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Home > Performance Mods > Transmission / Drivetrain > Understanding Power Loss via Transmissions Auto and Manual

Understanding Power Loss via Transmissions Auto and Manual

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Orin

Reg'd: Dec 08, 2005




I'm not writing this thread to explain how a transmission works, but just a few basic principles to explain some of the power differences in a manual transmission versus an automatic.


EFFICIENCY

Efficiency, that's my favorite word and unfortunately all cars lack efficiency (even at the engine)

One particular area where a car lacks efficiency is the transmission.

The engine creates it's power via internal combustion (blowing up fuel) that combustion is turned into rotating twisting energy to the crankshaft... that rotating energy needs to be transferred into wheels in motion for you

EXPLANATION

take a look an an actual automatic transmission that's been cut away....


^^^looks pretty complex doesn't it?



^this image shows a very simple 3 speed automatic transmission, power goes in one side and that power is transferred though the gears to the output shaft....

I said I wasn't going to explain HOW a transmission works, so I won't go too far into detail. It's because of the process of transferring power that transmissions aren't completely efficient.

How efficient is it?

An automatic transmission loses about 20-23% of it's power through the whole process of moving power from the engine to the wheels.

That means if a car has 300 hp you can usually subtract a percentage to find whp wheel horsepower. So based on a 21% loss, that 300 hp = 237 whp



MANUAL TRANSMISSIONS

A manual transmission is a little more efficient, but not by much. There are fewer moving parts and the power transfer is a little more direct, so the end result is more horsepower directly to the wheels


^^there is an image of a six speed manual transmission

How efficient is a manual tranmission?

A manual transmission loses about 15% of it's power to the wheels on average. Let's use the 300 hp car example again.

300 hp at the engine with a 15% loss = 255 whp that makes me a little less sad compared to the 21% in the automatic.

there are other advantages with using a manual transmission, but those needn't be covered right now.




Please feel free to discuss further on this thread, but please keep it on topic with the subject.


If I can't answer a question others will
[#] Jul 10, 2007 05:02pm
Aviator213

Reg'd: Apr 07, 2007

Scion Guru

Great write-up Orin
[#] Jul 10, 2007 05:03pm
andino

Reg'd: Mar 05, 2006

Godlike Advisor

good write up orin





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[#] Jul 10, 2007 05:05pm
Orin

Reg'd: Dec 08, 2005


thanks, I know I didn't explain everything, but I just wanted to create a basic understanding of power loss
[#] Jul 10, 2007 05:07pm
FloridaGirl

Reg'd: Nov 12, 2006



Aviator213 wrote:
Great write-up Orin


x2 thanx...I can honestly say I understand it a lot better now!


[#] Jul 10, 2007 05:08pm
ErnDawg

Reg'd: Apr 15, 2007

Vehicle Designer

nice. good write up.

[#] Jul 10, 2007 05:11pm
jboy510

Reg'd: Sep 06, 2006

Scion Guru

freakin awesome Orin. nice write up

So what if my girlfriend drives a Supra, I'm more sexier than she is! =)

************* CHECK OUT MY GALLERY *************

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[#] Jul 14, 2007 03:30am
Mayo

Reg'd: Feb 14, 2007

The Guru

Jeez, great explaination!

So what actually controls the gear changing in automatic cars?


"gonna wash my car before i take a nap.. can't rest well knowing i've got the entire cast of A Bug's Life on my bumper" - Vicious
-- Want to post a "For Sale" thread? Check out the rules first.
[#] Jul 14, 2007 11:54am
Orin

Reg'd: Dec 08, 2005


Mayo wrote:
Jeez, great explaination!

So what actually controls the gear changing in automatic cars?


it's a genius and really amazing device called a torque converter... and get this... it fluid to change your gears!!

it's too complex for me to explain, but check this link:

Introduction: How a Torque Converter Works

[#] Jul 14, 2007 02:29pm
07Scionide

Reg'd: Jun 12, 2007

Tire Changer

Forgot about axles, you loss power through those as well!

07Scionide
[#] Jul 14, 2007 03:31pm
curtislo9

Reg'd: Jun 20, 2007

Master Mechanic

smart man.

[#] Jul 14, 2007 03:35pm
Orin

Reg'd: Dec 08, 2005


bump

[#] Jul 26, 2007 02:17am
SiL3ntKiLL

Reg'd: Oct 22, 2007

Detailer

lol dude, i almost decked my friend in the face cuz he kept saying over and over that an auto car and manual car have the same horsepower. then he starts going on about how he grew up around racing(his dad is a racer for pepboys, he actually has a 6 second Z28 ), but i dont think he knows crap about it lol

[#] Nov 20, 2007 07:18am

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