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Old 04-13-2013, 01:22 PM   #1
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all three motor mounts toast...so I have a question...

So I am having them all replaced (they look BAD) changing water pump too as long as they are rooting around in there. Anything else they should do that would be easy while under going this work?
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Old 04-13-2013, 01:52 PM   #2
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160F T-Stat. It's right next to the WP and as long a coolant is out, might as well change it. The car will generally run cooler and that is a good thing.
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Old 04-13-2013, 02:42 PM   #3
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Old 04-13-2013, 08:42 PM   #4
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Of ur going to do the belt anyway (which u should!), might as well throw an under pulley on there... Why just replace when u can upgrade!



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Old 04-13-2013, 09:37 PM   #5
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Unless you track your car, an UD pulley is unnecessary...even detrimental to the accessories. Most notably, the power steering pump.
It makes everything spin slower, so could affect cooling(water pump) and AC also, though opinions and actual data vary and are conflicting.
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Old 04-13-2013, 10:31 PM   #6
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Unless you track your car, an UD pulley is unnecessary...even detrimental to the accessories. Most notably, the power steering pump.
It makes everything spin slower, so could affect cooling(water pump) and AC also, though opinions and actual data vary and are conflicting.
I guess I don't understand this statement... How can reducing parasitic drag on the crank and therefore freeing up more power to the wheels be unnecessary? How can working the accessories less be detrimental to them? How can working the PS pump less rigorously be harder on it (it should result in increased steering effort tho I've never noticed it). BTW, it does affect the cooling. This is a fact. I noticed temps ~5 higher then with the stock pulley but only in stop and go traffic. All other driving conditions results in temps right where they've always been.

By the way, the car is a lot peppier and freer reving now and a lot more fun to drive (IMO).
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Old 04-13-2013, 11:01 PM   #7
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The UD pulley is meant for cars that are tracked regularly and will sustain high rpm driving for long periods of time. The underdrive pulley reduces the RPM of the power steering pump, the water pump, and other accessories to lessen wear on them caused by sustained high rpm driving. During normal driving, this will cause accessories to spin at a lower rpm and therefore provide less power to them. Whether the effect is noticeable or not is debatable. However, the tiny bit of a horsepower you may gain by installing an underdrive pulley hardly seems worth the effort.

Again, it is meant for cars that are tracked and is for reduced wear on accessories in that situation, not for hp gain on street cars. Any hp gain would be minute...it is said that up to 5hp is gained at maximum rpm, but that would only be noticeable if you had an accelerometer in your butt. I have yet to see any before and after dyno results, but then I haven't looked either.
Not trying to bust your chops, just the facts from an engineer

Nothing wrong with installing it on your street car...until you are wondering why your AC isn't as cold as you'd like in the sweltering heat or why your car is running hot and dumping antifreeze.
That's just my opinion...and you know what they say about opinions

Personally, I trust the engineers at Porsche. At least, all except for the guy that designed the IMSB

Last edited by particlewave; 04-13-2013 at 11:06 PM.
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Old 04-14-2013, 02:48 AM   #8
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Another thing with UD pulley is alternator output. On standard generators, it will simply result in lower Amperage returning to the battery. In the newer Overrunning Pulley generators, it actually cause the pulley to stay engaged for longer periods than it was designed for. It results in the pulley seizing and loss of belt. As the OP's car is a 98 2.5 the alternator will be a normal design, so not a huge deal.

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Old 04-14-2013, 07:08 AM   #9
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Originally Posted by particlewave View Post
The UD pulley is meant for cars that are tracked regularly and will sustain high rpm driving for long periods of time. The underdrive pulley reduces the RPM of the power steering pump, the water pump, and other accessories to lessen wear on them caused by sustained high rpm driving. During normal driving, this will cause accessories to spin at a lower rpm and therefore provide less power to them. Whether the effect is noticeable or not is debatable. However, the tiny bit of a horsepower you may gain by installing an underdrive pulley hardly seems worth the effort.

Again, it is meant for cars that are tracked and is for reduced wear on accessories in that situation, not for hp gain on street cars. Any hp gain would be minute...it is said that up to 5hp is gained at maximum rpm, but that would only be noticeable if you had an accelerometer in your butt. I have yet to see any before and after dyno results, but then I haven't looked either.
Not trying to bust your chops, just the facts from an engineer

Nothing wrong with installing it on your street car...until you are wondering why your AC isn't as cold as you'd like in the sweltering heat or why your car is running hot and dumping antifreeze.
That's just my opinion...and you know what they say about opinions

Personally, I trust the engineers at Porsche. At least, all except for the guy that designed the IMSB
The slight reduction in accessory speeds does not impact performance at all. I was extremely worried about this before installing an UDP in my car, but the reality is that the PS, water pump, alternator, and air conditioning all perform exactly like they do with the stock pulley. The A/C will be as cold as it ever was and your car will definitely not be running hot and dumping antifreeze.

In regards to horsepower, you are correct. There is certainly a small increase in HP but it is impossible to notice in daily driving. If fact, it is impossible to notice on the race track. BUT it is noticeable when running nose to tail against someone with the stock pulley when every hp counts.

Whether this is worth it to anyone driving exclusively on the street is up to the owner. Some will say "not worth the money" and some will say "I want every hp that I can get". Choose your poison.
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Old 04-14-2013, 03:20 PM   #10
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Originally Posted by particlewave View Post
Nothing wrong with installing it on your street car...until you are wondering why your AC isn't as cold as you'd like in the sweltering heat or why your car is running hot and dumping antifreeze.

Personally, I trust the engineers at Porsche. At least, all except for the guy that designed the IMSB
No worries. Everyone is entitled to their own opinion.

I've had one on my car for a little over a month now and have put about 3000 mi on it in all possible driving conditions from long idles in stop and go traffic in 90 ambient heat to hour long blasts at triple digit speeds.

Other then a peppier and freer feeling engine, about the only effect I've noticed is a 3 mpg gain at highway speeds.

As for the ac, I really couldnt say what effect it has on that system because I control it with the + and - buttons on the dash. lol. If the underdrive pulley results in me having to push the + button one more time that i would have had to otherwise, so be it.

Are the results minor? Sure. I was guessing around the 8 HP mark which is in the same neighborhood as ur 5 HP guess. Regardless, I felt like it was worth it to me so each to his own I guess.

As for trusting Porsche engineers... I'm of the opposite opinion. Idk who designed this drive train but if their mission was to create the most ridiculous, finicky, and failure prone system possible, I'd say they could go ahead and break out the "mission accomplished" banner. I would consider damn near anything a Porsche engineer tells me to be highly suspect just based on this car.
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