Underdrive crank pulley
Thread Starter
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
Underdrive crank pulley
Does 6 1/8 sound right for a steel underdrive pulley? Using a tape measure on mine I am getting between 6 1/8 to 6 1/4 it is kind of hard to see. Trying to decide if i want to replace the crank pulley with stock or just get a smaller one for the altenator.. The altenator has a 2 1/4 and was thinking of going to a 2 to get the charging system working better..
Le Mans Master
Joined: Jun 2006
Posts: 5,642
Likes: 5
From: One day you're a Comet...the next day you're dust... Arkansas
With the 3 piece P & A aluminum March set you don't need a bigger alternator. Mine has been running great with a stock unit. The March Power and Amp set has a smaller steel alt pulley.
Thread Starter
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
from what i can figure out stock ratio with 7.125 and 2.25 was 3.166 most of the underdrive kits i have seen are around 10% underdrive and that lines up well with my measurement of between 6.125 and 6.375 with a tape measure and flash light it is hard to read the tape without removing a bunch of stuff but if we call the crank pulley at 6.375 and a 2 inch on altenator my drive ratio will be 3.18 colse enough for me as long as I can get a belt the right length if the one I have ends up being too long. Right now it is in the middle of the tensioner and has been on long enough to stretch as much as it is going to. I think I am going to need a belt about 0.400 shorter so may be out of range of tensioner. Maybe will call NAPA before I order the pulley to see what they have that is shorter than I have now in case i do have to change the belt as I know they have the stock one for the stock lower pulley just didn't want to work that hard..LOL
