Lightweight 400hp+ marine engine??

[larby]

Hi all,

It's been suggested that I try changing from a BBC to something lighter to gain speed, rather than upping power with my current motor and hitting sterndrive issues.

Trouble is, I can't think of what I could use! I don't mind tuning something to get there, and I don't mind what fuel it is, but it can't cost a fortune, I'm on a budget here!

I was also considering if there would be anything 200hp plus and even lighter that I could fit a pair of?

Any suggestions? Don't mind if they're well outside of the box!

James

[Paul E]

As you said in your other thread, what about an aftermarket ali smallblock?

[Renegade]

No offence mate but a blown bbc and cost/budget can't go in the same sentence.
May be a small block mpi motor and tune and remap it? Or carbed and run avgas? But 400hp is gonna cost you.

[larby]

Originally Posted by Paul E

As you said in your other thread, what about an aftermarket ali smallblock?

Wasn't aware there was such a thing for marine use? If there is, does that mean someone makes an ally big block??

Originally Posted by Renegade

No offence mate but a blown bbc and cost/budget can't go in the same sentence.
May be a small block mpi motor and tune and remap it? Or carbed and run avgas? But 400hp is gonna cost you.

I don't see why not... I've got all the bits for my big block and I'll be keeping boost as low as I can so it's just got a little extra kick to get it over 70mph. Should be pretty much as reliable as it was before if looked after?

Avgas is an interesting thought, could be tricky loading that amount of fuel from Jerry cans though, cheap fuel mind!

James

[Renegade]

Would it be rude to ask your budget? Light weight power could also be 2 merc efi? Or you do you wanna stay inboard?

[larby]

I'd quite like to stay inboard really. I don't have a fixed budget, but I've already spent way too much on this boat, so don't want to have to spend any more than I really have to. I may well end up having to accept running the BBC at a lower tune, but if there's a way I can change things about to get the extra speed I'd like to try it. I need to be doing 70+ to be competetive and thet's not gonna happen with a 400hp BBC in the back!

If I do end up changing engine, at least I can sell the BBC on to offset the cost.

Cheers, James

[Paul E]

Originally Posted by larby

Wasn't aware there was such a thing for marine use? If there is, does that mean someone makes an ally big block??


James

dunno about marine use, but they're definitely used in drag racing, and can produce silly power. Probably very 'peaky' though.

What about marinising an aluminum hemi, Keith Black or Donovan...

[Jon Holmes]

A small block Scorpion motor puts out 400hp at the crank, have a look at the new GM small block marine motors, they do a blown one that kicks out 500hp.

However, the small block (i am told) will use more fuel and provide less torque than a big block. In a lightweight application, torque should not be a problem but higher fuel consumption may be.

[larby]

Originally Posted by Paul E

dunno about marine use, but they're definitely used in drag racing, and can produce silly power. Probably very 'peaky' though.

What about marinising an aluminum hemi, Keith Black or Donovan...

Steady on, I don't have much of a clue about different american V8's, I'll have to chat that through with you in more detail some other time!

Originally Posted by Jon Holmes

A small block Scorpion motor puts out 400hp at the crank, have a look at the new GM small block marine motors, they do a blown one that kicks out 500hp.

However, the small block (i am told) will use more fuel and provide less torque than a big block. In a lightweight application, torque should not be a problem but higher fuel consumption may be.

Hmmm, yeah that sounds like a lot of expense for not much nett gain.
All I want is an extra 10mph, never would've thought it'd be this much of an issue!!

James

[TWIN RIG]

A friends got a brand new ford 4.6 signature engine that makes 425hp, they are fitted in the Cobra Mustang. He keeps threatening to put it in a P21 but can't see it happening.

[Matt]

If it were my money, I'd build a NA big block with ali, anodised, AFR heads, KE exhausts, hydraulic roller cam and fuel injection on a bow tie or aftermarket iron block. A gen 6 block would be ideal, as would mk iv.
Losing the blower and going ali with the heads saves a lot of weight. To achieve 600 ish hp, you'd have to up the max revs a bit or mebbe even bore and stroke it (not done the sums on a 502 as to how to achieve 600), but it'll also go a long way to keeping the torque levels under control vs a blower, and go efi to keep fuel consumption to a minimum and the idle and mid range as sweet as possible.
For "normal" use, you're then within the normal specs of the drive, but you've still got a load in reserve for when the occasion calls for it.
Going mk6 drive, or any of the other solutions I've seen would add an absolute shed load of weight and probably also $$, although I reckon the imco drive has got be worth considering due to it's compatibilty with bravo and it's generally just quite pretty. Those big drives (Im really thinking mk 6 here), extra gearboxes etc all add weight, complexity, and increase power loss, even if they are bullet proof.

