underdrive pulley

http://www.cheetahonline.com/products/n8039.html Has anybody ever done this for their 996 ? curious to hear from somebody who installed one of these...

Interesting ... That also means you have to change the belt.

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Never installed one on a Porsche but on other cars...they do not do much at all. I say save your money.

I saw a thread on the boxter forum. I think it make 5 HP? IIRC

It's not that it makes noticeable hp but that it helps keep your ps pump from burning up on track. And yes, you need a new belt that is proper sizing. Did this on my Spec Boxster. Let me know if y'all want to see before and after pics.

I've heard that it puts an unnecessary strain on the alternator?? and they slow down your water pump thus raising engine temps?

only needed if you are racing or doing a lot of serious track time.

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Beware of the Cheetah he is often missing in action for long periods of time!

Though $200 is not bad for a good quality under drive pulley, it'd be better spent towards a track event IMO, particularly for a street car.

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Are you boiling your power steering fluid on track? If not, skip this. -td [I don't get all this recent traffic regarding underdrive pulleys lately...]

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internet wizards...they put odd thoughts in one's head.

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There's the answers. Next topic.

ok thx for the insight guys.

We use them on all our race cars. My no BS .02 is way over kill for a street car. What they don't tell you is most (no idea about this pulley) under drive pulleys require you to cut down the TDC boss. Its not a big deal but something you should know about.

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your BS .02? overkill... why? what is a TDC boss? how much extra hp/torque do they give you... is it more on top end...?

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Yeah what is TDC Boss? what the heck does this have to do with Underdrive pullies? http://www.modernghana.com/news/2066...-contempt.html

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well its obvious.... or is it just me?

The pulley is smaller? I'm trying to see how it works. Can someone explain? "With the smaller diameter of the pulley, a shorter belt is also needed."

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eh, I'm pretty sure its a shorter belt too... try searching google. many other people do it especially in the muscle car world.

I think they've got it backwards on the referenced website. Larger diameter pulley, longer belt should reduce RPM on the pump to underdrive it. Am I missing it?

i believe he was referring to the smaller crank UD pulley- okay any torque gains?

Thx, I get it. So everything on the serpentine slows down.

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Yes Sir.

I fitted a Flat6 underdrive pulley to my Boxster S about 2 years ago - the reported improvement is about a 10 hp gain, which (according to my delicate bum dyno) is about right. Here are a couple of observations: You can definately feel the difference mostly in the low to medium rev range - once above 6,000 rpm its not that noticable. Yes, the pulley is smaller diameter and you need a shorter belt, which comes with the pulley kit. Yes, you have to shave off a small part (~5mm) of the TDC (top dead centre) boss which is a hollow alloy protrusion cast into the crankcase and used to fit a TDC rod when locking the camshafts. This is easily done and does not impare the boss. I did a before and after voltage test of the alternator output because it is turning slower with the new pulley. By the time the alternator is up to 1,800 rpm, its output is just about the same as with the standard pulley. The interior of the Boxster is quieter due to the lowering of the belt & accessories. Dollar wise, it is the best bang for yor buck you can get - I've had it on the car for 10,000 km with zero problems - I'm a very happy camper.... And you can always put back the old one if you need to.

I know this is an old thread, but I wanted to chime in anyway. Feel free to ignore. Here are a couple of fact-ish points about the UD pulley: 1) The pulley doesn't increase horsepower. It makes the other accessories driven by the serp. belt turn more slowly, making that extra power available to the wheels. 2) The pulley does not cause overheating. I ran the 4" underdrive pulley in my 2003 Boxster for 2+ years, and did not notice any significant temperature change before/after. A couple of folks have theorized that the underdrive pulley may actually prevent cavitation at higher RPMs, but I have no way to verify this. 3) The pulley does not cause charging issues. Although I use a battery maintainer if a car will be unused for more than a week or two, I did not notice any battery issues / electrical issues due to the pulley. The car operates at a wide range of RPM anyway. If you're worried, just drive a little faster. Over the four years I owned my Boxster, I installed just about every bolt-on performance mod I could get my hands on, and the underdrive pulley was by far the best "bang for the buck." In fact, I'd be willing to go out on a limb and say that it's the only bolt-on mod that I can actually tell made ANY significant improvement. It's also the only mod that is backed up by common sense: Using less power to drive the accessories results in more power at the wheels. As stated above, I installed just about every mod I could find on my Boxster. This pulley will be the ONLY bolt-on mod I install on my 996, at least until I can swing a turbo kit. *Disclaimer* Everything above is opinion . If you install an underdrive pulley and your car overheats, the battery drains, and your power steering pump explodes and kills everyone nearby - and starts a brush fire that kills a sign-language-speaking gorilla holding newborn panda twins - I am liable for nothing other than saying, "Dang, guess I was wrong."

who makes a good under drive pulley kit for the 996?

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If the UD pulley was such a "good" noticeable mod why wouldn't Porsche have used a smaller pulley thus increasing the HP avail. at the wheels and reducing the cost that is required to produce such pulley, thus reducing the cost of the car overall... Not bustin your ***** just an honest thought..

We love the UD pulley, but the unit we use has a solid center. The CVheetah looks fine, just don't use this one! We've seen three fail this year alone that came in one customers engines. This one didn't have another track day left in it. But it could have been worse. This is what happens when fashion is employed where it has no place. I have engines with hundreds of track hours using our solid center UD pulley with zero issues and thousands of miles. The top one above has less than one track season under its belt. The factory isn't the ultimate authority on these sorts of things, hell they are the ones who created an engine with 23 documented modes of failure, most of which occur on the street and not on the track.

