.......or number crunchers. Which makes more boost, the 4# lower pulley or the 2# lower pulley with a 280 size upper pulley combo? I don't think I've seen this question asked before now. I probably missed it.

I'm thinking that the combo makes more boost. How much more, if this is the case?

Roger

 

The same w/in a 100 rpms it seems

Here:

Stock Lightning lower is 7.5" and upper is 3".

7.5 / 3 = 2.5 (pulley ratio) x 5000 (rpms) = 12500 rpms

I believe a 2# is going to be 8" approx., and the 4# lower is 8.5 (someone correct me if I'm wrong, please!). So:

8 / 2.8 = 2.8571 x 5000 = 14286

8.5 / 3 = 2.8333 x 5000 = 14167

It should be basically the same give or take a few. The way pulley manufacturers actually measure is different from each. I've seen ASP state 2.78, so then the differences is extremely slim.

 

Stock upper is 2.93" and I think the 4lb lower is 8.75 (I may be wrong on the lower).

 

Stock Upper is 2.93 and a 2# Lower is 8.00 and a 4# is 8.50

2# Lower and Upper: 8 / 2.8 = 2.8571 x 5000(rpms)= 14286

4# Lower and stock 8.5/2.93 = 2.9010 x 5000(rpms)= 14505

Therefore the 4# Lower should make more boost and power than the other setup by a little bit! Also if you do this formula a 4# lower and upper will make a little more power than just a 5# Lower and stock upper.

Matt