Merc 898 WOT RPM range: 3,800 - 4,200 rpm. Why?

cecho

cecho

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I'm wondering why the 305 is limited to this range while the 350 of the same era is limited to 4400-4800 RPM. Is it the camshaft profile? Is the engine not capable of higher RPMs? Is it the outdrive? Will I leave the power range for the engine if I go above 4200 RPM?



Edit: P.S. I just realized I probably should have put this in non-repair discussions, but the "Mercruiser I/O & Inboard Engines & Outdrives" title gets me every time. oops.
 
Bondo

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Re: Merc 898 WOT RPM range: 3,800 - 4,200 rpm. Why?

Ayuh,... Usually it's the difference 'tween a 2bbl. carb, 'n a 4bbl. carb...
 
cecho

cecho

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Re: Merc 898 WOT RPM range: 3,800 - 4,200 rpm. Why?

Ahha, so it just has trouble breathin' then.
 
achris

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Re: Merc 898 WOT RPM range: 3,800 - 4,200 rpm. Why?

It's more than one single item that will determine at what revs an engine will make maximum power. Definitely things like camshaft specs, but also things like compression ratio, exhaust back pressure, intake manifold design, spark timing curve and of course fuel delivery.

Chris....
 
cecho

cecho

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Re: Merc 898 WOT RPM range: 3,800 - 4,200 rpm. Why?

I did some more research and found the Mercruiser 228 has a WOT range of 4400 - 4800. I honestly didn't even think about checking into that until Bond-o mentioned the carburetor. I guess that's where the extra 30 HP comes from in this particular case. The extra airflow the carb will allow. If I ever decide I need more power the first thing I'll do is replace the carb and intake. I seriously doubt I'll need more power though. 4 miles through an 8 mile lake goes by rather quickly at 45 MPH, and the torque shift prop I have should provide much more than adequate out-of-the-hole performance.
 
Bondo

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Re: Merc 898 WOT RPM range: 3,800 - 4,200 rpm. Why?

cecho said:
I did some more research and found the Mercruiser 228 has a WOT range of 4400 - 4800. I honestly didn't even think about checking into that until Bond-o mentioned the carburetor. I guess that's where the extra 30 HP comes from in this particular case. The extra airflow the carb will allow. If I ever decide I need more power the first thing I'll do is replace the carb and intake. I seriously doubt I'll need more power though. 4 miles through an 8 mile lake goes by rather quickly at 45 MPH, and the torque shift prop I have should provide much more than adequate out-of-the-hole performance.
Click to expand...

Ayuh,.... The 1st thing to do for More Power in yer case is to drop in a 350, insteada the 305.....

It's a Boat, 'n there's No replacement for Displacement....
 
achris

achris

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Re: Merc 898 WOT RPM range: 3,800 - 4,200 rpm. Why?

Friend of mine had a 305 (898) he wasn't too impressed with, so we pulled it out and dropped my old 4.3LX in... He picked up an extra 6 knots, and uses way less fuel in the process. Now he's a happy boater... :D :D

Chris......
 
cecho

cecho

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Re: Merc 898 WOT RPM range: 3,800 - 4,200 rpm. Why?

I don't see any reason to do a repower until the 305 starts to die. A 350 would certainly be replacing it if it does die though. No way I'm going to rebuild a 305 with all those 350s sitting around.


Doesn't the 4.3 have the same HP with less torque than the 305?
 
cecho

cecho

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Re: Merc 898 WOT RPM range: 3,800 - 4,200 rpm. Why?

Finally took her out. She ran great. GPS verified 44 MPH at 4500 RPM on a 17 pitch prop with plenty of hole shot. I look forward to getting the torque shift prop on shortly to get the top end down to the correct RPM range. :)

No need to drop a 350 in for quite a while I hope. The 305 has plenty of grunt for my purpose.
 
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