[1966conv]

I know this has been discussed recently but:
What is the reasoning for the increase in HP by using underdrive pulleys.
I seen posts stating they run warmer, however, by keeping the crank pulley the same and making the water pump smaller, won't that actually increase the speed of the water pump.(better cooling)? What am I missing? Alternator and PS I can see those being slower.

1966 Red Conv (200)
1966 White Pony Int.(289)A Code
1966 Coupe (289) C Code
MCA 36048

 

[Jim]

For underdrive, the drive pulley (crank) would be smaller and the driven pulley's (accessories) would be larger. This slows down the accessories. By moving them slower, it takes less power to operate them.

 

[1966conv]

The only pulleys I've seen listed for the 289 are WP, Alt, and PS no crank. This did not make sense to me.

1966 Red Conv (200)
1966 White Pony Int.(289)A Code
1966 Coupe (289) C Code
MCA 36048

 

[camachinist]

The old K-coder used a big alternator/generator pulley which, in conjunction with the stock crank pulley, slowed the rpms substantially and therefore required less HP to turn the accessory...

You could use a smaller crank pulley (if you made one) with the available larger accessory pulleys but might run into belt problems (finding the right length, not insurmountable *G*)....we did this on race cars before going to electric pumps for water and using an external generator to charge the batteries...

Pat
http://www.jps.net/binay/webdocs/strtmstng002_sml.JPG

 

[Jim]

If you replace your existing driven pulleys with larger ones, it will still slow down your accessories, just not as much as if you also installed a smaller crank pulley. Try to envision the linear velocity at the pulley groove. The farther away that groove is from the center, the faster it must move in order to rotate the center at the same speed. Since in this case the velocity stays the same, but you are moving it farther away from the center, the rotational speed at the center is less, thus slowing down the accessories. Clear as a mudpuddle? Another way of looking at is in to compare it to going to larger size tires - When you do this, your RPMs at any given speed goes down, right? Same with your alt, fan, and p/s.

 

[1966conv]

Actually it is clear, maybe the problem i have is that "Summit catalog lists March PS WP and alt pulleys as being smaller. "Smaller belts required", to me that would indicate(probably again incorrectly" that the pulleys are smaller not larger, like i'm thinking they should be.
I am probably just interpeting what they are saying incorrectly.

1966 Red Conv (200)
1966 White Pony Int.(289)A Code
1966 Coupe (289) C Code
MCA 36048

 

[Jim]

More likely, their catalog is in error, which it often is. Best thing to do would be to find a March website or get their catalog. You're right that it wouldn't make much sense to make the driven pullley's smaller, unless you were trying to get more performance out of your accessories instead of your engine. Sorry if I insulted your intelligence, as that was definitely not my intention.
Jim

 

[1966conv]

No problem, The theories there just did not tie to what I've seen here and wanted a more definitive answer *G*

1966 Red Conv (200)
1966 White Pony Int.(289)A Code
1966 Coupe (289) C Code
MCA 36048