Not sure if anyone has made a similar tool, but I threw this together so I can make on-the-fly pulley combo decisions. This is a comparison of blower speed ratios, with a direct relationship with engine RPM for various pulley combos to give you a good look at how your pulley combo might stack up against others. It is universal for any blower, so use boost/power figures of specific builds as reference. For example, a comparable pulley combo would be a stock lower with a 2.6" upper would give you a blower speed of 18,437 rpm at 6500 rpm, and a 6lb lower with a 3.2" upper would net you 18,484 rpm at 6500 rpm. It's safe to say that these ratios are very close, giving an edge to the latter. Without crunching hard numbers, you'd never know. Feel free to plop any boost/power numbers along with combo information.
Eng RPM @ 6500
S = 7.375"
2# = 8"
3# = 8.3"
4# = 8.6"
6# = 9.1"
8# = 9.55"
10# = 10"
S + 3.5" = 13,696 rpm
S + 3.4" = 14,099 rpm
S + 3.375"=14,203 rpm
S + 3.3" = 14,526 rpm
S + 3.2" = 14,980 rpm
S + 3.1" = 15,463 rpm
S + 3.0" = 15,979 rpm
S + 2.9" = 16,530 rpm
S + 2.8" = 17,120 rpm
S + 2.7" = 17,754 rpm
S + 2.6" = 18,437 rpm
2 + 3.5" = 14,857 rpm
2 + 3.4" = 15,294 rpm
2 + 3.3" = 15,757 rpm
2 + 3.2" = 16,250 rpm
2 + 3.1" = 16,774 rpm
2 + 3.0" = 17,333 rpm
2 + 2.9" = 17,931 rpm
2 + 2.8" = 18,571 rpm
2 + 2.7" = 19,259 rpm
2 + 2.6" = 20,000 rpm
3 + 3.5" = 15,414 rpm
3 + 3.4" = 15,867 rpm
3 + 3.375"=15,985 rpm
3 + 3.3" = 16,348 rpm
3 + 3.2" = 16,859 rpm
3 + 3.1" = 17,403 rpm
3 + 3.0" = 17,983 rpm
3 + 2.9" = 18,603 rpm
3 + 2.8" = 19,267 rpm
3 + 2.7" = 19,981 rpm
3 + 2.6" = 20,750 rpm
4 + 3.5" = 15,971 rpm
4 + 3.4" = 16,441 rpm
4 + 3.3" = 16,939 rpm
4 + 3.2" = 17,468 rpm
4 + 3.1" = 18,032 rpm
4 + 3.0" = 18,633 rpm
4 + 2.9" = 19,275 rpm
4 + 2.8" = 19,964 rpm
4 + 2.7" = 20,703 rpm
4 + 2.6" = 21,500 rpm
6 + 3.5" = 16,900 rpm
6 + 3.4" = 17,397 rpm
6 + 3.3" = 17,924 rpm
6 + 3.2" = 18,484 rpm
6 + 3.1" = 19,080 rpm
6 + 3.0" = 19,716 rpm
6 + 2.9" = 20,396 rpm
6 + 2.8" = 21,125 rpm
6 + 2.7" = 21,907 rpm
6 + 2.6" = 22,750 rpm
8 + 3.5" = 17,735 rpm
8 + 3.4" = 18,257 rpm
8 + 3.3" = 18,810 rpm
8 + 3.2" = 19,398 rpm
8 + 3.1" = 20,024 rpm
8 + 3.0" = 20,691 rpm
8 + 2.9" = 21,405 rpm
8 + 2.8" = 22,169 rpm
8 + 2.7" = 22,990 rpm
8 + 2.6" = 23,875 rpm
10 + 3.5" = 18,571 rpm
10 + 3.4" = 19,117 rpm
10 + 3.3" = 19,696 rpm
10 + 3.2" = 20,312 rpm
10 + 3.1" = 20,967 rpm
10 + 3.0" = 21,666 rpm
10 + 2.9" = 22,413 rpm
10 + 2.8" = 23,214 rpm
10 + 2.7" = 24,074 rpm
10 + 2.6" = 25,000 rpm
Eng RPM @ 6500
S = 7.375"
2# = 8"
3# = 8.3"
4# = 8.6"
6# = 9.1"
8# = 9.55"
10# = 10"
S + 3.5" = 13,696 rpm
S + 3.4" = 14,099 rpm
S + 3.375"=14,203 rpm
S + 3.3" = 14,526 rpm
S + 3.2" = 14,980 rpm
S + 3.1" = 15,463 rpm
S + 3.0" = 15,979 rpm
S + 2.9" = 16,530 rpm
S + 2.8" = 17,120 rpm
S + 2.7" = 17,754 rpm
S + 2.6" = 18,437 rpm
2 + 3.5" = 14,857 rpm
2 + 3.4" = 15,294 rpm
2 + 3.3" = 15,757 rpm
2 + 3.2" = 16,250 rpm
2 + 3.1" = 16,774 rpm
2 + 3.0" = 17,333 rpm
2 + 2.9" = 17,931 rpm
2 + 2.8" = 18,571 rpm
2 + 2.7" = 19,259 rpm
2 + 2.6" = 20,000 rpm
3 + 3.5" = 15,414 rpm
3 + 3.4" = 15,867 rpm
3 + 3.375"=15,985 rpm
3 + 3.3" = 16,348 rpm
3 + 3.2" = 16,859 rpm
3 + 3.1" = 17,403 rpm
3 + 3.0" = 17,983 rpm
3 + 2.9" = 18,603 rpm
3 + 2.8" = 19,267 rpm
3 + 2.7" = 19,981 rpm
3 + 2.6" = 20,750 rpm
4 + 3.5" = 15,971 rpm
4 + 3.4" = 16,441 rpm
4 + 3.3" = 16,939 rpm
4 + 3.2" = 17,468 rpm
4 + 3.1" = 18,032 rpm
4 + 3.0" = 18,633 rpm
4 + 2.9" = 19,275 rpm
4 + 2.8" = 19,964 rpm
4 + 2.7" = 20,703 rpm
4 + 2.6" = 21,500 rpm
6 + 3.5" = 16,900 rpm
6 + 3.4" = 17,397 rpm
6 + 3.3" = 17,924 rpm
6 + 3.2" = 18,484 rpm
6 + 3.1" = 19,080 rpm
6 + 3.0" = 19,716 rpm
6 + 2.9" = 20,396 rpm
6 + 2.8" = 21,125 rpm
6 + 2.7" = 21,907 rpm
6 + 2.6" = 22,750 rpm
8 + 3.5" = 17,735 rpm
8 + 3.4" = 18,257 rpm
8 + 3.3" = 18,810 rpm
8 + 3.2" = 19,398 rpm
8 + 3.1" = 20,024 rpm
8 + 3.0" = 20,691 rpm
8 + 2.9" = 21,405 rpm
8 + 2.8" = 22,169 rpm
8 + 2.7" = 22,990 rpm
8 + 2.6" = 23,875 rpm
10 + 3.5" = 18,571 rpm
10 + 3.4" = 19,117 rpm
10 + 3.3" = 19,696 rpm
10 + 3.2" = 20,312 rpm
10 + 3.1" = 20,967 rpm
10 + 3.0" = 21,666 rpm
10 + 2.9" = 22,413 rpm
10 + 2.8" = 23,214 rpm
10 + 2.7" = 24,074 rpm
10 + 2.6" = 25,000 rpm
