Thoughts on Mercruiser 4.5 and 6.2

andrewterri

Chief Petty Officer
Joined
Jun 25, 2014
Messages
437
achris,it is okay to underprop slightly as long as you don't let you rpm bounce at redline correct? I think I am where I need to be but a little hard to tell because of all of the growth on the hull. After a good acid wash it feels like a speed boat now. :laugh:
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
I do the same, I have a 15.5x15 on my 4.3 Cobra.
PS I think Subaru did make an inline 4 cyl on some of mini trucks they sold like the Sambar. A cool little trucklet available with 4x4. The engine was horizontally mounted under the truck bed and accessed via an access hatch in the bed. Very clever. Saw one for sale in upstate NY this summer with 4x4 and right hand drive.

The Corvair was one of those cars that really could have been great if:
GM released it in 1960 with the double jointed rear axle design that they finally upgraded to in '65
They perfected the 90* turn design for the cooling fan belt
They designed better seals to prevent CO leaks in the heater system.

these were the issues with the Corvair, it was better in some ways than many competing cars but got bad press from Nader, because of the use of swing axles. But VW, Porsche, M/B, Triumph and others used swing axles at various points as well. By the time it was redesigned in '65 it had the most advanced suspension design of any US built car except the Corvette.
 
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aimlow

Petty Officer 2nd Class
Joined
Nov 7, 2018
Messages
180
I

these were the issues with the Corvair, it was better in some ways than many competing cars but got bad press from Nader, because of the use of swing axles. But VW, Porsche, M/B, Triumph and others used swing axles at various points as well. By the time it was redesigned in '65 it had the most advanced suspension design of any US built car except the Corvette.

Ralph Nader was/is an idiot. "Swing axle" rear suspension had been used for decades by VW and others. The biggest issue was incorrect tire pressure.

Props? Ideally a prop is sized to deliver full rpm under full load and maximum "drag". Under light load conditions you may very well be under propped.

I just went on a sea trial..34' diesel. 1/2 dozen people aboard. The concern was..it wouldn't turn up the last 100 rpms on a 3400 rpm motor. Cut me some slack.
 

bman440440

Petty Officer 1st Class
Joined
Apr 4, 2011
Messages
266
IMO its OK to be slightly under propped... and definitely better than over propped... In my 20' maxum I run a 21" 4 blade on my 4.3... most of the time I use it to fish and pull tubes and skiers... when fishing I have 47 gallons of fuel, 35 gal bait tank, 3 big guys (225-300 pounds each) , 100 lbs of ice in a kill bag and all our food/drinks and fishing gear... and for water sports most of the time when I'm pulling a 3 person tube I have 4-6 people onboard (and 3 on the tube) and I never have any problems getting on plane or hitting 4700 RPM when loaded like that... now I have taken out and cruised the bay with my girl and my dog and around 3/4 tank of fuel and I have to be careful with the throttle because it will hit 5000+ in a hurry!
 

muc

"Retired" Association of Marine Technicians...
Joined
Jul 7, 2004
Messages
2,064
Even the 4.5 uses mostly stock Chevy parts.

This statement goes against what they told us in MerCruiser school. Can you tell us what parts your talking about?
 

muc

"Retired" Association of Marine Technicians...
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Jul 7, 2004
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2,064
6.2 is still a SBC....

The block and heads look different from the small block chevy. The valve cover gasket has a different shape to it. I haven't had one apart yet, but the crank, bearings, rods, pistons and valve train all have new part numbers that don't cross to the old 6.2
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
This new 6.2l doesn't seem to be related to the GM based 6.2l at all.

"...this engine is an all-new design created expressly for marine use, executed in-house by Mercury, and exclusive to the company. In this regard, the new 6.2L MPI follows the path blazed by the MerCruiser 4.5L MPI, a 200 or 250-horsepower V6 introduced last year. In fact, according to David Foulkes, vice president of Mercury product development, the 4.5L and 6.2L share about 65 percent common parts."
 

muc

"Retired" Association of Marine Technicians...
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Jul 7, 2004
Messages
2,064
Are these engines proven to be reliable? Any experience's? Pro's and Con's? I know they will be more to work on since mercruiser is building everything. Leaning towards 6.2 with 300hp.

Don't think anybody can say proven yet, they just haven't been out long enough.
So far we haven't seen any "pattern problems" and they seem to be good powerful engines.
Comparing HP to HP between Volvo and MerCruiser. The Volvo seems to have a much better mid range punch and maybe slightly better fuel economy. The MerCruiser seems to be quieter. I think facing the flame arrestor aft is a good idea. It's hard to tell because I haven't had the chance to run the different engines in the same hull.

My advice to people who ask which is better? Go with the one that has the best dealer support near you.

Unless you want a dual purpose boat (runabout/wake boat) then go with the Volvo forward drive!!!! That thing works so good when paired with a hull designed for the forward drive. They work as good as a wake boat but will ride like a runabout when you want.
 

andrewterri

Chief Petty Officer
Joined
Jun 25, 2014
Messages
437
thank you guys for all the good info. Muc, that forward drive would be nice and we thought about it but it is a 13,000 dollar option for the 300hp forward drive compared to 4,500 for the 6.2 300hp mercruiser. Is a revolutionary drive but they need to make sure they are not pricing themselves out.
 

jkatzman

Recruit
Joined
Jun 25, 2018
Messages
5
Andrew,
We recently purchased a 2018 Four Winns H230 w/ 6.2 Merc and Bravo III. It was a late season purchase from a Four Winns demo day that had 16hours, way too good of deal to pass up, stole the thing. Anyhow, the 6.2 now has 37hours on it, I cannot say enough good things about the motor. It's very quiet (at least compared to my old 3L Volvo), even at WOT you can talk to the people without screaming. As far as power, well, it'll throw a person down even when going 30mph then goosing it, very powerful, at least in the H230. It has no problems moving with 11 people on board and planing in less than 4 seconds, maybe even 3, just haven't timed it yet. Skiing, wakeboarding, towing is not an issue. Cruising is at 26-27MPH and is so smooth, you hardly notice the thing running, Bravo III also helps with that.

There has been one recall on mine which will be fixed before it comes out of storage in spring, the power steering pump pulley had an issue when it has been know to create undo friction and could cause a fire. If you have the solid pulley (the one without the holes), then it's under recall. For the reliability as others have mentioned, it's just too soon, but it does seem to be a very smooth, well built motor.

Take care,
John
 
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