Inline 6 Exhaust Sound

[swall]

The comments on sound quality in the X-Pipe vs H-Pipe thread prompted me to ask about sound quality from inline six engines. Some sound really cool, but some (like my Jeep Cherokee) sound about like a 1963 Rambler. What exhaust system tricks are used to make an inline six sound good?

 

[RossABQ]

Proper combining of cylinders' exhausts together in a manner that improves power and sound. That's why a straight six will always sound better than a flat or V-6. With the in-line arrangement, you can pair the cylinders that need to be paired, while on a V-6 in particular the cylinders may be on different banks.

Your Jeep is tuned to produce a lot of low-end torque, and pairing isn't as important at low end RPM's, so I would guess they opted for the cheapest exhaust manifold, not the best sounding. Emissions concerns also play into it.

 

[Junior33]

the cherokee uses a tubular manifold, if my memory serves it's 3 primaries to the first collector stage, then 2 into 1. I haven't had one in front of me in a few years, but I believe it's a cylinder 1-2-4 on the first collector, 3-5-6 on the second.

depending on the year of the cherokee they are tuned for torque and throttle response (of course this is a vast oversimplification, but for simplicities sake I'll use it).

Sound however is a very subjective issue. Mostly formed by association. From your post I would assume that you associate the sound of a BMW I6 that revs much higher and with much longer valve overlap. Both conducive to hp, but not necessarily to throttle response or low rpm torque (or crawl speed, something the cherokee was set-up to use).

Overall it comes down to association, personally I prefer the sound of a 4.0 AMC I6 over that of a BMW M3, mostly 'cause I associate the sound of the 4.0 with getting me home to a warm meal and soft bed in very hostile conditions while many other cars where in the ditch, and I associate the BMW with a guy who dated a girl that I liked in high school.

 

[Rob45]

The sound quality of an in-line six is mostly a result of the cylinders firing at equal intervals, something that is not true of many V6s, for example.
The reason your Cherokee sounds funny is a result of the muffler used, and its location in the system, and the fact there's a catalytic converter in there somewhere also (presumably).

The muffler is the main culprit, and whether it's original or aftermarket, you can guess that its primary design constraint was that it be cheap, and that it reduce noise, not that it sound pleasing. There is simply not enough space in this forum to discuss all the ways in which an individual exhaust system can be improved, but suffice it to say that a good muffler engineer could spend months getting a good sound from a system like yours. What you would NOT want to do is to change pipe diameters to something excessively large - no more than 2.5" diameter - nor to simply change to an excessively loud muffler like one of the "Flowmasters." Ideally, you would not have pipes of equal length ahead of and behind the muffler, but you might benefit from adding a resonator in the tailpipe if you can squeeze it in to the rear-axzle "kick-up" area, like in some Ford Explorers.

My personal favorite in-line 6 exhaust sound comes from an E-Type Jaguar 3.8 or 4.2L, turning around 6,000 rpm in top gear...

Regards,
- R

 

[RossABQ]

My favorite I-6 was the Austin-Healey 3000, the '60's Jags a close 2nd. Both had (as I recall) the same 1-2-4, 3-5-6 manifolding. TR-6's weren't bad either...

 

[swall]

The Datsun 240Z's had a nice exhaust sound, as I recall.

 

[SomptingGuy]

Additional info...

It may well be that the Jeep's sound (more likely intake than exhaust noise) has been tailored to its target customers. The same sound doesn't suit all vehicles. Vehicles that can allegedly go off road need to sound more "butch" than the corresponding luxury car with the same engine (& sometimes platform).

 

[Peter7307]

Anyone remember the original movie of The Italian Job with Michael Caine?
There was a very short piece with two E types and an Aston Martin being driven through the Italian hills.

Totally different sounds from very similar engines.

Nice engine acoustics from the Lamborghini Muira as well in the opening titles shots.

Pete.

 

[SomptingGuy]

SQ in general...

Interior (i.e. intake) noise is for the driver.
Exterior (i.e. exhaust) noise is for the driver's image.