Turbo inline 4, exhaust design sound

[Rat5]

I always wonder why, turbo inline 4 can sound so different ,

Like these for example have a "smooth sound" if i can say

https://youtu.be/wWr1uGbhAP8

While some have that particuliar aggressive sound that reminds of a subaru

https://youtu.be/tMjALs931aE

https://youtu.be/jjeBJd6ZynA

I would say its the exhaust manifold design, but can there be other design differences that could cause this ? (Theyre conventional flat plane 4 cylinders)

 

[TugboatEng]

I would guess that it has to do with the wastegate. When the wastegate is open you'll get a much more aggressive engine sound as you lose the muffling effect of the turbo. In the drift car example, the car isn't really running at full power so the wastegate may not open as much.

There may also be differences in the A/R of the turbine housing due to different power requirements. The 2wd drift car needs a much smoother power delivery.

 

[GregLocock]

The first function of an exhaust is to pass driveby noise regs. This is easier with a turbo as the turbo itself absorbs most of the firing order pulses (if sensibly designed). This means the exhaust developer does not have to waste space cooping with the firing order noise. So the rest is just a question of deciding which harmonics you want left at the tailpipe.

The problem with turbos is that the gas velocities tend to be high if the whole of the engine has not been redesigned for the turbo, and you get local mach 1 shockwaves which introduce an amusing 'raspberry' effect. That's apparent in your second video.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Rat5]

Thanks for the replies,

Greg, where would these Mach 1 pulses occur withing the egine ? Exhaust ports ? Or within the turbine ?

 

[GregLocock]

Typically in the downpipe, some production cars used a double walled downpipe to suppress them. This also kept the gas hot which helped with cat light-off.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Lou Scannon]

Subaru 4s (in fact, typical flat 4s) tend to have an exhaust rumble because the firing order in each bank is uneven.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[EdStainless]

Turbos will muffle some of the firing order and cam related noise, but not all of it.
And how much do you muffle the turbo noise itself? Do you want to hear the whine?
And please avoid the oversized 'fart can' exhaust.


= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed