:: EBS Racing :: Do You Know The Benefits Of An Underdrive Pulley?

Porsche left some performance on the table when they built the M96 engine in your sports car. With a large diameter crankshaft pulley, your engine is constantly working overtime to spin the air conditioning compressor, alternator, water pump, and power steering pump to higher speeds than they really require. Each of these accessories requires horsepower to spin them, and if you could slow them down, even a little, your engine would be able to send that power to the drive wheels instead. With an EBS Racing 'underdrive' crankshaft pulley, you can do just that. Possibly the simplest way to free up some horsepower from your Porsche's watercooled flat six engine is by 'underdriving' your engine's accessories. Wether for street or track use, you'll notice an improvement in throttle response, and your engine will rev more freely with this simple modification. This smaller diameter crankshaft pulley fits in place of the larger factory unit with zero further modifications necessary, and comes with the correctly sized belt you'll need. This is a simple modification that you can do at home, or drop off to your favorite independent Porsche shop to have this task completed easily. If you are planning to take your Porsche to the track, or if you frequently visit the upper limits of your engine's rev range, this underdrive pulley can also prevent your air conditioning pump or power steering pump from being spun too quickly, preventing undue stress and wear. The power steering pump is particularly vulnerable to such issues, and can develop an expensive leak from being spun too quickly. The cost of this pulley and belt is far less than the cost of replacing your steering pump, you can trust us on that one. The pulley itself is precision machined from aircraft-grade aluminum to have the correct metric-style v-belt grooves. Lightweight aluminum construction of the pulley saves rotational mass over the OEM piece, giving back even more lost power. The pulley also features a beautiful black anodized finish to not only make your engine look better, but also to protect against corrosion to keep it looking that way for decades. We're so sure of the quality of this pulley that it's also been given a 2-year manufacturer warranty, so you can rest easy knowing this is top quality. This underdrive pully is guaranteed to work with any M96-powered Porsche Boxster, Cayman, or 911 built between 1997 and 2008. This product is not compatible with Mezger engined cars (911 Turbo, GT3, or GT2) or 9A1 engined cars (Direct Fuel Injection engines from 2008 onward). For more information on product benefits or fitment, or to place an order, call one of our EBS Racing Porsche specialists at [phone removed]. To see more photographs or to process your order online, you can visit the product page here .

There was some talk about making these underdrive pulleys solid. What problems can arise from this Pulley not being solid? Also, Has anyone felt the power difference before and after? Any Dyno results of the power?

And do they allow the TDC locking pin to function/need to hack off the boss to lock at tdc ?

I know it has been discussed before. To have the info in this thread, what is the downside to having the underdrive pulley?

Downside is lower charging voltage depending on how healthy your charging system was to begin with. Very appealing upside for sure.

Quotes source post: 13981590

Apparently Jake fits them to all his engines so I assume there is a performance advantage but he mentioned before that it was important they were Solid.

looks like a decent upgrade for the price

Quotes source post: 13981608

Because https://rennlist.com/forums/boxster-...ley-alert.html

Quotes source post: 13981590

Thanks Ahsai Figured it would be good to have pros and cons in the same thread Does anyone know if you have to modify the timing boss with the EBS pulley?

Very interesting....never knew about these...

I ran one on the 986 the whole time I had it; I removed it from the 996 after 2-3 years. The combination of the alternator drop due to the UD pulley plus my LED taillights was making my ABS and PSM idiot lights come on every now and then. I'd already sold or given away one of my stock tails, so getting rid of the lights wasn't really an option, and I really didn't want to leave the car in a condition where my wife might be driving when the ABS/PSM went on the blink. Since removing the UD pulley, I have seen the ABS/PSM once more - when my last battery failed. If not for this situation, I would have gladly kept the pulley - there is a noticeable positive difference when you underdrive the accessories...

Quotes source post: 13981717

My guess is most likely as the timing boss is at that 2" radius (same radius as these UD pulleys).

Quotes source post: 13981608

It's important to know what grade of aluminum is being used. I'm not sure who the manufacturer was of the cracked pulley in the linked thread, but it is surely not ours. We've been using this pulley for years with no quality issues. As mentioned before, ours are fully warrantied for two years. We trust and stand behind our products.

