Ok, so I've gotten involved with yet another odd project.

Some of you may know that for the past five years a friend and I have been not quite finishing a project to build a jetboat, based around a Honda Civic GTI engine and miscellaneous parts. Real life keeps intruding, and as a result it's still nearly done.

So anyway, I was browsing though the local online crap for sale website, and came across an ad for a Dowty Trubocraft jetboat (this is actuually how it was spelled! They meant Turbocraft, of course), on a trailer for £150 or near offer, just down the road. After wrestling with common sense for more than thirty seconds, I went along with James (my cohort in this venture), and had a look at it. When we left half an hour later, we were £100 poorer and towing a trailer

It's a mid-seventies to very early eighties boat in very good condition under the horrible paint, with a decent trailer and a crap engine, which I think may be the original one (a 2.3L ford Zephyr), which is full of water. For instance, when you remove the spark plugs, you don't really want to find they're rusty.

The long and the short of it is that we need to put a new engine in, which is an easy job since everything's so accessible, clean it up, and do a little rewiring. A weeks work, tops, but...

Which engine?

The original one was about 90BHP, which I feel is not really good enough. Since Ford have been good enough to produce modular powertrains for many years, pretty much any european RWD Ford engine will go in nicely. We want to get this running before the weather goes horrible, so we need to make a decision in the next week or so.

Our options seem to be, based on what's available in scrapyards and the like for little cost:

(A) Granada Scorpio 2.9i V6. 145BHP, bags of torque, cool sound, but thirsty and getting difficult to find in good condition (no one can afford to run them anymore)

(B) Sierra 2.0i DOHC 4-cylinder inline. 130BHP, somewhat less torque, but higher revving, identical block size and shape to the engine we took out, can be race-tuned to buggery, and someone I know at a local car parts place has one on his garage floor with all the trimmings, known working, with 46000 miles on it. In addition I have a supercharger from a Mercedes 230SLK which would fit...

(C) Rover 3.9i V8. 200+BHP, god knows how much torque, low-revving and bulky, but about the same weight as the V6. Rather thirsty, more expensive, but very reliable. Would need a little more work to make new engine mounts, but easy conversion.

(D) Something else. Would need to be from a rear-wheel drive system with the same direction of rotation as the Ford engines.

So, given these choices, what would you do in the same position? I tend to favour option B, although James likes A because it would sound nicer

pca

Hmm. Can't help but point out a comparision - a (chipped) VW 1.8T beats the VW 2.8VR6. Who's going to hear the engine once you've installed an empeg?

Seriously though, if the 2.0i can 'be tuned to buggery' and you already have a suitable supercharger then I think the decision has already made itself. Contemplating (A) simply for the sound is little more than a distraction into the land of romantic fantasy IMO. It sounds like spares might be getting harder to find for that too. I'd favour (C) over (A)... at least for the added burdens you'd be getting some real grunt.

But face it. You want to tinker about with that supercharger. That's the only reason it's sat in your garage for so long... you've been waiting to find a use for it, and here it is.

Who's going to hear the engine once you've installed an empeg?

Well, in the original design the exhaust came straight out through the stern, with no silencer at all. I can assure you that even WITH an empeg you'd hear a V6 under those conditions

However, you're largely right about my feelings towards that supercharger. It's been dissasembled, cleaned very carefully inside, had the casing sandblasted so it's nice and new looking, and lovingly reassembled. It's a work of art, with teflon coating on top of ceramic coating on the rotors. I REALLY want to use it on something!

pca

So why not on the Rover V8? (C)

I'm guessing that the supercharger is too small - it's from either a 2.0L or 2.3L engine, and probably isn't capable of flowing enough air to do anything useful on the V8.

Whould the sierra be better because of the higher revving? I didn't think that torque was a big issue for jet boats, just higher revs. The higher the revs, the faster you go. Is that right?

Correct, I think. It might be possible to wind up the gear ratios to the point it would turn fast enough to pump enough air, but the results could be, well, messy if it failed do to centrifugal stresses.

