I have a 1995 35 fountain with hp500s. I want to get around 600-650 reliable hp. I am thinking of buying a set of m1 prochargers, but have had a couple of people tell me that since my motors are carburated, I should go with B&M 250's. I'm going to freshen the motors this winter anyway, and will change cams and possibly pistons. Does anyone have experience with either of these setups?
Thanks

jryan:
I have run both, and don't recommend either for reasons I would rather not go into here. I don't like bashing products, even if it's warranted.
I would get a blower shop 250. They have addressed the problems with B&M 250.
You will prefer the low end torque, looks, and sound of the Roots blower. Only drawback is vertical clearance.
I would add intercoolers if it's in your budget. With intercoolers, you should get real close to 700HP with pump gas.
I've got a 575SC with intercooler, reprogrammed ECU, 7PSI boost, and it's making 750HP reliably on pump gas. I had the blower shop rebuild my blower, and I'm pleased with the work.
Regards,
Steve

go with the 250s i ran all summer with no problems w/ a single 850 carb. was going to add innercoolers but never did.

Get a set of Whipples. You'll easily make 650 hp with about only 4 lbs of boost. They come with intercoolers. Height may be an issue but it will be worth it. I had a carbed Whipple on my old rig and it ran perfect for 4 seasons and is still going strong with the current owner. A B&M blower is old technology. A roots type blower heats up the air/fuel mix and can make detonation occur sooner than a Whipple would.

Blower Shop 250s.

I should have bought your motors. Hindsight.

i say bm 250 over prochrger for a carb engine. whipples seem would be best if available and if $$ is no object. wetehr bm or whipple tehy both look cool on top of an engine.

jryan26:

Here's some interesting data. I had an M1 equipped 454 on the dyno at Nickerson's a few years ago. It made 575 HP, then we removed the 1" tall brass flame arrestor inside the carb box and made 650 HP. But without the flame arrestor smoothing out the 100+ mph air entering the carb box the pulls were not smooth, the fuel numbers were jumping around. Then we swapped the intercooler and carb box for an Rtech supercooler and made 740 HP. The blower pulley was not changed for any of these tests, neither was jetting or timing.

The same M1 setup was then put on a 502 in a 250 Baja. Procharger stuff went 77 mph; Rtech supercooler went 85 mph. On the 502, which had better heads and more cam, we figure that little M1 was putting out 800 HP! Blower discharge temps were high and blower efficiency calculated out to only 60%, but these "sins" were covered up by the big supercooler. The owner has been FLOGGING this boat for two summers now and cannot break the engine. The key is cool air, properly calibrated carb, and increased capacity in oiling, cooling and fuel supply. So far his XR drive is surviving.

With the Rtech supercooler and a larger, more efficient Vortech blower Nickerson has dynoed 1000 HP on pump gas. That's his personal 496 stroker boat engine.

You can buy the Rtech system and make 800 HP on your engines. Your drives will not be happy. I know the original question was how to make 650 HP but that's not going to keep you happy for long. Good luck.

Tom

I like to use the Blower Shops equal to the 250. Looks good, runs good and if you have any problems they will help you out. I have used and will continue to use them.

John S.

I have built the combo you want with the 250's and it's awsome for power and reliability but with TOMCATS set up you have to admitt will look like one of a kind and also it's reliability is hard to beat I'm currious as to how much is the difference between the two set ups would be in price apart from weather there is a power difference. SIncerely Laz Mesa
P.S. We are working on a prototype engine with the procharger set up we're trying to show it at the boat show in Feb.