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Underdrive pulley recommendations?
I've been wanting to put a new pulley on and wondered if someone can recommend one.
I looked around Flat6 but didn't see anything there. I see a few out there for sale but would prefer a word form someone who has experience with one. Thanks Chris |
I am still testing our 4" pulley in real world conditions to see how it effects the operation of the charging, power steering and A/C subsystems. Its the smallest pulley on the market and so far has out performed every other I have tested back to back in the performance category.
I have not added them to our site yet because they haven't proven themselves thoroughly enough as of yet. I hope to have them on line by the beginning of the new year. I have almost 8K on the test pulley in my 996 and 14K on the unit in the Boxster test car.. I want to see how they perform in cooler weather. |
That's a very tiny pulley! How cold does it get in GA? I'm in CT and would be dealing with Zero temps sometimes.
Chris |
Dragon
you can go to boxsterspec.com and do a search for under pulleys, a lot of the spec boxster guys are starting to use them. One the members, Chris Amond, has his own design that I put on my car and I have been very happy with it so far |
I have the RSS UDP. Got it from stuttgartperformance.com Seems to be good.
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We see single digits here in the dead of winter, BUT the other cold weather data will be gathered by LN Engineering on their Boxster test car that I built the engine for in March of 09. They will certainly see temps well below zero.
In the heat of the summer this pulley did awesome both on the track and the street. |
now what is the threat here with the smaller pulley? the belt will move... slower and so affecting subsystems how?
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I installed BBI Autosport's latest light weight UDP. I am very pleased with it. Its difficult to qualify any performance gain since it was installed along with some other upgrades. However, the car feels great, and there is plenty of data to suggest that it adds hp. :)
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Thanks for all the replies. I put my stock headers back in and likely my stock muffler this weekend. I never got dyno data but car feels exactly the same. I had the original maxspeed headers. Now it makes the muffler sound lousy so back to stock till I can find a decent PSE. I want the pully and likely Pedro's techno torque instead.
Chris |
I am running the Mantis pulley at the moment with no ill-effects save some power steering pump wine on full lock while parking.....It is suppose to give 7hp. I did notice a difference when I first put it on...the engine felt it was now free to give! The car pulled just a bit hard on full throttle...this is all subjective feel of course.
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This one works pretty good.
Have not had any problems with this 4" pulley.
Chris |
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on a 2.7L 5 speed - would insalling this pulley create a noticeable difference in acceleration? would engine rev up faster... even if just a little bit..would it be enough to notice?
given the relatively modest price of a pulley - it might be a worthwhile mod if it didn't hurt anything and could actually make some gains that could really be noticed... |
I guess it depends on how sensitive your butt is. The pulley will add about 10hp.
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So far these pulleys have proven to give me the best improvements in real performance. They bolt on more than an ECU flash or a 3,000.00 exhaust system.
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I apologize in advance for the newbie question, but is there a noticeable increase in vibration? I threw an UDP on my 4 cylinder commuter and although I was happy with the small power gain, I do notice some resonance in the cabin.
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Ques - when you say Underdrive Pulley and HP gains, are you assuming w/o A/C?... or still have A/C connected?
Would there be more HP gain w/o driving A/C? thanks, kj |
yes no A/C would "gain" you more HP, if you were to remove the whole system also some weight would be lost giving you even more...
however, its more along the lines that you will just have more HP that the car makes already available to you. correct me if im wrong. |
Correct. They pulley does not create horsepower it only reduces the factors that rob hp from the motor. Another way to think of it is that the motor is just an air pump. It sucks, bangs and blows. If you don't change the amount of air it sucks or how big the bang is or how it blows you do no "create" hp.
That said all we really care about is how much hp we have at the wheels not how we get it, and the pulley does work. |
... sorry, I asked the question the wrong way. I know it doesn't create HP, I was just surprised at the estimate of 10 extra available to the drive train... that's pretty darn good for just an external pulley change.
I've been thinking about the pulley and instead of full A/C delete, just go with the shorter belt and eliminate the A/C drag from the equation. This pushes me a little farther along. You're right about the weight, that compressor feels like it weighs 20 lbs. alone... the whole system ought to net 40ish?... no? thanks, kj |
no worries boxster44. I think the reason there is such a large gain is because you are slowing down all the accessories but Jake can give us a much better answer.
and yes if you remove all the a/c stuff you will pull about 35-40lbs out of the car. |
Spinning the water pump, alternator, and AC compressor takes power. In the case of the pump and compressor, that power increases by the third order with speed. In other words, it takes 8 times more power to drive a pump twice as fast.