Iirc, the orange arrow 830 has over 900hp through a bravo xr drive and does a snifter under 100, yet Mange's drive seems to survive-but i'm sure he's spent a fair bit of time learning to throttle it well to avoid barking the motor.

I could be making this all up.......or I could have my dick firmly in the custard.

[Renegade]

Originally Posted by Matt

If it were my money, I'd build a NA big block with ali, anodised, AFR heads, KE exhausts, hydraulic roller cam and fuel injection on a bow tie or aftermarket iron block. A gen 6 block would be ideal, as would mk iv.
Losing the blower and going ali with the heads saves a lot of weight. To achieve 600 ish hp, you'd have to up the max revs a bit or mebbe even bore and stroke it (not done the sums on a 502 as to how to achieve 600), but it'll also go a long way to keeping the torque levels under control vs a blower, and go efi to keep fuel consumption to a minimum and the idle and mid range as sweet as possible.
For "normal" use, you're then within the normal specs of the drive, but you've still got a load in reserve for when the occasion calls for it.
Going mk6 drive, or any of the other solutions I've seen would add an absolute shed load of weight and probably also $$, although I reckon the imco drive has got be worth considering due to it's compatibilty with bravo and it's generally just quite pretty. Those big drives (Im really thinking mk 6 here), extra gearboxes etc all add weight, complexity, and increase power loss, even if they are bullet proof.

Iirc, the orange arrow 830 has over 900hp through a bravo xr drive and does a snifter under 100, yet Mange's drive seems to survive-but i'm sure he's spent a fair bit of time learning to throttle it well to avoid barking the motor.

I could be making this all up.......or I could have my dick firmly in the custard.

Did you get all that james? Lol

[larby]

Sweet jesus!! Everyone must be bored at the moment going by the amount of responses I'm getting!!

Matt, I see where you're going with that, but I'd still be exceeding the power limit of the drive, an I'm not the kinda person to just cruise around at part throttle, especially when racing, and my concern is that I would damage it during a race, but not find out till I'm out with the family.

As it happens, I was reading about the Arrow just a second ago and noted that he was running an xr, including race use! He uses fully synthetic oil (something I've been told can make a huge difference!) and changes the oil after every race.

It seems which ever way I turn there's not a solution that I could afford. Maybe I need to look into an Imco SC upper, stick with what I've got and see how it goes. May well survive with the boat being very light, I'll just have to cross my fingers for the first time it breaks!

James

[larby]

Here's a thought. Could I make a kind of 'ultra cushy' joint that would reduce the stresses on the drive as it wouldn't be so solidly attached to the motor?

I'm sure I remember an old-skool auto transmission that had a very viscous fluid, a bit like cornflour in water if you know what I mean, with paddles attached to input and output running very closely together.
Little sudden differences in rotational speed (such as prop re-entry) are easily absorbed, yet the main drive force is well transmitted.

Imagine it being like a big rubber drive shaft that can twist a bit when needed. It'd untwist a bit when the prop leaves the water and the torque is off, then absorb the shock impact as the prop re-enters, taking the damaging shock impacts off the drive? A driveline shock absorber. Crazy or plausable? Don't make me start another thread!!

James

[Matt]

Originally Posted by larby

...but I'd still be exceeding the power limit of the drive,

Mercury'll sell you a 600hp supercharged motor with a bravo xr.
http://www.mercuryracing.com/sterndr...0sci/specs.php

600hp on a single drive'll get you to 80, right? How fast you trying to go?

[PerformanceDodge]

Hi James

I found the following regarding engine power output ratings on a forum some time ago and found it so interesting I saved it, can't remember where I got it from so my apologies to the authors. Well worth reading and if you are not confused already you will be by the end.

