"Real" Horsepower VS Dynoed horsepower ?

[-86GTStang]

If the Dynonumbers are: 427.4 Hp and 397 Tq ...
Whats the approx number of horsepower installed in the
Car ? ( -84 Gt , GT 40 Engine 302, 5-speed )
If you say 225 Hp on a stock engine, how many Flywheel
Horsepower is that..?
Guess the belt system with the waterpump,alternator,PS,
etc,robbs about 14-16 Hp, and the exhaust system etc..?
Does anyone know how to calculate this ?

 

[crunchie12268]

if it is a manual, your one to take away about 15%. Sooo, about 363.29hp and 337.xx ftlbs/torque...

maybe a little less than that becuase of the accessories, but most engine dynos are ran with accessories right?

 

[tonydalrymple]

General theory is that you loose roughly 15-17% of your engine's power through the drivetrain with a manual & about 22-24% with an auto. 310hp at the tires in a manual tranny car would aproximate to 356.5 flywheel horsepower. The amount of "Power rob" varies greatly depending on how many assessories removed, fully rollerizing the transmission, etc. There are some good quartermile based E.T & horsepower calculators to give you a real good idea of what kind of power you have here.....

http://www.speedworldmotorplex.com/calc.htm

 

[-86GTStang]

Thanks...

Thanks Guys, interesting information. If a -97 Cobra got 305 hp from Ford, are the numbers at the wheel,or at the flyweel with all accesories running ?
Have to race this guy next summer... , His a good friend of mine !..( so if he wave goodbye to me, then i have to buy me a blower etc..) LOL

 

[sukkoi19]

I believe all manufacturers rate their engines with full accessories at the flywheel, its also corrected for standard atmoshere 29.92 HG and 67 deg and I dont remember the humidity factor.

 

[Michael Yount]

86GT - in your original post you say 'dyno numbers' but you don't say if it's an engine dyno, or a chassis dyno. Which was it? If engine dyno, then you'd subtract for any driveline losses and other engine losses (accessories that weren't hooked up on the dyno like power steering or air pump) to determine HP/torque at the wheels. How much to subtract? VERY difficult to determine - varies from car to car. But most folks use a number like 15-20% for a manual tranny; 20-25% for an automatic.

If your numbers were at the wheels, then you'd ADD a % back to determine flywheel HP. It's not an exact science by a long shot.

Dynos, especially chassis dynos, are fairly useful for measuring changes that occur with car mods when those mods are made and tested during the same strap down session on the same dyno with the same operator. Beyond that - there's not much sense in comparing anything - ESPECIALLY if you're making changes looking for small HP changes.

 

[-86GTStang]

86GT - in your original post you say 'dyno numbers' but you don't say if it's an engine dyno, or a chassis dyno. Which was it? If engine dyno, then you'd subtract for any driveline losses and other engine losses (accessories that weren't hooked up on the dyno like power steering or air pump) to determine HP/torque at the wheels. How much to subtract? VERY difficult to determine - varies from car to car. But most folks use a number like 15-20% for a manual tranny; 20-25% for an automatic.

If your numbers were at the wheels, then you'd ADD a % back to determine flywheel HP. It's not an exact science by a long shot.

Dynos, especially chassis dynos, are fairly useful for measuring changes that occur with car mods when those mods are made and tested during the same strap down session on the same dyno with the same operator. Beyond that - there's not much sense in comparing anything - ESPECIALLY if you're making changes looking for small HP changes.

...Michael, thanks for your info, and , yes its a engine dyno,Sorry should have mentioned that.... The engine was taken out of the car, and rebuilt. No accessories were added. The waterpump was driven by some connecting item, and then the dynotest was done.

 

[-86GTStang]

I believe all manufacturers rate their engines with full accessories at the flywheel, its also corrected for standard atmoshere 29.92 HG and 67 deg and I dont remember the humidity factor.

...thanks, even more to note down,

 

[Michael Yount]

There is at least one fellow on the boards that actually had his engine dyno'd in a similar fashion, and then had the motor put in the car and chassis dyno'd. I believe it had an automatic behind it. Numbers right around 400 HP/torque peak on the engine dyno turned into something like 290hP/350 torque peak on the chassis dyno. But you can't really conclude much of anything about some other vehicle based on those numbers, and, as I recall, even he was scratching his head as to why there was such a big difference in the HP number. But there was. It just goes to show you - other than for tuning & testing different combos, it's pretty tough to get accurate, repeatable results in a way that allow you to compare absolute numbers between two different vehicles/cars/engines even though people do it all the time.

 

[89331SC]

i know everyone always speaks of 15-20% drivetrain loss. im not familiar with automatics, torque converters and fluids. But in a manual transmission if its operating properly (aka clutch not slipping) there is a direct connection between the engine and the wheels. now the 20% may be an accurate number in a stock motor 225hp about 50hp loss to the drivetrain. now what i dont understand is now i put a big power motor in for ease of numbers lets say 1000hp. so now all of a sudden my trans and rearend decide they require 200hp to turn. from what i understand of physics the frictional loss in a gear will be the same at any given rpm no matter what is driving the gear. if i then swap out that motor and put in a 4cyl by that theory the motor wouldnt even be powerfull enough to move the car. i understand things may be diff in an automatic seing as the engine is not directy conected to the drivetrain. if someone could fill me in id apreciate it. id like to do a back to back test to see actualy results. which i will do when my motor is all squared away in the car. it btw engine dyno'ed at 620hp.

 

[85LXCoupe]

But to run a 1000 hp motor, you need a helluva strong tranny and rearend. More weight, more friction etc so yeah, it'll cost you more power. Will is cost 200 hp? Prolly not but it'll be a lot more than a T5 and a stock 8.8.

 

[Michael Yount]

SC - you're correct - a fixed percentage is not the best way to think about it in the case of big HP/torque differences. The frictional losses will go up, but not proportionally with HP. Said another way, the % factor will drop with power level through a similar driveline. But as a practical matter - for the vast majority of cars that we're dealing with here - which have between 200 and 350 rwhp - the 15-20% number for a manual, and 20-25% for an auto is probably a reasonable estimate. Drop the % down as the power goes up from there.

It's all rather arbitrary anyway since there is SO MUCH variation in chassis dynos - even among the same make. They simply aren't useful for measuring absolute power/torque. They're somewhat useful, if you're VERY CAREFUL, at determining change in power/torque when changes are made to the car.