Underdrive Pulleys : The Definitive Discussion

[akhilleus]

UDP's suck! At least on the protege. I saw very little gain from them, they were a b**** with my stereo, belt problems etc.... I would have spent my money elsewhere if there had been available parts at the time. Now if one were to add them to an already built vehicle then it might see more gain or if you had a full accessory pulley set. otherwise why bother. Although the difference in weight between the stock crank pulley and Unorthodox was substantial i think the underdriving was unneccessary. Also the exposed aluminum surface was a problem.

 

[Installshield 2]

Keep in mind that any solid body that is rotated will have a natural frequency. any adjustment in the mass or apparent load will alter that natural frequency. Sound design requires calculating those ranges of loads and determining the necessary mass values of the rotational inertia of the system to ensure that the given rotation will not hit a harmonic frequency.

For more information see: Tacoma Narrows Bridge (same concept in some ways, just not rotational based)

Install... I have a real hard time believing that the UDP is any different as far as frequencies than the flywheel. they are both DIRECTLY bolted to that crankshaft. They both are part of the crank for all intents and purposes. The one thing that I can think of though is the flywheel mass is spread out more.. but at the same time you would think greater reductions in that would make greater issues for the harmonics.

I think this is much like cryo.. lot of anecdotal statements and beliefs, but not a lot of actual evidence.

I 100% agree...I have never seen actual testing on the importance of this resonance balance on modern engines...only thing I have actually witnessed is lots of rumors, and 90% of the Miata crowd saying your BP, turbo'd with a UDP, will blow up...thats about it...and I agree with the natural frequency of an assembly...which was loosely what I was getting at with rpm balancing...they can hone out natural oscillation problems with rpm balancing, but its the load induced vibration (such as crank walking and oil pump problems when a UDP is installed)...which is vibrations caused by lateral forces on the engine, rather than the rotation itself...I had never even heard of this stuff until I attempted to balance my own engine...

and I don't know about the flywheel compared to the underdrive pulley...only that a lot of people claim the stock pulley balances more so than the flywheel...why I have no idea, and never saw a legitemate reason...so yeah...it seems I have simply been giving theoretical reasons on all this...but sorry men, thats all I have...It is my strong belief that the rumors; centered on everyone with a UDP will pop an FS even if still being NA, is simply untrue however...

 

[tonkabui]

so the bottom line question is, is this worth doing? is it worth it to get lightened pulleys where ever they are replaceable? and what are its major advantages (besides revving faster)? and how (or why) do the UD pulley manufacturers claim an increase in whp? is this all hype?

 

[twilightprotege]

they do make power, well not really make power, they reduce the loss in power. it's like going from a lightweight 14" wheel to a heavy solid chrome 18" wheel. it's all about reducing rotational weight.

 

[Brian MP5T]

UDP's suck! At least on the protege. I saw very little gain from them, they were a b**** with my stereo, belt problems etc.... I would have spent my money elsewhere if there had been available parts at the time. Now if one were to add them to an already built vehicle then it might see more gain or if you had a full accessory pulley set. otherwise why bother. Although the difference in weight between the stock crank pulley and Unorthodox was substantial i think the underdriving was unneccessary. Also the exposed aluminum surface was a problem.

(mswerd)

 

[dmitrik4]

so the bottom line question is, is this worth doing? is it worth it to get lightened pulleys where ever they are replaceable? and what are its major advantages (besides revving faster)? and how (or why) do the UD pulley manufacturers claim an increase in whp? is this all hype?

logically, they should reduce drivetrain losses. i don't see a physical reason they wouldn't. but until someone throws one on a dyno, we're not going to know squat.

 

[gino]

logically, they should reduce drivetrain losses. i don't see a physical reason they wouldn't. but until someone throws one on a dyno, we're not going to know squat.

I'll have mine on the DynoJet soon after installing my rr-Racing UDP last week.

I expect little, if any, WHP or torque gain. I will say, however, the engine has quicker throttle response and feels slightly stronger throughout the range. Butt dyno (which usually lies) tells me it was worth it, to what degree is obviously arguable. We'll see, but as most of us realize, any gain from modding the DE seems worth it, so long as the cost is within reason. I felt the GB at, IIRC, $115, was worth it.

The next thing is a good set of big decals...

 

[Maz2001MP]

yeah sort of...I never understood that part really...the first thing engine builders make sure of being correct is the trueness of the crank...meaning it is perfectly straigh from end to end through its middle section...this prevents vibration, obviously, from occuring at one end of the crank...which will literally in a matter of minutes destroy that ends journals, load points, and possibly everything...

So with that said, theoretically any vibrations occuring at end, say from the gear box and clutch/flywheel would most likely make it all the way to the oil pump too...somewhat, or get "damped" half way possibly...actually I don't know...but yeah turbo gurus have long said that UDP's are the one to look out for, but not so much for just a lighter flywheel...but NEVER both light flywheel and light UDP...instant grenade...

but you could compensate for the vibration by crank balancing, especially if you have experience with load balancing...which is hard as s***...I tried it, it sucks...depending on the equipment avaliable you have to simulate loads through calculus on certain points of the crank...and you have to do it with enough standard deviation to allow for changing engine conditions, such as a cold or hot day...and from there a computer helps you pin point pressure zones of which the crank may have a problem with load induced vibration...and it also deals with the rods/pistons themselves...I had to go through 3 sets of wrist pins because I kept getting an error saying they would cause extreme vibration on each thrust bear for that part of the crank...but if you can do it, I salute you...it will definately pay off, and destroy any need for a heavy damper...

I currently have the fidanza 9lb flywheel. so when you say instant grenade do you mean motor go pop? i was thinking about getting the perrin pulley

 

[TurfBurn]

Yes that is what he is saying... (pulley + light flywheel)*turbo = zoom-zoom boom club membership

Nobody has proven that yet that we know of, and it hasn't happened, but it has been the case for some other cars and maufacturers.

Thanks!

Steve

 

[Maz2001MP]

Yes that is what he is saying... (pulley + light flywheel)*turbo = zoom-zoom boom club membership


Nobody has proven that yet that we know of, and it hasn't happened, but it has been the case for some other cars and maufacturers.

Thanks!

Steve

hmmm... well i plan on staying NA for now so i wonder if that will give me a problem still... btw threadjack.. steve, did those spacers get shipped out yet?? and my friend will be contacting you soon, he has been extremely busy..

 

[TurfBurn]

No problem... I'll double check for you, and get you a tracking number. If they haven't gone out (I just got the parts in), I'll make sure they go tomorrow!!

thanks,

Steve

 

[twilightprotege]

i'm staying NA and i will be getting (i should already have it but USPS sucks) the fidanza flywheel and RR-Racing pulley

 

[Maz2001MP]

i'm staying NA and i will be getting (i should already have it but USPS sucks) the fidanza flywheel and RR-Racing pulley

Sounds good then, I'll probably go with the Perrin just so I don't underdrive my accessories. I might add an amp in the near future..

 

[twilightprotege]

depends on how much amps the amp is taking. i'll be running 370Wrms total amp power with the underdriven pulley. if there is any problems i'll just up the alternator (but still get the other bits underdriven)

 

[Brian MP5T]

I still think the money can be put to better use... HP...