b&m 250 boost chart
Anyone have boost chart with pulley ratio for b&m 250 marine blower kit?
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Boost pressures vary with the cubic inches of the engine.
This Holley chart will give you estimates based on the % of overdriven. The chart is toward the end. http://www.holley.com/data/TechServi...ech%20Info.pdf |
[(25.58) x (Blower displacement) x (Blower Drive ratio)]
(Engine Cubic inch Displacement) = Answer Answer - 14.7 = Boost |
Originally Posted by Rookie
(Post 3664934)
[(25.58) x (Blower displacement) x (Blower Drive ratio)]
(Engine Cubic inch Displacement) = Answer Answer - 14.7 = Boost Thanks, it looks to be pretty accurate :whistle: |
mx,
I still have my old B & M marine catalog at the shop and I am pretty sure it is in there. I will try to remember and look in the morning. I can scan it and send it to you if you still need it. Bill Koustenis Advanced Automotive Machine Waldorf Md |
Originally Posted by Rookie
(Post 3664934)
[(25.58) x (Blower displacement) x (Blower Drive ratio)]
(Engine Cubic inch Displacement) = Answer Answer - 14.7 = Boost However, that equation is pretty accurate on my new setup, using the 420 blower. it comes out to 6.6psi, and thats about where i was on the dyno. The 250's had very low hours on the rebuilds, so can't see it being they were tired. Maybe they just were'nt that efficent at 80% over, as the 420's are at 7% under. All i know is with the 250, I had a 5.5" lower pulley, and 3" upper pulley, gave me 7psi on a 460CI. The 3.25" pulley gave me 5psi. :cartman: |
Originally Posted by MILD THUNDER
(Post 3668207)
All i know is with the 250, I had a 5.5" lower pulley, and 3" upper pulley, gave me 7psi on a 460CI. The 3.25" pulley gave me 5psi. :cartman:
The equation came straight out of my owners manual and handbook for holley/B&M blowers. Do you think your boost might have gone up with dual quads Vs the single dominator? |
Originally Posted by Rookie
(Post 3668235)
Thanks, That is good to know. I have 5.5 lower pulleys and 3.34" uppers.
The equation came straight out of my owners manual and handbook for holley/B&M blowers. |
carbs have zero basis on boost,cubes and cams change boost levels.......i have a pair of 250 bm on my stock hp 500 dynoed in january with intercoolers 730hp plus to 785hp max at 5300 and there for sale just went with 850 sc
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Originally Posted by proboat-wes
(Post 3668263)
carbs have zero basis on boost,cubes and cams change boost levels.......i have a pair of 250 bm on my stock hp 500 dynoed in january with intercoolers 730hp plus to 785hp max at 5300 and there for sale just went with 850 sc
As for carbs not affecting boost, they can on a roots setup if the carb is too small. Roots blowers love a unrestricted source of air on top of the blower. That's why it's kinda hard to overcarb a roots. |
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