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Discussion Starter #1
So, I've got a new-to-me 2006 2.5i 5mt and am really displeased with how high it revs on the highway and how loud it is. First question is, am I putting undue wear and tear on the motor if I'm cruising at 3500-4000 rpms?

If not, has anyone added some sound deadening to one of these Outbacks to quiet the engine?
 

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Lawn ornament XT
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Lots of cars cruised at 4000+ RPM back in the days before 5-speeds. You aren't doing anything it wasn't designed to handle.

That said, I certainly understand the desire for less noise. The exhaust arrangement, thin floor and frameless windows conspire to make that vintage of outback pretty noisy.

You can add insulation to dampen the noise. Most people just turn up the radio- it's cheaper and less effort.

If you pull the carpets and add some asphalt compound (or a fancier more modern material) as an underlayment, you can cut the noise a fair bit.
 

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Discussion Starter #3
That's good to know. I'll look into doing the work on the interior. Is there value in adding sound deadening in the engine compartment? Anyone done it?
 

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Much of the engine noise is coming through the firewall and footwell area because the exhaust is very close on the other side.

If you put the insulation on the inside of the car, you can use much cheaper materials since they won't have to handle heat or weather.

Also you won't be interfering with undercoat/rustproofing. Adding a layer of anything on the outside creates a place for moisture to be trapped, which leads to corrosion.

Applying asphalt insulation is pretty time consuming in the first place, removing and reinstalling the carpets doesn't add much plus you get a chance to clean them while they are out.
 

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2013 Legacy Lim CVT Car: 2011 OB Prem 6MT Car: 2006 Miata GT 6MT mc: 2003 Honda GL1800A * Reunite Gondwanaland *
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... 2006 2.5i 5mt ... cruising at 3500-4000 rpms
If my information is correct, the 2006 5MT is geared for
22.2 mph per 1000 rpm in 5th gear -- so 3500-4000 rpm
corresponds to 78-89 mph. Does that sound correct?

BTW, the 2010-13 6MT has very nearly the same gearing
in 5th gear (22.4 mph per 1000 rpm).

BTW2, my '06 Miata's 6th gear (21.16 mph per 1000 rpm) is
lower than either of the above, so 3500-4000 rpm cruising is
completely normal, and the engine is perfectly happy at 4k+.

...rpms are our friends,

Looby
 

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Discussion Starter #6
I'll start with the interior, the corrosion issue makes a lot of sense and I had not considered it.

Those numbers do sound about right, maybe a tiny bit lower than I'm seeing though. I've not looked up specs, but I'm positive that my '93 Legacy L 5MT cruised at lower rpms. I suppose I will adjust, I'm just neurotic with new cars.
 

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I'll start with the interior, the corrosion issue makes a lot of sense and I had not considered it.

Those numbers do sound about right, maybe a tiny bit lower than I'm seeing though. I've not looked up specs, but I'm positive that my '93 Legacy L 5MT cruised at lower rpms. I suppose I will adjust, I'm just neurotic with new cars.
You can write off the slight difference to tires.

Any chance you have a way of measuring noise? I'd love to see before and after numbers but lots of folks don't have the gear or just don't bother.

These days a smartphone app passes for "gear"
 

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My OB turns 3400 at 75mph gps matched ..... Before the bigger tires i was turning like 3600-3700 at 75:28: speedo was 2mph fast from the factory also :rolleyes:
 
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