b&m 250 boost chart
 

Anyone have boost chart with pulley ratio for b&m 250 marine blower kit?

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

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

According to that equation, my engines should have been making 10psi of boost with the 250 blower at the ratio i was turning them. I actually had 7psi.
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:

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.

Do you think your boost might have gone up with dual quads Vs the single dominator?

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.

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

Very nice. I just got done with a 468ci with a 420 B&M, 800hp, no chiller, 6psi of boost. The b&m blowers are affordable and do work.

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.

I have #155193's and 5 PSI sounds good to me.

Are you putting the blowers on for this season?? Your engines have some compression in them now don't they??

The plan is next winter. I am around 9.7:1 with aluminum Dart heads from what the piston chart tells me.
The funny thing is I did do a compression test on both my engines last night and my cranking compression was only 100-107psi. Granted this was on engines that are cold and have not run since last fall. The cams I have in them now would just be blowing the boost out the exhaust. I might actually be able to put blowers on the setup I have and make about 2-3psi of boost. :)

I know a guy who runs 9.6 or 9.7 static, megablowers, alum heads, and 3psi on pump gas, and turns the boost up to 5psi and runs a race fuel mix. Works for him for years.

Your cams are prob on a 108 or 110lsa?

Here is the directions for the 250 blower kits if anyone needs them: http://dl.dropbox.com/u/42339868/250...directions.pdf

You got it 252/264 108*LSA

MT you have answered some of my questions on another thread i started on OSO. So what is the deal with your friends motor? Reliability and life with that set up? would this work with a 548 and a 250 charger with 2 /750;s on top? no intercooler, and cast iron heads?

His setup is utilizing a larger blower .

I would not install a 250 blower on anything over a 502ci, but that's just me.

Can you make it work, yes, but why. Selling the 250 and going to a used 420, 8-71, or preferably 10-71, won't cost a ton more money, you'll make a bunch more power, and have a safer setup.