Regards David

There are many differences between a limited duty engine and a continuous duty one. As an example , it is necessary to understand the difference between an SAE work test and a standard BRAKE test. Both tests are performed on the same device called an engine brake or engine dynamometer. Essentially the engine is run up against a variable load. This load device is mounted in bearings so it can rotate, but it is prevented from rotating by a lever which is attached to a scale. This scale will read out in ft. lbs.. So at any engine speed the maximum torque can be read. Because torque is one component of horsepower and speed being the other, horsepower can be calculated as well as fuel consumption, brake mean effective pressure and a number of other items. The important thing is the test program. A BRAKE test is where the engine is warmed to normal operating temperatures and then run up to maximum power and that's the end of the test. An SAE test, on the other hand is run up against the load for a sustained period (maybe 4 hours) until the maximum power is reached that DOES NOT exceed acceptable manufacturers operating parameters like oil, water, exhaust and head temperatures and pressures. In your example you mentioned the Chev. 305. This engine will brake somewhere around 220 to 280 HP depending on state of tune. The maximum SAE rating of this engine is 55 HP.

I suggest that if you were flying on a plane, or on an ocean cruise ship, you would want the engines tested under an SAE test program. The differences in design and build are many. Intelligently, you have to factor the type of usage you need from the engine and then modify the automotive engine accordingly. The greater the durability, the greater the cost. Nothing is for free and when a marinized automotive engine costs are comparable to the standard automotive variety, you must question it's durability.

From: plkruse@iu.net

I've found this thread to be especially interesting, especially the parts of it that deal with the power ratings of the engines. I'm much more familiar with diesel engines than with gasoline ones, (such that I can quote the spec's of some of the more common ones without having to look them up). So, the examples that I will site pertain directly to diesel engines, but the exact same principles apply to gasoline engines. In fact, I?ll use the CAT 3208 as an example, since it is a V-8 diesel very similar to a large gasoline engine. (636 cid)

The harder you run an engine, the faster you will wear it out. It really is as simple as that. Every engine therefore has many different power ratings, depending upon how hard you plan to run it and how long you want it to last. If I were to tell CAT that I was going to put the engine into a small commercial fishing trawler that was going to run 3500 hours pre year, for example; then they would tell me that the 3208 was good for 150 hp. They would derate the engine so that I could not get more than that much power out of it. If you were then to ask them for an engine for a high performance recreational boat that was not going to be used more than 300 hours per year, then they would tell you that the same engine was good for
435 hp.

What?s the difference between these two identical engines, that they would have such a different rated power? Chiefly this: In both cases CAT wants for the engine to last at least as long as the warranty. Since I?m going to put a whole lot more hours onto my hypothetical boat than you are, they will derate mine in order to achieve that objective. In another example, I was once going to put a CAT 3412 into an air boat. My customer wanted the most power for the weight and the cost, but was happy with an engine life of at least 1800 hours. This is a very unique case, in which CAT was willing to rate the engine at 1000 hp. On the other hand, a friend of mine maintains a fleet of work boats with this same engine in them. He runs them at about 500 hp and gets 50,000 hours between overhauls.

CAT has five different power ratings published for each engine. (If you present them with a special case, you will learn that they actually have more ratings than that.) These ratings go from "A" for continuous duty to "E" for highly intermittent duty. In this example, the A rating for a 3208 is 150 hp; whereas the E rating is 435 hp. Gasoline engines have a similar ratings system, except that the DIN and ISO standards for "automotive power" ratings will give you a slightly higher number than most "highly intermittent" ratings. In other words, it is the peak power you might use if you were passing uphill. It is certainly not the amount of power that you can expect the engine to put out for any significant period of time.

We are currently building two boats, both commercial fishing work boats; and are about to buy an engine for one of them. It will most likely be a Cummins B5.9 in one of its many versions. This is the same engine Ford used to offer in their pickup trucks, and Dodge currently offers. Cummins is telling me that they will rate it for
150 hp in our boat, but it is rated at 220-250 in its various automotive applications, and it is offered in a 300 hp version for recreational marine uses that do not exceed 300 hours per year. To put this into perspective, a pickup truck running flat and level at 75 mph without a trailer will require about 50 hp. The same truck with perhaps a 10,000 lb. gross load would require most of the 220 hp. The same engine in a 25 foot sport fishing boat would probably cruise at about 200-230 hp.

