Conservative performance?
 

Hello folks, I've been doing a lot of searching and reading, but haven't found a whole lot of info on the particular type of powerplant I am thinking of building. Maybe you can help?

Why don't I lay out what I have, what I am looking for, what I expect it to do, and what resources I have available to me, and maybe you folks can point me in the right general direction...

What I have...

- 25 foot Bertram, a rather different type of hull than most of what I am seeing discussed in the majority of my search results. The boat has no motors or drives, she's a blank canvas.

What I am looking for...

- I am looking to loosely flesh out a component list of what would be required to build a 350-400 Hp powerplant for the above vessel. I intend to run a Bravo O/D (3?).

What I expect it to do...

- I would like to achieve respectable performance, good fuel efficiency, and (hopefully) excellent longevity while pushing about the above vessel (figure about 5000lbs). Average usage will likely consist of about 10-15% at or near to WOT, 30-40% efficient planing speed, and the balance at or near to idle (trolling). I would like to do all of this without breaking the bank.

What resources do I have...

- I am pretty handy with a wrench myself, and have a few friends who are much more so. These friends are ready and willing to help, very knowledgable in performance engine building, can hook me up with cheap parts and supplies wherever they can, but, have no marine engine experience.

I want to get a good idea of what my requirements are before approaching my pavement pounding buddies as I know from my reading to date that there are some major differences between the two worlds and what they require from an engine, and therefore what goes into a build.

I thank you in advance for any help you can give. Feel free to ask questions if I have left anything key out.

I would seriously look at a single [or pair] of diesels, you AREN'T looking to run 100mph or Poker run the boat, the diesels will live almost forever, idle all day, low rpm, low maintainance and get great mileage. I am sure others who have forgotten more about this stuff than I will ever know will chime in, but, if it was me, I would look at Diesel power

Good Luck!
Michael

The problem with diesel is up front expense. Turnkey systems carry astronomical price-tags, and from what I can gather, you can just forget about the "roll your own" route. In contrast, gasoline power-plants are far more accessible, both in cost and availability of parts, and in the available knowledge base.

Don't get me wrong, I'd love to plop a diesel in there for a few specific reasons, but it just isn't in the cards right now. I figure my other options are outboards, or I/O's (or perhaps a jackshafted version thereof). I am leaning towards the jackshafted I/O's. I had been reading elsewhere about the Mercruiser 383/350, and this did not seem as though it would be a terrible fit, good torque #'s to go with that HP. and given that I have the resources, interest, and a sickness for DIY, I might try crafting my own version somewhere along those lines.

- One additional point I forgot to mention in my first post regarding my "resources" is that I work in manufacturing (machinist), am very capable, and have access to just about any type of machine tool, as well as personnel to perform any sort of manufacturing tasks I am not proficient in.

I would just get a stock low hour take out 496HO and be done with it.

What you're looking for is within the capability of just about any modern BBC-based Mercruiser. Are you thinking EFI or Carb? Sounds like you want to build it up?

From looking around at what is readily available it does not look like what I am looking for is at all unreasonable. My first thoughts were to keep it SB based for fuel economy reasons, as well as me thinking that doing so keeps me working with a power-plant who's popularity will help keep parts costs down. That is why I mentioned the 383, seemed like a logical choice to my inexperienced brain, but I am open to hear what those who know more have to say, top to bottom.

I am half way thinking EFI, with the assumption it will give me better economy per pony, easier starting, and more all around reliability/less hassle. What I am unsure of though is at what expense it will come, and if it is a manageable project for a rookie.

If at all practical, yes. Number one, there is the aforementioned DIY sickness. If I can do it myself, generally speaking, I do. Second, there is cost. I am betting, with a bit of help in component selection from you guys, some hands on help from my race car wrenching buddies, and my manufacturing abilities, there is a buck or two to be saved in there.

Is this the same dave as Boston reefers?

Install a bracket and hang a 300X on it and be done. I'm a die hard BBC guy but for all the work involved starting from scratch with no rigging, thats the way I would go. My 2cts worth.

It is.

That is an option, and I do have an outboard, rigging, and ability to do it. But, I am not sure if it is the best option for what I want to do with/get out of the boat/project. I appreciate the input, but I am more looking to get input on what people might think would go into a build like I am asking about rather than advice on what other directions I might take.

Sometimes, for me, it is "all the work" that makes something worth doing. It's a sickness, and I don't try to hide it. Nothing gives me more satisfaction than stepping back and saying "I did that!". I am too far gone, no point trying to talk sense into me.