I am about to buy a serpentine setup and noticed that some drive the water pump either 15% or 30% slower. Is there any benefit to doing this on a hot street motor or should I steer clear of a setup like this?

Steer clear of it unless you like flirting with overheating problems.

actually the underdrive setup give you back horsepower .
Ive installed the underdrive setup and noticed no increased temp changes.
if anything the temps got better.

So a 15-30% underdrive is fine since it allows the coolant to slow down and absorb more heat as it passes? Is a 30% too much for a street car? This is a 600hp 385 w/ 4.10 gears and a tko600. I could use any advise since I have never done this before.

actually the underdrive setup give you back horsepower .
Ive installed the underdrive setup and noticed no increased temp changes.
if anything the temps got better.

Not everyone has the same results as you do...

Overheating problems fixed!!!! A must read.

http://www.stevesnovasite.com/forums/showthread.php?t=58691


Temp reached 210 and then detonation started????

http://www.camaros.net/forums/showthread.php?t=19944

So a 15-30% underdrive is fine since it allows the coolant to slow down and absorb more heat as it passes? Is a 30% too much for a street car? This is a 600hp 385 w/ 4.10 gears and a tko600. I could use any advise since I have never done this before.

Slowing down coolant flow to give it more 'time' is an old wives tale. If you're serious about cooling you'll read up on the physics of cooling, where flow is king. More flow of coolant and air equals more cooling.

Some good cooling info:

http://www.arrowheadradiator.com/14_rules_for_improving_engine_cooling_system_capab ility_in_high-performance_automobiles.htm

http://www.stewartcomponents.com/Tech_Tips.htm

More flow of coolant and air equals more cooling.

Up to a point. Too much flow will cause overheating problems because the water is not in contact with the engine and radiator surfaces.

That's true, if you exceed about 8 feet per second flow rate through your radiator you'll possibly start to foam the coolant. How many gallons per minute does it take to exceed 8 fps through your radiator? That means if you have a 24" wide radiator, the water will go through it in about 1/4 second. If your radiator holds 1 gallon in the tubes, that's about 240 gallons per minute, sort of the high end of automotive pumps as we know them today.

Up to a point. Too much flow will cause overheating problems because the water is not in contact with the engine and radiator surfaces.

This is absolute and patently false when we are talking around the basic capabilities of the automotive systems here! The previous poster that puts forth the more flow is king is absolutely correct. The "slow the flow for more time in the radiator" is wife's tales! These people do NOT understand the physics of basic cooling. Check out the links... and decide for yourselve.

However, there are some factors of course that will inhibit the systems performance due to cavitation and aeriation of the coolant if you induce "unproductive flow" paterns which is usually due to poor system design and velocity issues, but these are so far and few between with today's high efficiency waterpumps, radiators and coolant concoctions. And, with the larger tubed systems such as an 1" tube, there has to be more flow to support the velocity thru the radiator for maximum effect.

I have been designing industrial and automotive cooling systems for years and I will tell you that flow is indeed king.. just like more air cools more. And, the more flow the more turbulence that is created as well. This is a double whammy.. because the "turnover" makes the system more efficient.

Visit the tech site as Stewarts. They know cooling!

If you don't know cooling.. don't make these false statements please!

Underdrive pulleys should be avoided!!!! The modern water pumps only take a few hP anywho.. so that's false too. If anything.. OVERDRIVE YOUR WATERPUMP for more cooling.

This is the reason I ask. I stated before this is for a 600hp 385, it has a weiand aluminum water pump ( not team g), fluidyne radiator, 180* t-stat and mark viii fan. I have not run this motor in the car yet!! I am wanting a serpentine belt setup for the car but....one from CV products since they are local and have ones for low mounted p/s pump and use light weight pulleys. Now they offer one in their brand name and one by krc which has a 15 and 30% reduction, I don't want to spend the money for a March that isn't for the low mount p/s pump and create more headaches. This is why I ask. I need the car to cool though that is why I went with the fluidyne radiator, mark viii fan and the particular pump. Maybe this will help explain why I am at this road

This is the reason I ask. I stated before this is for a 600hp 385, it has a weiand aluminum water pump ( not team g), fluidyne radiator, 180* t-stat and mark viii fan. I have not run this motor in the car yet!! I am wanting a serpentine belt setup for the car but....one from CV products since they are local and have ones for low mounted p/s pump and use light weight pulleys. Now they offer one in their brand name and one by krc which has a 15 and 30% reduction, I don't want to spend the money for a March that isn't for the low mount p/s pump and create more headaches. This is why I ask. I need the car to cool though that is why I went with the fluidyne radiator, mark viii fan and the particular pump. Maybe this will help explain why I am at this road

Take a peak at www.conceptonepulleys.com they are experts and are reasonably priced.

One thing to watch if you choose to underdrive your pulley system is your alternator will not be spinning fast enough a idle. You will need to get the correct alternator pulley to keep around a 3-1 ratio of the crank. I ran into this will the March setup before someone told me about the correct alt pulley. I was able to get aroun 2.7 -1 and it worked fine.

