Merc 305 Vs. 350 - Input Please!

[joewithaboat]

Re: Merc 305 Vs. 350 - Input Please!

Just some numbers on the engines and speeds. As already pointed out you won't be sitting on WOT all that often, but....

My 20' boat has a 2006 220hp 4.3L V6(that's crankshaft hp, Merc went back to rating stern drive engines at crankshaft 1-1-2003!) and pushes it at WOT to 49.6mph.

The old V6 (180 prop hp) got dropped into a 23' cuddy which had a 305 (228 crank hp). Originally that boat did just 34mph, with my old V6 it does over 41 mph....

Just at add some confusion to the issue...

The 305 was one of the worst creations of gm. Its a shame too because it could have just as easy been a 350.

 

[joewithaboat]

Re: Merc 305 Vs. 350 - Input Please!

http://www.mercurymarine.com/engines/mercruiser/

They all still say HP @ prop.

I did notice the Merc remans are labeled at crank.


But, what is disturbing, is that the 5.0L and 5.7L carb engines are missing. Have they been discontinued? If so, I assume it was emmissions reasons. I remember seeing some input about adding cats, but missed the demise of the sbc carb.

That damn EPA ....

 

[achris]

Re: Merc 305 Vs. 350 - Input Please!

http://www.mercurymarine.com/engines/mercruiser/

They all still say HP @ prop.

Interesting, because an official Mercury document I have (a serial number list by year) states quite clearly that as of 1-1-2003 horsepower ratings are at the crank... (PM me and I'll email it to you)
and at this website->http://www.mercurymarine.com.au/home/mercruiser/sterndrives/mpi-engines/43l-mpi.aspx it just says "Power", but if you click on 3.0L MPI it says "Power @ prop". I take it that the other engines are not power at the prop, therefore, at crank....

But, what is disturbing, is that the 5.0L and 5.7L carb engines are missing. Have they been discontinued?

Yes

If so, I assume it was emmissions reasons.

Yes again.

I remember seeing some input about adding cats, but missed the demise of the sbc carb.

Didn't we all....

 

[John_S]

Re: Merc 305 Vs. 350 - Input Please!

Even though the spec says "power" without specifing where, the numbers all match the usa website that does say @ prop.

I find it interesting that Merc would even consider changing back to that, after everyone going to @prop in the 80's. Those dogs!

Did we loose the sbc carb in 2011 or earlier, or just going into 2012? Looks like the V6 and I4 won't be far behind.

 

[jmw129]

Re: Merc 305 Vs. 350 - Input Please!

The 305 was one of the worst creations of gm. Its a shame too because it could have just as easy been a 350.

Wait! Why is the 305 one of GM's worst creations? Is it really that bad?

My mechanic mentioned something about the crank & cam being smaller / not as strong. Is that what you're referring to?

 

[jmw129]

Re: Merc 305 Vs. 350 - Input Please!

Just some numbers on the engines and speeds. As already pointed out you won't be sitting on WOT all that often, but....

My 20' boat has a 2006 220hp 4.3L V6(that's crankshaft hp, Merc went back to rating stern drive engines at crankshaft 1-1-2003!) and pushes it at WOT to 49.6mph.

The old V6 (180 prop hp) got dropped into a 23' cuddy which had a 305 (228 crank hp). Originally that boat did just 34mph, with my old V6 it does over 41 mph....

Just at add some confusion to the issue...

So you're telling me that the V6 180hp is pushing a higher top end than the 228hp V8 305? If so, are you sure the V8 wasn't tired? or wasn't healthy?

 

[thumpar]

Re: Merc 305 Vs. 350 - Input Please!

So you're telling me that the V6 180hp is pushing a higher top end than the 228hp V8 305? If so, are you sure the V8 wasn't tired? or wasn't healthy?

The V6 was rated at prop. The V8 was rated at crank. The V6 is also lighter. Like a stated in my old post, I prefer a 4.3l over a 305. We always referred to the 305 as a "turd" motor.

 

[GA_Boater]

Re: Merc 305 Vs. 350 - Input Please!

That damn EPA ....

If you want to blame someone, blame GM. How many carb motors do they make today? ZERO. Merc & Volvo buy what GM makes, they don't buy long blocks and make special common parts like intake manifolds and carbs. Everybody gripes about how much marine parts cost and then we want Merc/Volvo to keep supplying technology from the beginning of internal combustion. As an aside, it's getting to where you can't find a motorcycle with a carb.

 

[achris]

Re: Merc 305 Vs. 350 - Input Please!

If you want to blame someone, blame GM. How many carb motors do they make today? ZERO. ....

