Possible 3.0L volvo Penta Inboard to Honda K24 engine conversion.

StarcraftResto

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Jun 11, 2019
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3
Hey everyone,

I recently inherited a 20foot closed bow aluminum Starcraft, this boat is virtually a shell. My grandfather had plans to restore the boat however he passed before he could get around to the project. I have started stripping and cleaning the boat and intend on going with a two tone of a fully polished look along with a Metallic red higher up on the sides. This project is likely something that will not see the water for atleast the year. So I am starting with the basics, this is the engine, it is a volvo Penta 3.0L inboard motor.

I can't get over the resemblance it holds to a motor I am oh so familiar with. The Honda K series, I happen to have a full longblock sitting around that is looking to be the ideal candidate for this swap. I have everything from the engine, wiring harness to ECU and accesories. The main issue that Im dealing with will be the flywheel to drive adapter, and getting a proper setup that will withstand the upwards of 240hp this will likely be pushing through the drive. Anyone have any ideas on conversions? or upgraded Drive parts that will withstand this power? I will post a picture of the boat later today!

I have already created a list,

The motor will utilize a radiator system with eletric water Pump.
Will maintain current oil pump setup(No Dry sump needed, as maintaining good angle for pickup.
Will be switching to a marine friendly heaadgasket
2008 Acura TSX K24a2 longblock
Sidefeed intake manifold utilizing an aftermarket single cable throttle body
Full programmable ECU and engine harness
Aftermarket fuel system utilizing AN lines and aftermarket fuel injectors
Centered exit exhaust coming out of the rear, above the inboard motor
Will be removing all coolant ports on the engine except for the infeed and outfeed that will utilize a radiator and eletric waterpump
Rear or front mounted radiator
Marine grade Alternator and Starter to elimnate chance of fires ignited from fumes.


Keep in mind this motor is currently turbo'd making approximately 400whp in a car, however, to keep the project possible, this will be taken off and it will be naturally aspirated to increase durability and reliability.

I was intending on getting the Penta rebuilt, however for a 120hp outdated motor it does not seem worth it for the pricey cost of nearly $4000cad which more then covers the parts I have listed, that will double the HP, and drastically improve efficiency and reliability.

I would like any input from anyone else!
 

jbcurt00

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Oct 25, 2011
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24,829
As you dont intend to put a Volvo Penta back in, not a great spot for this, let me move it.

Try to keep this topic as a motor swap topic and the rebuild topic about the boat rehab rather then the motor

Thanks

Good luck w your project, sounds ambitious
 

Chris51280

Master Chief Petty Officer
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Jan 24, 2018
Messages
897
you might want to bring this over to the engine build section. And most likely they will tell you that it is not a good idea. Engine is not equal engine when it comes to boats. even though boat engines came from car engines, there are differences and reasons why it is the way it is. Boat engines have a very low rpm to torque curve. the exhaust is cooled due to temperatures in the headers due to long periods of 3000rpm (cruising speed). Alternator, fuel pump, starter are coast guard approved. Aluminum blocks are closed cooling only. Your cooling circulation with an electric water pump is again most likely not spark proof. The water circulation is different than a car engine. If you have a constant flow of cold water around your cylinders, your engine will not like that. You will never get to operation temp.
I have seen diesel engines put into boats from a vw. Cast iron block and no spark problems
 

GA_Boater

Honorary Moderator Emeritus
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May 24, 2011
Messages
49,038
I gotta ask - How does a GM OHV forklift/generator/industrial motor resemble a Honda TSX OHC motor in any way except both are 4 cylinders?


No parts are available to marinize a Honda and to connect it to an outdrive, any outdrive.. Just because you have a motor doesn't mean it can be used in a marine application. Now if Honda was known for tractor motors, you might have chance.
 

Mad Props

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Messages
1,766
I agree with Chris... Just to add on to what he said... Most high revving japanese motors make their peak torque at high RPMs. To get to your peak torque/hp that your engine is capable of, you will blow your volvo drive to pieces. You would need some sort of a transmission to gear your output shaft down before going to the drive.

Not to mention, none of your fuel system and electrical system will be coast guard approved, which may not bother you, but if your boat goes boom, if you survive, you will be responsible for everyones lives onboard, everyone near you in the water, any personal property that gets damaged, etc...

