Underdrive Pulleys

[TomoHawk]

I haven't seen anything on this subject...

Is there anything available for the L28 engine in the way of underdrive pulleys? If there is, is it worth the money and effort to use them?

thxZ

[SteveJ]

Why do you want underdrive pulleys?

[Kurbycar32]

I saw a set on either one of the Z performance catalogs or jeggs or something. The only set i have ever seen for the Z was something like $1,100 dollars so at that price point i had zero interest

In general underdrive kits are pretty awesome. The idea is that through "gearing" you can spin certain accessories at lower speeds than others, saving that energy for the motor. The effect is extra dramatic because lowing the load on essentially the crank is compounded throughout the engine, the same reason you want a lightweight flywheel.

On this motor though you are really only pushing two "accessories" which are the water pump and alternator. As-is the alternator barely makes enough energy and the water pump only produces minor drag. Ultimately on a stock-ish motor I don't think you would see much gain in an underdrive system. I put a set of underdrive pulleys on a late model V8 with AC and a bajillion amp alternator and saw a noticeable improvement, but I don't think that would be the case here.

[TomoHawk]

I thought that underdrive pulleys would lessen the drag from the cooling fan. But since you also install a new harmonic balancer to start, I will keep that as it is.

You would only benefit from underdrive pulleys (usually custom-machined and polished, which is why they're $1100) if you are really into something like drag racing, or for show. Drag racing guys spin the alternator and water pump at an ultra-low speed with underdrive pulleys, just barely enough to keep the engine charging and coolant flowing, or just run totally off the battery while racing until you get back to the pits. Then a small gasoline generator to fully recharge the battery. Even the water pump is powered by an electric motor, with the usual electric radiator fan.

For street or highway cruising, the fan clutch will really help in stead of underdrive pulleys, and modern alternators are well built with low drag bearings.

Edited March 27, 2014 by TomoHawk

[Mark Maras]

IMO a flex fan is what you want. My experience with one was- 71 Z, The fan-clutch failed in 1979. I didn't like the weight of the original or the replacement cost. A flex fan was my choice. They are lightweight, only pull air at low RPM, cooled great even idling in traffic over 100F and to my pleasant surprise I could feel the increase in power and it also revved quicker. I drove the car with the flex-fan in use, daily, for the next 17 years. They were not easy miles. Year round in the Northwest and my love of speed, it never gave me a bit of trouble. I'm putting a FF on my 74 Z as soon as it's on the road. An added thought, I'm going to compare my old one to the new ones, the old ones may be better. Mark in Portland

[madkaw]

So why did we start this thread- I'm confused

[TomoHawk]

OK, I know what the flex fan is, but I don't think they make one for an L28 engine. It might bolt on if you take the fan clutch off, but then you lose the purpose of the fan clutch.

[beermanpete]

For a street car removing the engine driven cooling fan and installing an electric fan would likely be the best compromise. For racing I think a larger diameter pulley for the alternator would help some, say about twice the stock diameter. Using a smaller crank pulley will slow down the water pump would likey lead to over heating. Also, the belt itself works best in a certain range or feet-per-second and the factory crank pulley diameter combined with the RPM range pushes the limit for good reliability and belt life.

[Mark Maras]

That's the point of the flex-fan, You don't need a clutch. The blades are cupped similar to a venician blind, At low RPMS the blades pull air due to their air foil shape. As RPMs go up the blades flatten out. at speed there is no need for a fan at all.

[TomoHawk]

I've read comments about flex fans both good a bad; the good is the lesser rotating weight and drag, and the bad refers to high-speed noise and un-predictable cooling.

I tend to prefer using the underdrive pulley system because it uses the stock parts (pulleys) although they pulleys are of an odd size, if you look closely. Considering the age and peculiarities of the electrical system, I'd rather not add to the complexity if I didn't really need to. But on the 280Z, with a modern alternator, powering an electric radiator fan shouldn't be much of problem.

So if you wanted to try a flex fan, you need to measure the diameter of the stock fan, and then guess at the length of the extension.

Does anyone happen to know the diameter of the stock fan?

[madkaw]

Tool shed

[Mark Maras]

I didn't experience any noise and the cooling was great. I suspect a lot of the negative opinions are not from experience. As I said before, I had NO problems and would install another one in a heartbeat. Mine was great. I'll measure my stock fan and get you some more info on it when I get home tonight. Mark in Portland