Underdrive Pulley Help/Questions - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Considering Pedro's Underdrive Pulley Kit but read that IMS Bearing Replacement should be done before because of the need to shave down the "boss" or Top Dead Center bolt receiver/holder/whatever (not sure of technical term). Can someone elaborate on why shaving down the "boss" may make this more difficult? Can enough of the "hole" be left intact to use it as a TDC guide? Any other problems experienced as a result of an Underdrive Pulley Kit? Recommend any other kit over Pedro's and why? Thanks in advance.

When the pin is through the crank pulley and in the TDC boss, it can have a substantial load on it, especially during an IMS retrofit. Because some under drive pulley's require you to cut a lot of material away, the ability of the remaining material to hold the engine at TDC can become tenuous. Some pulley's can actually block the TDC hole entirely, which also makes an IMS retrofit impossible.

Can't one just install the OEM pulley prior to an IMS Retrofit? Is there an alternative to using the boss for TDC work and is it a substantially more difficult task?

BTW Thanks for your Reply JFP in PA...my dad was born and raised in Altoona, went to PSU...

Quotes source post: 497503

With many of these units, to problem isn't the pulley, it is the amount of the pin boss you need to remove.

I haven't had a problem with the engines I've put UDP's on. Only remove the minimum of material needed for clearance. I switch back to the stock pulley if I need to lock the crank.

Do you recommend any particular kit over others? Why? Thanks!

Quotes source post: 497516

No..............

Thanks-- going to stick with Porsche engineering design choices for now. Macster from Rennlist shared this great explanation in support of Not installing an underdrive pulley... Can't help you with the shaving the "boss" question. I can offer that I'm not a fan of underdrive pulley setups. While one can get away with spinning the power steering pump and possibly the alternator at slower speeds, the last thing a hard working Boxster engine needs to slower flowing coolant. You can see why for yourself: Get a flat bottom stove top pot and put in around an inch of water and place on the stove at high heat. After a while notice bubbles start to form. Gently move the pot in a circular fashion to swish the water around. Notice how the moving water dislodges the bubbles? Let the water get hotter. The bubbles form faster now and are larger in size. One finds he has to move the pan with more vigor to remove the bubbles. This is essentially what is happening in the Boxster's cooling system. The coolant needs to be circulated at a high rate of speed to help prevent the formation of those bubbles, pockets of steam, preventing them from getting too large. If they are not removed where they form gets even hotter -- and they form at the hottest areas already -- and the bubbles/pockets of steam prevent coolant from contacting the hot spots and carrying away the heat. As a result localized overheating (and damage) can occur. There are tubes cast in the head water passages to act a tiny jets to direct/aim coolant directly at the hottest spots to increase the velocity and force the coolant has to ensure no bubbles form and remain in place. Slowing down the flow of coolant is the wrong way to go and for just a piddly amount of "HP" gain. Far and away if one is tracking his car the biggest benefit in cutting lap times and increasing speed is not by making mods to the car -- other than those intended to help the car sustain the ravages of tracking (mods like better oiling) -- but in improving one's driving skill with expert guidance and counsel from a highly regarding driving instructor. Not only does this make the driver a faster driver but a smoother driver which is not only safer for everyone involved but reduces the stress on the car and its subsystems. ***************

Let's be clear - there is no decrease in cooling system performance when using a UDP. I have driven my Boxster repeatedly on the track (continuous full throttle and shifting at redline) in weather up to 110F and there was zero difference in the cooling performance as compared to a full size pulley. Someone can "theorize" all they want, but the reality is that the UDP doesn't decrease cooling, power steering, or a/c performance. Every Spec Boxster in the country runs a UDP (and many street cars do also) and if there was some huge downside (like over-heating the engine), we'd have heard about it by now.

DRGETZ forgot to consider/mention that the coolant system is under pressure ~5-15psi and that the Radiator fluid itself is also increasing the boil temp and decreasing the formation of steam bubbles. https://durathermfluids.com/pdf/techpapers/pressure-boiling-point.pdf http://auto.howstuffworks.com/how-does-radiator-cap-work.htm Honestly if you do end up boiling the coolant then you are already in deep trouble and your gauge would be flashing long before that. Note that your temp guage is centered at 185 F and if it got to 200 you would definitively be thinking of starting to bring her down gently and still have at least a 40F or more margin before boiling. The higher the coolant velocity the more turbulence and more drag so if you were to measure the actual difference in coolant velocity through the system, I doubt it would be much different with the UDP and perhaps may even prevent pump damage by not having the pump cavitate at high rpms. Its all speculation and theory so us mortals just learn from the racers empirical results and take their word that UDP's work and cause no ill effects. I have a Tarret UDP and although not raced much it has been working fine and I feel like I'm saving wear and tear on the accessories and gained some faster responsiveness when hitting the throttle. I noticed a postive change immediately when switching to a UDP Perhaps a bit of torque increase at the low end as I'm feeling like a rocket launching from 1st to 2nd as the rear is gripping hard and thrusting me back in the seat. Love that feeling in my S.

