I have 2 in depth posts about roots blowers you may find informative.
The post entitled "engine builders check in Supercharging 454".

Unless you plan on putting around 15# of boost in, an 8-71 is way too big. You'll spend more hp just turning it then you'll be getting back.
Just to give you an idea; an 8-71 will put 10# of boost in a 350 at 20% underdrive. On a 400, 10#=10% underdrive.

Just as a comparison; a 177 Wieand (for example) is able to put UP TO 16# of boost in a 350.

A 6-71 is able to boost a 350 to 7# at 10% under drive and a 400 to 7# at a 1:1 drive.

Just giving you some food for thought.

One thing you can trust me on is an 8-71 is too big for a marine SBC unless you're in competition.

DAVE

Fishead,
I am running a littlefield 6-71 on a SBC. Been a long road getting it dialed in but I think I have finally got it. If I had it to do over again I would have built a BBC. But I am finnaly happy with what I have (for now ) What are your spacific questions? Drop me an E-mail and I will send you some pics. -------------- T

The 350's that I have are all forged 4 bolt mains,and Aluminum heads.The only thing that I would have to change is the pistons and the cam,so I think this is the way I am going to go.What kind of number could I expect (HP and TQ) with a blown SBC running about 5lbs of boost.

gary,
I am running Twin Disc 502's

fishead


Get in touch with Marv Hineman at The Blower Shop (661) 299-5483 www.theblowershop.com he'll be able to point you in the right direction.


Doug

fish,
If you need help feel free to email or pm.
DAVE

fishead
I'm lookig at setting up a cat with the Twin Disc trannys and swapping out the blown Kaama drives for a couple inline ASD 6s that I can get cheap. Do you have a manual or any practical info on the trannys?
How reliable are they?
Gary

I've never been much of a fan of AL heads on boats. Blow an impeller and you've warped it. But with the good internals,around 8:1 CR, the AL heads, and a good cam I would think you could easily push 5-7lbs of boost with a 177 blower on 92 octane.
You might want to contact one of the Blower specialists (back of Powerboat mag) for everything. They could probably give you exact hp numbers. My guess would be a little over 400hp.
BTW, dont forget a new ignition that will run 10 degrees initial and around 28 total.
Gary

I think I would try and duplicate what Hotrod magazine did as far as parts, and build a similar basket of parts. Seven pounds of boost and 600 ft/lbs. of torque with the weight advantage of a small block would make that an impressive combination. I have run aluminum heads on marine applications for better than 10 years and never had a problem. Mercruiser certainly seems comfortable with it. I think secondly the modern designs for better airflow in heads are done in aluminum so they get better return on RandD costs.

Fish, my buddy has a pair in his garage. He doesn't use them since his new boat has BIGGER power. I don't remember the details, he ran them in a 32 Skater. I think they were built by Troy Dennis. Let me know if you are interested.

Shawn