B&M 250 Supercharger HP guess
 

Hi Everyone i am not a boat owner yet but i do have a 454BBC with a BM250 supercharger ....oval port iron heads , cam of unknown spec but rumps a little timing 21 degrees locked , Hooker pro comp 2 inch primary headers running 8.5-9 psi with E 85 Fuel ......in a 83 GMC pickup truck it runs great with one quick fuel 1050 carb jetted up ....SO Anyone want to take a HP at the crank ...experience.... guess , i know a lot of guys are running this Blower on here ..

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I will answerbyour question with a question- have you run the truck on the drag strip? If yes, then E.T., trap speed, and final drive ratio should get you a pretty close guess.

Blind folded guesstimate would be 450-550hp.

Rick

Rick its got 39 inch tires on it and a 9 inch lift and we have no strip where i am so strip testing is prob not going to happen , with 5.13s it spins hard .....ill prob dyno it one day i was told a 30% loss with the driveline it has tire weight 400 etc ......the butt Dyno feels good though

im going to say not much with 21 deg total timing,thats way to low.you did not say what the compression ratio is,so im going to assume its 9 to 1 or less.you should be locked at 34 deg,also,no cam specs,but il guess it should make 550,maybe 575,if you get that timing where it needs to be.i guarentee you,it will wake that motor up.do the headers get cherry red near the exhaust ports,the egt,s have to be sky high with 21 total timing.

Mike i was just looking at the timing spec by Weiand they are saying 28-34 , so you think i can lock it at 34 w/o start up or general driveablity issues.... i set it at 21 thinking less timing would prevent problems ( im still trying to escape my Buick Granad national tunning ideas where 34 degress would be really bad 26 deg was a race set timming )....the dist does not have mechanical advance and the vacume is not hooked up or working when hooked up , i think it may have been out of EFI car that had computer controled ignition possibly why the mechanical advance is not there . The Comp ratio is unkown the this was a low budget neanderthal racing project the long block was never taken down and as is when i got the truck , i added the blower and fuel etc to it . Ive never noticed the headers red ive been driving it like that since last May ......im going to bump it and try it . i appreciate the advice that anyone has to offer . This is my First BBC and Roots blower project

http://youtu.be/MRfEBauB04Q
video of motor running

Mike the only a reason the headers may not be getting red is the E85 Fuel .....the AF ratio is good on the meter im gonna bump it up and see

250 b&m
 

We made 785 hp @ 5800 with a 250 ( intercooled ) @ 5 psi ( 7psi before the chiller ) 489 with 731 crane hyd roller . 9 to 1 static compression .
Your total timing is way to low ... I would run no less than 30 degrees depending on fuel used . We run 93 and saw the egt's shoot up @ 28 degrees ... engs were much happier @ 30 total.
B&M had a 174 blower they advertised bolt on 100 hp @ 5 psi back in the day . As already stated ... run your truck and get a ET ... that will get you a ballpark HP .

e85 has a higher octane rating than 93 gas,all the more reason to add some timing.-

I always run 29-31 in an engine set up like that.

I had a 468 like that that did 700 with 8lbs of boost and an intercooler.

no reason for there not to be 550+- in that engine.

I agree, I would lower the boost to 5-6lbs and run the timing at least 28 degrees. This engine has cast internals correct? Was the timing set at 21 degrees to avoid punishing the pistons? Any pre ignition is almost instant death for cast pistons.

As stated, get that timing up before you melt the exhaust valves. Luckily its in a truck, if it were in a boat, it probably wouldnt have lasted very long.

The only thing i can see holding you back some is the cast iron oval ports, especially the truck heads with small ports and valves. Of course the cam plays a huge role.

Measure your pulleys, or figure out how fast your turning the blower to get that boost. You can tell alot on how effiecient a engine is based on that. I can tell you to get 6.5psi on my 454's, i had to drive the blower at 1.83:1. A buddy of mine had the blowers on his 509's originally. The pulley that made 5psi on his 509, also made 5psi on my 454. That tells me my 454 probably made as much power as his larger CI engine. Theoretically, his 5psi pulley, should have made at least 7psi on my engines, but not so.

To get 6.5-7psi, I had a 3.0" top pulley, with a 5.5" bottom pulley. 5psi was with a 3.25" top pulley I believe.

I had the 6" bottom from teague and the 3" top. 6000 rpms sounded like death under the hatch. Never heard one scream so loud. It was great.

Do you know what pistons are in the engine? and valves in the heads?

I dont know the internals im guessing nothing much the E85 lets you get away with more than gas i do know , i do know it has 2 bolt mains , what i did figure today is the dist is advancing the timing it is not locked its possible the advance was frozen up as i belive that happens if its been sittting for a while .... it was advancing to like 31 deg from the initial 21 i had set , it is not a performance dist so i may add one this spring with the proper curve , i did bump the timing to 25 inital and it advances up to around 35+ or - a degree and took a quick spin around the block definitely felt a difference ....... ive had good luck with the way it was running with the higher boost and the E85 where the timing was at i mean it felt like it was making some power as it gets up moving pretty fast for a big truck esp with the tire size .......im gonna have to dyno it just for fun and ill post what the results are ....i was figuring at least 500 crank HP i like to be more conservative with guestimates until you have a slip or a dyno sheet i was just curious what similar setups were seeing of course we all like to belive that the motor makes a bazillion HP and knocks the earth of its axis when its throttled but real world numbers often burst that balloon .. when i had my Buick GN it made 530 HP to the wheels and 710 lbs tq on a mustang chassis dyno , which i was told is often refered to as " The Heartbreaker " as it reads more real numbers than the dynojet one ...at 3000 lbs with driver it ran pretty good for a street car .....Thx Guys for the input