Hot answers tagged

52 votes
Accepted

What is the point of the exhaust?

Safety, comfort, noise and space are the things that come to mind. Safety Exhaust gasses are hot as hell. Hot enough that we put heat shields all over the exhaust line. In engines, we are actively ...
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45 votes

What is the point of the exhaust?

Well, we can have a pipe going out the front of a car as in this design here: or its heavier predecessor: Arguably, the aerodynamic properties are not optimal in both, but here is a similar approach ...
40 votes

Is it possible for a vehicle to be manufactured without a catalytic converter?

You don't have to have an catalytic converter, they aren't required for the operation of an engine. Catalytic converters use chemical reactions to reduce the pollution in internal combustion engine ...
  • 15k
29 votes
Accepted

Why have I had to replace so many exhaust pipes?

Another cause of rapid exhaust system rusting is driving patterns which don't warm up the vehicle thoroughly. In this case, a "thorough" warmup means the entire exhaust is hot enough to ...
23 votes
Accepted

What's the purpose of having the cat right after the exhaust manifold

The main purpose of putting it right after the manifold is heat. The cat functions best when hot. Placing it as close as possible to the manifold helps the cat heat faster and stay hotter, which ...
23 votes

What does exhaust smell on oil and transmission dipstick mean?

First of all you're not smelling CO (carbon monoxide) as that is an odorless and colorless gas. What you are likely smelling are combustion byproducts and that is not at all uncommon in the engine ...
  • 10.1k
21 votes

Why do two-stroke engine exhaust pipes look so strange?

Briefly: The exhaust pipes are shaped to suck gasses out of the combustion chamber over a range of RPMs. Somewhat longer: Imagine a 2 stroke engine without an exhaust*1. When the exhaust valve ...
  • 589
21 votes
Accepted

Why do two-stroke engine exhaust pipes look so strange?

There is this nice animation of a 2-stroke engine with an expansion chamber Source It works like this: While moving downwards after ignition, the piston exposes the exhaust opening, and the burned ...
  • 7,017
21 votes
Accepted

What does pie cut exhaust mean?

This is a term used to describe the shapes of the pieces of tubing used to create exhaust pieces with very hard turns. Imagine an apple pie. Now cut it in 8 individual pieces (triangles). You can now ...
  • 3,363
21 votes
Accepted

How does condensed water get sent out of an exhaust system?

If there was ever that much water in the muffler such that it was sloshing around, it would be a sign of catastrophic failure in the engine, such as a blown head gasket and the "water" would actually ...
  • 2,827
17 votes
Accepted

How should I remove this corroded nut without rounding it?

The tool Thanks to you all for your many good suggestions, but I thought I'd share how I actually got these nuts off today. First, more PB Blaster, and then while I was at the auto parts store ...
  • 2,827
15 votes

How can I tell if I have bad cats?

Cats can stop functioning in a couple of ways: physical deformation due to high temperatures According to this article, the catalyst melts at temperatures above 2100 °F (1200 °C). In the event of a ...
  • 39k
15 votes

Is it possible for a vehicle to be manufactured without a catalytic converter?

That will depend on the market regulations for the target country ie which country that vehicle will be sold in. Cars built to be sold in Europe & US have to meet stringent regulations as regards ...
  • 34.4k
14 votes

Motorcycle exhaust rattling / clunking / popping / burbling on deceleration

Sounds like a lean condition Here's something to chew on regarding identifying a lean or rich condition on a motorcycle. Symptoms of Lean or Rich carb settings on a motorcycle What I believe you ...
  • 32.8k
14 votes

What is the point of the exhaust?

Several things; Exhaust coming out the front is dangerous. If the fumes are ingested into the cab the driver may be harmed. Normally a car is driven forward. If the exhaust is coming out the back ...
  • 15.9k
14 votes
Accepted

What is this yellow powder on my exhaust manifold?

IMHO that powder is either: Dust, that got "burned" by the hot exhaust manifold and transformed into some yellow-looking substance. Sulfur, as the color has a striking resemblance to sulfur. The ...
  • 7,953
13 votes

How can I tell if I have bad cats?

Even before a cat plugs, you can test your cat using a laser thermometer. You are looking to compare the inlet and outlet temps on your cat. Do the following: Run the engine up to operating ...
13 votes
Accepted

How does raw fuel damage the catalytic converter?

A catalyst is a chemical that contributes in a chemical reaction but remains unchanged after the whole reaction is complete. In a catalytic converter platinum is the catalyst that converts unburned ...
  • 1,502
13 votes

What is this yellow powder on my exhaust manifold?

If your engine was running / exhaust manifold hot; the yellow is then zinc oxide. It would result from a galvanized steel manifold which has naturally oxidized. At room temperature the ZnO is white , ...
  • 3,660
13 votes

Is it possible for a vehicle to be manufactured without a catalytic converter?

Yes, in theory. The government doesn't care how your engine hits the required emissions numbers. As an engine designer, you get a tabula rasa, and are free to build any system that will do the job. ...
13 votes

Why have I had to replace so many exhaust pipes?

3 in 4 years? That sounds like the engine mounts were loose or broken and putting undue strain on the pipe. Another possibility is hitting the exhaust on sleeping policemen - are the roads in good ...
  • 34.4k
12 votes
Accepted

Do naturally aspirated engines need back pressure in the exhaust pipes?

Pressure drop is to flow as voltage drop is to current With all else equal, removing the resonator or muffler will reduce the restrictions in the exhaust pipe. This means that the ability of the ...
  • 39k
11 votes

Should motorcyle exhaust headers ever glow red hot

I have typically replaced my stock exhaust systems with aftermarket race systems. Many stock exhaust systems have dual-wall designs so you never see the pipe that the exhaust is actually flowing into....
  • 32.8k
11 votes
Accepted

Do straight/short pipes burn out valves?

Human Error I have firm belief that the cause of burned valves with short pipes is due completely to human error, lack of understanding and poor judgement. I believe this myth has been perpetuated ...
  • 32.8k
11 votes

Porsche 918 - benefits of top mounted exhaust

I certainly don't claim to have any special inside knowledge as to why Porsche engineers decided to route the exhaust that way, but I think that we can analyze the possibilities and trade-offs from an ...
  • 2,827
11 votes
Accepted

What is the muffler? How does it work?

A muffler is a harmonically tuned chamber that is designed to reduce the noise created by the combustion process. Mufflers are usually designed with specific sound frequencies in mind. When a ...
  • 6,017
10 votes

Why no exhaust gas turbine generator in hybrid vehicles?

They Exist I was unable to find any manufacturers that have rolled out this technology into production vehicles but there are several manufacturers that have the baseline technology in R&D Formula ...
  • 32.8k
10 votes

My feet turn black

Cabin filters on modern cars use something called activated carbon (or at least some of them do) which is basically two paper / cotton sheets either side of a fine layer of carbon particles. It looks ...
10 votes
Accepted

How much room do I need to avoid carbon monoxide poisoning?

Is your Check Engine Light on? That's a rhetorical question, what I mean to say is that if your ’04 Forester is in good tune, it really should not produce that much carbon monoxide. Also, there are ...
  • 12.3k
10 votes

How should I remove this corroded nut without rounding it?

A lot of localised heat to the nut will help. A 1/2 inch spanner/wrench is slightly smaller than a 13mm, so that may still work after heating. If you can’t get a splitter on it, you could drill a line ...

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