Glad you guys like it.

 

Here's a good post here about the differences: http://forums.nasioc.com/forums/showthread.php?t=583691

Assuming what is stated is true, I wouldn't consider a mustang dyno to be the absolute truth. What's important isn't the actual number, but the gain compared with the baseline on the same dyno with similar conditions. Regarding which gear to use, AT should use 4th, and MT should use 5th as those are 1:1.

 

Why do people aim for a gear ratio of 1:1? The final drive gets multiplied in there, as well as rim and tire diameters, so even if every car on the dyno ran in their 1:1 gear, they're overal ratios from engine to tire would vary all over the place.

 

I Just dynoed my bone stock 2004 6MT and here are my results:

Run 1 240.28hp 236.35 torque
Run 2 238.66 236.48
Run 3 239.91 238.11

I'll be posting the dynos in a new thread.

Needless to say, I was quite pleased with these numbers.

Dynojet, 5th gear, 58 degrees, 29.61 in-Hg, humidity 6%, with no correction factor.

 

1:1 would give each car their best numbers, which gives some consistency

 

What makes 1:1 give a car it's overall best numbers? What about inertial losses, rolling resistance, etc? I'd expect the best numbers to come from the highest gear (lowest acceleration rate) in general, the limits being the max allowable speed on the dyno and speed governors of the car.

 

Sorry but you earned this now!!!!!!!! A$$Hat



Mod please delete/lock this thread!!!!

 

Aww, looks like someone is a little upset that they didn't hear what they wanted to hear. There's definitely too much real info in this thread, better lock it or delete it right away!

 

I don't believe he is upset. He just is tired of someone spewing a load of bs like you are. Especially about you argueing on the 1:1 part which made you look very dumb.

 

Another hater springs to life. You really think RubbinInRI would have attacked me instantly after my first post if I instead told him that he was really making more power than the dyno indicated? Yeah right, re-read it. I think I brought some rather useful information to those that can appreciate it in this thread. And you're right, we should all repeat "we must dyno in 1:1... we must dyno in 1:1..." rather than get to the bottom of why that is, or isn't ideal. I mean, it's a thread about dynoing... you're right, it's dumb to challenge the status quo.

 

I am not a hater. I just know when someone is wrong. 1:1 is more accurate. It shows the total amount of power. It doesn't multiply the torque or hp like lower gears would. You need to do some research yourself. Until then stop posting.

 

^ Again the smarter one!!! TY MechEE get off your high horse. Look at the way you get your "Real numbers" How many variables do you have??? A hell of a lot more then the same Dyno!!!! I'll repeat myself yet again!!!! I did this to get a #, I don't care if it's 1 or 1000 hp. IT DOESN'T MATTER!!!!!!! What does matter is that I have a number, being right or wrong, to go off now to see what a mod really gives me. Not some # probably made up by some number crunching geek came up with. By going to the same Dyno every time, I hope to eliminate any variable. I know this will be impossible but it will minimize most I hope. You have your point and the rest of the world has theirs. You **** people of by saying you know the better way or you're wrong.... etc. You know if you don't like it or have nothing better to do........ play with your dog!!! It'll be good for you and him! You have a special day!!!!

BTW: you should use your spell check function

 

It's pretty clear that "MechEE" is just a troll

 

You shouldn't just repeat what you hear like a drone without understanding it. But because I'm such a nice guy, I'll add even some more useful info to this thread so you guys can throw a bigger fit.

You accelerate the rollers on the dyno by applying a force through your tire contact patch on to the roller surface. How is that force generated? Well at a given instant your engine is producing some net effective amount of torque, T. That torque is then multiplied by the gear ratio, Ng, for a total of T*Ng. THAT torque is then multiplied by your final drive ratio, Nf, for a total of T*Ng*Nf. That is the torque present at your wheel, which is converted to a force through the radius of your tire, R (torque = force * radius), for an applied force at the tire patch of F = T*Ng*Nf/R.

So why do people think that making just the Ng factor in there equal to 1 magically make your car put out the highest numbers? They figure that transmission losses are minimized in this case, but that is not really true IF you are still transmitting through a 1:1 main gear set. There are losses that increase with relative gear speed, and losses that increase with gear load, both of which are hard to quantify. But you can be assured that they are not both magically minimized with a 1:1 ratio. In the "straight through" gear, you are still transmitting through a gear set. Easily 4th or 6th could have fewer losses at 5th since the losses are not directly correlated to the relative ratio. Also, the higher the gear, the more power lost to rolling resistance, but less power lost to accelerating parasitic inertias (wheels, flywheel, crankshaft, etc). Again it is not clear that the minimum just happens to be in the 1:1 gear.

So again, why the 1:1 gear? It has simply emerged as more of a standard than anything else, another very small variable to hold constant in the many dynoing variables. It does not necessarily give cars their best numbers, which was my point. Wasted on all of you I'm sure.

But this is a dyno thread, and is therefore neither the time nor the place to discuss issues relating to dynoing a car! We should be congratulating RubbinOneInRI on his outstanding absolute numbers. BTW, feel free to look up my dyno thread and "troll" me with some interesting technical banter. I, unlike most apparently, would prefer this over "yo dawg, nice numbers."

