air temp, engine oil condition, tranny oil condition, ECU’s happiness… – all play a factor.
It is VERY difficult to compare dyno results and claim a HP improvement without holding EVERY variable constant. Simply having your tires wear 3/32nd’s down can skew the results and make it look like you are putting out more WHP. (Remember gear ratios – your wheel is also part of the gear-ratio system…)
width, profile, wheel diam, Tread depth (# 32nds), tread depth (in mm), circumference, Radius
205 45 16 10 15.875 1477.2838 303.3875
205 45 16 1 1.5875 1462.9963 296.24375
Difference Circumference = 0.97% (2.35% difference in wheel radius)
So a new tire can yield a 2.35% difference from a worn tire. That’s about 3.25HP if all other factors are constant. (Torque is a measurement of Force, which is directly proportional to the radius of the wheel.) Having different wheel/tires on for 2 different dyno runs WILL get you more significantly different results, with all else the same. But, the measured power SHOULD NOT change with selection of gear if there are no losses in the system between the engine crank to the dyno drum and all else remains the same.
Before you go around claiming a ys1 tranny will “generate” more WHP (or 3rd gear generating “more power”, consider what’s actually happening –> the 3rd gear on the ys1 tranny COULD BE more efficient at bringing the power to the wheels. Is it capable of getting 7% more HP? That’s a topic for another debate. Wouldn’t want you to go around claiming something that’s not true… (like trannies “giving” you more WHP.)
this speaks for itself, you don’t even have any experience actually DOING ANYTHING! I’ve been to the dyno nearly a dozen times, I can ALWAYS repeat my results within 1-2hp tops, I can’t speak for other cars, but my integra has always been extremely repeatable. You sound exactly liek what you are, a bench racer who has never even done the things he’s trying to argue about.
Maybe one of these days you will actually goto a dyno, then you will change the gear ratios and notice a huge difference in the readings. And you will realize that how it should work, and how it actually does work are two different things.
Again I’ll ask, Dynojet themselves have admitted their dyno is susceptablke to gear bias, they have commited to fixing that problem in the post-2005 models. What don’t you understand?
You can blame a selectively or improperly applied correction factor to explain your power difference if you like. That I can agree with.
Umm…these are constant variables, they don’t change, so they couldn’t be responsible for the changes. And before you start spouting off about correction factors, it’s 1.07 here, and it’s been 1.07 everytime I’ve dynoed, the tiny variances in barometric pressure don’t do jack. And again, these would be random factors, and would not be repeatable, which they are.
If I can finally just see “OK, I get that ratios alone make no difference to measured power” I’d be a happy camper and deam the matter settled.
Sorry, since evertime I change gears I get substantially different reading on the dyno, and numerous people have claimed higher numbers by changing to an S1 gearing, and an entire Corvette board has formed a consensus that switching to 4.10 gears will cost you 10whp on the dyno, no…I can’t make that statement.
Chassis dynos are great tuning aids but they only give a approximation of power output as some of the important variables are not accurately controlled. Certain magazines seem to think that results obtained from chassis dynos are the gospel. They are not. In one recent independent test, hp figures varied by 11% simply by doing the runs in different gears and in another test, results varied by almost 4 % by doing the runs with a different wheel/tire combination. Tire alignment has been shown to affect results up to 3% as well. Note that Engine hp DID NOT change here yet the dyno recorded an increase in hp at the wheels. A change in wheels/tires also does not affect true, wheel hp either, only the rate of change on the rollers and the vehicle acceleration on the road. One can only conclude that inaccurate moments of inertia and correction factors are being used. http://www.sdsefi.com/tech.html
If everything you say was true there would not be an 11% variance in readings using different gears, it would be impossible to gain even a fraction of that power, friction of gears can not account for that much variance, bottom line.
I can’t put in any better than that, so I guess I’ll leave it here.
I sincerely hope this is not an attempt at name calling. I have tried to remain civil and back my points with indisputable evidence. (i.e. Fundamental laws of physics.) I try my best to listen to others and will be open to ideas if proven with logical deduction. If I’ve made a mistake in my calculations or in my reasoning, point out my mistake. I’ll eat a piece of “humble pie.”
The idea that “everyone got the same results” just isn’t enough to make it a “theory” let alone change laws of physics. It’s fine everyone got the same results – it is possible that 3rd gear produces less losses because of the design.
I have not disagreed with your claim that changing gear ratios affected your dyno results. I have actually wrote information to support your claims that WHP as measured can vary. (See my comment on wheel diameter – you quoted the same thing.)
However, you CAN NOT go around and say your “3rd gear produces MORE WHP than 4th gear.” It is Physically impossible. It IS fine if you go around saying “3rd gear is more efficient” – that is all. I would hope that you can agree that “gear ratios CAN NOT affect power output” in a closed, loss-less system.
Please, please tell me you at least understand and accept that part of it.
what I would go around saying is “due to flaws in the design of dynojet chassis dyno’s, raising or lowering your gear ratio can have a dramatic impact on the amount of power, as measured by the dyno”
Those last 5 words are very important, I’ve never once said that the gearing actually allows the ENGINE to make more/less power, it simply causes the dyno to MEASURE more/less power.
Tell us all why. I don’t buy blind faith or magic. I would argue that changing ratios will change the frictional characteristics of the tranny/differential/cv joints. Therefore, I personally have no doubt differing ratios would give differing results.
