Underdrive Pulley Install Guide
 

I just finished installing the 4" underdrive pulley that forum member Jaay sells, and I documented the process in varying degrees of detail to help anyone else out who's considering this mod.

Tools required:
Jaay's 4" pulley and belt
10mm socket and driver
24mm shallow socket
Breaker bar for above
Grinder, dremel, or hack saw
Porsche crank pulley removal tool (or see below)
Various common hand tools
Highly recommended: A pair of mechanic's gloves

Remove your rear subwoofer or whatever other accessory you might have on the rear shelf so you can get the carpet kit out of the way. Slide both seats all the way forward.

Remove the four plastic anchors so you can move the firewall carpet/insulation panel.

http://lh3.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02629.JPG

You will see the engine cover.

http://lh5.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02630.JPG

Remove the 10mm bolts and the two 10mm nuts around the perimeter of the cover.

http://lh4.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02631.JPG

Once you remove the panel, you will see the pulley to be replaced with the underdrive version - it's the pulley below the belt tensioner.

http://lh4.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02632.JPG

Use your 24mm socket and breaker bar to crank on the belt tensioner so you can remove the existing serpentine belt.

http://lh6.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02633.JPG

Get out your Porsche crank pulley removal tool, or be prepared to bust something out on the fly. You need to use the 24mm socket to loosen the bolt holding the crank pulley. It's tight.

Since I didn't have the Porsche part, I made something out of a bolt, my floor jack handle, and some plumber's tape I had on my workbench by fishing the bolt up behind the OEM crank pulley, adding a couple of nuts, and creating a strap to attach the jack handle to the pulley... Hopefully the pics explain better than this text...

First, I fished the bolt up behind the factory pulley. I taped a zip tie to the bolt so I could pull it through the hole.

http://lh5.ggpht.com/_wrxsG6O0kbU/Sy...8/DSC02634.JPG

I used another nut to secure the plumber's tape to the factor pulley.

http://lh4.ggpht.com/_wrxsG6O0kbU/Sy...8/DSC02636.JPG

This image sort of depicts how I used the jack handle for leverage, and the socket on the crank pulley bolt as a fulcrum, to get the bolt loose. The jack handle is in the wrong place in this image - it should be ABOVE the socket (lefty-loosey), but you get the idea:

http://lh6.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02635.JPG

With the old pulley out of the way, it's time to cut down the boss to make room for the new UD pulley. You can see in this pic the material that needs to be removed. I took off about 3/8" to make the boss flush with the other protrusions on the engine case.

I started out using a dremel, but the best tool I had for this job turned out to be a small hack saw I picked up at Home Depot a while ago - it looks like a stout coping saw and works great for cutting at an angle.

http://lh3.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02637.JPG

Install the new pulley. EDIT: At least one other write up I found indicated that the crank pulley bolt is not reusable.

http://lh6.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02639.JPG

This image shows the clearance between the cut-down boss and the new pulley. Make sure you remove enough material so the boss does not interfere with the pulley...

http://lh5.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02643.JPG

I used a strap wrench on the new pulley so I could apply the requisite torque (i.e. I "tightened the snot out of it" per Jaay's instructions!).

Use a shop vac or other means to remove any shavings you created while cutting down the boss...

Install the new belt (refer to your Bentley to ensure you get the belt routed correctly!).

http://lh6.ggpht.com/_wrxsG6O0kbU/Sy...0/DSC02638.JPG

Once you have cranked everything down and triple-checked the belt routing, fire up the motor with the cover off to verify that things look right. Specifically, make sure the new pulley is flat and unobstructed.

Shut the engine down and perform one last snot-tight torquing on the crank pulley bolt.

That's it! This took me about 2 hours, including taking pictures, lashing together my ghetto pulley tool, and drinking several beers.

nice write up. Did you notice a substantial improvement?

Thanks for the write up. I also would like to know what your experience is after doing this. Notice any extra power or other improvements?

Just got back from a decent drive. There is a noticeable performance gain - not enormous, but appreciable. Certainly more than I "gained" from my EVOMS intake.

Interestingly, all of the accessories running at a lower speed results in less overall noise. Maybe this is due in part to the new belt - but whatever the cause, I'm very happy with this side effect.

So - I'm happy! Hopefully I'll get an AX in sometime soon and get back with a proper review.