 

Wow, we have another problem child on the forum.

You are attacking a well respected member of this forum. And someone who has more knowledge on this subject and many others than you. Now that I have taken the time I will post below what is correct.

Dyno Thoughts and HP Losses

After reading various articles in numerous publications on dynos and horsepower, I feel I should put forth a few observations:

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.

On intercooled, turbo cars, there is usually insufficient airflow to ensure accurate results due to charge temperature variation which can be substantial. Even coolant temperatures may not stay down during the run which can affect power outputs considerably. The rate of acceleration is also important on turbo cars to be sure that the boost is not lagging the engine rpm. With RPM climbing too quickly, the boost has not reached a peak value so the hp figure is again inaccurate. Turbo cars should therefore be tested in top gear.

Without proper temperature stability and accurate moments of inertia on the rotating components, there CANNOT be accurate results as the scientific method is no longer being applied.

When all things are kept the same between runs and you get a tangible gain, it is a gain at least. How much, is open for discussion. It is important to note that as the oil temperatures in the engine, transmission and differential increase, friction usually decreases. This manifests itself as an increase in power at the rollers on each subsequent test. This factor should be accounted for when doing back to back runs. It may look like you are gaining some power on each run by making other changes when in fact this is due to reduced oil viscosity. When using a chassis dyno, always use the same gear and tires and wheels and start the runs from the same speed or RPM. Re-baseline periodically to see what temperature increases have done to power output.

Chassis dynos are quick and easy to hook up but have many of the above failings. They do not possess the accuracy of a properly calibrated engine dyno which has a more carefully controlled environment and condition set. Obviously, most non-professionals don't want to be yanking engines to use an engine dyno so chassis dynos do have their place.

Flywheel vs. Wheel HP

As most people know, there are power losses through the drivetrain so wheel hp is always lower than flywheel hp. Front wheel drive cars with transverse engines tend to be more efficient than most rear drive configurations due to the layout of components. However most publications overestimate these losses considerably.

Most rear drive cars have a 1 to 1, 4th gear which means that the power path goes directly through the mainshaft of the transmission. The only losses here are bearing drag which is less than 0.5% and the viscous drag of the gears running through the oil which is about 1% with hot oil. Indeed, published data indicates a transmission efficiency of 98 to 98.5% for conventional transmissions in 4th gear. The G35 would be 5th gear.

Losses within the driveshaft account for about 0.5% if they are properly aligned, balanced and with fresh U-joints.

Differential losses in the commonly used Hypoid type gearset is in the order of 6 to 10%.

The worst scenario case for a rear drive setup is on the order of 12.5% in 4th gear, not the 20 -25% often published. If 25% was being lost in the drivetrain, the oil would boil in the differential housing in short order and aluminum transmission cases would fatigue and break from the temperatures generated. On a 200 hp engine, something on the order of 37,000 watts would have to be dissipated out of the transmission and differential housings. Obviously, this is not the case.

Transverse, front drive transaxles usually have no direct lockup gears and no 1 to 1 ratio, however, since the torque path is never turned 90 degrees as in the rear drive setup and efficient helical gears are usually employed for the final drive set, losses are more on the order of 6 to 9 percent in the upper ratios.

Tire pressure and wheel alignment can have very significant effects on losses at the rollers. Tire pressures should be set the same between each test. Tire rolling resistance varies inversely with speed, another factor not taken into account by most chassis dynos when applying phantom flywheel hp formulas.

Comparing the Numbers

Many novices are quick to compare hp numbers between chassis and engine dynos and come up with all sorts of wild conclusions about drivetrain losses. These comparisons are essentially meaningless. Inertial dynos are based on the sound scientific priciple of accelerating a certain mass with a known moment(distance) over a given time. The rate of acceleration of that mass and moment is a result of the force applied (torque). If the RPM is known, HP can be calculated. On an inertial chassis dyno, it is virtually impossible to calculate the the moment of inertia of every tire, wheel, gear, joint , axle and shaft in the power train between the crankshaft and roller, therefore its results cannot offer an accurate HP figure. Even with coastdown drag measurements, these cannot be accurately calculated as different factors are affected in different ways. Some are proportional, some are inverse squared functions etc. Inertial engine dynos offer a very accurate figure if properly calibrated as only the flywheel's moment of inertia needs to be calculated and added to that of the billet. Water brake or eddy current dynos generally measure force (torque) directly through a ram or strain gauge so moments of inertia are not important on these in fully loaded tests.

Concluding that there was a 25% drivetrain loss by comparing HP achieved on an inertial chassis dyno and that obtained on an engine dyno is fundamentally flawed in that the chassis dyno numbers are highly suspect in the first place.

Other things to watch are correction factors applied for altitude, barometric pressure and temperature. These factors are NOT the same for atmo and turbo engines. Using atmo factors inflates the true, corrected HP figures on a turbo engine. In fact, look at the correction factor applied on your dyno sheets and see if they make sense. Many shady dyno operators simply enter a phantom correction factor to make the customer happy. This is a case where the dyno sheet DOES lie. Chassis dynos are essentially for tuning purposes, they are not well suited to giving an accurate hp figure.