Dyers 6-71 on a 460

Looking at a boat in the near future that has a 460 with a Dyers 6-71 blower and what appear to be a pair of 600cfm 4150 carbs on it. Going to hear it run, what should I be looking for to gauge blower and motor health? These should be otherwise stock marine 460's

Zero experience with roots stuff so looking for basic what to look/listen for on startup and warmup. Boat has pretty full compliment of gauges including boost.

Figured I'd ask this seperately since the boat titled question went belly up after two responses.

Thanks!
Jim

Jim there is only a couple people around here with roots blowers but hang in there I am sure they will chime in sooner or later.

Jim: I don't have a blower motor yet, but it's my intention to build one in the near future, so I'm doing a lot of reading of the do's and don't's. Speaking with builder's, suppliers, and end users, the consensus seems to be that none of them recommend anything smaller than an 8-71 for an an engine larger than 350 cu. in. A 6-71 would create an overheated air charge inviting detonation, especially in a boat running at a steady revs. Hopefully, others will chime in with their opinions.

Wayne (SAWDOFF) Pearce

Often times boats run an air to water aftercooler. With a constant supply of cool water you wont have to worry about overheating the air charge.

As far as checking the blower without disassembly goes, Open the throttle blades and bar the motor over. Look inside for scoring on the rotors. This will at least tell you if there is mechanical damage. For any more about the blowers health you will need to pull the carbs or hat and get some long feeler gages.

About the 6-71 part. Take a look at BDS' blower charts. A 6-71 is perfectly fine in many applications. They get way too much bad publicity from people who have never had any experience with blowers. Don Garlits, Don Prudhome, and a host of others made the world of hotrodding what it is today with those "little 6-71 blowers on top of 200 mph nitro hemis. Sure an 8-71 will be more efficient than a 6-71 but with a higher initial investment also. If I was buying a new blower it would be an 8-71 but for non competition that 6-71 is great too.

If its a pleasure boat and not used for competition its probably fine. Hope it helps.

Count the teeth on the pulleys and figure out the drive ratio. That will tell you how fast the blower is spinning and how much boost it should be making. If it has a boost gauge you verify that its close. That'll be a good indicator of its health.

http://blowerdriveservice.com/techcharts.php

AK posted while I was writin' this up, so I got to cut mine in half.

Marine engines tend to make a good base for mild blower apps as they usually already have the low C/R forgers in 'em.

Ask what type of fuel they're running. Keep an eye out for signs of excessive blow-by.

If there's ANY way you can have 'em put it in the water, do it. It's harder to spot problems when they're not under
a load. Also, you won't really get a useful boost reading if you can't go throttle it up.

Note there are two 6/71's, the large and small bore. For reference, according to the BDS charts, a large bore @ 1:1 and
6000 rpm would push about 7 or 8 lbs on the 460. A small bore, it takes about 15 to 20% over to do the same.

The manifold and drive will both work with an 8/71 if you decide to step up later.

Like anything, look it over close, then give yourself time to think about it.

Good luck and let us know back what things look like -

Thanks all! Successful start/run visual inspection gets a refundable deposit. Successful water run gets the balance.. I'm not worried about upgrading, beyond a certain point, there isn't enough hull or prop to deal with more power in a pleasure boat. Anyone have any pics of normal rotor wear versus scoring?

Jim

Blowers, unless it has teflon stripped rotors should be non contact so it shouldnt have any wear unless it sucked in some sand. IMO

I hope it works out for you. Post up some pics if you get it.

Good luck

If you can see the rotors from the top, (As per AK's suggestion, and a good one it is) look at the strip here marked "xx". That's
the highest spot on the rotors. It should be smoothly milled, and there should be NO sign of contact or heavy scratching. If
anything's amiss, this is the first place it'll show up. Check as close to each end as you can.



You should be able to open the throttle, then open the secondaries on the carbs by hand (if they're vac), to see as much as you
can. It may have a screen between the carb plate and the blower, a lot of 'em do. It should be coarse enough to see through.

Not a GMC, but here's a damaged set - note the heavy scratching all the way along the ridge. This = bad.



A random light scratch or two on that edge is usually OK, you'll be able to use your own judgment there.

That is awesome info, thanks!!
Jim

JIm.

Where are you located?
What type of boat is it?
V-drive, Jet, IO?
I need to know your cooling supply, for the engine and if at all possible "CHILLER".

let me know!

adam

If purchased the boat will be in freshwater in SW PA, it's an I/O setup that has only seen freshwater. Originally OMC, converted to Volvo. Not sure of prop specs, not sure exactly which Volvo outdrive yet either. No aftercooler from the pics, engines cooled in typical I/O fashion.

Owner has a hookup to run motor out of the water so part one is to hear run, verify basic hull integrity, accessories, gauges, controls, then part two when the weather is better, a water test of drives and seals.

Only real I/O experience is with a 25' Carver, Volvo duoprop, single carbureted 350 Magnum. Got rid of it before bellows needed done, but did get pretty good at changing props at the dock after spinning the hub or flattening a blade. This boat is a bit older and I've never worked with roots blowers so I'm always open to suggestions/help..

An old boat with a 460 in it should be dirt cheap. The Volvo outdrive is another price killer. Not saying the combo is bad, just being realistic as far as resale value/ purchase price.

Chances are you'll be able to buy the boat so cheap you can afford to fix a few things.

Greg

Is there a better outdrive for use in place of the OMC stuff? I've heard nothing but bad about repairing the OMC drives, and Volvo is the typical replacement... Boat is market fair for age, condition, etc, but even at that, a big ticket break like a blower or outdrive is not in the budget and that means it sits until next season so I want to pick all the brains I can before any money exchanges hands. Luckily weather has made travel difficult leaving more time on the table to research.

Thx
Jim

Man a new blower would be a lot less than a new drive. Trust me on that one. Unless you are prepared to do some pretty serious structural work on the transom then you're kinda stuck with the drive that's on it now. A Bravo won't just bolt in place of a volvo drive.

Greg