You can do whatever you want, and it would probably be a cool experiment, but all we can do here is give you our advice on what is a good idea, and try to save you from making an expensive mistake.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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from your description of your project, I can fully tell you know nothing of boats and why things on marine motors are done the way they are

you cant put a radiator cooled motor in a boat. there is not enough air flow and you cant get enough cooling. in fact in your car you cant get enough cooling. if you fully load your car continuously you will over-heat. most radiators are designed for about 50-100hp continuous heat dissipation and when you go to a 100% duty cycle application such as a generator, you find the radiator needs to get about 4X as large

boats are water cooled for a reason. the first is the heat rejection from the motor.

the next is the heat rejection from the exhaust (about the same BTU's as the motor).

since a motor burns fuel and converts 1/3 to block heat, 1/3 to exhaust heat and the remaining 1/3 to actual work, that would mean a typical 3.0 is cooling cooling system is dissipating about the same amount of heat as a 300hp generator would

you need a fully water cooled exhaust system in a boat. any surface must be 200 degrees or below or you risk igniting things in the boat such as the fuel and creating a fire or explosion

you cant use the non marine fuel system in a boat, or you risk an explosion

short of lots of development, you will need to determine how to run without O2 sensors as O2 sensors do not like to run in wet exhaust.

HP means nothing in a boat. its all about torque..... lots of it from idle up to 5000 RPM. it takes low end torque to get the boat out of the hole

your K series motor does not have enough low end torque. it topped out at 150 lb-ft or there about. the 3.0 that is in the boat now has is about 170 lb-ft, making well over 130 lb-ft of torque just off idle. stop thinking turbocharged high RPM car and start thinking dump-truck climbing a hill while pulling a trailer in sand with only one gear. attempting to use such a motor in a high-torque application and you will lug it, inducing detonation which will kill the motor.

anything higher than 5000-5500 RPM and the drive need serious work to allow it to live. that is all the drive is designed for. they are a high-torque, medium speed device

the drive that is behind that motor will handle more torque than you think. the same drive goes behind big blocks. Granted, with different gearing to use the torque to properly match the prop curves, however you get the picture.

I commend you for thinking out side the box, however first understand the design of a marine motor prior to attempting to use any knowledge from building a car.

a few other things to note. if your cam duration is more than 270 degrees on the intake, you will suck water in thru the exhaust and hydro-lock at idle and shut-down. you could build a complete jacketed dry exhaust all the way out your transom, however dry exhausts are custom made and cost more than a new 3.0

I would be looking to drop in a 4.3 if your boat is a blank canvas.
 

fishrdan

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Jan 25, 2008
Messages
6,989
Agree with the others.
Could you make it work? Probably
Would it be expensive? Yes
Would it open you to huge liability? Yes

I would look for a rotter hull that someone has neglected, but it still has a good drive train: engine, drive, all fittings and accessories. 4.3L Mercruiser or VP as Scott said. This could be cheaper than rebuilding the VP 3.0l engine, and certainly cheaper than the Honda conversion.
 

StarcraftResto

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Jun 11, 2019
Messages
3
Alright, I appreciate the feedback of all arrays. I do like the criticism, however the motors are very similar, both in height length, flywheel location and aswell bellhousing adapters. The criticism on the heating and cooling department is not something I am worried about as this motor would be running with a thermostat, that would not open until operating temperature. This engine is not like a torqueless gutless honda, it is made for a four door sedan, even at the 240 hp this engine will likely produce 150torque from 1400rpm onward, this motor does not have the requirement to be revved out as comparable older generation hondas used in coupes and hatchbacks.

It appears many of you are not aware that this very similar motor is utilized in a outboard Honda 130 & 150 motors. If you look up a company named 4piston, they are responsible for building and modifying these to utilize roughly twice stock hp in marine form. I can already see that this forum appears to be full of people afraid of thinking outside the box, there are already readily availible parts to make the fuel system, cooling etc work. The heat dissipation is something I am concerned about, but multiple options are availible via heat wrap and ceramic coating and was throwing around the idea of an air cooled rather then water cooled exhaust, this would allow the utilization of o2 sensors etc. If it is doable for a v8 motor I find myself questioning why is it not possible? Or is it more just unchartered waters?
 

Bondo

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I can already see that this forum appears to be full of people afraid of thinking outside the box, there are already readily availible parts to make the fuel system, cooling etc work.

Ayuh,...... Welcome Aboard,...... Go for it,..... It's Yer boat, 'n you can do it up anyway you want,.......

I've done Alotta things that were said that couldn't be done,..... sorta made a career outa it,....

Yer facin' an Uphill battle,..... Unfortunately, the summit equals Mt Everest's altitudes/ tasks,.....

One is yer drive's gear ratio is designed to efficiently put 140 hp into the water,......

If yer goin' for 240 hp, ya need a different drive, or atleast a taller gear ratio, along the lines of 1.50:1, possibly a 1.65:1,.....

