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Discussion Starter · #1 ·
Supposedly a 177 will make 650hp on a 454-496. Do you think a 250 will make 800-850hp on an AFR headed 454? I don't see much info on 250 and 256 blowers. I noticed Blower Shop makes a nice setup for $3k.

Thanks for any info or experiences!
 

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I've been studying blown engines for a planned upcoming build so I'm no expert. But from what I surmise you would want a minimum of 671 for a big cubic inch engine. Yes you can overdrive a smaller blower to get the needed boost but the faster you run it the more heat it builds. From what I gather, it's preferable to underdrive your blower.
 

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Discussion Starter · #3 ·
Thanks for the reply. I was hoping to get by with a single 1250 Dominator on a 250 and get a decent boost but it doesn't sound like it. I don't see much info on the 250/256 blowers, I guess that should tell me something!!
 

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First thing to consider in thinking about building a blower motor is how much power do you want to make, and what RPM range you want to make that power.

The small blowers were developed primarily for the smaller street motor that never saw a lot of RPM. High RPM requires far more air than these small blowers can pump without over reving the blower creating more intake air heating.

If you are looking at a street motor simply to impress yourself from idle to 4000 then go for it. You will be pleasantly surprised at the increase over a NA motor.

If looking to turn up the RPM there is no replacement for displacement. And this also applies to blower sizing.

An 80 inch Magnuson on an 80 inch Shovelhead at only 8% over will make a very substantial difference throughout the RPM range without excessively heating the intake air. Vibration on a Harley is an issue with boosted motors. 30+ years the rotors are shot, lobe castings loose on their shafts, needing replacement. But it has been one Hell of a lot of fun while it lasted.
 

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test was done years ago on a bbc, they put a 177 blower on the bbc with 3 lbs of boost the engine was around 660 hp, they brought the boost up to 5 psi and cracked 700 hp but it was about the limit of the 177 blower because of the blower speed and heat was starting to kill the hp with back to back pulls. blower speed was around 12,000 rpms

then they bolted on a 8-71 with 4.8 lbs of boost and made just over 700 hp with ease but the low speed torque was down around 25 ft lbs. once they boosted the bbc with 6.4 lbs of boost with the 8-71 then the power was better everywhere over the 177 and they made around 750 hp. 17% under driven with 6.4 lbs of boost.

the bbc was base lined at around 550 hp before testing the blower.

I would think the 250 would fall in the middle of these two somewhere.

I have a bbc with a 6-71 on it I built from scratch off a firetruck and with about 3 lbs of boost it took my bbc from 116 mph trap speeds to 121 mph and I don't even have it turned up, pretty much set on the lowest amount of boost because I'm running 10.2 to 1 compression and have my total timming pulled down to 28 degrees to save the bottom end.

I built the blower just to see if I could do it and didn't change nothing in my engine, figured I would build the blower make it work and if all was well then I could pull the engine out and lower the compression and turn up the blower for more power. Thats been four years ago....lol, so maybe here soon I will pull the motor and make the long block right for boost, I run 91 octane and have not had no issues of anything.

Before the blower my car would break the tires just barely loose at a 45 mph roll in 3rd gear (automatic with no kick down assist), now with the blower even on the low setting of about 3 lbs of boost it will do it at 55 mph with ease and I have two tiny 600 cfm carbs on my blower to boot ,which is choking the combo, so like I said I have done nothing to unleash the power, just built it to see if I could and haven't touched it in 4 years, I just get in it and drive it and it gets real sideways under 45 mph when you step on it and still can kick the azz end out at 55 mph but not like the lower speeds which gets out of shape in a hurry.


hope this helps
 
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