I read the links above and I see now what you mean about water speed and the tales that people tell. I am looking for a good setup now and see that March does offer the pulleys for a over driven water pump, that is one I will look at and will do some research on some others before I make a purchase. Has anyone run one of the Gilmer setups? I saw one on a guys camaro on here a while back but don't know how much of a drag they would create over just standard v-belts and serpentine pulleys, any ideas?

How low are your rearend gears ? This can increase your engines RPM to where you may want to decrease your waterpump speed. They also have large pulleys for your altenator if you run High RPM's for a long time. (stockcar racing)

How low are your rearend gears ? This can increase your engines RPM to where you may want to decrease your waterpump speed. They also have large pulleys for your altenator if you run High RPM's for a long time. (stockcar racing)

No..no..no...no..no and by the way NO! Don't reduce waterpump speed in any way. This is EXACTLY what we are talking about here.. underdrive pulleys are a huge no-no! More flow is ALWAYS good and makes the system more efficient! All this racing stuff does NOT translate to the street at all! There is so much misinformation out there on this.

Let me explain. It used to be.. in racing... commonly circle track applications, that motors ran full tilt all the time. This produced high rpms where the old style pumps (which were pretty inefficient by today's standards) would cavitate at these warp like rpms! So, aeriated water didn't cool so good obviously. Also, the older pumps were hp eaters relatively speaking! So, the solution was to slow the pumps down to accomplish two things. ONe, the cavitation went away. Secondly there was some hp savings (and it's aint much!) So, the system cooled correctly.

Today's waterpumps will easily take over 8000rpms and flow like %$&#! thru a goose! Very efficient and no cavitation... and thus will cool better at higher rpms. And.... they take only a couple of HP at those rpms. So, just say no to underdrive pulleys which were invented for racing issues moreover. How they worked their way to the street is head shaking to me????

I have desided to run the March serpentine pulleys with the over run water pump, larger crank pulley smaller w/p pulley to make sure enough water is flowing since Stewert pump s and the other articals said this was best. I guess the price is fair but not really bad concidering the quality of the parts. Thanks guys for all the input and with your advise it will be a headache avoided.

I run a 468 big cammed motor with 4:88s.

I underdrove the water pump and the temps are more stable. I have better cooling.
Before, I couldn't keep it at 180 despite my high flow 180 t-stat. Now it sticks right at 180. I did a heat test on a day we had a few weeks ago that approached 100 degrees.
I was actually doing it for the new trans and was more watching that temp gauge but anyway, it went up to 190-195 for engine temps when I sat at a light but as soon as I was moving, it dropped right down to 180 again.

So I've had better luck under driving. The deal there is, I don't know HOW MUCH I've underdriven it. It might be a little it might be a lot. But it helped.

I don't know the science and I don't claim to know it but I have seen this work for me so I'm a believer.

These people do NOT understand the physics of basic cooling. Check out the links... and decide for yourselve.


There's absolutely going to be a point where too much flow will cause a heat transfer problem. What that point is in an automotive system I don't know.

There's absolutely going to be a point where too much flow will cause a heat transfer problem. What that point is in an automotive system I don't know.

What would define that point?

There's absolutely going to be a point where too much flow will cause a heat transfer problem. What that point is in an automotive system I don't know.

Nope... Not within the constraints of the equipment available in the automotive realm today. Even the highest volume pumps will not overwhelm the system. The thing that would mostly push a system to inefficiency would be foaming of the coolant and cavitation not flow per se. As long as you can keep the coolant flowing without foaming.. it's a go! But, if you run high efficiency/volume water pumps they will NOT cavitate under 10,000rpms period. I know this because I have seen this with my own eyes and I know what racing rpms can produce.

Usually the inherent design "stopper" is the restricted coolant passages that are small or hoses that are small. If you create higher flow rates in a fixed volume.. this creates pressure in all kinds of ways. So, it is what it is.

I have designed industrial applications that move coolant at 10 times the speed of common automotive systems and are very efficient. They have to have all the cooling jackets designed to flow at these high rates as well. Sharp edges and deep cavities are not allowed because the sharp edges will create cavitation points and the pockets of cavities will create low pressure centers that pull/wring air into the coolant. So, as long as the system is designed to accept the flow rates.. it's all good!

I love this forum! So much knowledge, experience and passion is expressed - it makes my day :D and I learn a lot :thumbsup:.

I don't want to beat what is now looking like a dead dog but in case anyone is still reading and cares: When I converted to a serpentine system last year I discussed the various options with one of the March Pulley Reps. He strongly steered me away form the underdrive set-up that they offer. He basically said that if you're looking for every ounce of hp in a strictly drag race car then go for it but highly recommended the standard setup if doing any street driving. I suppose if you have a mega-cooling system in all other aspects (radiator, fan, shroud, etc.) and did install an underdrive pulley that you could quite possibly be able to offset any negative impact in cooling efficiency while capturing a gain in hp w/o experiencing any overall cooling problem. :yes: