V6mpi vs. carb V8 question

[toddbrown]

Hello. I am buying another boat and need some engine advise. I had a 98 Bayliner 1850 with the 4.3 190hp. I am looking at a V8 for more power. I noticed that I can get the 4.3 MPI and get about 225hp or the 5.0 V8 carbed and get 220hp. What is the benefit of the V8 over the MPI V6? Is there more low end Torque for wakeboarding with the V8?

 

[gatorred]

Re: V6mpi vs. carb V8 question

mpi is fuel injection try fuel injection on v8 at the end 5 hp is all it is the car dealer told me <br />pulling is torque more torque with v8 it's posible to have same hp but dfferent torque rpm but mpg goes up alot with fuel injection to that's why it's in car's. a though

 

[craze1cars]

Re: V6mpi vs. carb V8 question

What?<br /><br />Here's a translation....maybe.<br /><br />WOT HP will be about the same, so I'd expect top speed to be similar. V8 will certainly have a bit more torque. But, the V6 will be a lighter motor which may offset some of that torque loss in terms of accelleration. And I'm quite sure a V6 with EFI will get MUCH better fuel mileage than a carb'd V8. I do believe the MPI V6 is more expensive to buy, but I could be wrong on that.<br /><br />Benefits of MPI V6, rock solid idle, consistent turnkey starting for anyone without pumping or giving it gas, no flooding, no gas fume odor, quieter, lower emissions, less fuel consumption, lighter weight, and I'd predict better resale value in a few years when carbs are finally put where they should be...history books.<br /><br />Benefits of carb 5.0 V8, a little more torque on the low end. Might be cheaper.<br /><br />If it were me making the choice, I'd buy the MPI V6 in a heartbeat...or jump up in size to a carb 5.7 or an MPI 5.0 if you really want a more noticable improvement over what you have.

 

[craze1cars]

Re: V6mpi vs. carb V8 question

I'll also add this. I have a friend at a local Glastron dealer that has a boatload (no pun intended!) of brand new 195's sitting on their lot with the 5.0 Volvo carb motor. They have been discounting these things more and more for over a year and simply cannot move them no matter what. He told me everyone who wants that boat makes them special order it with either the Volvo MPI V6, or the MPI 5.0. Not sure if that means anything, but makes me think my prediction of resale value may not be too far off....they can't even sell them new.

 

[watered down]

Re: V6mpi vs. carb V8 question

Just as a general concept...higher hp effects top end WOT, while it's the torgue that gives you more ummmmph out of the hole. So the V-8 would give you more torgue in general.<br /><br />That being said, the above advice is valid. IMHO there are more advantages having fuel injected over carbed. As stated above, many of the left overs I saw out here were carbed...although 2 dealers told me they order more carbed cause thats what they sell more of. <br /><br />I did not want the carb for reason cited above and held out until I found a deal on the GXI. Good luck

 

[KCook]

Re: V6mpi vs. carb V8 question

My preference is a Merc V8. But weight is a consideration. In a 185-190 class boat the lighter weight of the 4.3L might make it a better choice. Larger boats could handle the weight of the V8 more easily.<br /><br />Kelly Cook

 

[toddbrown]

Re: V6mpi vs. carb V8 question

Thanks! I do 90% water sports so I am just trying to get teh best engine fo rthis. I think I will go for the MPI V6 even though the V8 has more low end torque. COuld I get a good used 19 footer open bow for 20K with the MPI?

 

[KCook]

Re: V6mpi vs. carb V8 question

Yes, I would think that would be pretty easy to find. Prolly for well under $20k for that matter.<br /><br />Kelly

 

[JB]

Re: V6mpi vs. carb V8 question

Let's move this to the I/O Engine forum.

 

[paulie0735]

Re: V6mpi vs. carb V8 question

If its tubing and boarding etc than 180 - 200 hp should be fine and a lot of torque is really not required for wakeboarding so the 4.3 MPI V6 will be very nice. But if you intend to slalom ski with adults in a 19 foot open bow style boat and be serious about it than you will need 250 hp plus!<br /><br />Think a head a little, test run and buy the best you can afford.

 

[Mischief Managed]

Re: V6mpi vs. carb V8 question

I have owned a boat with a 5.0 carb and it was great. My present boat has MPI and I don't think it's all that much better. Still stalls on occasion and runs rich when cold, just like the carb engine.<br /><br />The weight difference betwwen the 4.3 and the 5.0 is shockingly small. Well under 100 lbs if memory serves. This makes sense when you consider they are basically the same engine, the only difference being the weight of the two added cylinders. All the bolt on accessories and such, as well as the drive, are the same.<br /><br />Fuel injection is awesome in applications where there is a need to operate in wide temperature variations, with small throttle openings much of the time, and at varying elevations. That's why it works so well in your car Summer and Winter, gets great mileage (compared to old carb engines), and does not struggle when elevation changes. <br /><br />Carbs are best used in narrow temperature variations, with large throttle openings, and at constant elevation. Carbs are perfectly suited to recreational boats and the fuel consumption between carbs and FI in a boat is negligible. Is FI better? Of course, but the differences are so minor that they are not nearly worth the added cost up front if you intend to keep the boat. Unfortunately, it's harder to sell a used boat with a carb so the resale could take a hit. <br /><br />Here's a little secret Mercruiser would rather not share: that 5.0 engine will make about 250 to 260HP with a 4 bbl carb and intake manifold ($600 or so). They put small 2bbl carbs on them to keep them from making the same power as the 5.0 MPI engine. The difference is even better on a 5.7 liter engine. Boating magazine did a test a couple of years ago and spent $600 on a 4bbl carb, 4bbl intake manifold, and K&N flame arrestor for a merc 5.7 engine. The boat gained 6 MPH on the top end, the same top speed it would do with the 5.7 MPI.