And aren't you glad... As much as I like carburettors and how easy they are to strip and rebuild (except for Holleys and Quadra-junks), electronics offers so much more. Better fuel economy, more accurate fuel metering, better reliability, less maintenance, less pollution....

JMHO.....

 

[achris]

Re: Merc 305 Vs. 350 - Input Please!

So you're telling me that the V6 180hp is pushing a higher top end than the 228hp V8 305? If so, are you sure the V8 wasn't tired? or wasn't healthy?

That engine (the V8) had been rebuilt 5 years earlier, and that was the best it was ever going to do. It was originally an 898, but during the rebuild a 4 bbl manifold and carburettor were put on (the 2 bbl and 4bbl engines use the same cam and heads) and genuine Merc centre riser manifolds and elbows. I still think that V6 (4.3LX) is a freak of nature... It was a fantastic engine. I miss it a lot. My current 4.3MPI increased my boat speed by about 4 mph.... Was the change from 4.3LX to 4.3MPI worth it? Not a chance! Would I have my old 4.3LX back? In a heartbeat.

Chris........

 

[GA_Boater]

Re: Merc 305 Vs. 350 - Input Please!

And aren't you glad... As much as I like carburettors and how easy they are to strip and rebuild (except for Holleys and Quadra-junks), electronics offers so much more. Better fuel economy, more accurate fuel metering, better reliability, less maintenance, less pollution....

JMHO.....

Yes I am. And in cars/truck throw a chip at it if you want more/less power or economy and the ability to switch back and forth. Carbs are easy to work on (except the freaking Q-Jet), but carb tuning is an art.

 

[jmw129]

Re: Merc 305 Vs. 350 - Input Please!

That engine (the V8) had been rebuilt 5 years earlier, and that was the best it was ever going to do. It was originally an 898, but during the rebuild a 4 bbl manifold and carburettor were put on (the 2 bbl and 4bbl engines use the same cam and heads) and genuine Merc centre riser manifolds and elbows. I still think that V6 (4.3LX) is a freak of nature... It was a fantastic engine. I miss it a lot. My current 4.3MPI increased my boat speed by about 4 mph.... Was the change from 4.3LX to 4.3MPI worth it? Not a chance! Would I have my old 4.3LX back? In a heartbeat.

Chris........

So the 4.3LX was special why?

The engine weighs less so I get that. Are you refering to the torque? Trying to figure out why this 4.3 is so special?

 

[achris]

Re: Merc 305 Vs. 350 - Input Please!

So the 4.3LX was special why?

The engine weighs less so I get that. Are you refering to the torque? Trying to figure out why this 4.3 is so special?

Yes, great torque. Torque is what turns propellers, not horsepower. Weight difference is only about 80 lbs... so no biggy there. I would bin my current 4.3 tomorrow only because of the problems I've had with that stupid plastic timing cover, crazy idea!!! :facepalm:

I really don't understand exactly why the 4.3 performs so much better than the 5.0.... All I know is, it does...

Chris...........

 

[John_S]

Re: Merc 305 Vs. 350 - Input Please!

Chris, received the doc. thx, can't say I can make any more sense of it than you.

 

[achris]

Re: Merc 305 Vs. 350 - Input Please!

Chris, received the doc. thx, can't say I can make any more sense of it than you.

But it does say that as of 1-1-2003 engines are rated at crank, despite what websites are stating.... That also sort of fit with my experience between my old 4.3LX (180 prop hp) and the new 4.3MPI (220 crank hp). The original engine in the boat was a 165 (165 crank hp, about 135ish prop hp) and that pushed it along at 30 knots. The 4.3LX at 39.8 knots and the 4.3MPI at 43.2 knots. Had the 4.3MPI been 220 prop hp I would have expected a few (probably about 5) knots more, but as the crank power of the 4.3LX and 4.3MPI are so similar, that figures.... Does that all make sense?

Chris........

 

[TomB985]

Re: Merc 305 Vs. 350 - Input Please!

Yes, great torque. Torque is what turns propellers, not horsepower. .

Well that's just not right. How much torque can be applied to that prop with your engine? Probably around the neighborhood of 500 ft-lbs depending on gearing. I can apply the same amount of prop by pressing down with 100 lbs on a 5-foot bar. But how FAST can it be turned like this?

That's horsepower. Torque at speed = HP, which is why HP = (Torque x RPM)/5252.

I can make my 6 HP Briggs and Stratton lawn mower engine output 500 ft-lbs through reduction gearing. What I can't do is make it apply that much torque at anywhere near the speed your 4.3L can, because there isn't enough POWER.

 

[merchonda]

Re: Merc 305 Vs. 350 - Input Please!

