Under Drive Pulleys.

[Hemet8]

Yes, I felt like opening a HUGE can of worms here. Every forum I have ever seen on the net is always divided on these, especially when it come to the 660's. People say that the 660's are balanced out from the factory, so the underdrives will not hurt them. Others say maybe, but you still got to have the harmanic balacer on there to qell the vibrations (however slight they may be) from the bottom end, so the engine will last longer. I have seen dynos, they do actually add some power, usally not more than 8 horse, and that seems to happen at 4K and above anyway, but it IS 5-8 Horse more. So............yea or nay? I figure if i get any stright answaers on this, it will come from here. Thanks for the input!

[StudlyCamaro]

RE: Under Drive Pulleys.

ive had mine on for 40 thousand miles or so... and it is still running fine, if some damage were to occur from it, i imagine it would have happened already

i didnt notice any power change, but its not like you can really feel a difference in 5 hp

[geoffinbc]

You have a Camaro they have a 2 piece pulley and balancer assembly. So changing the pully has no effect

On the FWD motors the pully and balancer is one unit.

I would never remove the balancer. The postential negative effects far outweigh 8HP.

Does anyone make oversized pullies for the accessories? That way you would get the under drive effect and be able to keep your balancer.

[sil]

1988 forsure uses a larger diameter pully on the alternater
also a 98 lumina power stearing pump pully for the 3x00 is fairly large
water pump pullies that i have encountered are all the same size

[SappySE107]

Ah yes, this again:P The 91-93 DOHC also has a seperate pulley so it didnt affect me either:P Ok, it comes down to this. Balanced may help, and the firing order may help. THe rubber ring though is for the slight vibrations made every 60 degrees of crank rotation or so when the combustion event takes place. It is ideal to keep the rubber ring there.

Track record however beats theory and text books IMO. Perhaps on some motors like I have heard in other discussions on this come up,need that ring. V8s and such. Ive heard of people having the crank snap in half after they removed their harmonic balancer. Means shit to me. I mean, we aren't talking about every other motor, we are talking about a specific motor, your motor...a gen 3 60V6. There are quite a few people running under drive pullies on gen 2 and gen 3 motors, all internally balanced, all the same crank, all the same bearings. Have they snapped? Nope. Have they spun bearings? Not at a large scale to detect a pattern.

I say 8 hp is worth is for the track record that it holds. You can argue that theoretically it should shorten the bearing life some, but I don't see anyone doing a comparison of bearing wear with and without the pulley. They also can't blame the DOHC spun bearings on the pullies either, which I hear happening more on than the pushrods. High RPM and the larger oil pump probably have something to do there.

I would run one on a pushrod motor personally. I would prefer an UD pulley with the rubber, but I can't imagine the cost of that. Going with larger accesory pullies might be a better way but how far can you go with what is available?

Side note, electrical water pump would be a better option for power and keeping the torsional damper in place, but it costs more and you have to keep an eye on the motor cause its your cooling we are talking about. UD pulley is a lot easier than that.

[Manitcor]

my 2 cents

3400 pushrod, FFP UD pulley installed when I put the engine in, engine had 22k when I dropped it in. Engine has almost 80k on it now. Never had a single problem except that im still to lazy to pull the pulley and properly re-apply the sealnt so I have a very minute leak

[Hemet8]

ok then it is settiled. The powers here have spoken. I am going to get one for my engine when i do the swap, if the bearings go to hell and such, then i will post here, but if not, i get my 5-8 hp and feel good about doing it. This is why i love this site, no argueing, no BS, just honest answears. You people are great, thanks for the info.

[geoffinbc]

Since you have a thread about a big stereo and the need for more alternator output I would forget the underdrive pully.

4 5 6 8 10 or 12 Cylinders a piston engine needs a damper. The damper removes tortional stresses from the crank. Every time a single cylinder fires it is forced downward so hard it bends the section of the crank it is attached to and effectivly winds the crank up like a spring. As the journey downward begins the rest of the crank begins to accelerate. As it does it will spring past the downward traveling piston pin and then rebound back. This constant bouncing action can be very destructive if not controled. The dambers rubber disc and heavy outer ring will control this spring action much like a shock absorber calms your suspension.

Go ahead and remove it. Ben talked about snapped cranks. Well now you know why. With enough power at each cylinder you can imagine how much tortional stress could be exerted on the crank. Maybe a stock 660 will be fine for 40 up to 100 thousand. But I'm not about to test it out...

Balance wont effect tortional vibration. Crank and rod balance is on a different axis. But I supose an abnormaly light or heavy section of the crank could amplify the problem.

[RednBlack]

No offence guys. But an under drive pulley with a larger diameter alternator pulley actually turns the alternator slower. Not a good thing. You need an under drive for the alternator also. If all you need is to keep a battery charged, overdrive pulleys will work, and add some power. Less drag.

I have a UD, and I don't like it because it is tapered and my belt runs funny. Maybe just a bad pulley, but I am toying with a steel UD. Aluminum is my friend, but, it does wear. I drive my car a lot, and I'm willing to sacrifice an HP or 2 for peace of mind.

Willing to keep the aluminum one for the track though.

[Hemet8]

Perhaps you are right about the pulley and my need to have good amperage. I was going to "gear down" the alternator to try to compenstae for that, so the idle amps would not be touched, i'll have to see how that is. Thanks.

[pwmin]

i thought my ffp udp was messing up my belts, but it turned out to be something diff (balancer looked bad, but it was the tensioner. and my dad said it was prob the udp cause it was a/m.

[fivepointhustla]

I have a fiero with a 3.1 out of an APV. I put the fiero store underdrive pulley on it works like a charm. Not a shot of N20 by any means but you can tell the difference in off the line acceleration and it revs faster.

As far as charging system effects. At idle before the pulley it was at about 15 volts after the pulley it is at 13 volts at idle. When I drive it goes back up to 15 volts.

My crank dampner/harmonic balancer (I've heard it called both) and the the crank pulley are actually 2 different pieces. My pulley bolts on to the dampner/balancer and they both share the crank bolt (the big one).

[SHOoff]

Go ahead and remove it. Ben talked about snapped cranks. Well now you know why. With enough power at each cylinder you can imagine how much tortional stress could be exerted on the crank. Maybe a stock 660 will be fine for 40 up to 100 thousand. But I'm not about to test it out...

I dont understand the point in arguing about this. I've always looked at it like this. The manufacturer of your car/engine has designed it in mind of a long life. Since this is the case, wouldnt you think that changing any part of it's design would theoretically shorten it's life span?

Kinda like I say to kids about cutting their springs. Some engineer has spent hours upon hours designing that spring to make your car ride a certain way and last for a long time. And in about 5 minutes you're gonna go ahead and change those hours of design? What do you think's gonna happen.

[bszopi]

The manufacturer of your car/engine has designed it in mind of a long life. Since this is the case, wouldnt you think that changing any part of it's design would theoretically shorten it's life span?

Then why even touch the engine? If you are that concerned about it, don't touch anything. But on the other side of the coin, as Ben said, in the 3-4 yrs that UDPs have been around for these engines, we have never heard anyone having issues with them and the crank.

You can trust theory and issues with other engines or you can trust 3-4 yrs of history and make your own educated decision. If it works with no problems for you, then gereat. If you destroy your engine becuase of it, well that sucks, but at least we'll finally hear about all of these horror stories of cranks breaking because of UDPs.