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Discussion Starter #1
I have a 2010 wrx stage 2 with a catted down pipe and a cobb stage 2 93 octane. My car excelerates good through all the gears but I just started getting a weird noise/feeling when I excelerate on the highway. When I'm in 5th at about 65mph and I get on it a little to get around people my car gets the same feeling it does when you go under 1500 rpm. The same like heavy vibration and noise like it is lugging. It only does it till around 75mph. I'm open to any ideas or suggestions as to what it may be. Thanks, Matt
 

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Vibration and noise would make me think broken engine mount, but that seems unlikely for a 2010. My suggestion is to take it to the dealership and have them take a look at it since it's still under warranty.
 

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Downshift into 4th and get back into the power band...does the condition still exist?
 

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Any modifications?

It sounds to me like the classic vibration associated with the outrigger bushings.
 

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Discussion Starter #5
Any modifications?

It sounds to me like the classic vibration associated with the outrigger bushings.
Only stage 2 with the Cobb AP, other than that I'm completely stock.

Downshift into 4th and get back into the power band...does the condition still exist?
No it only does it in 5th gear, but I never noticed it before and I usually don't downshift on the highway to pass people.
 

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You should be downshifting to pass people. 5th gear is extremely long, and it's very bad on your clutch to do full throttle outside of the power range in 5th gear.
 

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You should be downshifting to pass people. 5th gear is extremely long, and it's very bad on your clutch to do full throttle outside of the power range in 5th gear.
Can you explain this? Purely from a technical perspective, I'm not doubting you.
 

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Sure.

Aerodynamics follow an asymptotic curve... Meaning that as you go faster, the resistance increases exponentially. In addition, the gear ratio in 5th gear is longer than any other gear because it's designed for gas mileage. These two facts equate a much larger amount of load in 5th gear than any other gear. When you're outside the powerband... the engine has to work MUCH harder to overcome those two detriments I just mentioned. If you downshift to 4th to pass, then your engine will be in the sweet spot of the powerband, and it'll be easier to pass. It'll also save you gas mileage because even though your RPMs are higher, your throttle isn't as wide open, and you're not injecting as much fuel per revolution.

This explanation is super abbreviated, but I can explain it further if it didn't make sense.
 

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Discussion Starter #9
You should be downshifting to pass people. 5th gear is extremely long, and it's very bad on your clutch to do full throttle outside of the power range in 5th gear.
I'm not going full throttle in 5th. I'll maybe be at half throttle at the most, but do you still think thats what it is? Just because I'm out of the power band?
 

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[snip] The gear ratio in 5th gear is longer than any other gear because it's designed for gas mileage... When you're outside the powerband... the engine has to work MUCH harder to overcome those two detriments [/snip]
Crystal clear, it was not intuitive that the engine has to work harder at low rpms (out of the power band).
 

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I'm not going full throttle in 5th. I'll maybe be at half throttle at the most, but do you still think thats what it is? Just because I'm out of the power band?
This is exactly what I was eluding to :)
 

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It just makes no sense I've had the car for 2 years and it just started doing it.
Then head over to the dealership, and see what they have to say. It's tough for us to say from over the internet without going for a ride. We just bring up the most common causes to problems.
 

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It'll also save you gas mileage because even though your RPMs are higher, your throttle isn't as wide open, and you're not injecting as much fuel per revolution.
This is actually not true, believe it or not. Most engines have something called a "BSFC", or Brake Specific Fuel Consumption. This is fairly constant (although things like crazy rich AFR's to keep knock down make this worse). This has units of (units of gas volume or weight)/(units of power). What this implies is that you can approximate the amount of fuel needed to generate a certain amount of power as a constant (and the way the approximation falls apart actually helps my case).

In order to accelerate a certain amount, you need a certain amount of force, and since the radius of your wheels is constant, a certain amount of torque. Let's assume that you'd be going WOT in 5th gear, and if you downshifted, you would only accelerate as fast as you could going WOT in 5th gear (although most people tend to go WOT no matter what gear). This requires some certain amount of torque. Power, as you may know, is linearly related to torque and rpm - that is, for units of horsepower and foot*pounds, power=torque*rpm/5250. What this means is that if you want a certain amount of torque, at a higher RPM, you are also producing more power. Going back to the original point, that fuel consumption is directly related to power, you can see that, no matter what, you lose out on fuel economy by downshifting.

That said, everything else is accurate. If you ever drive a car with a failing clutch, it is very easy to see that, yes - pulling in 5th gear is the worst thing for the clutch in terms of torque it has to hold.

As for the OP's actual problem, you should be able to accelerate a bit at 65mph in 5th without any discomfort. Take it to a subaru dealer if you're in warranty, otherwise, to diagnose it yourself, start datalogging. Check that the load values aren't going nuts and make sure your AFR's are staying correct. Beyond that, if it's mechanical, think bushings. Good luck.
 

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I'd like to respectfully disagree with you on 2 separate points: Load, and Boost.

The increased load from 5th gear's longer gear ratio means that there is additional load required to accelerate. Power is required to overcome load. It's going to take more power to overcome a greater load in 5th gear than the shorter ratio in 4th gear. That means more fuel will be consumed.

If you're full throttle in 5th gear, you'll get early boost compared to 3rd or 4th (again due to load). That's why we occasionally have kids come on here complaining of p0244 when going full throttle from 2k in their highest gear. The boost means additional air intake and fuel injection, so fuel consumption will be higher.

Your thinking is spot on if you have identical gear ratios that you're comparing, and no forced induction.
 
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