Topic: Message #1126714

[blackdiamond]

Depending on the dyno and what it takes into account, no, if you take a bone stock toyota, put it on the dyno for a baseline, then put in 4.88 gears and re-test, the power and torque number will be different yes. And if you put on 31'' instead of 28'' the numbers will be different too.

"Higher ratio gears will give you lower chassis dyno numbers for a strange, but logical reason. In essence, the DynoJet calculates hp based on the time it takes to spin up the 2800lb roller assembly. It's basically work divided by time and rpm. Think about this: If you car is at idle in neutral and you stab the throttle, it will take time to accelerate to redline...let's say 1.1 seconds. Now let's say it takes 8.2 seconds for your car to accelerate the DynoJet from low speed to top speed with 3.23 gears and 7.3 seconds with 3.73 gears. Dyno printout says 355 rwhp with 3.23 gears and 346 rwhp with 3.73 gears...why?

Think aabout this: In the 8.2 seconds it takes to spin the rollers with 3.23 gears, it would still take the motor about 1.1 seconds to overcome its own inertia (idle to redline). There's about 13.4% of the work used just to accelerate the motor itself. With 3.73 gears, the time to reach redline decreases to 7.3 seconds. Divide the 1.1 seconds into the 7.3 seconds and you will see that overcoming the internal engine inertia costs 15.1% of the work with 3.73 gears. There is less hp available during this time period to spin the rollers so the DynoJet will read a slightly lower hp figure. Make sense, or did I lose you?''

That is why you are still waiting for chassis dyno or dyno tests, it will never happen, because the increase can't be calculated properly. It has repeatedly been shown on the drag strip, for one example, where the numbers on the dyno will be lower but the 1/4 mile time will be much lower and mph faster.

Whether in off-roading or road racing or bicycling, lower gears will give better acceleration period, you don't need a physics paper to explain it, understand it or prove it, it is common knowledge since gear ratios have been invented.

The maximum rear wheel torque as measure by the dyno is not real world RWTQ, but a computed number useful for comparing one engine to another.

Lower gears give you more "leverage". Just yesterday I was able to have some fun in my Sequoia by dropping into 4low and unleashing all of the horsepower. It's a quick trip to 30 mph and then you start to need more gears.

The biggest improvement from the engine is extending the useable range into higher rpms which allows you to stay in a lower gear long which give you more "leverage" just like low differential gearing.

I have always enjoyed this explanation for horsepower vs. torque.

http://www.zhome.com/ZCMnL/tech/torqueHP.htm