How to make a Boxster faster *More HP!* pt 2 – Underdrive pulley tested | Road & Race S02E34

How to make a Boxster faster *More HP!* pt 2  –  Underdrive pulley tested | Road & Race S02E34

This time on Road and Race does fitting an
underdrive pulley give you more horsepower? In my research to find cheap ways to make
my car faster I came across something called an under drive pulley. For about £130 you get a smaller and lighter
version of the existing crankshaft pulley. This pulley drives devices such as the power
steering pump, coolant pump, alternator and air con. The theory here is that a smaller pulley will
turn slower thus turning these devices slower thus releasing power back to the engine. The manufacturer claims up to 10 horsepower
can be had. So today we are going to fit one then go to
a rolling road to find out how much extra power we get. Cue the montage…. First you need to get access to the pulley. In a Boxster you’ll need to put it in Service
Mode, remove this carpet then remove the access panel. Put a breaker bar on the tensioner pulley
and pull the serpentine belt out. The crank shaft pulley needs locking in place
before it can be removed. Porsche will selling you special tool no.9593
but we just used an alan key. Now this is where it gets a little, awkward
shall we say? The under drive pulley snags on this piece
of engine here so out comes the multi tool. And because we’ve made a terrible mess out
comes the vacuum. Now we can fit the new pulley. Put some of the supplied thread lock on the
new bolt and hand tighten it. Torque it to 50 Nm (37 ft-lb)
The kit also comes with a new longer belt so release the tensioner again and fit it. It goes on like this:
Then to finish up put the engine cover and carpet back on, take it out of service mode
and go for a test drive. We’re back at Surrey Rolling Road to see
how much extra power the under drive pulley we fitted has given us. If you’ve not seen the previous episode
then the car was making 273.7 horsepower. Well, as you can see the car is made 273.8
horsepower which is basically exactly the same as before. I’m actually a little shocked by this. I wasn’t expecting to get the full 10 horsepower
but I was thinking something along the lines of 3 to 5. Just goes to show that on this Boxster at
least fitting an underdrive pulley does not increase horsepower. If you’ve fitted an underdrive pulley in
your car and found it shown an has increase please leave a comment letting me know. Maybe I’ll put together a show in the future
showing everyone’s results. Next time on Road and Race
We discuss the ECU performance remap then go back to the rolling road for the final
horsepower figure. If you’ve found this video useful please
Subscribe and hit the Like button as it really helps us make more shows. Please feel free to get in touch by leaving
a comment on this video and I reply to every one. Links to follow us on social are in the description
box. Thanks for watching.

About the Author: Michael Flood


  1. I have this mod and am not sure it provided more HP, but when you're on the track you're not cooking the power steering fluid as much.

  2. an underdrive pulley is often used in race/rallycars, not so much for extra power but to prevent cavitation of the waterpump and powersteering pump while running the engine at sustained high rpm. You can imagine while running at sustained high rpm that the pump impellors have to rotate at equally high speeds. If cavitation occurs it can cause cooling problems or problematic steering servo assistance. (oil with get frothy and foamy)

    if you use such an underdrive pulley on a streetcar and you end up in a trafficjam for a prolonged period of time the engine may eventually have cooling problems and electrical problems (fans often switched on , AC on, that will drain a battery pretty quick. No problem at cruising speeds but at idle speed the alternator might not be able to keep up.

    personally i would never use such an underdrive pulley on a streetcar. It is just not worth the bother. On a trackcar? maybe

  3. thanks for your time again on this vid Neil , PS would love to hear your opinion or even touch on a 987 boxster s and if you would consider getting one in the future thanks

  4. I'm curious as to what an after market exhaust would do as those usually claim to free up a handful of hp as well. Other than that I think the only real gains you're going to see are by adding forced induction. Keep the vids coming though!

