Pulley Combo Boost ?

[boca ron]

What kind of boost numbers are guys seeing from a kb blower with 6# lower and 3 upper on cammed motors. I'm seeing 14# that seems a little low to me. What say you? Yesterday I removed 8# lower, I can tell a big difference dropping down to the 6 seat of the pants feels like I dropped 50hp plus the tune was way off, way rich, retuned it and was able to add a little timing, better but still not the same for sure.

 

[Fade 2 Black]

With an 8 lower, 3.25" upper I see 15-16# on mine. It's a 3:1 ratio same as a 6 lower 3" upper. It may be down lower now though due to the heat. You may be fine down in S FL.

 

[boca ron]

So a 8 lower 3.25 is equal to 6L 3U? correct?

 

[01redbolt]

Don't know if it will help but I'm running a 3" upper and 6lb lower on my stock motor, stock cams and getting 22.5lb's of boost, this is with the JLP sheet metal intake.

 

[boca ron]

Don't know if it will help but I'm running a 3" upper and 6lb lower on my stock motor, stock cams and getting 22.5lb's of boost, this is with the JLP sheet metal intake.

omg, that thing is makeing big boost, it must run like hell

 

[Fade 2 Black]

So a 8 lower 3.25 is equal to 6L 3U? correct?

Yes. Divide the diameter of the upper pulley in inches into the diameter of the lower pulley and you get the driven ratio of the s/c and both of these combos equal 3:1.

 

[fuzzie]

So a 8 lower 3.25 is equal to 6L 3U? correct?

I'd be real close Ron. In good air with my 8lb lower and 3.1 upper I was making about 21psi. That was with a JLP Sheetmetal plenum. Around 20psi with the 3.25.

 

[boca ron]

gotcha thanks for the info,im putting the 8 back on truck feels slow

 

[2bscrewed]

Just as reference I see 17#'s with a 10# lower and a 3.1 upper, so you sound in the ballpark with your combo.

 

[CHIZ]

i'm seeing 10-11lbs on a 4# lower and 2.8 upper....i'm guessing i'm having belt slip or something. i just went and adjusted the boost actuator, so i'm hopeing that'll help.

chiz

 

[boca ron]

Just as reference I see 17#'s with a 10# lower and a 3.1 upper, so you sound in the ballpark with your combo.

wow, that beast is flowing real nice. what vacum you seeing on idle in park?