Belt selection help...Upper-Lower-with Alt pulley

[mj8]

I can't seem to find out which belt will suit me the best for my application. I will be running a 2.93 upper a 6lb lower a 3.5 alternator pulley and one 100mm idler. Does anybody have a similar setup if so let me know...I would prefer to use a GATES belt.

 

[IronTerp]

Hmmmm.....probably in the 81" range. But, I'd reconsider the 3.50" alternator pulley. With the 6 lb lower, the 3.5 will underspin your blower by 11.05% from the factory 2.60" alternator pulley rpm. With a 3.20" alt pulley, you're only underspinning by 2.71%.......Just wouldn't sacrifice the voltage.

 

[mj8]

IronTerp you are correct and before I called PA alternators I was planning on going with the 3.2. After talking with them they told me that the alternator is overspun from the factory so upping the alt pulley will extend the life of my stock alternator. The graph below is what is recommend to spin the alternator at not what the alternator is currently being spun at if that makes sense. You kind of have to rob Peter to pay Paul in way. If you get a real huge alt pulley you will slow it down...it being the alt..in the upper rpm range 6000-7000rpms but you will severely under-drive the alt on the idle side and will have problems charging and running accessories..3.5 seems to meet a little in the middle.

 

[CobraBob]

Subscribing.

 

[mj8]

Ok I bought 3 belts all Napa Gates belts...

79 (2008)........................ K080785
80 1/4 (2040) ................. K080797
81 1/8 (2060) ................. K080806

I will post back when I find the right one...lets hope it's one of these....

 

[mobius]

ok were do i get a 3.5 alt pulley as i have a 8lb lower.....

 

[mj8]

ok were do i get a 3.5 alt pulley as i have a 8lb lower.....

Metco makes and sells them. You can order them through BilletFlow as well, pretty competitive prices.

 

[mobius]

also what belt do i need with that setup? stock upper/8lb lower/3.5alt

 

[Antex]

also what belt do i need with that setup? stock upper/8lb lower/3.5alt

I've got the 3.10/8lb, 3.2 alt with old style BF aux idler and the Gates 816 fits fine. I'm thinking you need an 820+ belt

 

[Oxford Snake]

New 4 # Metco lower - 3.2 or 3.5 alternator?

 

[CobraBob]

ttt

 

[Oxford Snake]

After further searching it appears the consensus is to leave the stock alternator pulley on with the 4 # lower????

 

[IronTerp]

After further searching it appears the consensus is to leave the stock alternator pulley on with the 4 # lower????

Not necesarily.......Still a lot of debate on this one. There are those, supported by the fine folks at PA Alternator, that say the OEM alternators are overspun from the factory in the first place, and that pretty much any kind of lower pulley change, merits a bigger alternator pulley. PA says that no alternators should be consistently subjected to rpm's over 16,000 and your alt pulley needs to reflect this, dependent on your lower pulley size obviously.

And then there's those that feel the Ford engineers did an okay job with the factory system and that those instances where the alternator rpm is above 16,000 are so short and infrequent, that it does not lead to premature failure of the factory alternator. After all, who cruises around at 5,000 to 6,000 engine rpm anyway????

The truth of the matter???? Who the heck really knows! I've unofficially volunteered to be a test mule for the 4 lb lower/ factory alternator test and am at 9,000 miles now with this combo and 22,000 miles on the alternator. And if/when the alternator fails???......I'll let you know and then am going to go out and buy.........A PA alternator!!!

Really though, when all is said and done, a 2lb lower is probably okay with the factory 2.60" alt pulley, the 4 lb lower should probably take a 3.20" alt pulley, a 6 lb lower would be a 3.20" or even a 3.50" pulley, and a 8lb lower, better get a 3.50 alt pulley for sure..........

 

[CobraBob]

Great info IronTerp. This post is worth bookmarking/saving. Which I've done.

 

[dynobobstieg]

I can't seem to find out which belt will suit me the best for my application. I will be running a 2.93 upper a 6lb lower a 3.5 alternator pulley and one 100mm idler. Does anybody have a similar setup if so let me know...I would prefer to use a GATES belt.

Running a 2.93 Upper with a 6# Lower= TOO MUCH BOOST

 

[wizdawg]

After further searching it appears the consensus is to leave the stock alternator pulley on with the 4 # lower????

I think this is split down the middle. Seems 1/2 of the people on here leave the stock alternator pulley on. The other 1/2 will put a 3.2" on with a 4# lower. I will be using the 3.2 alt pulley when I put on the 4# lower.

 

[goodquest]

ttt

 

[FireRed04Vert]

I am willing to bet you that unless you run some serious drawing amps, etc, that you could put a 3.2 alternator pulley on a stock car and NEVER notice the difference.