Horsepower losses in gearing

[vwracerdave]

With 2 cars being equal except for gearing which car would use more horsepower to move. (numbers are just made up for simple math)

Car A = 5.00 ring and pinion gear with 1.00 - 4th gear for a final drive of 5.00:1

Car B = 4.00 ring & pinion gear with a 1.25 - 4th gear for a final drive of 5.00:1

Would there be a noticeable difference in performance?
Which car would use more HP to move?

I'm interested in getting a new transaxle and not sure which way to go. I'm guessing car B would use more HP and be slower in the 1/4 mile.
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[Anvil]

Gear efficiency goes down as the ratio goes up. Could be a wash but my guess is the that 4.00 R&P with the 1.25 4th will be more efficient than the 5.00 combo since you're limited by ring gear size so the pinion on the 5.00 will have to be much smaller which would further decrease efficiency and the change in the direction of the R&P has a bigger affect on efficiency than inline gears (transmission gears).

Back in the real world, I don't think it'd mean squat in efficiency and more likely an issue with durability, with the 5 to 1 R&P being less durable.
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[VWCOOL]

So, you are looking to minimise driveline losses...?

I have been thinking about this recently, too, for one of my projects

I reckon a slower-turning transmission will soak up less power (less parasitic/pumping losses etc)...

...but... or?

Good question!

[raygreenwood]

You can do it that simply. It depends on the torque band of the engine.

For instance the stock 82 hp injected type 4 1.7L is just fantastic with a 1:1 4th gear from factory (in the 004 four speed obviously) and a 3.79:1 final drive. It runs at about 65mph at 3200 rpm. Its best torque band is from about 2800-3400 rpm....and its a 66mm stroke x 90mm piston with 8.2:1 compression

Take a type 1 of slightly less displacement but 69mm stroke...and it would be a slug with a 3.79:1 final drive and 1:1 4th.

I know...not a very complete example but....

It matters what the prime torque band of the engine....and then go with the gears that allow it to run in that band at top cruising speed or at peak speeds/rpms right before shift points. Just some thoughts. Ray

[modok]

I think option B is "faster". In either case I think you end up limited by what 1st and 2nd gear ratios you need.

If we are talking type-1 VS bus of course the type-1 is faster. The bus box uses a hypoid final drive which is stronger.........but less efficient.

[VWCOOL]

Raygreenwood, what you say is correct but maybe out of context, I think vwracerdave is looking to reduce driveline losses to liberate more actual power at the surface of the track for drag racing (?)

I too have an interest in this as I am investigating a taller tyre to reduce parasitic tyre, aero, CV and wheel bearing losses for more speeeeeeed....

[Brian]

I have never raced a second in my life:

I agree that it depends on the torque to negate if it needs to spin faster or not to launch.
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[fastfil]

- Would there be a noticeable difference in performance?

I think it would be more noticeable if you took a dump before driving.
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[andk5591]

I don't race, but everything I have ever read about gearing has been more about having your power curve where you need it the most for the type of racing you are doing. The power loss through the gears is something I never see in the discussions.

A taller gear will lower engine RPMS at a given speed. So in something like drag racing, lets assume your car is spinning at redline through the lights, but you needed more speed and the engine had sufficient power to push it faster, then going taller than what you have would increase the trap MPH. This also is assuming that you can still accelerate sufficiently.

Every kind of racing has different needs - the way an autocrosser gears their car is a whole different animal - all about keeping the powerband where you need it. So - having a dyno curve of your engine, finding some of the on line calculators and plugging in a shitload of numbers would be the smartest way to make your decision.

Keep in mind that changing the rear wheel size does the same thing. If you want shorter gears for certain tracks or applications, bolt on a smaller tire and vice versa.
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[gears]

While there may be arguments for using the lighter ring gear for acceleration, there could also be arguments for using the heavier ring gear for highway cruising. But since you mention drag racing, all four ratios must be tailored to provide same four final drive ratios, not just 4th gear.

But the difference is so minimal that you should be considering other far more important factors, when deciding between two different transaxles. There just isn't enough information in the examples provided to do this. JMO
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[vwracerdave]

I'm only interested in this one example 1-2-3 or 5-6-7 gears doesn't matter if they are of equal final drive ratio. Power curve of engine doesn't matter as A & B are exactly the same final drive ratio. All I'm interested in knowing is which will take more HP to move the car. Which will accelerate faster A or B.

thanks.
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2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[modok]

It'll come down to the efficiency of the final drive.........which hypothetically, is hypothetical.

Good question tho, I was wondering yesterday why they don't use lower primary gears more often. Today I remembered, the cruising gears are kept near 1:1 so they don't whine.

[VWCOOL]

[Splitdog]

Theoretically, they would be exactly the same. But I believe that extremes are no good. So I would go with B. The closer to 'equal', the more efficient I believe.
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#notacallooker

[Anvil]

As I stated before, the higher the ratio, the less efficient the gear, i.e., takes more power to spin it. 4 - 1 is better than 5 - 1. Secondly, it is less efficient, i.e., takes more power, to change direction (ring and pinion) than it does to drive inline gears. All else being equal, the 4 - 1 drive will be more efficient requiring less power to drive.
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[smkn_vw]

[Splitdog]

Wrong. 5:1 is 5:1. No matter how you slice it. RPM and speed will be the SAME. The only difference being one way the pinion bearing might take more force, but even then, at the exchange of the 4th gear being less.
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CH³NO²

Z = z² + C

Der Blitzkrieg Kafers

#notacallooker

[smkn_vw]

True if he's going to drive it in 4th all day. Are you keeping it in 4th Dave? haha maybe a trick question fishing us.
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[Brian]

[modok]

It's a hypoid-thetical question