nopistons94

kahren = pimp god

Lynn E. Hanover

Excuse the late post.



I was looking for a piece of data and found this scramble of ideas. I see people who have it right and have difficulty explaining it. And people on the wrong track who have compelling arguments.



The truth is out there.



The inertia dyno measures a rate of change. That means from RPM "X" to RPM "Z" in some time factor.





This data is collected at the end of the drive train that has mass and bearing drag and lubricant drag and in some cases hypoid drag (sliding spiral bevel), and a book full of drag from sidewall flex and tread pattern deformations, and a few more things I have not thought of.



First, look at what trans gear would be most effective.



That is whatever gear is the one to one ratio. Where the input shaft is locked onto the mainshaft, with no reduction in the trans at all.

This will be 4th gear in most boxes, but may be 5th, in some 5 speeds and even 6 speed boxes.



There will be energy lost in the box as always, all of the gears are engaged with the mainshaft and all of the gears turn all of the time in modern "Constant Mesh" gear boxes. However if no torque is being pumped into the countershaft as would be the case in any other gear, and then transferred back into the mainshaft, the losses from the two additional gear sets meshing under load will be eliminated. So, the one to one gear is the correct gear. In front drive cars, the same thinking applies.



In any case, all of the gears will appear as part of the inertial load, as all must be accellerated, no matter which gear is selected.



The drive shaft is part of the inertial load. Lighter drive shaft = less inertia = higher rate of acceleration.



The rear drive car will report less power than the front drive car, because the hypoid gearset is a bit less effiecent than the bevel gearset in the sidewinder. One reason for Detroit going to front drive is better fuel mileage without any real engine developement.



Years ago I watched Logan Blackburns 240Z after a race, as little ***** of fire dripped from his differential.

The crew chief seemed unconcerned. I asked what that was, and he said that it was the plastic locking compound from the nuts that hold the diff together. They used up a ring and pinion each weekend.

So, the hypoid is less effiecent, and the lost energy appears as heat.





They had run out of Jet nuts and used what they had on hand. So the ineffiecent hypoid gears show off the extra drag as extra heat. Any (most) energy lost as a result of burning fuel in the engine appears as heat. About 28% is converted to mechanical work and the rest is lost in trans heat, differential heat, tire heat, exhaust heat, and so on.



So, in lower gears you have mechanical advantage over the driveline, and dyno load wheel but higher drag from the gearsets. Plus the time between the RPM points will be shorter and the drive line mass will be a higer percentage of the inertial load. So if there is a time related problem with the tune, like turbo spool up time or similar, the lower gear with be a larger disadvantage.



Another way to think about is this: the longer the time spent on the run, the closer to a steady state dyno run it gets, and the more accurate the reading.



No?



Suppose the big dyno wheel had very little mass, and when at full throttle from say 3,000 RPM to 8,000 RPM

the run takes only one second. The run would then not include full boost, and stable injection rates. How would you gain any usefull tuning information from that dyno?



Still sound wrong?



But it is the rate of change that is the basis of the test, so in order to have any accuracy at all, the dyno must have a massive load wheel. So the test will last for some extended time period.



So Bob's car has a light flywheel, 5 1/4" Tilton clutch pack, an aluminum drive shaft, and BBS wheels.



And Jeff has an identical car with the stock flywheel, stock steel clutch, stock steel drive shaft, and stock wheels.



On the Stuska (or Go Power) both engines are identical. Who will win on the inertial dyno?



Why Bob of course. In fact Bob could win with less HP on hand than Jeff.



If there is a constand load feature on the dyno then the HP would be seen as identical or very close to identical, where rotational inertia is not a factor.



The most important factors to maintain between runs, are: same wheels and tires every time. All weather related items corrected to a single setpoint every time. Usually automatic, but write them down anyway.

All runs in the one to one gear. The one thing that makes the biggest difference between passes will be inlet air temperature. Know it, and write it down for each pass.



Never change more than one item between passes. As in leaner and more advance. Just one at a time tells you what made the difference and which way it went (better/worse).



The inertail dyno cannot report the exact HP at the front end of the driveline. It infers a HP reading. (HP at the rear wheels is what it can accurately report) And that number is always lower than the actual brake HP of the engine.



I like the Stuska.





Lynn E. Hanover

1point3

There are new computers that will allow the engine to be tuned for each gear, and yes honda is one of them..



so read up before you trash talk to kahren, hes done a lot of tuning and building and he knows his stuff..



I think it depends on the dyno, I've seen mustangs dyno and then install ONLY gears dyno again and lost 5-10rwhp, but then some wont lose any hp... I believe its the dyno.

defrag010

I can trash talk whoever I want to, because what he had to come back with in reply had absolutely nothing to do with how a dyno really works with the gears of your car.



He came up in here saying that the whole dyno gear thing (WHICH HAS BEEN PROVEN since dynos have existed) is false, and expects that no one who actually knows how a dyno works is going to call him out about it? He clearly doesn't even know the mechanics behind why the gearing would affect anything at all.



The only explanation he could come up with was "it is also easier to dyno a higher gear on the dyno since the car is smoother to drive with hihger gear as some people have trouble transitioning the throttle.". I mean come on, give me a break....



It depends on alot of things, not just the dyno.. ambient temp, air temp, coolant temp of the motor, tranny fluid temp... all of those have affects on power, so two dyno runs on the same car will Never be exactly the same.