I'm sure this is a stupid question but I figured I'd ask anyway. I like to know the answers...

Lately my "stock" muffler (not sure if its' been replaced but it's the stock-like replacement) had been falling apart. There was a small hole in the bottom that soon became a large hole. I jig-rigged it the other day with some sheet metal, high-temp silicone and a crap load of sheet metal screws. Yep, definitely a red-neck fix but the truck is relatively super quiet now and oddly enough I swear that the performance (more so throttle response) has increased a noticeable amount. Going up smaller hills the engine has more pull that it did yesterday.

Is this possible or am I just imaging things? There's not cat converter and the emissions equip are disconnected. Just sayin' It's seriously been that much more of a pleasure to drive my truck with a quiet exhaust. I always loved the rumble of a v-8 especially the ford engines but lately I've found myself becoming an "old man" and liking quiet in the cab. This is my work truck and sometimes the noise just aggravates me.

Anyway, thanks for the input.

Al

 

Sometimes it might get better, because the guts of the muffler have blown out. Sometimes it can get worse, because the guts of the muffler have rusted and collapsed, blocking the flow.

 

You need SOME back pressure. Dunno why but i always felt the same as you. You can notice a differencewhen you go from straight pipe to a lightly restricted system.

 

That is a myth, you dont need backpressure.

 

Everytime i have swapped from straight pipe to a normal type exhaust i could feel a seat of the pants improvement.

 

I think this is one of those terminology issues.

Actual back pressure is detrimental.

I'm not a rocket scientist on this........but an exhaust system with inadequate flow speed (as an extreme example, imagine a 6" pipe where the exhaust just 'spills' out) is also detrimental to breathing performance.

Exhaust velocity is needed for both a scavenging effect on the exhaust gases, & also to help draw in the next incoming charge through the inlet valves (inlet & exhaust valves overlap open for a short period).

 

I believe it. But if someone can. Please break this down.
Exhaust pipe size. It will take some searching to find the printed source but it was dyno broke down like this.
2" was about perfect to 250hp
2.5" ~300hp
3" or dual 2.5" 400hp
3.5" or dual 3" 500+hp

Why would performance drop if i put say a 3.5" full tube on a honda accord?

 

According to what Ken Blythen said, if a Honda has 3" exhaust, not all the exhaust would be expelled, and less fresh air would be drawn in, correct?

 

I see that but im missing the connection.
On one hand the smaller diameter pipe works better which would have more"pressure of some sort"
On the other hand the pressure is negating power. The more free flowing the pipe the better.

Not just kens comment. All the shows, mags, shops promote larger free flowing pipes. To me this is like people in seattle owning convertibles.

 

The way headers work (as an illustration) is that the four primary pipes coming off the head are all exactly the same length & finish flush with each other at the collector.

That means that while an exhaust charge is exiting one pipe, it creates a slight vacuum at the end of the next pipe, which helps scavenge the exhaust gases from that second pipe.......& so on continuously, with each pipe 'vacuuming' the next.

Ideally, the gases should be travelling as fast as possible through the pipes, but not to the point of pressurizing (back pressure).
Header primary pipe diameters are carefully calculated (with some compromise for variables) to suit the engine they are for.

So free-flowing is important, but not so 'free' that there is a loss of velocity through the system, actually reducing performance (with either headers or cast manifolds).
The y-pipe gives an extra scavenge effect in a 2-1 exhaust, helping torque, as long as the system is correctly sized.

As well as from getting rid of burnt gases, the efficiency of the exhaust system also has an effect on the engine in the split second that BOTH the inlet & exhaust valves are open, near TDC of the exhaust stroke.........if there is exhaust back pressure, there will be a delay in the new air/fuel mix entering the cylinder.

 

Your smarter than me! Makes sense.

 

Great information. I was just clarifying for my own knowledge earlier.