Megan Header Dyno Results - Toyota Yaris Forums

largeorangefont · 01-10-2007, 06:28 PM

Quote:

Originally Posted by acrbill

largeorangefont,
when I google the transmission ratios I get hit for 3.722:1 and 3.941:1.
Perhaps

If you have access to a tach, get a RPM reading at 80 mph in 5th and we can figure it out. My guess is 3.9.. but I could be wrong.

Russelt3hPirate · 01-10-2007, 06:32 PM

Quote:

Originally Posted by largeorangefont

If you have access to a tach, get a RPM reading at 80 mph in 5th and we can figure it out. My guess is 3.9.. but I could be wrong.

I has access to a tach :)

Defi Concept HUD in my yaris FTW!

largeorangefont · 01-10-2007, 06:49 PM

Ok here is a quick and dirty version of how the dyno figures out horsepower. A dynojet is the simplest, because there is no load. The dyno takes the known weight of the roller(s) and derives hp based on how long it takes the car to get the roller up to speed. So if you have the car in 2nd for example, the roller is going to spin up faster, relative to a 4th gear pull. It is just like doing 30 on the street in 2nd gear vs 4th gear.

In real terms you *should* have the same horsepower either pull, but the curve will be very different looking. Think how the car pulls from 30 mph in 2nd vs. 4th gear, and how that will translate to a HP curve.

Some dynos will measure more horsepower just from switching a lower final drive and some don't. You arent gaing HP, but you are spinning up the roller(s) quicker. You can see how the dyno could then traslate that difference into more HP. I have personally seen this happen, and it is obviously incorrect. Alot of newer dynos are calibrated not to do this, but just be aware that is can happen.

The reason you want to use 3rd or 4th gear on a dyno pull is to put more of a load on the car. For tuning, you want to see what happens with the air fuel ratio and timing high in the load range. Tuning in 1st and 2nd does not give you an accurate picture of how the car will run in higher gears with more load.

Depending on the dyno operator and the car, sometimes shops do their tests in 3rd gear because speeds are too high in 4th on some cars. For seeing gains of a particular part, as long as you can eliminate every variable possible, you should get an accurate picture. Dynos, their calibrations, and HP numbers can vary greatly so it is not valid to compare numbers from dyno to dyno. Just think of the dyno as a tool to check gains. I would always try to go to the same dyno facility, and make sure that all calibrations are as close as possible each time you dyno for the best result.

Hope all this helps.

Ashley

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01-10-2007, 06:49 PM	#3
largeorangefont Break'em off some. View User's Garage Drives: 07 Yaris LB, 04 Cobra Join Date: Jan 2007 Location: So Cal, OC Posts: 854	Ok here is a quick and dirty version of how the dyno figures out horsepower. A dynojet is the simplest, because there is no load. The dyno takes the known weight of the roller(s) and derives hp based on how long it takes the car to get the roller up to speed. So if you have the car in 2nd for example, the roller is going to spin up faster, relative to a 4th gear pull. It is just like doing 30 on the street in 2nd gear vs 4th gear. In real terms you should have the same horsepower either pull, but the curve will be very different looking. Think how the car pulls from 30 mph in 2nd vs. 4th gear, and how that will translate to a HP curve. Some dynos will measure more horsepower just from switching a lower final drive and some don't. You arent gaing HP, but you are spinning up the roller(s) quicker. You can see how the dyno could then traslate that difference into more HP. I have personally seen this happen, and it is obviously incorrect. Alot of newer dynos are calibrated not to do this, but just be aware that is can happen. The reason you want to use 3rd or 4th gear on a dyno pull is to put more of a load on the car. For tuning, you want to see what happens with the air fuel ratio and timing high in the load range. Tuning in 1st and 2nd does not give you an accurate picture of how the car will run in higher gears with more load. Depending on the dyno operator and the car, sometimes shops do their tests in 3rd gear because speeds are too high in 4th on some cars. For seeing gains of a particular part, as long as you can eliminate every variable possible, you should get an accurate picture. Dynos, their calibrations, and HP numbers can vary greatly so it is not valid to compare numbers from dyno to dyno. Just think of the dyno as a tool to check gains. I would always try to go to the same dyno facility, and make sure that all calibrations are as close as possible each time you dyno for the best result. Hope all this helps. Ashley