OK, due to having to work and Easter, I haven't got a lot done other than chase parts and finish the belt. I haven't cut the upper pulley off--yet. I talked to Holley, they wouldn't express an opinion either way. I'm leaving it for now...
All of the following ONLY refers to using the Holley AC bracket with GM brackets like mine. If you are using all Holley brackets you should probably just follow their directions. Also, I am using the later R4 compressor with the 4.5" pulley. If you have a 5" Pulley, as Holley recommends, then your measurements will be different. (Measured at the pulley surface.)
This is what I did: Holley's directions are not very explicit if you're using the GM brackets for the Alternator and the PS pump. If you look at the picture in this post, there are two pulleys by the AC compressor--upper and lower. The upper is the one I don't think you really need, looking at the picture you should be able to see why. When you buy the kit, it does not come with the tensioner--the bottom pulley--they specify what one to buy. They also specify a pulley you need to buy to replace the one that comes with the tensioner. You then take the one that was on the tensioner and use it as the upper pulley. They also list a second pulley you can use as the upper pulley; it is a smaller pulley that allows more clearance and is in fact required in certain setups. (The bigger one that came with the tensioner can interfere with some throttle bodies.)
The new lower pulley they specify is 76mm in diameter. That probably works great with all Holley brackets, but there are other choices. I ended up replacing it with a 70mm pulley. That allows me to not cut off the upper pulley boss and still use a common belt. It also puts the belt right in the middle of the acceptable range.
When you put the belt on, you check it with marks on the tensioner. Holley describes two marks in the directions--confusing because there are actually three marks. When you look at the tensioner, there is a reference mark. It lines up somewhere along the three reference marks. Here is what is not included in the Holley directions: The two marks closest together show the range for a brand new belt. As the belt ages and stretches, you use the two marks furthest apart to determine if the belt is still serviceable. If you use the pulleys specified by Holley, you can't find a belt that ends up in the "New" range. At least you can't with my setup. The Dayco 5061093 is too short and the Dayco 5061098 is too long. There is nothing in between. (Cross reference those numbers to see other brands; there is still nothing in between in any brand.) Even with the smaller Upper pulley you are out of luck. You could cut off the Upper Pulley Boss. Doing that results in the 5061093 fitting--barely. (BTW, the 5061093 is commonly available, the 5061098 is special order only everywhere that I tried.) However, if you switch to the smaller upper pulley that Holley specifies, AND you switch to a 70mm lower pulley, the 5061093 fits right in the middle of the acceptable range. I haven't run the engine yet, so this presupposes that I am getting the tension where it will be after the engine has run. I believe I have, but I'll have to verify after the L94 is running.
Anyways, I'm leaving the upper pulley boss intact because it seems like I get the best results this way. I may change my mind after I run the engine the first time.
I used Dayco parts because their website allows you to look up belt and pulley specifications.
http://www.daycoproducts.com/online-...1?part_type=20
http://www.daycoproducts.com/online-...1?part_type=60
You need a single bearing 17mm ID pulley for both upper and lower pulleys. (A dual bearing pulley may or may not work; I have no idea.) The upper pulley is 6 rib, the lower pulley is smooth. Changing the diameter of the lower pulley makes a much bigger difference in belt length than changing the diameter of the upper pulley.
BTW, The Holley directions for determining belt length didn't work so well. They tell you to subtract 1 1/8 inches from your measurement. I got much closer by not making the subtraction. Why? using a string to measure belt length measures inside circumference. Belts are spec'd using outside circumference. Regardless, I only got close, be prepared to return the belt and try another one.
The easiest way to install the belt is to remove the upper pulley and then install the belt. Then install the upper pulley.
BTW, you can't play with the idler pulley by the alternator. no room to go bigger and going smaller would cause belt interference with an alternator mounting bolt.
