Does anybody know the diameter of the high altitude smaller pulley for the 525sc? Tried searching for it and can't find it, thx all

3"

Good luck finding one. I have never heard of a 3" splined pulley, assuming it has the Merc shaft. I have seen splined 2.85" pulleys though. If the shaft has a keyway (automotive style) there are more choices in pulley sizes available.

Well Old Navy I have that unicorn lol. 3" pulley for the 177 with a merc shaft. 525sc stock pulley size is 3.25", I got the 3" pulley and put it on August of this past year and ran it for the remainder of the season. I saw a 2psi increase with it.

I know somebody looking for a smaller than stock 525SC upper pulley if anybody has any leads.
The smallest I ever heard of was 2.75" There used to be quite a few places that sold smaller ones, but that was years ago.
I think I had a 2.88" on my 525SC and it made just under 8# of boost.

Makes sense Griff I was seeing 7psi maybe a touch more with the 3" pulley.

Put it on a lathe and make it as small as you want

I think it is the 3.10 pulley, but close enough for discussion.

I have not measured it with a pair of micrometers to get the EXACT size, but have with a tape measure and I remember it being 3". When i go down to my builder again I will measure with mics and see exactly what it is.

I measured the pulley and it is 3", however I found out it is a cut down stock pulley. I got the pulley from a local guy, and by complete chance my dyno operator is the one who cut the pulley down for the guy who I bought it from lol. He recognized it when they were setting it up on the dyno and he asked me where i got it, when I told him he said he knew he recognized it and that he cut it down from a stock one. So I am not sure what size the low altitude pulley is, but if you take a stock 3.25" pulley and have it cut down to 3" you'll increase boost around 2psi.