No power gain from Underdrive Pulley?...
 

This guy posts up some interesting videos about the Boxster. This one shows no gain after installation of an underdrive pulley...

https://youtu.be/CvFdH11y4EI

When I installed a UDP, it wasn't because I thought it would give me more hp, but rather because it drives the accessories at a lower speed, especially when you are on the track! Power steering pumps, and the like, don't like to run at constant, near redline speeds and can cause problems or fail when pushed too hard.

I don't doubt that statement. Years ago, I actually had a water pump failure right after I had redlined my engine during some spirited driving. :) What I find amusing is the sellers of these UDPs claiming instant 5-10hp gains.

VJ should have included a before dyno run in the same environmental conditions as he tested the UDP afterward. I think you loose 10~15HP between seasonal air densities. It can be difficult to track small power gains sometimes.

My Boxster gains about this +10hp... when the wind blows from behind loll

Perhaps he forgot to install the shorter serpentine belt required to make the kit working?

I think he says in the video that he put in a "longer" belt! :D

oh did he. missed it

Correct. Pumps cavitate (the fluid stops flowing and creates voids Article on wikipedia) when turning too quickly. Water pump, power steering pump, oil pump. Their pulleys are all designed to run at low(1000) to mid RPMS(4000). That's why when at a stop some cars forces the engine to rev a little higher when it senses that its not providing enough cooling or power steering help. Now I personally wouldn't replace it unless you are really having spiking temperatures when on the track. Most of us will get stuck in traffic more often then run 7K RPM constantly at the track. Then again its an easily replace part.

Example:
My Sr20det revs up to 8k RPM and I was chasing some power-steering and cooling gremlins. Past 7k for too long and I was running into some cooling problems. I under-drove the power steering and water pump and it mostly helped the cooling side. But its more of a band-aid. Finally installed some power steering cooling lines with a filter and that was able to keep the viscosity in check and help deaerate the oil.

Back to the power. The pulley doesn't have enough significant mass to provide any substantial effect on the inertial of the system. Actually smaller pulleys would make it harder for the engine at lower RPMs to turn accessories by the loss of mechanical adavantage.(lever arm)

* Torque the bolt to 50 NM (37 ft-lb) and then tighten an additional 90 degrees.

I don't wanna believe this. :(

+1 ^^^^

The dyno baseline test was on 10/22/16 whereas the UDP test was on 11/26/16. The temp and humidity correction (or poor correction) could easily result in a margin of error equal to the magnitude of the difference under test (3-5hp).

He needed to do a baseline and the UDP test on two consecutive days at the same time of day when the weather was generally constant to be able to accurately measure the difference.

Me neither...

Maybe psychological but I could feel it when I did mine, mostly in first and second, but I primarily did the mod for power steering longevity.

Considering the difficulty of the change. This could be planned on the same day. Then again we are talking inertia change. Just like a lightweight flywheel but at a microscopic scale. Engine will rev faster without load. That's if the parasitic drag of the equipment doesn't increase from the pulley size change. With load, nothing will change.

Hey if you are looking for most horsepower output, try running a lighter oil both in the engine and transmission. You will have way less parasitic loss and more income loss.

To be honest, I feel my boxster would benefit from a beefier flywheel looses revs too fast for my taste which makes up shifting a rev match fest(6 speed).

Agreed. I thought I could feel mine too. But I did the secondary cat delete pipes at the same time. So easy to break the tires loose in 1st and 2nd now.

Any truth to some comments in the video that the stock pulley acts as a harmonic dampener, and that replacement risks engine damage? One comment even sites an article claiming so.

Can't personally confirm this scientifically (quickly anyway), but yes, natural freq will certainly have different critical speed as "per design" requirements originally set by Porsche Eng. You'll introduce a whole new set(s) of vibrations to the engine (in engineering terms)

Read Rotor Dynamics

Hmmmm...interesting. Anyone get over 100K miles on an UDP yet? :D

not on the 986. Its a simple aluminum pulley. It has not harmonic dampening whatsoever aside from its weight, which is not much different than the aftermarket ones.

On 987 cars, they have a true harmonic dampner which is why you have to buy a much more expensive underdrive.

Whats the word on this boxster making 273 wheel hp? Or is this one of those stupid dynos that converts to engine hp?

It's not wheel horsepower. It's estimated at crank.

I use this same dyno. You get print out of both. The owner normally talks the crank figure because he knows most customers just want to hear the big number and these are the figures peopke can relate to when they read the manufacturer spec on the websites.

Wouldn't you want to compare the wheel HP before and after? The pulley wouldn't actually create more HP, just more of what the engine does make would get to the wheels. At least that was always my understanding of how it would work. It is supposed to FREE Up HP not create it.

I have absolutely no doubt it gave me felt low end torque / HP.