th400 power loss
Thread Starter
Racer
Joined: Dec 2004
Posts: 336
Likes: 0
From: crystal lake Il.
th400 power loss
I`ve read that a th400 uses 20% of your engines power thru drivetrain loss. I have a 75 l48, 165 hp. So that would mean about 30 hp. I`ve made some mods and now I`m about 300 hp at the flywheel. Does that mean the drivetrain now requires 60 hp. This weekend I`m putting in a 383 in exess of 400 hp. So now does it take 80 hp? It doesn`t make sense.
Safety Car
Joined: Oct 2004
Posts: 3,725
Likes: 5
From: Minnesota
Originally Posted by painterman52
I`ve read that a th400 uses 20% of your engines power thru drivetrain loss. I have a 75 l48, 165 hp. So that would mean about 30 hp. I`ve made some mods and now I`m about 300 hp at the flywheel. Does that mean the drivetrain now requires 60 hp. This weekend I`m putting in a 383 in exess of 400 hp. So now does it take 80 hp? It doesn`t make sense.
Race Director
Joined: Apr 1999
Posts: 15,136
Likes: 477
From: NM
Have always wondered about those % losses. Why would it take more HP to turn the transmission just because you engine makes more power? So it takes 50 hp to efficently operate the transmission. If you engine makes only 100 hp, that would be a huge loss. But it your engine makes 1000 hp then why would it take more than 50 hp to efficently operate the transmission?
Guess the good thing is that everyone with that transmission has the same loss
tom...
Guess the good thing is that everyone with that transmission has the same loss
tom...
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Its not a matter of how much it takes to operate the transmission. The Transmission TRANSMITS power from the engine to the drive line. As with any transmission system ( sattelites, CB Radis, Walkie Talkies, Alison and CAT drives) they have losses (% of effencies) Not all the power generated in the engine makes it to the rear wheels. If you puch 100hp thru a 80% tranny you get 80 to the wheels. Same tranny, now crank the throttle to 300hp out, now you lose 60hp in the transmission, heat goes up a lot, each HP is 314 wats, 314x60 = 18840 watts. Thats a lot of heat. One of the reasons they invented a Lockup converter. Without the slippage that makes a converter work, its a lot more effecient. Same deal with a clutch, less slippage over time, less heat generated, more efficient.
thats enough rant for now
thats enough rant for now
Racer
Joined: Jan 2006
Posts: 265
Likes: 0
From: Bowie MD
Automatic transmissions have losses compared to manual transmissions because manual transmissions physically link the engine to the driveshaft. Automatic transmissions transmit the power from the engine to transmission through a fluid, which causes the two to slip against each other. There is no mechanical link between the engine and transmission. All things being equal, ATs do not "use power", but incur losses when compared to manual transmissions. Losses become evident at constant RPM when compared to manual transmissions.
You get some percentage of loss that is greater than zero, and less than ridiculous.
You get some percentage of loss that is greater than zero, and less than ridiculous.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,117
From: Crossville TN
Automatic Tranny Losses
The major losses thru an automatic tranny are for the hydraulic pump (several horsepower), the inertia losses for the rotating parts, and friction losses. In no way does that eat up 20% of your total engine power. The auto tranny does help out via torque multiplication (due to torque converter/stator design), so it's not all bad news. Mileage is a bit worse than with a standard gear box, due to these additional losses.
CF Community Team
Joined: Oct 2004
Posts: 19,363
Likes: 5,243
From: Cape Cod, Mass.
2025 C6 of the Year Finalist - Unmodified
2025 C8 Z06/7/E-Ray of the Year Finalist - Unmodified
2023 C3 of the Year Finalist - Unmodified
2021 C8 of the Year Finalist Unmodified
2020 Corvette of the Year Finalist (performance mods)
2019 C1 of Year Winner (performance mods)
2017 Corvette of the Year Finalist
2016 C2 of Year
2015 C3 of Year Finalist
There are drivetrain losses in horsepower for manual transmissions also. They are not as great as they are for the auto trans but still significant. You are never going to get all the horsepower that you have at the crank to the rear wheels in an auto or a standard. The loss, while greater in an auto than a standard, is not 20% greater in the auto.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Safety Car
Joined: Oct 2004
Posts: 3,924
Likes: 735
From: Youngstown Ohio
Originally Posted by SIXFOOTER
Its not a matter of how much it takes to operate the transmission. The Transmission TRANSMITS power from the engine to the drive line. As with any transmission system ( sattelites, CB Radis, Walkie Talkies, Alison and CAT drives) they have losses (% of effencies) Not all the power generated in the engine makes it to the rear wheels. If you puch 100hp thru a 80% tranny you get 80 to the wheels. Same tranny, now crank the throttle to 300hp out, now you lose 60hp in the transmission, heat goes up a lot, each HP is 314 wats, 314x60 = 18840 watts. Thats a lot of heat. One of the reasons they invented a Lockup converter. Without the slippage that makes a converter work, its a lot more effecient. Same deal with a clutch, less slippage over time, less heat generated, more efficient.
thats enough rant for now
thats enough rant for now
.....totally agree w/ SIXFOOTER......whether it's heat or resistance, the power loss number rises when more force is generated: a 4cyl. engine loses little HP when corked to a 2" exhaust pipe, but a 700 HP engine may lose 100 HP through that same pipe.....my .02 added.....
400, 700r4, c3, corvette, dragging, drivetrain, horsepower, losing, loss, manual, motor, percentage, power, th400, transmission, vs
