I'm getting ready to take my WRX to the mountains this weekend for some snowboarding. The way up is mostly flat except for about a 10 mile stretch where it gets pretty steep and stays that way for all 10 miles. Last time I drove up this incline I was in 5th the whole way running approx 7-8 lbs of boost at 75mph. My question is this: does it damage the turbo/engine to run boost for 10 minutes straight, or should I have shifted into 4th at 75mph and spent the whole time at 4500-5000 rpms, but without running the boost?

 

Our turbos are water cooled...I think you should be fine, especially if you run synthetic oil. Idle the car for a minute or to in order for the to car cool down before shutting it off. I'd think if it was a problem, Subaru would have put a stock boost guage in the car...what were they thinking?
Having said that, I have wondered the same thing. The owner's manual of my '79 Saab 900 turbo warned against prolonged periods of boost as well as towing. But it also had a boost guage next to the tach from the factory. It was not a water cooled turbo either.

 

You are not making boost when driving on a flat freeway at 75mph, even at 3000rpm. Check your gauge.

 

doesnt matter if you are boosting, the cars built for it, it can take it all day long. If it couldnt do you think they'd sell the car man? Lol, silly...

 

Then your valves are going clicketty-clack that much faster. Following your logic that would put more strain on the cams and valve train instead of the turbo. I honestly think driving up the hill at 75 in either 4th or 5th is fine. If you need the power downshift, if you're cruising leave it in 5...

 

Subaru's suffer from partial throttle, mid-high load high EGT temps. High EGT temps can cause engine damage. If the car is 100% stock, it shouldn't be a problem, but if you have ANY engine related mods, you have to be careful.

There are few solutions for that. All of them eliminate this condition and even add more power throughout the RPM range.

Going uphil 1t 75mph is better in 4th than in 5th. In 5th, you would be putting unnecessary load on the engine cauing it to boost when it doesn't need to. You will also suffer from a reduced gas milage.

Uphil, in 4th at 5600 RPM will consume less fuel than in 5th at 4000 RPM.

 

Yes i'd like to know more info on this issue as well. I drive up to the mountains and notice that i am under boost for long periods of time as well.

Another thing, i have a boost guage and when i downshift to 4th i've noticed that the boost stays near the same as when it is in 5th. but it may have just been an isolated incident so i could be wrong.