Quotes source post: 497606

Thank you for your replies thstone and jb92563. Thanks for increasing my Boxster knowledge and taking part in my Porsche education pursuits. I've chose to share the information below to explain why I plan to just replace the OEM belt and leave the pulley upgrade for (perhaps) another day. But after writing the response (and finding virtually nothing about Porsches and Okinawa online) I realized some may benefit from my Boxster S buying experience on a small approximately 70 miles long by 2-17 miles wide Japanese island that hosted the horrific and WWII-ending battle against the Japanese imperial military forces and cost over 240,000 lives in less than six months. My concerns have more to do with the need to alter a part of the engine (the boss) that many have reported as important to an efficient IMS bearing replacement. I live on Okinawa. The nearest Porsche dealer and Porsche authorized/trained mechanic sits on another Japanese island (part of mainland Japan) nearly 500 miles across the ocean. (My particular Boxster S did not come with the amphibious option. Spotting a few non-amphibious Porsches testing the ocean waters during some 2011 Tsunami videos has ruled out any ocean-crossing attempts unless by ferry.) Okinawa Population approx. 1.25 million; Porsche population: probably less than 100. You can drive months without seeing another Porsche unless you head towards the capital city of Naha. The previous owner of my car and I searched for several weeks trying to find a Porsche specialist but did not find one. We found plenty of mechanics willing to work on the Boxster S but that seemed like a gamble that could likely result in more problems and less money. The first garage he recommended, because the original owner specialized in performance foreign (non-Japanese) vehicles, had two boxsters sitting in their bays that had reportedly been collecting dust for over a year. The owners apparently did not want to pay for what the garage/mechanics claimed as necessary repairs. If I didn't see all the dust and what appeared to be half-completed work started months, if not years, ago I would not have believed the abandonment tales so easily. So, before I negotiated a price for the externally excellent looking Porsche, I knew I'd personally perform as much maintenance, preventative maintenance, and repairs as possible rather than ending up in an Auto Mechanic Extortion Scheme of Some sort or "A MESSs". I plan to do as much work as I can on my own as I trust my own mechanical abilities, attention to detail, thoroughness, ability to learn, retain, and apply new information and technique combined with the patience, persistence and willingness to do things correctly over some questionably-skilled mechanic that has neither driven nor seen a Porsche engine: and, due to language barriers, does not have access to the wealth of Porsche technical information and tutorials available in English. Nor do I trust any mechanic with two Boxsters collecting dust in their bays along with a BMW. The only clean car of the five, a late model Ford Mustang - probably the mechanic's. Though I have yet to locate a Porsche specialist on Okinawa, I do have access to hydraulic lifts and ramps through the US Military Autoskills Facilities as well as their extensive array of tools and some general technical support from the Autoskills Center employees. I purchased the car after raising her up 5 feet and performing my own 3 hour Pre-Purchase Inspection that included an oil and filter change and an inspection of both oil and filter. Also purchased a BlueDriver OBD tool that showed no trouble codes. Plan to buy the more thorough Durametric: and, purchased the car knowing I would perform the following: 1. Replace Fan belt, Air and Cabin Filters 2. Replace the engine mount 3. Replace Spark Plugs, Tubes and Connectors (and coils if needed/cracked) 4. Replace Pads, Rotors, and install stainless steel brake lines 5. Replace both rear axle assemblies 6. IMS Bearing retrofit/replacement The previous (2nd) owner stated he only changed the oil every 5000 km or at least once a year for the last 12 years. Only mechanical/electrical replacements included a new water pump, fan belt, window drop regulators, MAF and O2 sensors. Knowing that he had done little in terms of parts replacement and preventative maintenance (and probably even less by the original owner of 4 years) I knew I'd need to perform several replacements and some preventative maintenance. My pre-purchase inspection aided me in negotiating from his initial listing price of $17,500 to $11,700. During our month-long inspection/negotiation process, he actually had a new glass-windowed top installed that he purchased from a stateside Porsche dealer during a recent trip to the US. The top looks great and functions well. The previous owner also "threw in" several hundred dollars in new oil & air filters, two new O2 sensors, three window drop microswitches, a dozen different new light bulbs, two new brake sensors, two liters of Porsche Transmission fluid, all of the manuals, an unused Porsche car care kit, an unused Blue "siren light" that came with the Stuttgart-built Boxster S, jack and Porsche tools as well as a few other items. I'd like the extra hp boost that coincides with the UD pulley upgrade but not at the expense of a less difficult IMS Bearing replacement. I asked about the TDC locking alternative to using the "boss" and no one has replied even though I posted the question on three forums (Rennlist, 986, Pelican); so, for now the UD Pulley upgrade goes to the back burner. It only made it's way to the front of the line after searching and reading about fan belt replacement on the Boxster. Whether or not I perform the IMS Bearing retrofit/replacement, or hire someone to do it, the task seems daunting enough without adding another time-consuming aspect to the already lengthy and difficult task by rendering the boss useless. I welcome any knowledge/experience you wish to share... love learning so thanks in advance. Respectfully, Mitchell

Quotes source post: 497622

Hello Mitchell, this is my story (background).. Many years ago, I installed a BBI UDP after burning two steering pumps on the track with the SoCal summers, and also installed a small oil cooler on the return port of the steering rack. Then a few years later, after removing the gearbox to replace the input shaft bearing, I noticed that the IMS cover was leaking a bit and to replace the seal, I first installed the two cam lockers (thanks to BYProdriver and Healthservices..), and then locked the crankshaft at the rear, using two metal straps bolted between the bell housing and the crank (at the flywheel mounting flange), then removed the chain tensioners before removing the IMS cover. This worked out for me because after removing the gearbox I knew that it was not going to be easy to remove the large bolt on the UDP with the flywheel and the gearbox supports removed. Good luck with your car, are you going eventually be relocating to the Iwakuni base? Regards, Gilles