TheSleeperS

Nothing against Sia ... infact, he did a great job posting his dyno result ... very good reading material and well put together .. for a guy with little clue on mechanical stuff .. he sure did a good job ! .. hats down !

As a consumer, I have read the result to be inconclusive owing to 2 factors .. method used to determine the findings & a sense of biasness in responses from Sia and his supporter (JD).

I felt the obligation to share the following. Truly text book stuff for you folks to make your own judgement.


An extract from ...

Dyno Correction Factors - commentary by John Card

Its amazing what you can dig up on Google these days. Old posts never die on the internet. John Card (of Dynapack USA) offers some insightful comments below on Dyno Correction Factors.

"OK guys, here's some info on why the dyno correction factors are all over the place. A good amount of the power losses associated with a roller-style chassis dyno are due to tire rolling resistances. Mustang makes single roller dynos and dual roller dynos - I get the impression from the previous posts that it was a dual roller Mustang unit that was used in this case. If you think about the contact patch of the tire, it is designed to meet a flat surface on the bottom as it rolls - after all, tires are designed for roads, not dynos. Even on a flat surface, a tire has rolling resistance, but if you put it on a surface that concaves the tire inward on itself, that makes the rolling resistance worse. A sharper diameter of the inward concave will be produced by a smaller diameter roller and more drag will be produced that a roller of a larger diameter. This is one reason why Dynojet has chosen a large diameter roller - the other is that it makes a better "flywheel" for their inertia requirement, but that's a different subject. The only advantage (in my opinion) to a small roller is in the packaging of the dyno (smaller platform or hole in the ground for the dyno), but now you have a traction problem and difficulty keeping the car balanced on the small roller, so they use two rollers and the vehicle is a little more stable, but now has TWO small diameter contact patches, so tire drag is increased further. This tire drag is variable.

Variations in horsepower loss vary due to different tires, different pressures, different vehicle weights, and even different methods of strapping down the car - that's why I have heard everything from 10% to 35% for estimated power losses "in the drivetrain" on a chassis dyno. I put the drivetrain in parenthesis, because this loss isn't all coming from the drivetrain, some of it (again, it's variable) is being contributed by the dyno and the tire/roller interface. Do you think an auto manufacturer would really accept a 35% power loss from their drivetrain engineers? Some dynos say they can measure your drivetrain loss by doing a coastdown test. They tell you to get the vehicle up to a certain speed. pop the car in neutral, and let it coast down - they measure the time to decelerate, and this is supposed to be the drivetrain loss. Think about this: Under acceleration, the gears are smashed hard against each other, the bearings are being side loaded, the pinion is trying to unscrew itself out of the rear-end, etc. During the "coast down test" everything is unloaded and freewheeling as it decelerates and he gears are being driven on the opposite sides of the teeth - the car is now being driven by the wheels and there is no load at the input shaft of the transmission. The frictional loads and losses are not the same as during hard acceleration. If the loads aren't the same, then what good is the test. Sure, you've got data, but it's worthless.

TheSleeperS

we be constructive this time ... you'd said coming from an engineering background ... did you graduate ???? ... or one of those correpondent degree ???? ... u can't even recognize that this fellow John is talking textbook ... freaking unbelievable, you know so little and is look upon a big brother in the forum !

Youreviltwin

Whatever enyone says... I saw for my self before and afters on 3 cars... REVO made power.

JDBlueAudiS4

4th year.... Also he talks about different tires etc.... how much different can the coefficent of friction be between different tires of the same line, say two high performance tires. In the real world the tread pattern as it meets the ground will change the ammount of grip one has, also if debris or water is standing on the road, how the tire disipates these things. On a dyno your dealing with the true friction your getting from the tire. Now I can see saying that the rim size and weight will make a difference on your results. Just like the problem with rotating a mass of mass m, your rotating the wheels which hasve a mass w. Without getting overlly technical the angles in which the force is applied to the rollers by that mass as well as the location of the center of mass as it rotates. Larger rim will most likely have a center of mass thats farther out. (im starting to get rather tired so if some of this is a little foggy im sorry) Now you say by using a hydrolic hub attached dyno you have fewer variables. While this is correct, however you fail to take into account several variables that change because now your not reading real workd horse power (AKA what your actually putting to the ground) but whats coming off of the drive train. Even still, I think that dynos in general have theorhetical and physical issues most of which cant really be fixed.

TheSleeperS

and making even more power with AmD's ... but one cannot post pledging that his findings is accurate ... it must hold water, ... that's why we were quite about our findings.

And now we have two clowns in the forum making their finding like a new invention on roller dyno. And worst off, and from my perspective, it sounded like colaboration with the tuner.

Where is the credibility ???

TheSleeperS

don't disappoint your parent ... I always tell that to my son when he was in his 4th year.

JDBlueAudiS4

the main reason I have setup independent testing..... Also you can tell a lot about the power a car is making by logging certain engine variables. In face you could do some fancy calculations to get the power a car is putting out without using the dynoes numbers and just using numbers begin generated by the engines sensors (which will be done to confirm the dyno findings).

JDBlueAudiS4

but i still had to go throught the basic engineering classes that are designed to kick your a$$

TheSleeperS

It's the rough variables you do not want in the HP equation ... noticed the "hop and twist" on vehicle @ the last leg of the pull ... that infact will throw your numbers up. For us to get virtual increase of HP ... we would snap the thing and make it hop and twist. Now, what the fvck kind of variables are those ?????

JDBlueAudiS4

when the operator let off the gas and put in the clutch that "hop" wouldnt be factored since we would have already passed the measured MPH.