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Who owns boats with 900SC's

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Old 09-14-2002, 07:28 PM
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PhantomChaos: They are busy getting them serviced.



LOL!
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Old 09-14-2002, 08:24 PM
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JJ - at 4200RPM it makes about 2, or 3 lbs of boost. Boost doesn't really come on strong til after 5,000RPM.
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Old 09-14-2002, 10:30 PM
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Heres a nice shot of KWB's Tiger....Thing is F*CKIN Bad ASSSSSSS!!! And runs like a bat out of hell!
Of course I couldn't hear for like 3 hours after coming back from Catalina....Those big ass blowers whine a bit

PIC:

http://www.scopeinfo.com/images/Kenny-BIG.jpg
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Old 09-14-2002, 11:19 PM
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Great looking Tiger! Anyone happen to know what cylinder head, valves, springs and rockers Merc uses in the 900SC?
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Old 09-15-2002, 12:31 AM
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I wish me.....in a 27 Fever! Lots of fun....... I can see it now....but hunny.
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Old 09-15-2002, 05:48 PM
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JJ-

At 4200 the boat runs about 72 - 75mph (depending on conditions) - that's turning 5 blades 17.5x29
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Old 09-15-2002, 05:55 PM
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Default JJ - From Dennis in the Tech forum

Valve rebuild
I never got around to asking what the Mercruiser High Performance Division had in mind when they suggested a complete valvetrain rebuild after 50 hours! Even when I worked for Hallett Boats (almost 9 years) we didn't see many 900 SC engines. On the few 900 SC engines that we serviced I suggested that we rebuild the valvetrains on the engines and everyone looked at me like I was nuts! (what did I know, I was only the mechanic!) Even very knowledgable boaters can't believe that this type of service work is required after only 50 hours of running time. If it ever would have come down to rebuilding the 900 SC valvetrain I would have inspected everything and only replaced parts that looked worn out (or ground the valves if they needed it).

I would say that to make 900 horsepower that the camshaft has some really fast opening and closing flanks that require high spring pressures to keep the lifter following the lobe. The stiff springs puts extreme pressure on the lifters/lobes at idle (when the engine is running at high speeds the upward inertia of the lifter counteracts the downward pressure of the spring relieving some pressure on the lifter roller but at low speeds you have less upward inertia of the lifter, this creates excessive downward pressure on the lifter/lobe from the stiff valve springs). This would make camshaft and lifter INSPECTION (not necessarily replacement) very critical. You should find out as much as you can about these parts and learn the signs of failure.

Closing the valves very quickly with a combination of steep closing flanks on the lobes and stiff valve springs would be very hard on the valve seats. Owning a 900 SC for any length of time would mean investing in a good valve spring compressor, periodically remove the heads and inspecting the valves and seats for damage (learn as much as you can about valves and seats). It might be economical in the long run if you also invested in a valve spring tester. These two tools could save you some money by fortelling future engine failures (knowing when to replace the parts) and give you confidence and peace of mind in your engine while you are out boating.

No one (but the boat salesman) said that owning a 900 SC would be easy.

Sincerely
Dennis Moore
Mercruiser Master Tech


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Old 09-15-2002, 09:05 PM
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Dennis,

I was suprised to see your name at the bottom of you post since I just finished your book "Big-Block Chevy Marine Performance". I am doing some research before having my next motor built. I currently have an aspirated 502 with many of the suggested modifications using a Gen 5 block. I am looking to build a blower motor either a 540 or a 572 using a Merlin II. Have you published anything on building blower motors? I have heard quite a few different opinions on longevity of a 4.375 stroked motor vs. 4.25 stroked motor. I agree with you in that there's no such thing as "too much power" and I would rather spend a few more dollars building the 572, but not at the expense of longevity. In your experience, can a 572 hold up as well as a 540. There are quite a few 540 blower motors that have well over 300 hrs between freshening where I boat, but only lately have people been going to 572s that I know personally. Then again, everyone with the 540s that I talk to wish they had gone bigger when initially building. Thanks for your input, and great to see you are on OSO.
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Old 09-15-2002, 09:10 PM
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DUH -

KWB... I just saw that you posted this from the tech section. You got me
I will go post this question to Dennis there.
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