I have got an enormous Wade roots-type supercharger off a DAF 2-stroke diesel, which would easily blow enough for a mere 4L V8, but it's HUGE!

pca

I didn't think that torque was a big issue for jet boats, just higher revs. The higher the revs, the faster you go. Is that right?

Well, certainly the faster the impeller goes the faster the boat will go, up to a point anyway, but more torque (especially at the low end) equals more acceleration. You need to have a good 0-60 time after all

pca

Put some decent pipes on it and the Rover V8 will sound sweeet, and being a GM design straight out of Detroit it's OK with me....

Gareth

Think: Last of the V8 Interceptors.

Supercharge baby.

-Zeke

Ford 460 V8

If you go for the Ford, go for the 2.0i DOHC - lots of parts (and performance parts) available. Very tuneable.

But my recommendation is the classic Rover V8. Hard to break, and if you do, lots of spares available at any breakers yard or land rover garage.

Important things to think of in a marine application are you do not want a highly stressed car engine in a boat as a car will never go for an hour at full power where as a boat will. So a low stressed big engine works wonders.

Make sure you have either a keel cooler or a heat exchanger as putting raw water cooling through a car engine can result in a dead engine pretty damn quick.

Once you have your engine connected to jet drive be careful when running it as there is a good chance that the bearings are water lubricated and cooled so stick a hose pipe up its arse to cool it.

On engine choice what about a bike engine small damn light with built in gearbox to get right speed for jet but possibly too high stressed. Or a diesel which uses less fuel and you can use pink diesel and since it needs less fuel can actually work out lighter than a petrol, also none of those nasty electrical things to go wrong.

One cool thing about jets is since they have a bucket door for reverse instead of a gearbox you can go to zero thrust with bucket door half way down then give full throttle go no where then open the bucket and scream off with full thrust at zero boat speed.

as a car will never go for an hour at full power where as a boat will.

Obviously you've never been in Rob Voisey's Supra!

Make sure you have either a keel cooler or a heat exchanger as putting raw water cooling through a car engine can result in a dead engine pretty damn quick.

This is obvious to you, me, and anyone with any ability, but not to the previous owner of the boat. Which would explain why the plugs on the original engine are rusty. For the time being, we're going to use the radiator that came with the engine, but a heat exchanger will be fitted as soon as we can find a good one.

Once you have your engine connected to jet drive be careful when running it as there is a good chance that the bearings are water lubricated and cooled so stick a hose pipe up its arse to cool it.

Yes, I'd already worked that one out, from reading the documents on the jet drive I found on the web. Not only is the rear bearing water cooled, but it's made of rubber!

We ended up getting the 2.0L DOHC engine, which we picked up yesterday. Today is buying the marine ply and replacing the decking day. Hopefully, we'll have everything running by the end of the week.

pca

If you are looking for a cooler my father might have one poking around in his garage somewhere

But my recommendation is the classic Rover V8. Hard to break

Hard to break? Rover made a damn good job of it when they bored it out to 4.6 - avoid those ones!

In reply to:

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Make sure you have either a keel cooler or a heat exchanger as putting raw water cooling through a car engine can result in a dead engine pretty damn quick.

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I used to have an old 35-foot wooden fishing boat up in the Gulf of Finland. It had a 42-hp Volvo marine engine - basically an "marinized" Amazon engine running on low-quality fuel - and with seawater cooling. Ran great, but needed a new head every 6-7 years

Old cast steel engines can almost survive raw water cooling but a modern alloy engine i would imagine would end up as a furry lump of sludge in no time.

volvo marine engines are not too bad but the parts can be damn silly in price. A mate had an old volv diesel and it was slightly mre expensive o buy a new engine from perkins than it was to get a new gasket set for the engine for an overhaul.

That would be handy, if you have one going spare.

pca

Okay you got mail

One thing that the get might have that i saw on a small hamilton jet drive was a connection that provided water at pressure for cooling purposes otherwise you will have to rig a second water pump off the engine.

You said the boat came with a radiator how the hell did that work