Looks good Glad the install went well.


Chris

anyone know the torque spec for that bolt holding the pulley?

Did you happen to take a picture of the new and old pulley next to each other or weigh them? Is there a reduction in size, weight or both? Why only change the crank pulley and not all the accessary pullies, seems like there would be a more profound effect and free up some more hp?

It's in the Bentley manual - I'll add it to the write up tomorrow, as it's too darn cold to go to the garage.

BTW - and I'll revise my writeup above - I read somewhere else that the crank pulley bolt should not be reused.

Nope.

Both. I bet you're gonna ask me to quantify it for you, but I can't.

I'm not sure how much you can underdrive each specific system - but underdriving the crank pulley does them all at once, rather than having to replace each accessory pulley. I'll have to defer to the experts - like Jaay, Jake, and others - I'm just a guy who bought one and installed it. ;)

Step 1: Torque to 37 ft-lbs.
Step 2: Tighten an additional quarter-turn (90 degrees)

Thanks for the write-up, as this is a mod I'm currently considering (always need a spring project). Anyone know what the protrusion is for, that needs to be milled down? Almost looks like a point where a bolt would go to lock the pulley (not sure it lines up)...it must be there for a reason.

I believe jmatta is right. The boss in the casing that must be cut down is a top dead center locator. You align to TDC and slip a retaining tool through the stock pulley to hold the crankshaft in place. It is useful when changing timing chain tensioners to keep everything aligned so don't cut it all the way off. There are other ways to fix the crankshaft at TDC but this is a quick way that techs are familiar with. On one car in our club the casing boss was completely cut off and the Porsche techs had to get creative as they could no longer use the tool.

Fig. 25 confirms it's for TDC.

http://www.pelicanparts.com/techarticles/Boxster_Tech/Disc163/BoxsterTech-163.htm

Very good visual, indeed. Do you think the point is strong enough to hold so you could loosen the crank bolt? The only experience I have is that is remotely close is the tool that holds the pulley for removal in an older air cooled 911.

It is strong enough. The bolt is on there way tighter than the fan/alt nut on the air-cooled 911s incidentally. (just did this mod today)

Why not remove the stock pulley with air tools?

There's no room in there. You could do that if you dropped the engine.

It is strong enough, I just cut a large hex key to fit in the hole and it worked like a charm. You will need a large breaker bar and a 24MM socket to get it loose.

Installed
 

Great write up. Easy to follow instructions. I did it in the wee small hours of the morning today.

The only thing I did differently was to use a screw driver head instead of his leverage contraption. I put the screw head through a hole in the stock pulley, and into the boss (see pics). This held the stock pulley in place while I loosened it.

http://www.flickr.com/photos/backman_z/4845265417/
http://www.flickr.com/photos/backman_z/4845884042/

Thanks again sd/boxster! :cheers:

You will quickly notice that the new under drive pulley is dollar for dollar the best bump in performance one can do for their boxster. Good luck.

I realize this is an old post but wanted to add a little information for those who may later come across this thread like I did.

I installed my RSS pulley last night. I weighed the factory crank pulley - 327 grams. The RSS under drive pulley on the right is smaller but weighed more at 376 grams. http://986forum.com/forums/uploads01...1345396492.jpg

Had a chance to drive it yet and notice any difference?

Hello Mike-

I did take it out for a short drive. I believe it IS the best $219 (includes new shorter belt, pulley tool, and shipping) I've spent on this car. Peppier in the lower rpms. Can't really tell above 5500 rpms. I need to get back on the track to confirm as I have zero access to a dyno.

Have a good week.

I just completed my installation of the updated Mantis Sport underdrive pulley. The engine feels a bit more free and when I say a bit, I really mean just a bit. Good value mod though. The hardest part was cutting the boss, everything else was really straight forward. I actually got the pulley for free, and got the belt for $52, so a nice inexpensive mod.

Thanks for all the technical data and installation steps, they made the job really easy for me.

http://986forum.com/forums/uploads01...1350112959.jpg

I just bought a TRS underdrive pulley and just wanted to know how the hell you got any of the tools in there to do this. Does anyone have pics of the crankshaft removal tool...specifically the tool that uses the threaded bolt to push against the crank to force the pulley off of the tip? I'm sure this must be a shorter threaded bolt than the average kit you can find in any auto parts store, but pictures would go a lot further to explain that part of this process. Thanks!

