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Question on what speed to expect from 375 hp 496 mag in 262 Monterey cruiser
I'm thinking of buying a 2001 Monterey 262 cruiser. It has the 375 hp
496 mag in it. Dry weight is listed at 5,500 lbs. Specs say it should
go about 50 mph top speed, but I'm assuming that's under ideal
circumstances and at sea level. Test drove the boat at 4500 feet of
elevation and top speed was 38 and it held 30 mph at 3700 rpm. Does
that sound about right or might something be wrong? Would greatly
appreciate if anyone with relevant experience could help.Thanks! |
LakePowell
Apr 30
2006
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| What was the engine's RPM at wide open throttle (WOT)? The engine should
turn about 4600 rpm at WOT give or take a couple hundred RPM. I'll assume
you intend on running the boat at Lake Powell, based on your ID. If so,
you'll gain some performance , since Lake Powell's elevation is at 3591
feet. This assumes that your test elevation was indeed at 4500 feet. The only way to set up the boat properly is to take it out at the elevation
you intend to run at, load the boat as you would normally use it, and then
run it at WOT for a brief period and monitor the tach. Mercruiser specs a
WOT RPM for that engine of 4400-4800 RPM. If you're turning less than that
range, you are over propped and working the engine harder than you should.
Since the engine is fuel injected, there are no adjustments to the engine
that are necessary or possible. The only way to bring the engine into its
recommended operating range is to change the pitch of the propeller(s). If
you need to increase WOT engine RPM, you need to step down in propeller
pitch. I'm guessing you probably have a Bravo III behind that 496 mag. If
so, prepare to spend mucho dinero for a new prop set. Been there. |
RG
Apr 30
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| The rev limiter cuts in at ~4800 on that motor. It appears that you are
way over pitch on the props as set up now... 4600 would be a good WOT
max, and at about 44-45 mph for 4000 feet. Other factors to consider
too before jumping to a new prop set - did you use the trim for optimum
performance, does the boat have trim tabs, and were they used properly? Rob |
trainfan1
Apr 30
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| RPM at WOT did eventually get up to 4500, but it took quite a while to
get there, and the boat seemed slow out of the hole. No gear on the
boat, but we did have about 1,000 pounds worth of people. Test
elevation was slightly over 4500 feet, though most of my family's
boating will be at Lake Powell. Bravo III outdrive, so two stainless
props. So, while the WOT RPM is in the range you mention, it was sluggish
getting there. Prop pitch, if I remember right, was 26. If you don't mind, a couple more questions... 1) Would it help to go
down a notch in pitch or will it over-rev? 2) The props are in
excellent shape...any idea of whether you can trade props in for a
reasonable fee? 3) Does the Bravo III require stainless props or can
you go aluminum to save some $? Thanks for the info--very helpful! LP |
LakePowell
Apr 30
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| Rob, it does have trim tabs...tried with the boat trimmed and with tabs
flat. Didn't make a big difference. Actually got it to 39 or 40 mph
once, but it started bouncing so I had to trim it back down. Bravo III
outdrive, so two stainless props. RPM at WOT did eventually get up to
4500, but it took forever to get there, and the boat seemed slow out of
the hole. What do you think about go down a notch in pitch given that
additional info? Does it sound like that would help? As I mentioned
to RG, we did have about 1,000 lbs. worth of people on the boat, but I
was still expecting better performance even at 4500 feet elevation.
Thanks for the info--very helpful! LP |
LakePowell
Apr 30
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| I believe that what you are witnessing is simply a boat that is slightly |
RG
May 1
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| Thanks for all the great info. Yikes. Will definitely have to be
careful of those props down at Powell if they cost that kind of money.
It would be an expensive mistake to ding them up on some rocks,
especially if dinged beyond repair. Your questions: 1. Is there any reason to believe that the engine was not performing
to
it's potential? I don't think so... It sounded smooth. I had the compression checked,
and all 8 cylinders were between 145 and 155, so really quite good.
Shifting was unbelievably smooth and no odd noises from the
transmission that I could tell. That's one of the reasons I was
wondering if the boat should have performed better...wondering if it is
a possible sign of engine problems, though there are no other
indications. 2. Possibility of stale gas? That's definitely possible--hadn't thought of that. It had just over
1/2 a tank, which was probably in there from last summer or fall. It
was professionally winterized, so I would think they would have added a
stabilizer, but stale gas is a definite possibility. That engine calls
for minimum 89 octane if I understand right. Not required, but would
premium make a difference? 3. Was the boat's bottom clean? Bottom was clean. I found out for myself the impact this can have.
Had a 21' Rinker open bow with a 350 mag engine in it a couple years
ago. Hit 57 mph at Powell and still had some throttle left. Then the
bottom got grimed up from sitting in a slip at a different lake. Took
it back to Powell without cleaning it, and top speed was 35 mph!
Couldn't believe that was all due to the dirty bottom, but it was back
at peak performance after a good acid bath. Amazing. 4. What lake were you on when did you do the 4500 ft. test? Utah Lake. Minimal winds, water pretty smooth. Elevation 4559. Thanks again for all the good info. Do you have any opinion of
Monterey or the 262? LP |
LakePowell
Apr 30
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| Modern gasoline blends are inherently unstable. They start to lose their |
RG
May 1
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| Again, thank you for all the great info! |
LakePowell
Apr 30
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| It's nice to have a relationship with a marina &/or a prop shop who will
let you test/borrow a prop set now & then... figure $1k for a stainless
Volvo prop set, the B3 sets should be similar or less. I would try before buying on the props, & at your home water. Rob |
trainfan1
Apr 30
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