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I see this same question asked on every car forum I've ever been a member of. "If this mod is so great, why doesn't it come from the factory this way?" The underdrive pulley is a way to eke out some improvement over what Porsche provided. Porsche could also have bored out the cylinders and strapped a turbo onto every 996 that went out the door - but they didn't. Porsche - just like Hyundai or Ford - has to strike a balance between performance and reliability. Every mod you make - whether it's an underdrive pulley or an aftermarket supercharger - runs the risk of decreasing reliability in the name of increasing performance. This mod is no different. Running the water pump, power steering pump, air conditioner, etc. could keep that piece of equipment from performing optimally, and might even shorten its life. No car maker that offers a warranty ships their product performing at 100% potential output. It doesn't make sense. When you dial back the performance a little, mean time between failure increases exponentially. Machines that operate at 100% fail quickly - consider how long drag engines last. I don't think you're busting ***** - but assuming that Porsche wrings every HP and ft-lb of torque out of their engines from the factory is a fallacy. You wouldn't WANT to own such a product. Porsche provides a great product, but there is always room for improvement. Modding your engine is a risk-vs-reward scenario. The mods with the greatest reward also carry the greatest risk.

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The solid center is the one I used on my Boxster and will use on the 996. Making a part nobody will ever see this pretty - at the cost of reliability - is insane.

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That is some scary stuff!!!!!!!!

I installed the UD pulley Saturday. What was a 3-4 hour job on the 986 is a 30 minute job on the 996. There's even room for a RotoZip w/ grinding wheel attachment to take care of the TDC boss, much nicer than the mini-hacksaw I had to use on the Boxster.

Really old thread but to be meaningful, voltage measurement of the output of the alternator with a UDP will need to have full load on it. At some point the slower-turning alternator may not be able to keep up with the demands of the car. If you turn on headlights, rear defroster, AC at full blast, wait until the car is hot and radiator fans are on, and turn on the seat heaters, you need to be sure the alternator can produce enough voltage at the RPMs you will be running at. Just saying that there is likely a spectrum of possibilities. Slower spinning accessories can be a plus or a minus depending on what you need from them.

Um, wanna sell the pulley for a good price? Too soon? Sorry, I'm a vulture that way. Rarely use accessories. I'm local.

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This research has already been done on ours cars and the general data shows anything under 2k rpms, the aftermarket UD pulleys can't match factory output. Other than that, they are identical in output above 2k. So bottom line is unless you sit in traffic more than you drive or you like lugging the engine, you shouldn't notice any issues. Here's mine and pretty much supports what I said above.

I've had BRRacing in Los Gatos do some work on my car lately. Those guys know how to set a car up for the track as well as anyone. I asked Bruce what he thought about the UD pulleys and he told me it's all good, nothing bad and almost a necessity on tracked Boxster/caymans. I'm going to have the one I got recently put on since I'm looking for all the cheap power I can get!

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BRRacing set up my PSS9's. Great guys, and the car's working great now. I wonder if GT3's had higher output alternators or smaller alternator pulleys? They came stock with a smaller crank pulley. I need to get one b/c my power steering pump is starting to weep at track days after sustained high rpms.

That's why mantis pulley is has a solid center.

Gentlemen, silly question on these things. I'm about to install one on my 986 boxster, and every instructional guide tells me that you must use a tool or some other sort of device to lock the crankshaft pulley to keep it from moving when loosening or tightening the crank bolt. Now, with the car on the ground, with the transmission in gear and the parking brake engaged, the crank should not turn and the pulley is held relative to the crank with a keyway. So, in light of that information, no tools should be needed to keep the crank from moving. Am I missing something here? Thanks

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What you are doing, by using the driveline to lock the assembly, is killing the dual mass flywheel.. the link that connects all these items to allow the crank to be locked. The load it is experiencing is also opposite of what it sees in operation. I use a strap wrench, and a second person to hold the crank pulley when removing it. I don;t even trust the locking pin boss on the crankcase, as I have seen them break when doing this job.

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Hadn't considered the dmf. Thanks for your excellent response

FWIW RSS pulley comes with a tool.

Anyone try the EBS Racing underdrive pulley? Im considering buying this one. Seams to be built well and the price is great. $165 and it comes with the belt. Sold on eBay. http://www.ebay.com/itm/Porsche-Boxs...pZlc4V&vxp=mtr

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The advantage of machining out the center on this pulley to reduce weight, does not offset the weakness of the pulley. Go to a brand with more material in the center. I am not sure about this pictular brand, but the majority of the ones that have failed, from my research are the machined out centers. Take a look at RSS, mine was made very well.

I have a used mantissport underdrive for a good price if anyone wants it

Just a Note, The original MantisSport prototype under drive pulley is still in use from 2006. Approx 20,000 miles of racing on it. No failures reported.

The RSS underdrive pulley I have (installed by previous owner) does not have a locator hole to pin TDC (no room for it due to smaller diameter), nor any TDC alignment markings on the rim. How does one find TDC once these pulleys are installed?

I spose you could do some geometry with the stock pulley and its keyway vs. the locating pin and transfer that to the new pulley, but the easier version is probably just to reinstall the stock pulley temporarily or use the old stick in the spark plug hole trick.

If you removed too much boss and now find yourself needing to use the TDC pin, it wouldn't be much of a project to temporarily restore the boss with JB Stick Weld or one of they hobbyist low-melting-temp plastics so it will work with the stock (temporarily reinstalled) pulley. You can grind or snap off the newly-added boss material after the repair is complete so you can reinstall the UD pulley.

I was hoping there was a TDC indicator somewhere else, like the notch on the flywheel in a 944. I suppose one could use the cam end notches (used for locking the cams once at TDC) to determine TDC, then mark the crank pulley.