Hey guys, great guide here with pictures and everything!

you dont need a special tool to remove the factory crankshaft pulley, i found an old bolt that was the correct width to push through (dont need to thread it) one of the holes on the pulley into the boss (which later you have to cut off). this will stop the pulley from turning allowing you to undo the nut.

then removing the pulley is a case of gently levering it off with a long screwdriver.

i bought this one
https://patrickms.s3.amazonaws.com/p...EY-WITH-AC.jpg

Crankshaft Pulley Kit (For cars with AC)


I can feel the difference, it is a small gain, but its worth it.

Lighter rims & wheels will definitely feel the difference too, much more peppier at low rpms.

Someone had said that there would be no AC at idle with a 4" UDP, so I thought I'd post my results to clarify.

I installed my Tarret 4" under drive pulley and all went well and better than predicted.

Particularly, I am happy to report that a 2001 S with the 4" under drive pulley still allows full operation of the air conditioning at idle! :)

Here is the Proof below:

With the Tarret UDP installed and the engine up to full operating temperature,
Ambient temperature 70 F as shown on the guage, and ~750 rpm at idle for over 5 minutes, airconditioning set at full the temperature of the air leaving the vent is ~38 F.
https://lh3.googleusercontent.com/-2...tarret_UDP.jpg

Tarret UDP and Original
https://lh4.googleusercontent.com/-v...rret_UDP-2.jpg

Can anyone explain how they torqued the new bolt down without having a hole in the pulley to lock it in place?

You need a pulley that has at least one hole in it so you can use a bolt, but if no hole then you will need to clamp it with a vise grip and some pieces of wood to protect the pulley.

Having driven my Tarret 4" UDP for a few days now I'm very pleased with what feels like extra torque and power.

It also seems like the engine sounds smother and quieter.

The extra torque in first gear needs a bit of getting used to, as it was raining this morning and I have been getting a bit of tire spin using my old familiar technique.

A little slower application of throttle in the wet is required. :)

Overall, I have to say it was a much easier install than I thought it would be, although grinding off the casting protrusion was a pain because I did not have a right angle grinder that would fit in that tight area so I had to use an airtool saw and file to get at it and tidy it up.

A 90 degree die grinder air tool with cutoff wheel would have been the perfect tool to get in there and get it done quickly without fuss.

No problem getting the old pulley off either as the shaft is not tapered so simply prying it off with a long screw driver is all that is required.

You also need a cheap 24 mm socket and cut it down to the minimum to go over the bolt head with a grinder as its a tight space in there and not much room for the socket and wrench.

Well worth the ~$200 and perhaps the most HP bang for your buck of any mod you can do to a Boxster.

about to do this mod and well I'm a bit confused by something.

The crank pulley looks like it slides over a keyway. If you leave the car on the ground and you put it in 5th gear with the parking brake on, the crank shouldn't turn, hence there should be no issue with removing or tightening the bolt.

Am I missing something?

Thanks

Tightening the crank bolt is not the issue, but if and when you go in for an IMS swap, or some repairs involving resetting the cam timing, be prepared for a significant up charge as the shop is going to have to remove the under drive pulley and reinstall a factory unit in order to lock the crank at TDC, that is assuming you have not removed too much of the pin boss from the engine cases when you installed the pulley. If you did, the trans will have to be pulled so that the engine can be locked at TDC from the flywheel. Oh, and the latter adds roughly $3K to the bill of whatever else is being done.

Thanks for the tip. Pretty sure I will have enough of the boss remaining the crank at tdc.

That doesn't answer the question of why the crank is turning during this job...it shouldn't be

you seriously cannot remove too much of that boss. It's pretty deep. The center hole extends in deeper than what you can cut off.

Don't bet on it. We have had cars come into the shop with the entire boss hacked off, which allows enough slop in how the pin holds the pulley to make it all but useless.

RSS supplied a wrench with the pulley kit. Kit included a belt pulley and a pin type wrench.

I had to remove 1/4" of the boss Plenty of hole depth left.

I hacked off a decent amount of the boss, but there is definitely plenty left, even with excellent clearance to the pulley. Not too concerned about that.