  5. Ha! I love this. Too many people spend time and money on totally untested performance "upgrades". Like you, I expected some gains from an underdrive pulley. The theory makes sense, after all. Now, this video has left me wondering why it doesn't improve horsepower.

  6. Another great video and not the result I expected either 🤔Perhaps with the final remap it will all come together!

  7. What was the bit you chopped off from the engine? Not necessary I hope. The M96 engine is one of those engines that can't really be improved on in terms of power. I few people have put the 3.4 996 engines in the 986 Boxsters but still a huge load of hassle and expense, much better to buy a later 987S (Gen2) 310hp! If you can afford it. I have a 99 2.7 and use it for holiday trips around Europe every year, you can thrash the living daylights out of them in Germany and they thank you for it. Great for 120mph all day..fantastic cars for the amazes me how cheap you can buy a mid engined flat 6 cyl Porsche convertible. Great vids ..keep them coming.

  8. The reason for no real improvement is that while on a rolling road your car is not using power steering, the battery is probably fully charged so no load on the alternator, probably no a/c on in the UK…therefore the only thing is the water pump which you really want to be working well to keep the engine cool..all the other things have no load on them so it makes no difference.

  9. The baseline test and the final test were separated by several weeks. Temp and humidity corrections on dyno tests are notoriously inaccurate. Thus, the possible error in the temp correction is probably on the same order of magnitude as the difference that was being measured. Remove the UDP, get a new baseline, then install the UDP and re-test the next day at the same time of day (assuming that the weather doesn't swing much). This might help improve accuracy.

  10. Exactly it's only mental power. It revs only "faster" under NO load. Under load will act identical to a normal pulley. The real advantage is having the accessory equipment work as intended at higher average engine RPMs. Only cars who see a larger average or track time will benefit from this. On the mechanical side, the driving pulley has less angle of "belt wrap" which will lead to faster wear of the belt. I say faster in a very broad sense since we are talking about a occasionally used vehicle and won't effect the overall enjoyment of spending money.

  11. I'm not sure that this underdrive pulley is safe for your engine… That front crank pulley, does it act as a harmonic damper/balancer? If it does, you are losing some power and a significant amount of reliability without it. A proper underdrive pulley should be a kit that increases the size of the individual components' pulleys; new larger A/C pulley, new larger power steering pulley, etc, and lengthen the belt. You want to leave the harmonic damper alone. Here's an article by Steve Dinan (of Dinan BMWs in America) explaining it:

  12. Yeah pulleys don't do much, I have a kit on my M3, and they did nothing to the dyno numbers.. I do advise you to put your stock crank pulley back, these pulleys don't have dampeners in them, the stock one does, not having the dampener is bad for your engine

  13. Hello neil keep up the good work. Could you give me the name of the song during dyno testing? Grtz ramzi porsche fan

  14. Great video! I think the best way to boost up the HP is to get another car… lol I meant it. Don't think there's a lot of potential on 986 as the factory has already squeezed most juice out of it. Unless you throw a turbo in it (is it even possible?) but the mod would probably cost more than just buying a 911..

  15. It will be interesting to see the final BHP figure after all of the mods have been mapped in properly. Are there any plans for a remap?

  16. Crank horsepower will be the same, but bhp to the wheels should increase with less resistance from the auxiliaries. Been wanting to fit 1 to mine for a while. According to the forums it defo makes a difference.

  17. I have done ud pulleys on a 3000gt, starion turbo, and most recently a g37. Especially on the g37 It wakes up the motor incredibly. It shot to redline way faster than before. the other two cars also had great results. Does anybody know if you can do one on a gen2 cayman s (2011)?

  18. maybe someone should ask what fuel you are running. if its not high octane, its probably pointless chasing a few HP lol…also, you have to be using the power steering, etc to notice any difference. to just run it on a dyno without engaging parasitic losses, wont show anything

  19. is 290 – 300 hp realistic for a boxter S? 3.2L? Your videos are great ! amazing detail and concise information

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