Somebody once told me that the louder the engine, the less horsepower?

Answer 1

As has already been noted, no truth to this. In fact, it's almost the opposite - as you open up an engine to make the exhaust flow more efficient, you tend to make it louder. There are points of diminishing returns, and depending on the use of the car and the specific engine, you may want to maintain more back pressure (a small engine in a commuter car would be an example, as the loss of back pressure will have a negitive effect on the already lacking low end torque).

Now, the thought that energy is somehow being wasted in sound? To a point this is true... in an ideal system you would convert all of your energy to the drive train (and the drive train itself would then also be 100% efficient). The problem is, this is not an ideal system, and the choice is not to have noise or not. You have it either way! The question is if you want to muffle it and by how much.

Think of it like punching a pillow - when you punch the pillow, you will hear a pop! Using larger and larger pillows to cushion the blow will decrease the pop, but will not increase the amount of energy that is transferred to the object you are punching (the opposite).

Answer 2

Well, you have a lot of answers here and many of them are good.

In the simplest general terms, mufflers, catalytic converters, resonators, etc... in the exhaust system generate back-pressure or resistance to exhaust flow. That resistance causes your engine to work harder to expell the exhaust gasses. That extra work the engine has to do translates into less horsepower available to propel the car.

So your friend was definitely wrong.

However, modern street engines are carefully designed from front to back to work together. Changing the back-pressure on a production car will change the volumetric efficiency of the engine. That is other parts of the engine system now must compensate for the lack of backpressure. Usually reducing backpressure helps increase airflow through the engine and so the engine computer must compensate by making the air-fuel mixture richer. If the computer didn't so this, your engine would be running too lean and you could get exhaust popping among other problems. And you could lose power...

On racing engines, the exhausts are usually built very short, large in diameter and with no mufflers. They run with almost no backpressure, but they also increase the fuel mixture to very high levels to compensate for the improved efficiency. They produce lots of power and can make lots of noise as well. Aircraft engines operate much the same way and many don't use mufflers.

As for whether a louder muffler will yield more horsepower, that is largely a myth. There are some very quiet mufflers which produce very low back-pressure and some very loud ones which produce a lot. Car Craft magazine did a test of mufflers in the 1970's which included loud Cherry Bomb glasspacks, along with some stock factory mufflers. The one which produced among the lowest back-pressure was a stock Chrysler Imperial muffler which was very efficient and quiet. Next were the Corvair Turbo mufflers and the Charger Hemi muffler. Great info...

So while in an ideal sense, an uncorked exhaust will make more noise and horsepower, it will only do so if the rest of the engine system is tuned along with the change. And making your car louder doesn't necessarily means it will be faster.

Answer 3

Not always true. Sometimes the loudness doesn't come from the engine, it comes from the pipes or glass packs they put on the exhaust. If an engine is just loud, it could be a weak horsepower issue, but if it purrs then it has a lot of horsepower.

Just think of diesel engines or race car engines. They're loud and have loads of horsepower.

Answer 4

Just because it has a muffler doesn't mean it is not a tuned exhaust system. Think of exhaust as "bullets" from each cyclinder. Just as one leaves the tailpipe that "momentary vacuum" behind that bullet draws out exhaust from a cylinder that has just fired at the engine. When you have a noisy exhaust(the cheapest way is to drop the muffler) now it is not in tune and backpressure would be more likely to happen, not clearing out the cylinders as well as a tuned exhaust. These are exacting lengths...not just any old lengths. A header can be tuned to as it is made to an exacting length. But somebody strapping on a "blue bottle" muffler for a "hotter sound" is not doing anything exact. So it just sounds faster and powerful.

Answer 5

Horsepower at rpm (xxx@xxxxrpm) skill the optimal generated means of the engine at that rpm(revolutions in line with minute) Horsepower is genuinely a stupid way of measuring means imo. If the two engines from chevy or pontiac grew to become into to produce means and be the two useful on the comparable rpm because of the fact the honda than i'm particular their numbers could be a tad bit closer. i think of the different 2 designed their engines for low end grunt and in turn sacrificed an prolonged powerband to produce means at bigger rpms. there is commerce offs for each little thing so i does no longer bounce to the top that a million is greater valuable then the different. do no longer base you assumptions on top numbers. of direction optimal generated means revolves around too many variables. seem up volumetric performance and learn up on your chemistry.

Answer 6

Not true. The noise comes from the exhaust. The noise depends on the type of exhaust you have. Usually 8 cylinder engines are the loudest. Sometimes even louder than 10, 12, and 16 cylinder cars.

Answer 7

Not really. It is true that straight, open headers will have a little (very little) less HP than a setup with a little back pressure, in general, a quiet exhaust system will be more restrictive than a loud one. That means less airflow, and less air means less fuel can be burnt efficiently. That's why a turbo/supercharger works - getting more air through the system faster is the best way to increase HP without increasing the bore or stroke.

Answer 8

This is sort of kind of partially true but not really.

Basically any engine produces a total amount of energy at any given point in time. What counts is how that energy is used. The more energy that is "wasted" on noise the less energy that is being pumped out of the drive shaft. However, the amount of energy to produce loud noise is pretty negligible.

Answer 9

Nope, not true. But it does seem there is a certain element of drivers that buy underpowered vehicles and then try to convince the world they are better by modifying the exhaust to make it louder.

Answer 10

That's just stupid.
Ever go to a NHRA event?
The top fuel cars are putting out 4,000 to 6,000 HP and they are the loudest engines around!
tc