Inboard options 6.0 vs 5.7 vs Diesel

[OSEAD23]

Hi

I am considering refreshing my power on my 23 IB. My carb 5.7 is running Ok but i would like the economy of a MPI or diesel and I'm ready to step it up. some of my questions are:
Has anyone gone with a 6.0 crusader or similar in a 23 IB? i would think the 6.0 with all the extra torque would allow me to turn more pitch and get more speed. My crusader is a 270Hp will i feel a worthwhile difference with a 330Hp MPI 5.7? I have heard guys complain about the performance with new diesels like the yanmar BY any real world experience?

I would like to get a real world cruise in the 25 knot to 27Knot range if possible. today i feel like I'm pushing the 5.7 to hard to run continuous at that speed. Maybe it me babying it but i likes to run at 3k to 3200 rpms and thats about 22knots +/-. I top at 31knots today at 4300 rpm.

Jim

[77SceptreOB]

Beautiful boat!! Your WOT at 4300 rpms seems a little low for a SBC. Maybe you are swinging too large a prop?. On my standard 454 i was 4500-4700 WOT

[OSEAD23]

thanks

i have a few props and yes i have 16x16 that will run to 45-47 and a 17x17 that will maybe hit 4400. the bottom line though is the speeds are similar just i hit the cruise numbers i gave with the 17x17. the other prop everything happpens at a little higher rpm.. I know the 16 is better for the engine longevity

jim

[Briguy]

Well a diesel will cost 30k all said and done. Even a 454 mag will only run a knot or 3 more.
Yes increase your HP a little but don't expect miracles. Do what's cost effective.

[Islandtrader]

Can't say what difference an inboard will make. However on my 6.0 mpi stroker i/o merc.
At 3000 rpm I am pushing 27-30 mph. With a burn rate of 8.5 gals or 3.35 mpg.
Top rpm is over 5k an 50 mph.

For what it's worth no matter what the configuration is. A 350/383 will burn around 8 gals per hour. I have had 3 boats, 3 different setups and 3 different lengths, and have put on over 3,000 hours between them. When I go back and look at the logs...different cruising speed...but same burn rate.

[Bushwacker]

Originally Posted by OSEAD23

. . . I would like to get a real world cruise in the 25 knot to 27Knot range if possible. today i feel like I'm pushing the 5.7 to hard to run continuous at that speed. Maybe it me babying it but i likes to run at 3k to 3200 rpms and thats about 22knots +/-. I top at 31knots today at 4300 rpm.

Jim

Hey Jim,

I'd suggest you install a vacuum gauge on that rig, as it will give you a real good idea of how hard you're pushing the engine. Although a limit of 5" Hg is typically used as "Max Continuous" on HD aircraft engines, very few marine engines have sodium filled exhaust valves, stellite valve seats or positive valve rotators like the AC engines, so a limit of 7" is probably more appropriate for your engine.

Although the tunnel drive eliminates some of the loss most inboards have due to the steep shaft angle, prop efficiency is probably less efficient than an outdrive with a prop running on horizontal shaft in cleaner water. So I'm not sure that you would necessarily benefit from a bigger engine as much as if it were a sterndrive. Similar situation to muscle cars in the '60's, where engine power easily overwhelmed the tire technology available at the time! Your inboard configuration (NICE rig BTW!) may not have the speed/efficiency potential of an I/O, but it sure is hard to beat the CG/ride benefits and simplicity/reliability of a straight inboard! If you run offshore very much, I would think a softer ride and much less maintenance is a good trade for a few kts of speed! Denny

[pelican]

here's my 2 cents:

5.7 merc,MPI motor - put the correct prop under the hull.FORGET THAT SPEED !!! you want speed ? buy a contender/regulator/yellowfin...you have an inboard powered boat,not a twin outboard powered rig.
attempting to raise your cruise speed by upping prop pitch/diameter isn't the way to go.
ride of the hull suffers - time to plane suffers,and you're killing the motor,along with killing efficiency of the motor - you're sucking fuel like a jet...
running a gas motor,that's overloaded is kinda like holding your feet to the fire...the motor is overloaded,you need to open the throttle further,to get rpms - this causes the exhaust temp to rise - leading to lots of potential problems: detonation,valve failure,etc...all of which spells disaster for the motor....

diesel sounds good - but in a smaller hull like your's,it's not cost effective to spend that kind of money on diesel.stick with gas,gas motors when set up correctly,are incredibly efficient and reliable
little more to it than just dropping a diesel in - you're gonna need to modify the exhaust,bigger diameter is needed.you're gonna need to add return line fittings to the fuel tanks - this could turn into a big pain in the butt - you've got wiring,batteries - lots more to it than meets the eye

i'm not a huge fan of the stroker motors - seen quite a few problems internally with those...
i'm also not a fan of "reman" or "long blocks" - I like NEW,as in NEW,complete motors


speed:

everyone is obsessed with speed :

truth is,20/22kts in normal conditions is a good speed - you're not beating up the boat,killing the motor and beating up yourself.the 23 center console inboards,these ride the best !

speed costs money - increasing speed requires increasing both hp and torque ... there's a huge difference between that old 270 crusader and a new MPI motor...I believe you'd be very happy with a new MPI 5.7,propped correctly...

[FLexpat]

The crusader 6.0 is not a stroker - it is the GM L96 (or LY6) truck engine from GM Marine - about an inch wider and an inch longer than a SBC with a little more power for the extra 50 lbs or so but it has some great features like variable valve timing, a lot of torque and a very flat torque curve, great economy, good reputation in both trucks and boats (Volvo makes a 420HP version and Marine Power makes a 385HP version), yadda yadda yadda
It isn't cheap though, it is all electronic (no carb or distribuitor), and parts may be a little harder to grab.
It is what I would do if I had the cash.
Since my kids are still on the dole, I would look hard at the 5.7MPI.
I'd change the prop first though.

Pelican's 0.02 on this, corrected for inflation, are worth a whole lot more than that - I'd pay close attention.

[Islandtrader]

Originally Posted by FLexpat

The crusader 6.0 is not a stroker - it is the GM L96 (or LY6) truck engine from GM Marine -

You are correct...however I still stand by my statement...it will burn around 8gph at cruise.

[pelican]

Originally Posted by Islandtrader

You are correct...however I still stand by my statement...it will burn around 8gph at cruise.

a stern drive - hard to believe,IS more efficient than a straight inboard...


multiport motors are more efficient - freshwater cooling helps too

carb'd motors are tougher to get dialed in,load can effect when the secondaries kick in(4V ) motors

getting a boat dialed in can be a battle on occasion - propping isn't a set in stone science,it's trial and error

taking the time to set it all up will pay off big - pays off in both speed and fuel efficiency.

not trying to turn this into rocket science,or launching a space shuttle - repowering is a little more than just dropping a new motor in and hooking it all up.taking the time to get things right and actually improving the boat is what it's all about - that's what seperates a true repower from an engine replacement....