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New Blowers...........

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Old 02-02-2003, 02:43 PM
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Question New Blowers...........

Okay, here is a question for all of you OSO members out there who are more knowledgeable than myself when it comes to motors. I currently have stock 525sc's that use Wieland 177's and are attached to beefed up Bravo's. I am looking at moving up to a newer larger blower. The ones I'm looking at are the B&M 250's, B&M 420 mega, the 6:71, 8:71, and 10:71. I'm curious how much increase I will see with each and which one is the best choice for good performance upgrade with better reliability and won't destroy my Bravos every season. There are a few of each for sale on this board and I'm ready to go for it, I just need help deciding where to spend my money best.

All suggestions will be greatly appreciated!!!!!!!!!!!
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Old 02-02-2003, 04:02 PM
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Come on everyone, help a guy out.................lol
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Old 02-02-2003, 04:37 PM
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the 177's start beating themselves to death around 575 hp. Making more heat than boost.

the 250's are good to 700 horses.

420s are fine to anything you'd ever want to couple a Bravo to.

6-71 probably compares in size to the 250.
8-71 a little less than a 420.
10-71 a little more than a 420.

the -71 series of blowers are based on old GM diesel scavenging pumps. They are usually modified and fitted with rotor seals when converting them to a performance application - but in my opinion, the "made for performance" B&M pumps are a better match for you.

As far as "which one will make more power for you" the question requires more to answer properly.

Each larger blower has larger components, larger gears and bearings in its drive, and more swept area (assuming it uses teflon contact strips on the rotors). This means that for a given rpm, each larger blower requires more horsepower to turn which it removes from the net power available at the flywheel. This is further compounded by the blower belt situation. Each larger, meaner looking belt, requires more power in its operation.

Notice above that I specify that each larger blower requires more AT A GIVEN RPM. A given blower may deliver more volume at a lower rotational speed than a smaller one.

With that said, I hope that you can see that there is a good reason for so many different sizes of blowers.

You gotta figure out what your target horsepower is. Then, from the size and state of tune of your motor, one must determine the appropriate charge volume that must be delivered in order to reach that goal. The state of tune (heads, cam, etc) you are running will dictate the boost level and volume that will be necessary (a high flowing motor will require a given volume of charge for power but the volume will be delivered to it at a lesser boost than would be needed for a lower flowing motor). Once the volume/boost curve is approximated, it is easy to size the blower to the motor.

A "too small" blower will operate above its efficiency curve and not give good results. A "too large" blower will rob too much in the way of parasitic drive loss. It will also possibly fall below its efficient pumping range at lower engine speeds due to rotor seal leakage which will soften the engine's torque curve at low rpm which may or may not be desirable in its given application (rotor seal leakage does not affect output that much in the blower's normally efficient rotation speed range - only at low rpm and at high boost levels).

On your application, you may be able to add an intercooler and pulley your way to a safe 600hp without replacing your blowers, especially if you upsize your cam.

250's will allow you to do anything "within reason". especially when paired with intercoolers.

420's will be overkill, but they do look cool...
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Old 02-02-2003, 04:44 PM
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mcollinstn,

WOW! That was extremely helpful. I think my target horsepower is around 700-800 because I think anything over that is way too risky with my Bravos. I just put scoops on my hatches in preparation for these upgrades. Can I safely put 250's on w/o inner coolers and be safe? What would you do if this was your setup and you were upgrading?
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Old 02-02-2003, 04:47 PM
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a few years ago i had a 90 40 fountain with 454/365 mags in it and was looking at different blowers. B&M put out a pamplet on their different blowers and what they would do for the different motors with the 525 and the mega blower you could expect 750hp because the 525's had lower compression to begin with you could raise the boost, i have also read that the B&M blowers are not the best for making serious HP because of their rotor designs, hope it helps a little, this season we have to get to gether i know your at loto and so am i but were just on different parts of the lake im at the 6.5mm and your up around the 26mm if i remember correctlly , but hell lets make it a point.
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Old 02-02-2003, 04:54 PM
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Dave,

I totally agree we must make it a point to try to get together this summer!!

So am I reading that you'd suggest the 420's or the 250's?
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Old 02-02-2003, 04:56 PM
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The 420 B&M is claimed to be about a 6-71. Almost anybody's 8-71 will make more boost, more power. The B&M (now Holley) is pretty good for it's size, though.
 
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Old 02-02-2003, 05:00 PM
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blown1500,

Which would you choose?
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Old 02-02-2003, 05:11 PM
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Sheesh,

If I already had 177's and was gonna trash them, I'd dang sure skip straight to 420's. UNLESS you have a line on a raging deal on a pair of 250's.

Your target hp 700-800 will keep you happier longer if you bite the bullet and pop for intercoolers. 250's or 420's, I'd go with intercoolers.

On your 454's and stock heads you're gonna be staring at probably 12 pounds of boost to see 800hp. I can't IMAGINE NOT running an intercooler at those numbers...

You're gonna HAVE to do some work to your heads AND upsize the cam a LOT to see 800 hp inside of a reasonable boost range (less than 9 pounds).

Maybe I'm offbase here.
Somebody please give him better news than mine...
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Old 02-02-2003, 05:23 PM
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mcollinstn,
What do you expect I'd see with 250's and inner coolers?
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