Just keep Us posted here at iboats,.......
I'd Love to follow yer adventure,...... ;)
 

Chris51280

Master Chief Petty Officer
Joined
Jan 24, 2018
Messages
897
I wouldn't say they are afraid of thinking outside the box.It's more a caution on educating what can go wrong and why things in a boat are build the way they are. You would be surprised by some questions here in the forum, including myself that are sometimes just too....uneducated. And I'm thankful somebody took the time and told me. That's why this is here.
Like Bondo said, your boat, do what you like. There are some things that are required by the coast guard for safety and security reasons. They are there to ensure your and your passengers safety. So are things for the road and there are also regulations from the DOT. Doesn't mean you can't change them and do what you want. Just be prepared for the consequences if you don't follow them. A little common sense is always a good thing. There are some that put a jet drive in an aluminum boat or a vw diesel in a boat or convert to an electric drive that cost 20k.
It sounds like an interesting project and would be a cool thing to see come to life. Just be cautious to not put anybody in danger, that is a big no no.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Alright, I appreciate the feedback of all arrays. I do like the criticism, however the motors are very similar, both in height length, flywheel location and aswell bellhousing adapters. The criticism on the heating and cooling department is not something I am worried about as this motor would be running with a thermostat, that would not open until operating temperature. This engine is not like a torqueless gutless honda, it is made for a four door sedan, even at the 240 hp this engine will likely produce 150torque from 1400rpm onward, this motor does not have the requirement to be revved out as comparable older generation hondas used in coupes and hatchbacks.

It appears many of you are not aware that this very similar motor is utilized in a outboard Honda 130 & 150 motors. If you look up a company named 4piston, they are responsible for building and modifying these to utilize roughly twice stock hp in marine form. I can already see that this forum appears to be full of people afraid of thinking outside the box, there are already readily availible parts to make the fuel system, cooling etc work. The heat dissipation is something I am concerned about, but multiple options are availible via heat wrap and ceramic coating and was throwing around the idea of an air cooled rather then water cooled exhaust, this would allow the utilization of o2 sensors etc. If it is doable for a v8 motor I find myself questioning why is it not possible? Or is it more just unchartered waters?

Dude, I have been involved with many many marine engines over the years when I designed heat exchangers, from all the OEM's this includes some really weird stuff that never made production, however most that did. I was exposed to much more when working for a large diesel manufacturer that also made marine motors. Engine installations and applications were my specialty, and that included custom extreme low-volume water-cooled exhaust for unique applications.

Much like Bondo, I also made a career of doing stuff outside the box.

there is no fear of thinking outside the box, just caution that your approach to cooling and fuel system if flawed. you cant do air cooled exhaust on a bilge motor. period. you need water cooled exhaust to the point it is international law (check out CFR 182.425 - the exhaust section in the US federal regs based on international law on boat building ) that whole issue of 200F being the flash point is serious. if you cant put your hand on it, its too hot.

outboard motors can **** fuel all over them selves and they wont kill people if they explode, as the fuel vapors would be outside the hull. put that motor in a bilge and fuel vapor will cause the boat to blow up into little itty bitty pieces that will take a CSI team a month to identify once the divers spend a week with nets picking the pieces off the bottom

all marine motors with the exception of one or two outboards run a thermostat the block and heads. however most of the cooling flow is going thru the exhaust to keep the boat from burning to the ground.

you need torque from off idle. what a car has that a boat doesnt is multiple gears.
 

H20Rat

Vice Admiral
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Mar 8, 2009
Messages
5,199
Convert to a jet drive... Unless you are swapping to a truck-like cam, your performance is going to suck bigtime. Your stock torque for that engine from idle to 2000 rpm is virtually unmeasurable, and unless you figure out how to get direct injection grafted on, a turbo will make that low end torque worse.

Basically the boat will be a dog out of the hole, you will have all your friends leaning over the front of the boat to get it on plane. Once on plane, it will probably be ok, but the engine is going to have a short life.

In a car, you don't run high boost for very long, parts tend to turn orange, and do that long enough, things fail. Turbo's in a gas vehicle aren't meant for max boost 100% of the time. In a boat, you are doing exactly that, you are driving a dump truck and the engine is running at 50-70% of its power output all the time. (going down the highway in a car takes maybe 10-15% of the engine)

And lastly, how about the little things like an alternator? You can't use your automotive alternative if you want to actually live very long (or be legal). You need a marine alternator, and you will either have to find one for that engine (probably doesn't exist), or try to graft a chevy alternator on it.


Back to my original point, jet drive. Jet drives don't require low end torque, they are a constant load on the engine and work much better to a typical automotive power curve. Going along that same line of thought, 'jet boats' often run open engine compartments, so the explosion risk is gone, and the rest of the automotive parts can be used.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Here is another view....

Toyota/Lexus put the 4-cam 400hp V8 in a bunch of ski boats about 16 years ago....,supposed to be the best thing for boats at the time if you believed the marketing hype.

Toyota missed the whole low-end torque thing needed in boats. The Toyota powered boats were such a flop, toyota actually spent a few million buying the boats back and they pulled out of the mainstream marine market due to the negative response
 
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