underdriven pulleys...

underdriven pulleys...

Joined: June 4th, 2007, 2:57 pm

December 19th, 2011, 5:52 pm #1

has anyone experimented with these? opinions? if so, did you convert to serpentine or keep it v-groove? Thanks...
Last edited by job1bf on December 19th, 2011, 5:54 pm, edited 1 time in total.
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Joined: May 20th, 2005, 4:48 pm

December 19th, 2011, 5:56 pm #2

...serpentine and V-belt style setups. You can't really tell a seat-of-the-pants difference, but I've never tried them on the dyno. I will say that the alternator may not charge as well and water pumps may not be as efficient turning at a lower rpm.

Brent Lykins
B2 Motorsports, LLC






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Joined: October 1st, 2004, 8:05 pm

December 19th, 2011, 9:25 pm #3

has anyone experimented with these? opinions? if so, did you convert to serpentine or keep it v-groove? Thanks...
I wouldn't install an under-drive system on a street car unless the car is equipped with low gears. Trailered race cars do indeed need to slow the alternator & coolant pump down.

The factories installed under-drive pulleys on alternators when the cars were equipped with low gearing off the show room floor. Since under normal driving conditions the motors in these cars would be operating at higher rpm, the pulleys served to slow the alternators down to operate at "design" speed. It is also supposedly possible for the rotor winding in an alternator to fly apart if the alternator is spun at too high rpm. I don't think the main purpose was power saving, although I'm sure there was a couple of horsepower saved by slowing down the alternator.

It was once quite common to see larger pulleys on race motor coolant pumps too, one goal is to operate the pump below the speed where cavitation sets in. Of course, cavitation does indeed rob horsepower. The factory coolant pump begins to cavitate around 5000 rpm, a pump with a curved vane impellar (Edelbrock) doesn't cavitate until about 7000 rpm. The Edelbrock pump should be worth about 5 BHP at 6000 rpm in comparison to the factory pump. Another goal is to slow down the rate at which coolant is being circulated so it has time to absorb heat in the motor and time to release heat in the radiator. As in the case with the alternator, power saving was not the primary goal, but slowing down the coolant pump does indeed save a few bhp.



-G
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Pantera Photos | 351C Historic Information | 351C Technical Information

If you use a 351C 4V powered vehicle for a grocery getter ... the eggs aren't going to make it home!
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Joined: January 10th, 2002, 5:53 pm

December 20th, 2011, 4:10 pm #4

has anyone experimented with these? opinions? if so, did you convert to serpentine or keep it v-groove? Thanks...
I set my 6 ribs up with a 2004 March water pump pulley, stock 5.0 lower and the slightly larger alternator pulley from an Aerostar. The WP is overdriven about 1.04 with this setup. The alt pulley is about 2 3/8" vs 2.0 for the stock 5.0 and lets the alternator turn slower. It still puts out 14.6 at idle, even with the larger pulley.

I've never had a problem with belt slip with a 6 rib. I've lost one belt due to the alternator bracket cracking and allowing the alternator to move and eat the belt. I later switched both engines to electric (Moroso) water pumps but kept the alternators. At my 6800 shift point, the alternator is around 14,000 RPM. Them's good bearin's in thar.

1967 Falcon 4 door 351C-4V
1970 Mustang 351C-2V
http://raceabilene.com/kelly/hotrod
Owner built, owner abused.
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Joined: June 4th, 2007, 2:57 pm

December 20th, 2011, 4:45 pm #5

thank all for contributing info...if the gains are to be believed, swapping pulley's while the engine is out is cheap and easy. But, since this is street driven - George makes a valid point on cooling. I don't want it hot. Perhaps I will the un-broken alone...
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Joined: July 21st, 2005, 12:13 am

December 20th, 2011, 6:11 pm #6

As stated above, the key is what RPM your engine will operate at, if it's partially street driven. If you are keeping it 6,500 and below it is probably not be worth the potential headaches in traffic or at car shows, cruising, etc. The slight gain in power will not be noticeable, but poor charging or overheating you will notice.
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Joined: February 3rd, 2003, 5:22 pm

December 20th, 2011, 6:29 pm #7

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Joined: October 1st, 2004, 8:05 pm

December 20th, 2011, 11:32 pm #8

I never saw that claim before, fans using up to 45 horsepower. EEK

One of the "tricks" we performed in the Jurassic era was to replace the factory spacer & flex fan with a fan clutch & fixed blade fan from a more expensive model, like a Lincoln. It was supposed to save 10 to 20 bhp, but the engine also ran much quieter. It was a nice upgrade for a street motor.

Since electric fans are more readily available today, with more choices to select from, it seems they would be the way to go nowadays.

-G
____________________________________________________________

Pantera Photos | 351C Historic Information | 351C Technical Information

If you use a 351C 4V powered vehicle for a grocery getter ... the eggs aren't going to make it home!
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Joined: July 21st, 2005, 12:13 am

December 20th, 2011, 11:44 pm #9

I agree with you George that electric fans are a good way to go. However, second hand on the internet I have noticed a lot of people with electric fans have cooling problems. My take away is that a person should be careful when selecting and setting up an electric fan to make sure there is adequate air flow. Don't just buy any old fan assuming it will work.
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Joined: February 3rd, 2003, 5:22 pm

December 21st, 2011, 12:00 am #10

I never saw that claim before, fans using up to 45 horsepower. EEK

One of the "tricks" we performed in the Jurassic era was to replace the factory spacer & flex fan with a fan clutch & fixed blade fan from a more expensive model, like a Lincoln. It was supposed to save 10 to 20 bhp, but the engine also ran much quieter. It was a nice upgrade for a street motor.

Since electric fans are more readily available today, with more choices to select from, it seems they would be the way to go nowadays.

-G
____________________________________________________________

Pantera Photos | 351C Historic Information | 351C Technical Information

If you use a 351C 4V powered vehicle for a grocery getter ... the eggs aren't going to make it home!
The dyno testing, by the highly regarded Westech race engine shop no less, of numerous fan combos by a major magazine with test results published to back it up, is a great little article that's as valid today as it was when published 11 years old now.
Last edited by machoneman on December 21st, 2011, 12:08 am, edited 1 time in total.
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