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Actual performance specs vs advertised performance specs
https://www.smwebhead.com/phpBB3/viewtopic.php?f=2&t=11936		 Page 1 of 2
Author:  jayjay4735 [ Mon Jul 08, 2013 5:59 pm ]
Post subject:  Actual performance specs vs advertised performance specs
I'm just curious how you guys do with your boats performance wise, in relation to what the advertised performance specs are for your boat.

I realize that those advertised specs are under totally optimal circumstances so I'm just curious how close everyone gets to those specs in normal use.

According to FW my boat should run at 39 mph at 4500 rpms and 41 mph at wide open throttle. In actuality the highest I get out of it if I run wide open (which I never do for long periods of time) is 30 mph at 4000 rpms. Engine is a 5.7 GSi DP.
Author:  230 Mike [ Mon Jul 08, 2013 6:27 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
Mine hits the advertised specs exactly. However, boats tend to drop off of those numbers as they age, for lots of reasons. Worn plugs, aging fuel pumps, dirty injectors, damaged props, added weight from the accumulation of toys & accessories, etc., etc.
Author:  jayjay4735 [ Mon Jul 08, 2013 7:42 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
Yeah I kind of figured that the age of the engine had a lot to do with it, but was just curious if everyone else saw similar results. Just had it tuned up before this season, and just had the props re conditioned as well. I'm also imagining that 14 years of bottom painting it has added quite a bit of weight. It still is good enough performance for me .. I don't mind cruising in the mid 20s.
Author:  ric [ Mon Jul 08, 2013 8:57 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
Age of the engine regardless of hours is the biggest factor in loss of power/speed.

Boats are tested empty with gas fumes, an 80lb driver at sea level during a high pressure system with air temps in the 50s. Load your vessel up with 6 people, full tank of gas, beer, etc and your speed will be substantially less.
Author:  230 Mike [ Mon Jul 08, 2013 9:30 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
It all depends. With full tanks, two anchors, tubes, 4-5 people (one of whom is substantially heavier than 80 lbs), I hit the specs and quickly regardless of weather conditions. When my boat is 20+ years old that won't be the case, I'm sure.
Author:  schoolsOut [ Mon Jul 08, 2013 9:46 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
I am pretty much on spec too with my family of 4 and all of our gear. It is very rare that I run at WOT though. Just feels like a bad idea when I am doing it.
Author:  ric [ Mon Jul 08, 2013 10:00 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
I don't cruise above 3200 or ever go above 3500. It's not a speed boat.
Author:  deafwish [ Tue Jul 09, 2013 3:36 am ]
Post subject:  Re: Actual performance specs vs advertised performance specs
We're not all driving steam powered locomotives! :lol:
As long as your tune is safe (fuel/ timing), you're running the correct octane fuel and propped correctly, you're safe as houses to run in the higher useable RPM range.
Most Chev/ Ford based marine engines run a flat tappet cam, which will wear out over time - giving less lift & duration.

There's nothing more rewarding than being trimmed to the hilt, flying over on glass water! 8)

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Author:  Walt [ Tue Jul 09, 2013 5:14 am ]
Post subject:  Re: Actual performance specs vs advertised performance specs
I try to run 5000-5200 RPM at least once per outing. Too bad the wind noise drowns out the exhaust at that speed. After putting on the K&N, I can't quite run WOT without over revving, but like the added hole-shot when loaded.
Author:  ric [ Tue Jul 09, 2013 9:41 am ]
Post subject:  Re: Actual performance specs vs advertised performance specs
Growing up with SBCs going higher than 3500 constantly wears the crap out of the valve stem seals and bearings. They're not high rpm engines. The new 6.0l 380hp Volvo? Ride all day at 5000.
Author:  jayjay4735 [ Tue Jul 09, 2013 10:52 am ]
Post subject:  Re: Actual performance specs vs advertised performance specs
I'll only run it wide open for a few minutes every time I take it out .. its definitely not a speed boat but it is a nice feeling when you have some room and can really feel the wind on you. I generally cruise around 3500 .. but I'm really not going fast at that rpms ... I'm not exactly sure, I'll check next time I go out .. but I'm pretty sure at anything less than 3200 I'm not going to stay on plane.
Author:  deafwish [ Tue Jul 09, 2013 4:45 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
ric wrote:
Growing up with SBCs going higher than 3500 constantly wears the crap out of the valve stem seals and bearings.


Have you ever torn one down, inspected what actually wore & rebuilt it?
4500RPM (+/- 200RPM) is certainly not high RPM for these engines.
Dependant on hours, valve springs should be upgraded if you're swapping out cam's etc, due to float.
SBC's are a very resilient engine.
Author:  LouC [ Tue Jul 09, 2013 9:10 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
jayjay4735 wrote:
Yeah I kind of figured that the age of the engine had a lot to do with it, but was just curious if everyone else saw similar results. Just had it tuned up before this season, and just had the props re conditioned as well. I'm also imagining that 14 years of bottom painting it has added quite a bit of weight. It still is good enough performance for me .. I don't mind cruising in the mid 20s.

For sure 14 years of bottom paint will add weight and slow it down. Mine has at least 10 seasons worth and I'm sure it's slower than it would be otherwise.
Author:  Walt [ Tue Jul 09, 2013 9:12 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
deafwish wrote:
ric wrote:
Growing up with SBCs going higher than 3500 constantly wears the crap out of the valve stem seals and bearings.


Have you ever torn one down, inspected what actually wore & rebuilt it?
4500RPM (+/- 200RPM) is certainly not high RPM for these engines.
Dependant on hours, valve springs should be upgraded if you're swapping out cam's etc, due to float.
SBC's are a very resilient engine.


Yup. I've torn down 302's from '69 to '92 (3 Mustangs and a Bronco). I assume a 377 has a comparable valve train, and agreed on the springs when freshening the upper end. I tend to take Ric's statements with more than just a grain of salt.
Author:  Decision [ Wed Jul 10, 2013 10:15 pm ]
Post subject:  Re: Actual performance specs vs advertised performance specs
Our 2001 328 Four Winns Vista will achieve the Four Winns posted WOT speed and RPM for my twin 5.7 litre GSI engines.

Personally I feel it is benificial to give your boat a short WOT run in reasonable weather/wave conditions at least once a season to compare your achieved speed and engine rpm's with your boat's expected values.

You just may to able to dectect a problem that is starting before it gets worse or fails at a crappy time. Like with guests or bad weather.

On engine age - On my previous 1988 Doral Prestancia (30' twin 5.7's with OMC drives) I would give her a brief WOT run a couple of times a year and record my findings in our maintenace log book. I owned this boat for about 7 years but I can say I achieved my best speed the year before I sold this boat to purchase our 328 and I got a GPS 46 MPH and those engines at that time had about 1000 hours on each engine. I thought that was pretty good with geting my best speed ever at about the 1000 hour age.

Mike.
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