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Why would a UDP be bad for the engine... if anything it's less load at higher RPMs (and all RPMs for that matter). And I read that it's more like 3-4hp

From what I remember, UDPs tend to destory the engine if it is not balanced properly...

Flyer wrote:From what I remember, UDPs tend to destory the engine if it is not balanced properly...

The UDP itself or the whole assembly?

From what I remember on the ProbeTalk topics, it seels that the underdrive pulley disrupts the harmonic balance at different RPMs and messes with the accessories due to the belts not moving as fast as they should be. Really a bunch of theory.

In the end, it's your call. I say go for it and see if theory holds true

As Onlytrueromeo said, is not the UDPs that will destroy your engine, but your foot.
UDPs will give you the chance to rev your engine higher, longer. If you don't control the temptation, you may end up with a heavy paperweight.

Other than that, I agree they're not worth the money.

Arghhh this is so frustrating: http://forums.probetalk.com/showthread. ... underdrive" onclick="window.open(this.href);return false;

There's guys that say they have no problems and there's guys that say not to do it. And as for power gains, someone said that some magazine tested out a probe with a UDP and got an 8whp gain, that's pretty good for the price and simplicity of the mod. It's just frustrating cause it seems the community has mixed opinions on this but nothing conclusive. Even with all the risks, there have still not been any documented failures, in fact one guy on PT said he's had a UDP in his every Probe and 5 years later no problems.

UDPs are like turbos, in the sense that they both are as good or as bad as you make them.
You can turbo your engine, and if you use it sensibly, it will last just as long as if it was NA, but if you leave each street light revving your engine right to the redline just because you like the sound of your BOV, your engine will be toast before you know it.
Same with UDPs.

besides that, just like everything else, what has an advantage, also has a drawback. UDPs don't give you more power. They just divert less power to the accessories.
That means your alternator will generate less electricity, your A/C will cool less, etc. I'm not sure if that will create a problem with the power steering. I guess it depends on how low you're going.

Anyways, if you don't have (or plan to have) a sound system, or any other modification that may require extra power, and if you're ok with your A/C not blowing so cold, UDPs may be an option for you.

i just heard that underdrive pulleys aernt as good of a harmonic balancer with is therefor detrimental to your engine. whether or not this is true im not completely sure.

but lots of other cars out there use underdrive pulleys. lots of civics, they are generally a good modification.

Yeah I would never get one for the sake that I really need my alternator at max performance. With my sound system, and future car PC.. it's essential.

Unless your engine is internally balanced (most older cars are not from the factory), using an underdrive pulley could cause vibrational damage to the engine, mainly the bearings.

The stock pulley is a harmonic balancer/dampener, and the rubber absorbs the imperfections in mass in the rotating assembly and crank deflection. When you rev higher, the frequency/amplitude of these vibrations increases, as does the potential for damage without the harmonic balancer to absorb them.

Many companies that sell UDP's will tell you this is BS...but it's science.

The crank DOES flex and there ARE imperfections in the rotating assembly. Every engine is different, so some may have better factory balancing than others and may not experience problems with an UDP.