Exhaust Silencers, bad for the engine?
 

So I have RB headers -> bonez high-flow cat -> Apexi N1 Evolution. I have the standard tail silencer which I use for going on long trips (4 hours from school to home), and I've noticed that when I step on and hit like 4k~ there's a gas/oil smell that's not normally there. I figure it's just the silencer restricting all the flow, but is that hurting my engine? I try not to go above 4k with it in.

Also when I take the silencer out there's sometimes a like steel wool material around it, any ideas what that is? :scratch: The parts are all relatively new since about the summer.

The silencer should have nothing to do with engine performance besides slightly restricting flow. The steel wool would probably indicate your muffler falling apart and the gas/oil i have no idea about.

the silencer is no more restrictive than a stock exhaust.

the steel wool happened to me, my theory was that the restriction caused slightly higher pressure, leading to more heat (PV=nRT!) which blew out your muffler packing, and yeah, the gas smell was there for me too, but i also have a theory on that. plugged exhaust is not something the stock ecu can account for, so you run richer than neccesary, sending out more exhaust/exhaust fumes.

having a restriction at the end of the exhaust creates more backpressure than simply having smaller diameter piping for the whole length. yes, it is hurting your engine with increased EGTs.

those who say it has no effect simply do not know or have not tested this. raw gas smell is from the charcoal canister, a symptom that your exhaust/engine are running too hot as blowby from the engine is pushing too much vapors through the canister for it to work efficiently. my exhaust manifold also cracked when i started swapping around exhausts to quiet the car down meaning too much transition from hot to cold/vice versa too quickly.

1) The ideal gas law(pv=nrt) doesn't explain your hypothesis; see combined gas law: (P1*V1)/T1 = (P2*V2)/T2

Say you have an extremely restricted exhaust with about 12psi of backpressure. You would be wrong to assume that the temp of the gases is going to increase in the exhaust system. Due to heat transfer between the gases, the tubing, and surrounding air, the exhaust temp will decrease at a rate proportional to the distance from the exhaust port. As the exhaust cools, the volume decreases (see combined gas law). This is why you can hold your hand near the exhaust tip and not be burned.

2) The ECU WILL account for increases/decreases in backpressure through a lower AFM reading, it would be unable to account for this on a MAP based system though. The engine is an air pump, it can't intake more air than it can expel. Also note that a rich exhaust will have a lower temp than a lean exhaust.

1) The ideal gas law(pv=nrt) doesn't explain your hypothesis; see combined gas law: (P1*V1)/T1 = (P2*V2)/T2

Say you have an extremely restricted exhaust with about 12psi of backpressure. You would be wrong to assume that the temp of the gases is going to increase in the exhaust system. Due to heat transfer between the gases, the tubing, and surrounding air, the exhaust temp will decrease at a rate proportional to the distance from the exhaust port. As the exhaust cools, the volume decreases (see combined gas law). This is why you can hold your hand near the exhaust tip and not be burned.

2) The ECU WILL account for increases/decreases in backpressure through a lower AFM reading, it would be unable to account for this on a MAP based system though. The engine is an air pump, it can't intake more air than it can expel. Also note that a rich exhaust will have a lower temp than a lean exhaust.

If you have a muffler that is straight through, but then you have to install a restrictive "silencer" in the end of it which shrinks the area of the exhaust down, you are absolutely killing your power and you are doing it so severely that a stock exhaust would be much better. Use a better muffler. Those types are pure junk. It doesn't matter whose name is stamped on it.

I notice when I push it, which isn't often just in passing or so. Think that's still hard on it?

It can take very little time for exhaust temps to climb, and since you notice these issues when you push it then yes, it's probably hard on it. Not as hard as it would if you were running 100% on a track, but still hard on it.

I think the silencer is causing enough back pressure to the exhaust to force extra exhaust flow small gaps between the flanges or poor weld points. I have a single flange on my catless system after the resonator. (not including the header flange) Whenever I put my exhaust silencer on, I notice the familiar "Rx7 smell" emanating from the flange area.

Would the back pressure damage the engine?

When I had my Imotoria exhaust, there was enough pressure to blow out my silencer from the mufflers when I was gunning down the highway....
I wouldnt say it hurts the engine, more like, it makes the engine work harder to expel the exhaust out.

^^ +2. I have bent a few exhaust silencers. I say there shitty, but I have to say they do tone it down a bit.

too much backpressure results in higher EGTs in the engine, which can result in blown apex seals under extreme circumstances. usually these circumstances aren't that extreme unless you are using one on the track and coolant temps are already well above 220*F and oil temps are around 300, which means the inside of the engine is already baking. usually worst case is blown gaskets, warped steel type of manifold flanges and cracked stainless manifolds.

I drove it home for about an hour and a half without the silencer and smelled a bit of a smell here and there my thought was it may have been cleaning out some of whatever was backed up with the silencer.

Well I just checked my muffler. It blew where they welded the canister together. There's way to much back pressure, so time for 2 mufflers with no silencer design.

RB presilencer is pretty sweet, I shoot flames!