Jeffrey

Seems that the consensus favors a Whipple charger in this application. I am sure it is an excellent system, however, I have always liked the looks of a polished roots blower. May not be as efficient, etc. - but it sure looks great!

Here is my question. If I purchase a set of 8-71 roots-style blowers with twin 850cfm carbs - what modifications (if any) do I need to make prior to putting the blower on. The seller mentioned that I would likely have to re-jet the carbs as they came off a 509ci motor. He also mentioned something about changing the power valves.

Aside from these two things are there any other recommendations? Also, any opinions on the level of boost that is safe to run without intercoolers. Finally, what is the expected horsepwoer with 4-5 pounds of boost.

Any other comments would be appreciated as well. Thanks.

Jeffrey

obnoxus

One thing I would also do is change the head gasket to the " ring style " to prevent from popping a geasket in between the cyls.

SteveDavid

Jeffrey,

Depending on the hours on your existing engine, you should consider changing:

@The head gaskets
@Valve springs

Prior to adding the blowers, check for compression and do a leakdown. If either are not within 10% of where they should be, (minimum 150 lbs per cylinder and less than 8% respectively) then consider a rebuild, with new rings, and a valve job.

HP gains are app 25-30 HP per 1 lb of boost, assuming no other changes.

Anything over 5 lbs and you should strongly consider an intercooler. If you're going to be running 4-5 pounds it would not (the intercooler) be a necessity.

Needless to say if you're adding blowers your outdrive's are going to be stressed. If you are not currently running a B Max, IMCO SC or newer Merc sportsmaster and XR or equivalent top, you're going to blow outdrives soon. It's not if, it's when.....

Good luck Jeffrey!

Steve

Jeffrey

Thanks guys for the recommendations. I am currently running standard Bravo One outdrives. The one thing in my favor is that my boat is one of the four carbon fiber Cigarette Top Gun F-2 boats built in 2000. It weighs in at 7800 pounds.

Three things contribute to outdrive failure: big horsepower, a heavy boat,and bad throttling. I believe that if I am relatively careful and the horsepower increases to around 600hp with a relatively lightweight boat ... I should be okay. I had a Cafe Racer back in 1995 with 625SC motors and that boat weighed in at 10,500 pounds. Never blew a drive. I am planning an engine rebuild at the end of this season. For the time being I figured I would simply slap these on and run them. Keep your fingers crossed for me! Thanks again!

mltdwn12

I'll agree with SteveDavid and add a couple of things. One of the most important things with a blower motor is not to lean it out This is mind, ensure you have adequate fuel pressure at full throttle. You want at least 5 pounds on the top end. A lean motor runs hot and starts eating up little parts...like pistons Good fuel pump, 1/2" lines (at least) fuel pressure gauge(s). I think the HP's already have "Severe Duty" intakes and Inconel exhaust. Also upgrade your ignition to an MSD. Finally it's a hassle if you can't yank the motor yourself, but the $500 they charge to dial a motor in on a dyno can reap benefits for seasons to come. You know when you hit the key at the lake for the first time, it's right!

Craig

puder

JEFFERY DON'T DO IT!!!!!!!!!!!!!!!!

just "slapping them on" never turns out to be as simple as it sounds.

The ONLY way to just slap them on is if your engine biulder can GAURANTEE when they will be finished and ready to run by. Otherwise do you really want to run the risk of turning a perfectly good (running) boat into a trailer queen?

FYI i tried that last season, i hope to have her running in the next few weeks its been about 10 months and a new drive and engine since it ran.....

dean campbell

puder,
what happened to your other engine???

Sean

Jeffrey,

Are you panning on running intercoolers? There's an incredible amount of heat generated by cramming all that fuel into the intake and most people recommend intercoolers...it will increase the longevity of your motors.

Sean

puder

well after some issues installing the blower, finding that my exhaust manifolds were leaking and getting heads cleaned up and valve job and changing head gaskets i developed low oil PSI.

I never even got the chance to tune it properly to see any mor eMPH. I pulled the ebngine and realized it needs soem love adn rather than spend this summer rebiuldign i decieded it was probably easier and cheaper to buy a new engine and rebiuld my old one over the next few months on rainy days when i can't go boating

Whipple Charged

Jeffrey,

We polish ours too! Have you talked with Paul P yet? In a big boat like yours, 8.75:1 compression, I would not recommend running non intercooled. You'll be able to maintain a higher manifold pressure for longer periods because of the boat size vs. load and therefore will create a tremendous amount of heat with the 871. With the screw and centrifugal, you can get away with 4-5lbs. max without an intercooled on that engine. As for prepping the engine for SC's, it depends what hours you have. If you have over 200 hours, I would recommend replacing the head gaskets and freshing the top end.

The main objective is having somebody tune it that has the proper ability to jet the carb. If you stick with our standard system, it's already done, go to our stage 2 system or roots setups, you will need to have it properly jetted and either dyno or lake tested with proper instrumentation.

Contrary to what some say, you can get many hours out of supercharged stock engines, water and fuel are the most important. If you want more power, by far the best way is to install Dart Pro One aluminum heads with the SC of either choice. These flow far more air, have a much larger tolerance for detonation and can take either leaner air fuel ratios, more boost or more timing with very little if any down sides.

Thanks,
Dustin