I've had an UD pulley for the past 6 months and 8 or so track days. No complaints. You'll need to machine/grind a piece off the block for clearance. Was hard to tell how much impact this had directly because of the many other parts that were installed at the same time (LWFW, LSD, etc). Car revs insanely quickly now.

Yes, the throttle response with the underdrive pulley was one of the best things about it.

Between underdrive pulley and catless exhaust, my track car dynos out 20rwhp more than my DD(same dyno within an hour of each other).

I have an UD pulley on mine, however it was installed by the previous owner so I don't have a benchmark. So far no lights and I use a trickle charger to keep the battery in good shape. Might be my imagination but if this under drives the power steering pump can it make the steering slightly heavier at very low (car park manoeuvring speed)?

Quotes source post: 13981576

Others have commented on the issue of keeping the battery topped up and heavier steering at slow speed. A bigger concern to me is the slower circulation of coolant through the engine. A hard working engine puts out a lot of heat. To keep this heat under control requires a lot of cooling and coolant flow. The coolant flow requires some velocity to help prevent localized overheating. If the coolant circulates too slowly it can fail to dislodge small vapor bubbles that form on the hottest areas of the cooling system. These vapor bubbles can coalesce into a steam pocket which can then block or divert coolant flow and the area becomes hotter to the point damage occurrs. One can see what I'm talking about with a simple test in the kitchen. Take a pan of water and put on the stove. Turn the burner heat control to high. Wait and watch. After a while you will see small bubbles start to form on the bottom of the pan. They may even take on some kind rough image of the burner coils if you have an electric stove as directly under the coils where these touch the pan is the hottest. If you the let the pan remain still the bubbles will grow larger. You can move the pan -- gently -- in a circular motion and easily dislodge the bubbles. Let the pan and water get hotter. It becomes harder to dislodge the bubbles. You have to move the pan about around with more vigor. The cooling system of the engine is no different. In some cases engine makers position tubes in the head mold to direct a stream of coolant at a particularly hot spot -- around the exhaust valves primiarly -- to ensure the coolant strikes/flows past these hot spots with enough force to dislodge any bubbles and to prevent their growth into a steam pocket which then results in localized overheating. Cars makers are under pretty severe pressure to cut emissions and improve gas mileage. Just how much pressure I think is evident from the VW diesel cheating scandal. (It is also evident by every car maker coming out with hybrid or all electric vehicles.) If in this case Porsche has settled on a drive pulley size that it believes (and probably has test data to back up) spins the accessory drives and the very very important water pump at an appropriate speed to reduce this speed even further for the possible gain of a few horsepower and under extreme operating conditions -- on the track -- is very risky. While the engine may be ok at higher engine speeds every time the RPMs drop the flow of coolant drops. Yet the heat load that is making its way to the coolant passages is the heat load that was generated at much higher RPMs and has to be dealt with by the reduced coolant flow that the underdrive pulley produces. (There is the issue too of with a smaller drive pulley the belt makes less contact with the pulley and slippage could be a problem. Probably not continuous slippage but periodic slippage that could shorten the life of the belt.) It is amazing to me so many owners take a preventative maintenance stance and replace the IMSB, water pump, and the like to address what they believe are shortcomings or weak points then turn around and create a weak point in one of the two most engine critical systems (the other being engine lubrication) by installing an underdrive pulley.

^^Great info!

For the Track guys the advantage is not overspeeding the p/s pump. For the rest of us...

Quotes source post: 13987358

WOW ! You really cooked one up there - literally. Unlike your pan of bubbling water on the stove - your Porsche has a pressurized system and therefore boiling point is raised to a higher value. Also you are driving - not sitting on a stove top and therefore a fair bit of movement is going on i.e. over bumps around bends thus the coolant is not just sitting in your engine boiling and forming bubbles but flowing and rocking and rolling. Once you are over 2500RPM everything is as normal - it is only if you sit in a lot of traffic a lot that you would experience any issues with everything running slower.

Quotes source post: 13987057

You could put the clutch in and rev the engine a little to get things going more whilst turning the steering wheel...

Quotes source post: 13988152

Yeah had thought of doing that but it's so minimal not really worth it I'd like to say the performance factor is there but I've only ever driven one other 996 and it was a tired 02' tiptronic.