b&m 250 boost chart
#2
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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
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
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#5
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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
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
#6
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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.
#7
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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?
Last edited by Rookie; 04-19-2012 at 08:27 PM.
#8
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I don't recall, maybe mine were 3.34 upper at 5psi now that u say that. I had 3 pulley sets , part #155192, 155193, 15594. The 193 gave me 5psi, 192 7psi.
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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
#10
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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.