Under drive pullys.
 

Who has them on their Z? What kind of gains do you typically see with them?

Re: Under drive pullys.
 

Hey Rich,

I have them but have no ideal the gains since they were installed with everything at once. I have SRP pulleys (entire set) and love the quality, fitment, looks and had no issues at all with it. If developed by Randy Woods and father then I trusted it for what it stated and great folks that are way, way, way smarter than I will ever be. Sorry, that is all I can share about my experience with the product. :handshak:

Craig

Re: Under drive pullys.
 

Too bad the entire set is not available. Im at that while Im there point now. Craig sounds like he has a great setup there. Anybody have a set here that they want to get rid of???? Or havent installed ?

Re: Under drive pullys.
 

Craig are you also running the ATI super balancer on your car? Any clearance issue with these mods? I called SRP today and emailed them this morning I have not heard a peep yet

Re: Under drive pullys.
 

Ok got a few PMs from a few folks. Something the community should know. At idle the temperature can ride high faster due to less mass. Does this makes sense. These folks have upgraded their radiators.

Where is TomTom when you need him ;)

Re: Under drive pullys.
 

Got the Wood's pulley with an ATI damper on the 441.Fluidyne radiator too.....no heat problems here.

Re: Under drive pullys.
 

Daryll, I'm confused (yep, again). Where is there a reduction in mass that is going to cause higher temperatures at idle? The only way I could see pulleys changing idle temps, is if the water pump is rotating more slowly, circulating less coolant through the radiator. Not sure where mass comes in to play here?

-Andrew

Re: Under drive pullys.
 

Your not confused. I was. That was what I was pmed. The waterpump moves slower at idle

Re: Under drive pullys.
 

Aye,Aye Cap'.....reporting as ordered. Yea, I thought about the 10% under drive would be a help for the high rpm by pass of our cooling systems...but ya can't have something for nothing. Yes in theory at low rpms the pump will move less water so the temps would have to rise a bit.

I had thought a 10% reduction would give us a bit bigger cushion on the twisties so you can hold that 2nd gear longer in tight Essses. At low speeds the pump output would have to cause the temps to rise a bit just because the pump is moving less volume due to turning the impeller less. Ya can't have your cake and eat it too!

5500 rpms = the complete by-pass target rpm on a stock system. No circulation thru the rad core. 10% reduction in pump impeller speed = only yields a cushion of 550 rpms....which is useless if you're in 2nd gear @ 6500 thru a series of Esses! Drag racing application only is JMHO, if your a road racer this will not answer the sustained high rpm volume that gets by-passed because there are no radiators that can handle the volume our w/p's put out. I had thought about buying these but the radiator core is still the issue and I'm not calling some F1 team to make me a radiator that will handle 100 gpm flow.....it's cheaper to redesign the impeller to lower the flow rate, JMHO.:o

:cheers:
Tom

forgot this, in drag racing where engine acceleration is related to reducing rotating mass, these pulleys would contribute to less rotating mass so less hp is lost thru parasitic drag which leaves that hp to accelerate the car. Just like the Fidenza flywheels let the motor turn up faster than a D/M flywheel.

Re: Under drive pullys.
 

Tom,
Just exchanging some thoughts with you on some of your comments about fluid flow, no offense intended.

Flow will follow the path of least resistance. The bypass does not shut off flow through the radiator, just offers a path of lower resistance to the high flow rate at the specified rpm. There is still flow going through the radiator. If "no" (100%) circulation through the radiator was actually ocurring, the engine would not operate for much time at all before seizing.

While I believe that to be true for the stock radiator, I am unaware of any flow tests through the Ron Davis radiator, or even other aftermarket radiators for that matter. Ron Davis does provide some empirical test results regarding exchange rates, but they offer no info concerning maximum coolant flow rates. I talked with them about this specific subject 7 or 8 years ago to find out if it was feasible to completely eliminate the LT5 bypass system. Although other factors may affect the obvious, a 5 core radiator should yield less resistance to a given flow rate with it's assumed, proportionatly greater cross sectional flow area, anf therefore have higher volumetric flow capacity. All othe factors being equal, the result would be the ability to handle the flow capacity of the LT5 with out damaging the radiator. The same may also be true for other aftermarket radiators.

There is another factor that also come into play, coolant velocity through the radiator. Removing the thermostat completely in many cases results in overheating. I Fluid velocity affects both heat absorption and dissipation.

Back pressure in the cooling system would also need to consider the flow capacity of the thermostat. If the flow capacity through the thermostat is less than water pump output, then that problem must also be addressed, regardless of which radiator is used. I am a believer in the modification originated by Lingenfelter, drilling 3 or 4 small holes in the t-stat flange.

This whole issue of the high flow water pump, the bypass system & damaged radiators could really use a good evaluation, but would require setting up a test apparatus to test all known radiators and the thermostat housing for flow capacity, just to see if the bypass system could ever be eliminated.