7.4 mpi vs 6.2 mpi

S

skiprinaldi

New Member
Aug 5, 2009
1
I am looking at two 340DA's. The older one has 7.4mpi v drives and the newer one has 6.2 mpi v drives. I would appreciate comments from those of you that have either ending and how you like the engines.

Thanks,

Skip
 
Skip while I have no experience with these engines in this particular model I will chime in and tell you that in my opinion when it come to gas powered big boats there is no substitute for cubic inches. Mercury came up with the 6.2 around 2000 when GM stopped producing the 7.4. They needed a motor to replace the 340 ish HP 7.4 that was smaller than the 8.1 that replaced the 7.4 but larger than the 5.7. They actually make the 6.2 themselves at their plan in Stillwater, OK by stroking a GM 5.7. For my .02 I would opt for the 7.4.
 
I own a 6.2 HO and love the power... If your 6.2 is older than 2004, I'd opt for the 7.4. They had a couple of oil sender problems on earlier 6.2's. Nothing big, just need to carry a spare if it goes. Very easy to pull the old one and install the new one at the back of the engine. But the newer ones are awesome and very high tech enabling you to check on virtually every aspect of the engines operation with a vessel view or other monitor system. If these 6.2's have the air pressure winterizing option, I'd jump on them. Takes me about 45 seconds to winterize and or drain the entire engine of raw water.

6.2's are lighter and take up a smaller footprint and are much more economical than the 7.4.
 
J Levine said:
Skip while I have no experience with these engines in this particular model I will chime in and tell you that in my opinion when it come to gas powered big boats there is no substitute for cubic inches. Mercury came up with the 6.2 around 2000 when GM stopped producing the 7.4. They needed a motor to replace the 340 ish HP 7.4 that was smaller than the 8.1 that replaced the 7.4 but larger than the 5.7. They actually make the 6.2 themselves at their plan in Stillwater, OK by stroking a GM 5.7. For my .02 I would opt for the 7.4.
Click to expand...

+1:thumbsup: The 6.2 does not come close to providing the torque that the 7.4 does. In a much lighter boat the comparison in overall performance and economy would be closer but in a heavy craft like the 34' Dancer you need all the torque you can get. In heavy boats, horsepower becomes pretty much a meaningless number. You want powerplants with the highest and broadest torque curve you can get. With gasoline engines you get that one of 2 ways...cubic inches or supercharging.

Given the choice...go for the big blocks.
 
Go Aweigh2452 said:
6.2's are lighter and take up a smaller footprint and are much more economical than the 7.4.
Click to expand...

I agree with your comment as it applies to a small boat, but there is quite a difference between a 24 footer with a stern drive and a 34 footer with twin inboards, again there is not substitute for cubic inches.
 
What years are these 340s (new and old one)? I'm guessing the older one is the '99-02 generation, which all seem to have 7.4s. The newer one is '03-08? I found ONE with 6.2s on boats.com. That's a fairly beamey 15K lb boat - with 6.2s you'd be borderline underpowered.

Then there's always this alternative!
http://www.boats.com/boat-details/Sea-Ray-*34-Sundancer*/19937061

Those Yanmars look NICE in there. Repowered?????

You wouldn't even have to change the name on the transom.
 
You know why I went with the 6.2 the fuel tank would have to be made smaller 70 gallons not enough I would have needed to add saddle tanks somewhere...ect...
6.2@320+100gal@10gph.....Ilike the math
 
sprink56 said:
+1:thumbsup: The 6.2 does not come close to providing the torque that the 7.4 does. In a much lighter boat the comparison in overall performance and economy would be closer but in a heavy craft like the 34' Dancer you need all the torque you can get. In heavy boats, horsepower becomes pretty much a meaningless number. You want powerplants with the highest and broadest torque curve you can get. With gasoline engines you get that one of 2 ways...cubic inches or supercharging.

Given the choice...go for the big blocks.
Click to expand...

TORQUE AINT CHEAP:thumbsup:
 
New boat has gyrocoptor blades on radar arch a helicoptor turbine power talk about getting on plane...
 
As previously stated ... The 6.2 does not even come close the 7.4 in terms of torque and getting the 340 going. The 454bHorizons were rated 380 hp, the 7.4 MPI was rated 310 hp and the 6.2 320 hp, but the 7.4 has 100+ lbs./ft. more torque and that's what counts.
 
We have twin 454 in a 38 aft cabin. If I was to get an other boat I would go for a deisel as the 454s use 25+ GPH each at 3800RPM at 1200RPM they use 4 GPH each. At 1800 RPM they use 10GPH each. Have had no problems with the 454s replaced one raw water pump and all the water heat exchangers. Total 1400HR on each.
 
J Levine said:
Skip while I have no experience with these engines in this particular model I will chime in and tell you that in my opinion when it come to gas powered big boats there is no substitute for cubic inches. Mercury came up with the 6.2 around 2000 when GM stopped producing the 7.4. They needed a motor to replace the 340 ish HP 7.4 that was smaller than the 8.1 that replaced the 7.4 but larger than the 5.7. They actually make the 6.2 themselves at their plan in Stillwater, OK by stroking a GM 5.7. For my .02 I would opt for the 7.4.
Click to expand...
Ditto
 
There was only one reason and one reason only why the 340 was offered with the small block engines. They were significantly cheaper. It allowed certain dealers to complete at a lower end of the market with stripped-down boats.

Immediately after the 7.4 went out of production, the 8.1 was ready. Well, GM was ready with it. Took Mercury two years to shake out their marinizing bugs.

Get the big blocks. The hull needs them.

Best regards,
Frank
 
I just swap two 454MPI for two diesel in my 310. 454 are very good reliable engine but for me now Diesel is the only way to go in a boat and will never ever buy a gazer again.

The fuel economy is simply amazing and very few gazer boat could follow me on the cruise. When we go on a trip with other boaters im the first there and cost me 1\4 than before
 
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Stephane
Tell us about your experience and what it cost to repower your boat with diesels
 
A heavy34' boat must have big blocks. Getting dangerously close to needing diesels. Boats weighing over 14k with the twin 454ci start to work harder, Really hurting the MPG.
Stumbled across some of this info when I was researching boat weights and engines for a repower a few month back. Big blocks start getting really thirsty above 3200 rpm.
 
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northern said:
Stephane
Tell us about your experience and what it cost to repower your boat with diesels
Click to expand...
Brand new Volvo D4 260 hp 440 lbs Tq with duoprop. $ 30k
The D6 is like 32K Heavy flybridge 26' boats get 3.2 mpg with them packages.
 
repower could be an expensive experience for me I got a realy good deal on used one but if you need to buy new engine etc....IMO better buy a boat already with them in
 
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