Again I’ll ask, Dynojet themselves have admitted their dyno is susceptablke to gear bias, they have commited to fixing that problem in the post-2005 models. What don’t you understand?
How physics can take the day off.
If there is a problem with gearing bias with dynojet’s inertial dynos, it would be more to do with the software’s interpretation of the raw data. Which may be what you have been alluding to. That I can understand. That may also play into what you were saying about dyno imperfection. If that is what you meant, I can agree with that. However it would again be an example of an intervening variable that I mentioned countless times, and not a fault of the raw data.
Umm…these are constant variables, they don’t change, so they couldn’t be responsible for the changes. And before you start spouting off about correction factors, it’s 1.07 here, and it’s been 1.07 everytime I’ve dynoed, the tiny variances in barometric pressure don’t do jack. And again, these would be random factors, and would not be repeatable, which they are.
OK, don’t blame the correction factors. I just threw the idea out there in case you hadn’t considered it. If you feel that temp/humidity/air pressure aren’t significant, then that’s cool. You may have tested on somewhat consistent days. I mean, I’m not there, I was just offerring a potential explanation. Like I said, any explanation of why your readings don’t make sense is purely conjecture.
However, if you think that the corrections dynos use are irrelevant, then sadly we are at an impasse again it seems. I was hoping above that maybe you meant that through dyno error you meant that the way dynojet software interpretted raw data might cause the differences you observed.
Sorry, since evertime I change gears I get substantially different reading on the dyno, and numerous people have claimed higher numbers by changing to an S1 gearing, and an entire Corvette board has formed a consensus that switching to 4.10 gears will cost you 10whp on the dyno, no…I can’t make that statement.
So you are convinced there there is no possibility that different amounts of parasitic loss could play a factor? The fact that a car with final drive 4:10 ratio versus a stock 3.42 losing power due to frictional loss is not possibly? I dunno, I think a %3 power loss could be explained by a tranny and pinnion having to spin almost %20 faster. But frictional power loss is BS right? But wait, a low gear ratio works wonders in the S1, how can this be? Could it be that there is some magical mid point? Could it be that maybe each car has a ratio where frictional loss is minimized and power transfer effciency improved, causing a gain in measured power to the wheels? Poppycock! We must dyno in 1st for mad power!
edit:
Actually having read your response to waferGS, maybe it is the software interpretaion of data you are blaming for the gear power difference?
I guess my question then becomes:
So you understand that the power output shown on the dyno graphs are flawed due to how the data is interpretted by the dynojet, and that the actual power to wheels is the same using different gear ratios?
I guess I may have been wrong earlier, maybe we were saying close to the same thing. Except I called it a interveneing variable and you called it a imperfect dyno.
ya pretty much, the end result is the dyno shows more hp for our cars when they switch to the shorter gears like the S1.
to top this thread off with a little cherry on top, I emailed dynojet, here’s their reply:
Question:
Hi, my friend and I are having an argument and I though maybe you could clear it up.
When I dyno my car on a Dynojet the dyno shows a 5whp gain when using 3rd gear as opposed to 4th. Now I think this is due to the higher gear ratio in 3rd, however my friend claims that the dyno measurements are independant of your gear ratio, therefore the variance must be due to other factors like parasitic loss or increased gear-drag. To me that seems like a huge difference to be cause solely by increased friction or parasitic loss.
Are your dyno’s affected/skewed by the gear ratios?
Reply:
The one-to-one gear (or closet to if a true 1-to-1 is not available) will always yield the highest horsepower on the Dynojet Dynamometer. One-to-one is usually fourth gear. Gear ratios can certainly affect horsepower numbers but this is usually only seen with significant changes. For example going from a 3:27 final drive to a 4:10 will show a loss of power. Also keep in mind that any changes in rotational mass (tire size, tire pressure, wheel sizes, etc.) will effect horsepower.
As for why your car shows more in 3rd than 4th, I am not sure. I would have to see the actual dyno run files (not the printed graph but the actual file) to provide an answer.
Will Fong
Dynamometer Marketing & Sales
Dynojet Research, Inc.
2191 Mendenhall Drive Suite 105
North Las Vegas, NV 89081
T (800) 992-3525
F (702) 974-0608
Yeah, I wouldn’t say that email is a slam dunk for me, but it seems to correspond exactly with what I’ve been saying.
It says that there can be a variance, but that the variance would be due to the greater effeciency in 4th (or the ratio closest to 1:1). That supports my previous assertions.
Also, that a deeper gear would show a loss in power. That makes sense as it would force the drivetrain components to spin faster, creating a greater frictional loss.
And he finds your 3rd gear power a mystery like me.
good debate guys…i’ll admit that my assumption of why the readings are different when using different gears is misleading, but i’m still certain using different gears gives different results
I say kudos to scooby for actually posting that e-mail even though it wasn’t really all together favourable to his point. That took some balls. :rockon:
Props for the email to the dyno folks. The email does support Stang’s (and mine) arguments on physics though. A change in the “FINAL” drive ratio does affect measured WHP. It’s kinda like using 185/40/14" wheels and getting more WHP than using 225/60/18" wheels.
I guess we’ll never really know for sure why 3rd gear gets more WHP readings… :think:
Scooby - Please update the post when a possible answer comes up.
Any aspiring Mechanical Engineers on G2IC??? :idea:
