High Volume Pumps with Underdrive Pulleys

kingkobra · #1 (**permalink**) 07-29-2003, 10:49 AM

I'm planning on using underdrive pulleys for my 5.0L to get a few extra hp. I'm also considering using HV oil and water pumps. Will this just back me up on hp and fluid flow to near where I started with stock components? If so, I can keep my stock pulleys and buy new stock pumps and save hundreds of dollars.

speed220mph · #2 (**permalink**) 07-29-2003, 12:11 PM

Just a note: Don't use a hi-volume oil pump. They waste power by pumping more oil than the engine requires. As for under-drive pulleys, the oil pump is not affected, but the water pump sure is. If cooling is marginal, it won't be if you go to a slow water pump, so I recommend that you stay with the stock stuff at first, then make a decision.

kingkobra · #3 (**permalink**) 07-30-2003, 11:01 AM

Thanks for the reply.

I bought a standard flow Melling oil pump.

I also have a High Volume water pump but I'm trying to decide whether or not to keep it and run underdrive pulleys or swap it for a standard volume and keep the standard pulleys.

Sounds like you'd recommend keeping everything stock at first??

Thanks again.

Hotfingrs · #4 (**permalink**) 07-30-2003, 12:49 PM

Water pumps should be overdriven by 7-11 %...that is if you want them to cool....

fxbill · #5 (**permalink**) 08-02-2003, 06:55 PM

I run underdrive pulleys on my stroker with stock pumps....never had a cooling problem...even in the desert or Ca traffic...

B. SMITH · #6 (**permalink**) 08-06-2003, 02:14 PM

I DROPPED ALL PULLEY SPEED AT THE BELT BY 30% WITH A SMALLER CRANKSHAFT PULLEY.
I LEFT THE REMAINING PULLEYS ALONE AND JUST CHANGED THE BELT LENGTH ACCORDINGLY. EVERYTHING WAS SLOWED DOWN BY 30% WITH NO PROBLEMS.
THE ALTERNATOR AND THE AC WERE NOT NOTICABLY AFFECTED EITHER.
TRY IT FIRST WITH JUST THE CRANKSHAFT PULLEY, THE WORK FROM THERE. THE OIL PUMP IS NOT AN ISSUE.

B. SMITH

EarlsflyinCobra · #7 (**permalink**) 08-06-2003, 06:35 PM

I'm getting ready to put my engine together, as soon as the cam gets here, and now you guys tell me "NOT" to use a high volume oil pump. I purchased a Melling HV pump to use on my 302, bored 30 over, with an E303 cam, moderately stock heads (heavier springs and rolloer rockers), and a Garrett T4 turbo......so, I guess I should go back to a normal Melling oil pump??????????????????????

wizard · #8 (**permalink**) 08-06-2003, 08:16 PM

Law of physics on the water pump issue. Stock pump moves "x" amount of water using "a" horspower. High flow pump move "x+y"water using "a+b" horsepower at the same rpm. Reduce the rpm by the appropiate ratio on the high flow pump and you will come back to the same flow as on your stock unit. Since the movement of water is "work" ie engery consumed, it will take the same horsepower to move the same amount of water. Nothing really gained. Money not spent wisely. If it's HP you want, go underdrive with a stock pump. If cooling is an issue go overdrive with high flow. One more thought. The 1-5 HP gain might give 3 at the wheels. What does that translate to in ET.

Wish these were my original ideas. They are not. If you want are more detailed theory, try this web site

http://www.stewartcomponents.com/

They are much more articulate.

I need cooling, My Stewart Water Pump is on the way.

kingkobra · #9 (**permalink**) 08-07-2003, 08:57 AM

Wizard's comments were exactly what I was getting at in my original post.

Thanks for all the responses and links. They've been helpful.

Unfortunately, the question I posed doesn't have all the information needed to make anything other than a general response, which was what I am looking for.

Truly, to make a decsion I first need to find the worst case heat rejection requirements for my engine. Then I can calculate the necessary coolant flow to meet the cooling requirements. Next I need the pump curves for the pumps I am considering and the pulley diameters for all the pulleys in the considered belt drives. From there exact (theoretical) hp and flows could be calculated.

The problem I am having is that the information needed for the required calculations has proved difficult for me to find. So I am looking for rule-of-thumb type responses from experiences with various water pumps on 5.0L (mostly stock) Mustang engines in Cobra kit machines for street use.

B. SMITH · #10 (**permalink**) 08-07-2003, 04:15 PM

THERE IS GENERALY NO NEED TO SPEED UP THE WATER FLOW TO THE RADIATOR. THE SAME BTU TRANSFER TAKES PLACE WITH COOLANT MOVING FAST OR SLOW.
HOWEVER, ENOUGH FLOW IS NEEDED TO PREVENT HOT SPOTS IN THE SYSTEM OR TO SPREAD THE HEAT AROUND.
I HAVE SEEN WATER PUMP RPM SPEEDS AS SLOW AS EQUAL WP PULLEY SIZE TO THE CRANK SHAFT. THIS WOULD BE THE LOWER EXTREME, LIGHT CAR, SHORT DURATION LOADS, MOST HP.
SMALLER WP PULLEY SAME CRANK PULLEY SPINS IT FASTER, USES HP TO DO THIS , OFTEN UNNECESSARILY IN A COBRA APPLICATION.
EG. YOU WILL OFTEN SEE TRUCKS WITH A WP PULLEY MUCH SMALLER THAN THE CRANK PULLEY TO SPIN IT FASTER FOR SUSTAINED LOAD CONDITIONS. SUBTRACTS HP BUT SPREADS THE HEAT AROUND.
IN NORMAL COBRA USE, NOT MUCH SUSTAINED LOAD, LESS FLOW, = HP GAIN.
I AGREE WITH SLOWING DOWN THE "STOCK" PUMP WITH PULLEY JUGGLING.
SAVE YOUR $ FOR MORE FUN STUFF AS HP GAINS ARE SMALL, WELL UNDER 10 RWHP AT HIGH RPM.

B. SMITH