Merc Sportjet Vs Inboard 351 Jet

[Boats]

Which is more economical?

What are the advantages to one over the other?


Thank you in advance.

Brian

[weekender]

Pro's for the sportjet are the initial purchase price, and the small amount of room it takes up. I'm sure there are more, but I dont own one.

Pro's for the small block are the ease of maintanence, the abundance of power, and the ability to run a multi stage pump.

My guess would be that the sportjet probably gets a little better fuel economy, but with the oil it burns, things might start to even out?

I know this much. My current boat has a SBC in it and my next boat will have 4 stroke outboards.

[WaterDog]

The sportjet is cheap to operate. No oil to change and very little maintenance, no winterizing. In a smaller and lighter boat it’s a great package. Very reliable. It depends on the boat but if you stay out of the throttle (below 4500rpms) it will burn less fuel.

With an inboard you get more power, a better ride (due to weight), optional heat/defrost, Ability to carry a larger load (somewhat pump dependant) but a larger dog house.

How big of a boat are we talking about? 20feet and under I say SJ. 21 feet and over go inboard.

I’ve had both.

[weekender]

It seems to me that your changing the oil everytime you pour another gallon in the reserviour?

I'm curious, what do sportjet's mix at? 40-1? 50-1? Make sure you calculate the price of oil with your operating costs.

[TheRogue]

computer controlled.....anywhere from 100:1 to 40:1 (don't quote me on those), so it's tough to come up with an exact number. I can say that in the 40 hrs on my big motor in the last year, I've probably burned maybe 6-7 gallons total of mix.

yes, it's another operating expense. however, I firmly believe that general maintenance on a SJ is quite simple and cheap. You give it gas and fill the oil reservoir. When it starts running rough, eventually you might have to change the plugs. Easier than an inboard v-8.

It's the "fixing" that gets expensive.

TR

[jimh]

From what I've heard, Sportjets aren't as fuel efficient. They are two strokes and have to work very hard to push a loaded boat and are always running at a higher rpm. Inboards can push a heavier load. Inboards can produce heat and have freshwater cooling.

Otherwise, I agree with Weekender.

[Mark Vickers]

I haven't had the 351, but I can tell you what I get with my Sportjet 175 in my 19' Thunderjet Luxor.

6 gallons/hour running at normal cruising speed which is roughly 35 mph with a couple of adults and their fishing gear. I can push it up to 46 mph but I notice that the fuel consumption increases markedly when I really push the engine hard. Because of that, I don't have a good measurement, but my guess would be 8-10 gallons/hour.

There are a number of older threads on the advantages/disadvantages of the Sportjet.

[weekender]

cough four stroke outboard cough

[SlipKnot]

I've only been in one sportjet powered boat, but it was cold blooded, loud, and a little stinky. The V-8 is heavier, not cold blooded, and has heat when running.

Not sure how they compare on the gas mileage. I have the 351 and it really depends on how I drive it. If I stay out of the throttle all the time, it isn't bad.

My impression is that the V-8's are cheaper to repair as well but that is debateable I'm sure. The powerhead for a sportjet is $$$$$$$ I've been told.

[TheRogue]

My 240 is loud...but is NOT cold blooded, and minimal on the fumes, thanks to the fuel injection. It is a gas pig when I wind it up though!

TR

[Away2Long]

Sportjet in a MM 19' -
negs : cold blooded, smoky for a bit
***: reliable, simple, lightweight, small doghouse
As for the GPH issue - I have a fuel flow meter and burn 6.5-7.0gph at 4200 rpm(best) = 26-30 mph and 13-15 gph at 5500 rpm(WOT) = 42-46 mph.
Them are the facts for my sportjet and I yes I do like it.
Alot.

[Mikeymoto]

Here's some SJ info from Willie's web site:
TEST RESULTS

Engine Speed Fuel Fuel
(rpm) (mph) (gph) (mpg)
3000 25.0 5.0 5.0
3500** 28.0 7.0 4.0
4000 33.0 10.0 3.3
4500 38.0 12.0 3.2
5000 45.0 15.0 3.1

[sorryhoney]

I've got a 502 Marine Power (425 hp) in a 23ft. T-Jet Maxim. Please sent cash or check donations to my Chevron credit card account. Gulp, Gulp, Gulp! :bigshock:

[WaterDog]

sorryhoney, Any idea on your gph? I've got vortec 496/HJ212 in my 22' and see 10 to 14 gph.

I saw about the same gph as Away2long on my 18' MM Outback. The 175 is the cold blooded motor.

[Pickles]

The 175 is cold blooded, but there is a fix. Unless your buying this spring though, you will no longer be able to buy the 175 as mercury is discontinueing all there non DFI 2 stroke sport jets this summer.

[Orion]

From what I have heard and seen on the river, the 175 is somewhat cold blooded, and smokes a bit. I have a 200 Optimax (which was the recommended choice by the fine folks at Willie Boats). The engine fires right up, does not smoke, but is a bit noisy. The thru hull exhaust helps a bit but when running at full tilt, but you can't communicate easily with the passengers up front without yelling or hand signals. But then again my hearing is not that great to begin with! If you go with a Sportjet, I highly recommend the 200 Optimax, and would avoid the 175 if possible.

My two cents,


Orion

[Away2Long]

pickles -
what is the fix for the cold blood?
If it is the ignition switch to pump route then yes it does fire up quicker, but it still takes a while to warm up and stay fired up. I prime mine and it will catch pretty quick but I usually have to hit it again 2 or 3 times to get it to keep running.
And yes, I did have it serviced very recently.................
Still, a good motor for my needs.

[Pickles]

Yes you are correct. that was the fix I was referring too.

[skybuster]

The sportjet may be a little cold blooded, but I always like to warm up both motors before I leave the dock anyway. I like to hear both of them run and make sure they are warm, and also make sure that I won't have any problems once out on the water. After the motor warms up, 3-5 minutes, it is usually good to go the rest of the day at a turn of the key. I can't imagine that a big inboard would be any easier or cheaper to operate than mine has been.

I have the 19' T-Jet Luxor with the 175 SJ and it has performed well. That said my next boat may have a 4-stroke outboard.

[GWB]

Pickles & Away2Long

Could I get some further information on the rerouting of wires to aid in the cold start up on the sportjet. Mine is a @!*% to get started when cold. I have had all of the usual servicing, carbs adjusted, plugs changed.

GWB

[HntnFsh]

Great White,
Go to the Stevens marine "Boat Doc" forum, and on page 2,the 3rd post he explains the modification with a list of material you will need.

[Pickles]

GWB I sent you a link to a past thread with pictures of the the modification.

[StinkyH]

GWB I sent you a link to a past thread with pictures of the the modification.



Pickles - could you please PM me that thread link too?

StinkyH

[HntnFsh]

I was thinking there was another 1 posted on here but couldnt find it after searching for awhile.

[Pickles]

sport jet fuel pump mod link (http://www.ifish.net/forum/showflat.php?Cat=&Board=UBB1&Number=556748&Forum=, c1,&Words=&Searchpage=1&Limit=25&Main=27185&Search =true&where=bodysub&Name=2749&daterange=1&newerval =6&newertype=y&olderval=6&oldertype=m&bodyprev=#Po st556748) :cheers: