Anyone know what the percentage of drivetrain loss us people with automatics have? If say I have 450 at the crank, what would I have at the wheels?

 

Its safe to say that with the mods I have, I prob would pull 350 at the crank. I dyno'd on Brenspeeds dyno at 288wr hp back in May. Thats real close to 18% loss through the drivetrain.

I took 18% from your 450 and got 369wrhp.

My equation is probobly not scientifically correct, but I believe its close enough to give you an idea.

 

It’s tough to say and from the reading I have done the rule of thumb is 15% - 18% for manuals and 20% - 25% for automatics.

However, here is the thing, your actual loses based on the drive train (transmission auto vs. manual, drive shaft, rear differential etc) will remain constant so as your horsepower goes up you still only lose the same amount of horsepower through the drive train.

If you lose say 50hp with the stock 300hp then when you go to say 450hp you still only lose 50hp with the drive train as long as nothing has changed.

With that said I have no idea what the rule of thumb is based on. If it’s based on a 200hp motor then and auto would lose 40hp to 50hp and manual 30hp to 36hp. If that were true then a vehicle putting out 300hp would actually be around 13% - 17% lose for an automatic and 10% to 12% for a manual.

Since stock mustangs typically have approx. 260hp at the rear wheels there is a lose of 13%, that is true IF they are truly putting out 300hp at the crank and NOT more.

Does anyone have some dyno data on autos vs. manuals to see what the actually percentage of loses are?

 

Now don’t forget if you add a supercharger you’re going to have parasitic loses based on the motor using horsepower to spin the blower so that lose would have to be added to the drive train loses…

 

Yeah it's a toughie without knowing a lot of factors. Certain autos will see more of a loss also depending on how they are set-up too, i.e. where the torque converter is at, etc. etc.

I have an auto that sees about a 25% drivetrain loss because how it is set-up. It is an AOD 4 speed with a 3800 stall TC. Don't worry about being a dyno queen though, losing the HP on the dyno doesn't mean you're losing ET. Many autos putting out less HP are actually faster...

 

Excellent point about being a dyno queen. Peak horsepower and torque don’t mean a whole lot. It’s about what’s under the hp and torque curves and how they run. Someone could have higher hp and torque peaks but still lose to someone else that has less hp and torque peaks…