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.

As far as the drive you may want to look into the bravo 2. It was designed for heavier sport cruiser models. They are reliable and reasonably priced.

The 25 Bert is a great hull! which style do you have? I've owned two, they both came with 4cyl and alpha's. A single big block is an easy conversion, the Bravo 2 worked well but the bravo 3 or volvo dp gives a little more stern lift and better performance. A 383 could work well but you may need to shift some ballast around. I think your best bet would be to buy a complete package. You can get a worn out one cheap and rebuild it, at least then you'd have all the pieces you need. 496's can be found cheap and 454mag's and mpi's.

Sport convertible, I am planning a cc conversion.

What sort of power have you tried in your Berts, or did you stick with the fours? Do you have any rough performance and efficiency numbers?

With a boat that size and weight the fuel savings is nothing, in some cases the SB fuel mileage can be worse because it works harder to cruise.

I agree to start with at least a blown up Gen V, VI or 496 BBC Merc. The accessories and rigging will blow your budget real fast if you shop for them ala carte.

Nice to see you, I have been on reefers for a couple of years(mostly lurking with the same sn) I doubt you will be going alpha 1 on this but I have a garage full of parts(gimble rams etc.. as well as some sbc parts.. all alpha 1 gen 1.
Good Luck with your build.

Aye McReeferson tis the irish
 

Since you do not have a marine rigged engine - I would say you should try to pick up the entire engine assembly from e-bay. Often pull out motors are for sale when another individual is upgrading. Saw two HP500 Merc Racing engines pulled for sale couple of months ago.

Another angle would be to contact a marine engine builder. You would not believe the amount of "take off" equipment laying around this sort of shop as well as compete engines looking for a home. Some negotiation would get you the whole assembly.

It takes a wise man to appreciate what a "stock" engine is. They are built by engineers to perform a specific duty - give good fuel use, and live a long time. Usually the larger and simpler the better. I would say the 454 MAG Mercruiser - 385 hp - or the 502 MAG Mercruiser - 415 hp. Both of these engine short blocks are still in production and were widely manufactured ten or so years ago so used parts and equipment availability is good. Also these engines used forged components - crankshaft, rods and pistons all of which take a considerable beating in a marine engine owing to the load and operating speed. These are long living engine designs. Both of these engines were used in offshore hulls as well as large cruiser hulls and can easily perform well in each design. These engines can be serviced by any Mercruiser dealer from the Florida keys to the State of Maine. Usually custom built racing type equipment is an absolute headache to get service if you cannot do it yourself.

Carburator or fuel injection is another choice, I am guessing that the carb would be the most servicable and easiest to keep up. Most Mercruisers used automotive designs by Holley, Carter or Rochester and marinas are fairly familiar with them. This would mean a motor built before 1998. Fuel injection is newer and probably more economical with regard to fuel consumption, but getting the advanced electronics worked out and or repaired is sometimes a hassle.

Bravo Mercruiser is the easy sterndrive choice. The Bravo is incredably strong when used with a stock engine. It is widely serviced and comes in three forms. Bravo I - is the standard performance drive, Bravo II - swings a very larger propeller for work boats and barge use. Bravo III - is usually the drive of choice for cruisers and has two counter rotating propellors for more fuel efficiency. This can be an expensive setup to prop in. Although companies like B-Blades propellor will loan test propellors through the mail to help dial in propellor selections.

This is all very helpful info, thank you all for chiming in. There are so many options to go over, it is hard to figure out where to focus my attention, all of this input certainly helps with that.

I had kind of figured I would end up going with the Bravo III option, but what to mate to it was a big blank for me. Now I guess it is time to start looking for a suitable motor in need of rebuilding.

I know that (of course) every motor is going to be it's own unique can of worms, but perhaps some of you can chime in on what you may expect I may need to put into a "tired" mercruiser to breath new life into her and ensure reliable service. Again, I know every motor is going to be different, but, if you were to pick up what you considered to be an ideal candidate for a refresh, what would you be expecting to put in right off the top before you really started digging?

Engine rebuild
 

Dave,

Marine engines are usually automotive engines by design. So the process and procedure for repairing them - of refreshing them are fairly standard. Because the marine engine runs at near full power a great deal of the time they get much more wear.

Basically the engine wears in several standard ways. The crankshaft has bearing surfaces that are ground true and straight. The engine block is bored with round straight cylinders. In the life of the engine these two components are the heart of the engine. The crankshaft bearing surfaces often wear in an out of round condition and are refinished by a crankshaft grinding company. The engine block wears the cylinders into taperd cone shape. Usually this is repaired by boring out the cylinders and installing new oversize pistons. Engine block cylinder head surfaces are examined for warpage and flatness and refinished if necessary. Prefered crankshafts are always forged steel.

Cylinder heads often warp where they contact the block and are checked for straightness. The valves are removed and usually replaced because of the stress they encounter with quality marine valves. The valves run in valve guides which are holes in the heads and are checked for taper and wear and replaced if necessary. The valves are seated in the head by a grinding operation that adjusts the seat surfaces to match the face of the valves. Valve springs are usually just replaced with new marine parts.

Valve gear is usually the weak spot in most marine engine design because the manufacturers will not pay for truely quality rocker arms and pushrods. Replacing these with racing equipment is standard operating procedure.

Engine pistons are fitted with new piston rings which are machined to fit the diameter of the cylinders and the grooves of the pistons. Forged pistons are prefered over cast aluminum pistons because they are stronger

Connecting rods are examined for any damage and for straightness and roundness of the holes in each end.

Pistons, rods, and crankshaft need to have the balance checked so that they run without vibration.

Crankshaft bearings are purchased new and checked for proper fit when the engine is assembled.

Camshaft is examined for any damage - the timing gears and chain that drive the camshaft are usually replaced.

Now all the parts in a marine engine are of the severest duty design and automotive parts are not suitable substitutes.

Usually it is more economical to have a marine engine builder complete all these operations as they are beyond the scope of most mechanics.

Dr. d

Very helpful, thank you for taking the time to write that up.

- Dave

Thanks Bill. Yeah, I recognized the SN right away. Haven't been doing much of the reefing lately. Just had a kid, and something needed to give. I grew up on the water, and still live on an island, so the boats aren't going anywhere...