Horsepower Confusion?

[Elijah]

Hello this has been puzzling me everyday since I got a car. Car manufactures have ratings of horsepower and if you goggle such as “2008 suzuki forenza HP” it comes up with 127HP. But after looking into why my car is so slow I cant seem to figure out if the car is just slow, which it is dont get me wrong, or if its just some marketing scam or if something is wrong somewhere between the engine and the wheels. At WOT in 2nd it barely accelerates and a OBDII reader is looking at a max of 50HP at the wheels. Where this calculator is showing with 127hp at the crank I should be getting roughly 100hp. So what gives, is the car just that slow where it feels like it doesn’t want to accelerate? or could it be an issue somewhere in the powertrain? I’m not looking for diagnosis but I want to know if anyone has a clear answer to the rating of horsepower in cars. Because I dont want to go on a witch hunt looking for the issue if nothing is wrong in the first place.
Thanks for any insight on this topic.

Topic

[James P Grosso]

“Horse Power” was created by James Watt as an advertising gimmick to show how much work was done over time by his steam powered engines.
You can look up how one horse power was estimated, but today the standard equation is HP = (RPM * Torque)/5252
The “advertised” HP would be the peak power at some high RPM, but does not tell you much information about the torque levels at the various RPMs, and tells near nothing about acceleration (rate of change.)

What you really want is to test the vehicles acceleration over a fixed distance, like a 1/4 mile drag race, and get the miles per hour at the end.
Then compare that to the normal, or use a HP calculator that uses the 1/4 mile speed divided by the vehicles weight to get a more accurate horse power estimate at the wheels.

Also, you need to factor in the altitude and weather conditions, as the density altitude can really reduce the power at high altitude.

[Greg]

You also have to factor in the parasitic drag of the drive train and the final gear ratio. The HP rating off the crank will always be more than the rating taken from the wheels. Also be realistic. 127 HP off the crank is not very much power to begin with.

[James P Grosso]

I find this an interesting post, and it seems to be asking multiple questions?

1 – What is Horsepower?
2 – Why is my car slow?
3 – Is this level of performance (or lack of) normal?
4 – Is something wrong that needs to be fixed?

Skipping #1 and #2 which is more theory, and going straight to #3 and #4 which seems to be more applicable, then to determine if #4 – does something need to be fixed, you would really need to have a comparison of a proper running vehicle of the same type (in the same operating conditions.)

This assumes no obvious trouble with the vehicle like “Check engine Light” (CEL) being on, or misfires, or other obvious issues.

So, 127 advertised HP, and I think 131 ft/lbs torque in a mid-size is not going to be a really fast car, but transmission and final drive gearing could make it peppy or a slug. I did a quick internet search, and did not find too much related to performance specs, but found this:
http://www.zeroto60times.com/vehicle-make/suzuki-0-60-mph-times/

looks like if you can go 0-60 in 11-seconds and maybe 18-second 1/4 mile times, I would consider that about normal?
Now if it is taking 15 to 20+ seconds to go from 0-60, I would think you have problems?

I had a 1995 Ford Contour 2.0L rated at 125 HP, but I think the performance may have been better? Not sure if the gear ratios were better or it weighed less, or maybe had a better engine torque curve, even though the “advertised” HP was less?

[Bluesnut]

Those numbers are also going to be for a new car. Once worn in those numbers will likely drop significantly.

Engine wear, clogged converter, clutch or auto transmission slippage are also reasons why it may be sluggish.

I agree that maybe doing a few 0 to 60 runs with a stop watch is a good idea.

Many years ago I used to own a SAAB 900 non-turbo with an auto trans. It was rated at 110 HP and was a total dog. Get into an 8% grade in the Colorado Rockies and it would be lucky to wheeze over the top at 25 MPH.

[Caleb Stovall]

If you want to know the true horsepower of your car have it dyno tested.
Manufacturers measure horsepower at the flywheel, wheel horsepower is what is actually applied to the road and will be different.
Your car is 8 years old now so it is likely that it has lost power, how much depends on how well it has been maintained.

[Mike]

At the end of the day, HP is just a mythical number that is mathematically derived by manipulating torque and rpm values. You can’t actually measure HP directly. A dyno measures torque and rpm, and then does the math for you.

For many years, I drove an old VW Rabbit non-turbo diesel, which was rated at 55 hp when new. Never had an issue with city or highway driving. If you feel your vehicle is sluggish, you should be investigating its torque output. HP is something of a red herring.

[James P Grosso]

[quote=”Evil-i” post=175553]
For many years, I drove an old VW Rabbit non-turbo diesel, which was rated at 55 hp when new. [/quote]

My sister had a VW Rabbit diesel car and her husband had the truck version. They were slow, but got great fuel economy.
Driving the Rabbit up in Colorado going skiing with four people was constant shifting from first gear to second gear and back trying to get over the higher passes. Same with my parents 1980 Pontiac Phoenex. I think it had a whole 85 HP? I think we crawled over wolf creek pass at maybe 10-15 MPH at max throttle. Most of those 1980s car were so underpowered you drove with the throttle on the floor almost all the time.

[Jason White]

To start out, don’t pay too much attention to HP ratings. The government, EPA, CARB, DOT, ect don’t give a damn about horsepower ratings, because all they are focused on is emissions and safety. Also, so many ways they can get those numbers that can clear them of any false advertising liabilities. Like others have said, the transmission and all can have a large role in this, Weight and aerodynamics has a role as well.

Sorry to say, I’ve driven one of those Forenzas. They are slugs. If you want something faster, you’re going to have to sell it and buy something faster.

[Author]

Replies