You can imagine that if you spin the pumps more slowly, more of the engine's power can go to twisting the wheels. And because of the third order relationship the faster you spin the engine, the more power is saved compared to a larger pulley. The drawback is that at engine lower speeds, the pumps may not flow sufficient water to keep the engine cool in an extreme environment, or the alternator may not provide enough current to a car with a very high draw stereo with the lights on. As Mr. Raby has found, everythimg works fine in his region. |
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if money is no object. (but usually it is!) you could do AC delete and replace all panels on the body with Fiberglass or carbonfiber and that would net you quite a bit of weight. I have also heard that the sound proofing removal is quite good too. |
I surprised that no manufacturer has gone to an electric water pump, with it's speed electronically controlled. There's lot's of power and efficiency to be gained, though I'm not sure it would ever be as reliable as a belt driven pump. (though Boxster water pumps haven't proved that reliable!)
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There are significant advantages to an electrically driven water pump: 1. Reduced mechanical drag on the engine (frees up HP); the higher the engine revs, the more power is saved (drag goes up with engine speed). 2. Slows down the circulation of coolant to a constant speed (higher RPM’s actually reduce the ability of the coolant to exchange heat with the air at the radiators because it is moving too fast). 3. Compact; no pulley or belt is required, so it takes up less space. 4. Works if the belt fails. By-the-by, electrically driven water pumps are commonly used on race engines for the above reasons…………… Te primary reason that more aftermarket manufacturers are not involved with making them for the M96 engine is the small population size of the application. |
1) where can I get this U/D pulley?
2) how much does it cost? 3) how much will my mechanic likely want to install it? (i'm not even going to try to do it myself) this sounds like a great bang fgor the buck mod! |
Lobo,
Yes..... I think amondC (Chris, right?) can really go into detail there as I believe he's with the Spec Boxster group in Texas and they do lots of things with their cars. kj |
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1. You still have mechanical drag, just at the alternator instead of the WP, plus inefficiencies of conversion. 2. A smart variable speed pump that measures coolant temp and maximizes heat transfer at all rpms would definitely be useful. A real plus if there is such a thing. I have just never seen one this sophisticated. 3. We already have a belt and pulleys on our cars, no space savings. 4. Works if the belt fails, not if the circuit fails. Seems like a wash. |
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1. You still have mechanical drag, just at the alternator instead of the WP, plus inefficiencies of conversion. Many electric pump applications (racing apps) do not use an alternator; but those that do definitely see a measurably reduced drag (seen on the dyno) compared to a mechanically driven unit. It is not a "wash"; it is a net gain...........hence their use on race cars. 2. A smart variable speed pump that measures coolant temp and maximizes heat transfer at all rpms would definitely be useful. A real plus if there is such a thing. I have just never seen one this sophisticated. You have not for a reason, they currently do not exist. Attempts to do this, even with digital electronics, proved to be overly complicated, not dependable, and added weight. Running the pump at a fixed speed electrically offers simplicity, better cooling, lower weight and free power without all the complications. 3. We already have a belt and pulleys on our cars, no space savings. Electrically driven pumps are definitely smaller and lighter than their belt driven counterparts......... 4. Works if the belt fails, not if the circuit fails. Seems like a wash. And if the car gets hit by a meteorite, or is swamped by molten lava, it doesn't work eithereither................ :confused: |
AC compressors have a clutch, thus when the AC is off - the electric clutch is disengaged and the compressor pulley is spining free (not much drag there). Removing AC all together will save you weight, but wont give you any power gain.
Installing an underdrive pulley will slow down the AC compressor as well thus it will have less drag when the AC is on (similar to Honda guys installing smaller compressors on Accords I guess) Just my 2 cents |
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But have a nice day anyway........................:ah: |
I have evaluated the 4" pulley with both A/C and without.. The gains are real, not to mention reduced coolant temps and dramatically reduced power steering temps while on the track.
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Actually, there is at least one aftermarket electric water pump with an electronic controller that varies pump speed to control engine temperature, manufactured by Craig Davies.
I don't think any automotive manufacturer would lack the resources to design such a system. They manage to map fuel injection & ignition timing using dozens of sensors, over all possible operating conditions, while controlling emissions. Controlling a water pumps speed would be a piece of cake. |
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pm sent...... |
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The engine's design is the variable... |
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Yes, the Boxster's tight packaging is problematic, which of course an OEM could solve, but as JFP mentioned, they have no real incentive to do so.
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