 

[toddbrown]

Re: V6mpi vs. carb V8 question

Interesting! Is it hard to change out the Manifolds and carbs? I have some mechanical skills but not a pro.

 

[Mischief Managed]

Re: V6mpi vs. carb V8 question

Originally posted by Todd Brown:<br /> Interesting! Is it hard to change out the Manifolds and carbs? I have some mechanical skills but not a pro.

It's very easy, especially on a carb V8 engine since it's all right there on top. Hardest part is cleaning off the gasket remnants from the heads and maybe setting the ignition timing when you are done. The throttle linkage may take a bit of fiddling too, but nothing too terribly complex.<br /><br /> You should use a marine intake manifold and MUST use a marine carb, but all the stuff can be found online. Try Summit Racing for the parts. They may not have a marine intake though. You can also eBay the old parts and get back some money to buy a new prop to take advantage of the new HP too...

 

[4.3sunbird]

Re: V6mpi vs. carb V8 question

nothing wrong with carb'd 4.3 v6's either <br /><br />there are plenty of them you can buy cheap with a cracked block and build you a slightly modified fresh engine <br /><br />I dont mind sharing whats in my lil 4.3 ..It runs real good for a carb'd 4.3<br />If I had a real outdrive I would inject mine and hang a turbo on it

 

[180shabah]

Re: V6mpi vs. carb V8 question

OK, this will probably make a few people mad. Bottom line, Chevy's 4.3 has always been more powerfull(hp AND torque) than the 5.0 V8. The Bore of the 5.0 is much smaller than that of the 4.3(or 5.7) this seriously restricts airflow through the valves, thus reducing power. Merc and Volvo are getting more power from the FI motors for one very important reason. The FI motors use a camshaft with more lift. I personally would not choose a 5.0, get the V6 or of you must have a V8 skip the 5.0 and spring for the 5.7.<br /><br />Hey 4.3sunbird, is N.N. Newport News, I just moved to South Boston from Williamsburg this summer. I would love to know what changes you(or anybody else) have made to your motor and what the net gains were.

 

[Mischief Managed]

Re: V6mpi vs. carb V8 question

Originally posted by 180shabah:<br /> OK, this will probably make a few people mad. Bottom line, Chevy's 4.3 has always been more powerfull(hp AND torque) than the 5.0 V8. The Bore of the 5.0 is much smaller than that of the 4.3(or 5.7) this seriously restricts airflow through the valves, thus reducing power. Merc and Volvo are getting more power from the FI motors for one very important reason. The FI motors use a camshaft with more lift. I personally would not choose a 5.0, get the V6 or of you must have a V8 skip the 5.0 and spring for the 5.7.<br /><br />

While a 5.7 would be better than a 5.0, you are mistaken about the 4.3 making more HP and torque than a 5.0. All three engines are quite similar in design, so bigger displacement means more power, period.

 

[4.3sunbird]

Re: V6mpi vs. carb V8 question

I have trucks with both 4.3 v6's and others that had 305's (now 350's) .. the 4.3 will out pull the 305's at lower rpms <br /><br />bigger bores do make alot of difference with unshrouding the valves alowing better flow <br /><br />the 4.3 like the 350 are know to have a good bore to stroke ratio.. the 305's just dont have enough bore to push the stroke (all 3 have same stroke btw)<br /><br />180shabah : feel free to hollor at me <br />all my contact info is on my site I havent done much with www.evtbs.com<br />btw : I dont do mornings

 

[Mischief Managed]

Re: V6mpi vs. carb V8 question

Originally posted by 4.3sunbird:<br /> I have trucks with both 4.3 v6's and others that had 305's (now 350's) .. the 4.3 will out pull the 305's at lower rpms <br /><br />bigger bores do make alot of difference with unshrouding the valves alowing better flow <br /><br />the 4.3 like the 350 are know to have a good bore to stroke ratio.. the 305's just dont have enough bore to push the stroke (all 3 have same stroke btw)<br /><br />

A newer 4.3 may make more power than an older 5.0, but it's more due to the Vortec heads than the bore to stroke ratio. <br /><br />My statements were about boat engines of the same vintage. For isntance: Today, a carb 4.3 makes 190 HP, a carb 5.0 makes 220 HP. An FI 4.3 makes 225HP (I think) and an FI 5.0 makes 260HP. All HP numbers are by Mercruiser and measured at the prop shaft.<br /><br />My last boat was a Regal 2100 LSR. The base engine was a 4.3 carb that topped out at 49 MPH GPS with the stock aluminum prop, according to www.boattest.com. Mine had a 5.0 carb and topped out at 54 MPH GPS with the stock aluminum prop. It was able to reach 58 MPH GPS with an SS prop and a light load. A friend of mine has one with an FI 5.0 that tops out at 66 MPH with an SS prop. FI does not affect bore or stroke, so it's pretty obvious the 5.0 engine is able to breathe just fine the way it is designed.<br /><br />BTW, Mercruiser FI and carb 5.0s and 5.7s all use the same camshaft Part number: 431-811658. VP uses longer rockers on their 320 HP 5.7 variant to get extra lift from the same cam as their 280 HP variant.