If I recall, the parts for a 305 block will bolt right on to a 350. Doubt that you'd notice much of a difference between them. Your real issue is dryrot and corrosion for any rig of that vintage. As for v8 vs 4.3L, your extra two cylinders will pack away the gas a bit quicker but the old v8 block is pretty reliable unless its been flooded out. If you use the boat for long rides, you'll feel it--otherwise, I woudn't worry too much about it since lowering your capital outlay and avoiding loan interest will probably offset your higher fuel costs--even with today's gas prices.

 

[achris]

Re: Merc 305 Vs. 350 - Input Please!

Well that's just not right. How much torque can be applied to that prop with your engine? Probably around the neighborhood of 500 ft-lbs depending on gearing. I can apply the same amount of prop by pressing down with 100 lbs on a 5-foot bar. But how FAST can it be turned like this?

That's horsepower. Torque at speed = HP, which is why HP = (Torque x RPM)/5252.

I can make my 6 HP Briggs and Stratton lawn mower engine output 500 ft-lbs through reduction gearing. What I can't do is make it apply that much torque at anywhere near the speed your 4.3L can, because there isn't enough POWER.

So, SA, explain to me why a smaller capacity engine making huge power (like a fully revved up 350 making 400hp @ 6,000rpm) is crap in a boat where as lumbering big displacement diesel making 250 horsepower @ 3,000rpm is so much better in the same boat. If that's not a statement about torque vs horsepower, nothing is!

 

[jmw129]

Re: Merc 305 Vs. 350 - Input Please!

So, SA, explain to me why a smaller capacity engine making huge power (like a fully revved up 350 making 400hp @ 6,000rpm) is crap in a boat where as lumbering big displacement diesel making 250 horsepower @ 3,000rpm is so much better in the same boat. If that's not a statement about torque vs horsepower, nothing is!

Very interesting.... Not quite sure who is right here or maybe both right in their own ways??

Is there a non-bias study by experts explaining the truth between torque & hp? I would like to know. If I can get the same HP from a V6 / Top End vs. V8 I would be open to hear more?

My mechanic told me that 2 cylinder's such as V8 vs. V6 vs. V4 make's a difference and claims you can feel it. He is a fan of V8 and thinks that anything less in an inboard boat is average to below par at best.. For example he said the 3.0 135hp was whimpy.

I have noticed that smaller engines run at higher Torque / RPM so I assume that is to get more TOP END while still saving on gas..

I want TOP END in the 45mph - 55mph range, ride comfort, and more I can save I'm cool with that. Does this exist in a V8?

 

[achris]

Re: Merc 305 Vs. 350 - Input Please!

Very interesting.... Not quite sure who is right here or maybe both right in their own ways??

Is there a non-bias study by experts explaining the truth between torque & hp? I would like to know. If I can get the same HP from a V6 / Top End vs. V8 I would be open to hear more?

My mechanic told me that 2 cylinder's such as V8 vs. V6 vs. V4 make's a difference and claims you can feel it. He is a fan of V8 and thinks that anything less in an inboard boat is average to below par at best..

Without wishing to start (another) fight, your mechanic is talk with his hat on backwards, it's more 'horses for courses'.. I have a friend with twin 260hp (350cu-in) engines in a 28' boat. My V6 powered boat out-performs it in every way; top speed, fuel economy, easy of maintenance....

For example he said the 3.0 135hp was whimpy.

Again, that mechanic needs to shut up! Because he hasn't a clue what he's talking about.... When I had my dealership we were dropping those 'whimpy' engines into 18' half-cabin boats and they were doing up in the 40mph area. The owners were reporting that they RARELY used anything near WOT, same as my old V6 in the 23'cuddy. His wife refuses to be on the boat if he uses anything more than 3/4 throttle....

I have noticed that smaller engines run at higher Torque / RPM so I assume that is to get more TOP END while still saving on gas..

That's more to do with lower reciprocating mass. Lighter crankshaft, less pistons will spin easier than lots of pistons on a heavy crank. With a smaller engine you need to make up for the lower displacement with high revs (and compression). For us in the boating world it's more about torque than top end horsepower. We rarely use WOT, and the main rev range we cruise in is the midrange, so we want a good strong torque curve lower down, which conflicts with high output at the top end... Without getting into superchargers, you can have fantastic power at high revs, or good solid torque mid-range, but rarely both...

I want TOP END in the 45mph - 55mph range, ride comfort, and more I can save I'm cool with that. Does this exist in a V8?

It exists in any boat you want it to exist in. Just get enough power into it and it will travel... As I stated earlier, my V6 powered 20' boat tops out at 49.6mph.... right in the middle of your desired range....

It's all to do with hull shape, weigh and torque characteristics of the engine.... That's why most boat engines use 'truck' type cams.... Not race car cams....