quick underdrive pulley question

[greenstang1313]

Just a quick question, can I run 2 aftermarket underdrive pulleys (BBK) and put my stock alt pulley back on? Will belt still fit?

Thanks

 

[nmcgrawj]

It should, thats how i ran mine for a while...

 

[94-302-vert]

Depends...

On my car the belt that was on with the "stock" pulleys was not the size in the computer, and the belt I needed after the pulleys was also not the right size... But I think my car is early production 94 or something...

 

[legalize420]

just wondering, why does everyone want to run the stock pulley on the alternator? the pulley for the alternator that came with my underdrives is smaller than the stock one. if you run the bigger stock pulley you get less rotation and actually slow it down. if its charging issues you guys have it backwards. i ended up getting an even smaller pulley than the one that came with my set and it helps.

 

[94v6GT]

it probably varies from kit to kit. 'legalize' what kit are you running.

 

[legalize420]

it probably varies from kit to kit. 'legalize' what kit are you running.

its been a while but if i remember right they are from the mustang depot on ebay. not sure of the brand.

 

[greenstang1313]

i dunno but my headlights never dimmed and my battery gauge never jumped around when I had my stock pulleys on. I'm putting on a new alternator and it came with a pulley and I figured I'd just use the new pulley because i dont wanna deal with the charging issues.

 

[The Green GT]

My MAC pulley was like 1 MM bigger.

And yes, I could run the same (stock) belt with both setups.

 

[nmcgrawj]

Im pretty sure my stock one is smaller. The water pump is bigger for under drives right? And the crank is smaller. I thought the idea was to get the crank pulley to spin faster and the accessories slower making the motor have more power. Cause my stock crank is huge and my stock water pump is tiny.

 

[toyman]

Crank pulley doesn't spin faster. One revolution is one revolution. Let's try an example. If the stock crank pulley is 5" then for each revolution it will move the belt 5"x3.14(pi)=15.7". If the underdrive crank pulley is 4" then the belt will travel 4"x3.14=12.56" or 3.14" less per revolution of the crank. If follows then that all the other accessories are rotating slower with each revolution of the crank. To slow the accessories even further requires that their respective pulleys be larger in diameter. So underdrive pulleys have a smaller crank pulley with the water pump and alternator pulleys being larger than stock.

 

[nmcgrawj]

Crank pulley doesn't spin faster. One revolution is one revolution. Let's try an example. If the stock crank pulley is 5" then for each revolution it will move the belt 5"x3.14(pi)=15.7". If the underdrive crank pulley is 4" then the belt will travel 4"x3.14=12.56" or 3.14" less per revolution of the crank. If follows then that all the other accessories are rotating slower with each revolution of the crank. To slow the accessories even further requires that their respective pulleys be larger in diameter. So underdrive pulleys have a smaller crank pulley with the water pump and alternator pulleys being larger than stock.

YEP








































You're right!

 

[94v6GT]

YEP






You're right!

what does he win? lol
so from what i see many people get by with the stock alt pulley and underdrives. what potential harm is there from moving the water pump slower?

 

[toyman]

Overheating in stop and go traffic on hot days. There is no risk at speed. Again the theory is, if accessories are turning slower there is less power needed to drive them with the "saved" power now going into the drive line or something like that. Hence, RWHP gain.