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YOUR RESEARCHUnderdrive Pulley Kits and Tow Hooks in Stock
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Install on my 986 and the first thing i ordered
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The UD pulley was the last mod I installed on my 986 and the first thing I ordered for my 996.
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There are also several race teams that have used these pulley kits.
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Suggestion · Original poster
We change pulleys on all GT3 engine upgrade cars we do here, and even the factory does this for the RS models which further helps throttle response.
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Suggestion · Original poster
If we had a test car and dyno here, I would test their product myself.
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Suggestion · Original poster
If we had a test car and dyno here, I would test their product myself.
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We are now stocking underdrive pulley kits from RSS for the 996 and 997 NA cars (pre-2009). These are made from 6061-T6 aluminum and offer improved HP & TQ by reducing drag from the power steering pump, A/C, water pump and alternator.
On a modified 997S (with headers/mufflers/cats), the power gains were +16 HP / +8 ft lbs TQ, and I would expect similar gains on a stock car:
The standard pulley fits 3.4L and 3.6L applications, and can be ordered directly from our web site here:
http://www.sharkwerks.com/products.php?pid=400
3.8L 997S require a slightly different (dampened pulley):
http://www.sharkwerks.com/products.php?pid=401
These re-use the existing belt. Here is the installation document from RSS:
We are also stocking most RSS parts now including these high quality Tow Hooks:
Perfect for a track day!
These can be ordered here:
http://www.sharkwerks.com/products.php?pid=399
The UD pulley was the last mod I installed on my 986 and the first thing I ordered for my 996. I approve.
...and the install on the 996 is way easier than on the Boxster.
Apparently because race car. Incidentally a week after I ironically spray painted the tow loop on my Range Rover bright red for the aforementioned reason, said loop was used to pull it onto a 10ton flatbed with airbrakes when the rear diff shot a bolt through its case. Karma I guess.
I'd like to hear your first hand experience on your 996 on whether you noticed a butt dyno difference of power, or if you think it's merely throttle response improvement. Any noticeable effects on A/C cooling?
Off hand since I'm at work, are the factory 3.4 and 3.6 pulley's dampened?
Is there a shorter belt that we can use as an alternative to having to use a die grinder to shorten the boss on the engine case? Not really sure how many of us would feel comfortable making a permanent modification of that kind.
no, on the 996 the factory pulleys are not dampened.
I have the tarett engineering on mine, definitely butt dyno approved.
I live in Texas and both engine cooling and AC do just fine even in stop and go traffic.
Only difference I have noted is that I don't seem to get quite enough juice from the alternator at idle. Once RPMs are up then it stabilizes ~13V. Not a big issue for me since I have a mini battery, so not much to recharge.
A small battry and an underdrive pulley is about the worst combination for a street car. 16hp or even just 8hp is a massive amount of power. There is no way an underdrive can pull this much away from the acessories. Just think about it. You push lawnmower is 3.5hp a riding one is under 16hp. Even if you reduce the acessory speed by 50%, there is no way you can save that much power. Now if you want to reduce the accesory speed at redline to make it last longer (under racing conditions) then an enderdrive pulley makes sense but to make 16 or even 8 hp is just nonsense.
Sorry for posting up another manufacturer's dyno, I think these numbers are from an optimstic case (a 3.8L car that's already been modified). On our own 2006 Cayman S 3.4L engine we picked up some power on Evolution Motorsports' mustang dyno, I think this dyno sheet is MIA now but I'll look for it. There are also several race teams that have used these pulley kits. RSS does not have a dyno in-house so I guess it would be an independent dyno, however I was not there and cannot verify the test process or if they followed what we would typically do for a dyno tune (which is 10+ pulls until the numbers settle at a consistent peak number, then tune and repeat the ~10 pulls). If we had a test car and dyno here, I would test their product myself.
I think the factory alternator generates around 130 amp, 13.8v = 1794 watt = 2.4 horsepower (so it takes more than that to turn). Maybe someone can confirm.. Not sure about A/C, water pump, power steering or which items would clutch at WOT (A/C would probably decouple at WOT, but the others would remain mechanically connected). I think it's a fair assumption that between all the accessories, there is at least 10-15 HP being drawn from the engine, if not 20+. If this pulley underdrives by 15%, that would be just 1-3 HP.
I do not know the pulley size ratio or the actual accessory numbers, so I can't say for sure what the power would gain. But I would bet 100% of my money that it will gain *something*, and on these cars that's hard to do. Let's say it's just 2 HP. At a price of $179 if you DIY, that's actually a better return on your investment than many mods that might actually cost you power (hot air intakes, unresearched headers etc.) and it's up to you to decide if it's worth it. Another benefit of underdriving accessories is better throttle/engine response which can't really be measured on a dyno.
While not a "new" idea to the industry I think especially for modded and/or track cars it's traditionally always been a neat and cost-effective idea of gaining a few ponies. As a side benefit on the Cayman we were able to somewhat reduce the stress on the power steering system at the track (1st gen caymans were notorious for having power steering issues).
We change pulleys on all GT3 engine upgrade cars we do here, and even the factory does this for the RS models which further helps throttle response.
6hp at what point in the graph? But regrdless you will not feel a 6hp gain on a 300hp car. There is at least that much variation on the dyno depending how tight the straps are. Sure there will be some gain with an underdrive pulley, the question is, is it statistically significan and more importantly, can you feel the improvement. If you can't feel it, what's the point on a street car.
Well actually one thing we've always noticed with upgrading pulleys is the improved responsiveness. That doesn't translate on a dyno but even the factory does this with different pulleys on later GT3RS' vs GT3s
Common trick. I think some of us try to get whatever edge we can sometimes
On our 3.4L Cayman one of the other side benefits was it helped reduce the power steering overheating issues at the track too.
I respect you as you typically have good inputs on the forum, but there's no black magic here.
Your accessories rob ~25hp (10hp power steering, 10hp+ AC compressor, 5hp alternator). Your power steering pump has to put the fluid @ 400+ PSI, you can't compare that with a push lawn mower.
The underdrive pulley reduces the accessory speed by 20%. With the mad assumption that the hp loss is linear with the rotation speed of the accessories (certainly not exactly true), then you gain 5hp.
Bottom line, I have one on my car and I clearly felt it. If you want to call it placebo, fine, that was still only $200.
The underdrive pulley will probably save some power on the power steering pump (you get less steering boost) but for A/C and alternator, I doubt there's any saving. If the A/C compressor spins slower, it has to spin longer to achieve the same cooling. Same for the alternator, if it spins slower, more current needs to pump into the rotor to maintain the same power output, which requires more force to spin.
A/C compressor and alternator require fixed power at any point in time (depending of what appliances are turned on, and the cabin temp settting, etc.) so regardless of pulley size, they will rob same power from the engine.
Super User , we use a DYNO PAK dyno, each rear hub is bolted to the rear drive hubs of the dyno, there is no slippage. We came up with the underdrive pulley to reduce the power steering assit , heat from excessive pumping which not needed at constant high rpms when "racing". 6 hp is a safe increase for little money. The Cayman is raced at 4000 to redline. Reducing the water pump speed allows the water to pick up a bit more heat as the speed of the slowing coolant has time to pick heat. In racing small things add up.