There is a difference between the way commercial truck engines and car engines are rated. (A pickup truck is a car for the purposes of this discussion.) In the case of a diesel truck engine, they are rated pretty much at the power they are operated at. In a gasoline car engine, however; they are rated much higher than you would ordinarily ever use them. I know of another example that illustrates that point nicely. They are two almost identical 35 foot sport fishing boats that typically run over a 100 miles off shore together, where they troll for deep water fish. One has twin Cummins 6B5.9 engines salvaged out of pickup trucks and converted to marine use. The other has twin 454?s, also salvaged out of automotive service and converted. All four of these engine are rated at 250 hp, or within five percent of it. These boats normally stick close together all weekend, until it is time to run home; at which time the diesel boat will beat the gasoline boat home by about six hours. The difference is that Cummins recommends that the diesel boat back off of maximum rpm by only 200; whereas no one is going to run a gasoline engine that hard for that long. That captain backs off about a thousand from maximum rpm. To exceed that speed for long periods of time causes cooling problems. This is very consistent with the way the engines were designed to operated during their first lives as automotive engines.

To sum it all up, an automotive engine will typically run at 20-40 percent of its rated power. (In this case, I?m using "automotive power ratings.") It will only exceed these limits under highly unusual circumstances. If you put the same engine into a recreational boat, it will typically run at 60-80 percent of its rated power. A commercial diesel truck engine typically runs at about 60 percent of its rated power. (Flat, level, 75 mph, maximum legal gross load.) That same diesel engine installed into a recreational boat will often run at up to 95 percent of its rated load, with bursts perhaps as high as 105 percent. If these same engines are installed into commercial work boats, then their service lives would be more similar to the truck or the car. It is all a matter of how long you expect to run your engine before replacing it or overhauling it.

All the numbers I quoted in this article are from my memory. If I were at work, where I have all my reference books, I would have checked them more carefully. They should be fairly accurate, and are certainly good enough for the comparison purposes for which they were intended. Since the same engine is sold in so many different versions, you would certainly want to check the OEM specifications on your particular engine before making any critical decisions based upon these numbers.

[motorvator]

Originally Posted by Matt

Mercury'll sell you a 600hp supercharged motor with a bravo xr.
http://www.mercuryracing.com/sterndr...0sci/specs.php

600hp on a single drive'll get you to 80, right? How fast you trying to go?

I'm with Matt, Over 850 hours on my 502 mpi and the only thing I've never blown up is the bog standard Bravo 1 on the back of it.

Standard engine is 415 hp at prop which probably equates to something in the order of 440 hp at crank. That equates quite easily to low 70's unless you have built a floating brick!

Play with heads etc and you will get it to 500 hp but it will be the rods etc that let go not the drive.

And remember racing is about the average speed you maintain not a once off top end. The most important parts of that are the hull and driver not the engine.

[larby]

Freddy - Thanks very much for that article, made for very interesting reading! The ironic thing is that the whole time I've been discussing this hp vs drive thing, I'm well aware that it's torque which kills them, not hp.

As that article confirms, most of the time I'll be putting well under the rated level of hp and torque through the drive. It's just the odd occasion that it'll see a sudden spike of torque and may get weakened. That was what I was trying to solve by adding a driveline 'shock absorber' to reduce these spikes.

Matt & Kerry - I never realised that Merc offered engines that powerful with a bravo drive! I guess I was spending too much time looking at other options to check the merc catalogue! What a muppet!

Ok, so the long and short of it is I'm gonna have to stick with a bravo variant. I'm told the Imco SC upper is a good option too?
Hopefully the past lack of speed from the hull was due to the way it was built. Now it's nice and stiff that should help. I also took a 1" or so hook out of the bottom when I was rebuilding, it was caused by the trailer being too short. I've adressed that too by converting to bunks and extending it.

Thanks for all the help everyone, I don't know what I'd do without this place sometimes!!

Cheers, James

[topgun]

Originally Posted by TWIN RIG

A friends got a brand new ford 4.6 signature engine that makes 425hp, they are fitted in the Cobra Mustang. He keeps threatening to put it in a P21 but can't see it happening.

510HP if its blown in the GT500 !

[Cookee]

Just to add more confusion, I raced a Phantom 25 copy in Malta with a 496 in it (420hp standard?) which had a "Procharger" bolted on the front - 600hp! The thing got to 90 in pretty much no time at all and would probably gone even faster if it had been flat enough! It was driving an XR drive by the way!