I was just wondering is it possible to use a regular nitro car or truck engine in a boat? I have plans to construct a water cool head for the engine but before I begin this endeavor I want to know what the outcome will be since they make so many more RPM's. The plan is to use a 2.5hp 30000 rpm motor in a 43" hydroplane.......... Is it possible?

you could leave the origional head on the engine, the large heat sinks on most car engines will keep it cool....you could also wrap copper tubing around the heat sinks to dissipate some of the heat also....what size is this motor your talking about...sounds like its got some power behind it....

Thanks for your help do you have any idea what prop I should use I am new to the boating world and this boat I am building is my first one.... I have several nitro trucks but this is the first boat

What size engine are you considering? My reason for asking is a 43" hydroplane is going to be heavy and will need lots of oomph to get it going.

I have a Super Tigre 4.4 at 2.5hp 30,000 RPM and I also have a Nitro Star 4.6 at 2.9 hp 32,000 RPM I was going to use one of those and also fabricate a clutch system so the motor could build some RPMs before it takes off. The reason I am trying to use one of these motors is because I am building this boat on a budget and I happen to have found these motors for free the Nitro Star is brand new never used broke in or anything. I was looking at marine engines like the 61 that was in it and they only make like 2-3 hp that I have looked at and make a lot less RPM's so I didnt think that using one with more RPMs and the same power would really hurt anything. The original motor that was in it was junk when I got the boat it was an Irvine 61 which made like 1.3 hp and 22,000 RPM's by the specs that I found so I thought one of these motors would be a big improvement........................ If I can make them work anyhow

I've never been enthused with running airplane engines on boats. However, since you're on a budget, and you've already got them, try whichever one has the most power. The boat won't be a rocket, but perhaps it'll run ok. I'd suggest not trying to use a clutch. It will just add weight and will rob power.

Those are actually engines from four wheel drive monster trucks but thanks for your help I appriciate it

Oh, ok. In that case, you need to be sure that the shaft has room for the flywheel and shaft collet.

You're going to need an engine in the .61-.67 range to move a boat that large. Clutches don't work well in hydro's besides all you have to do is give it a toss to get it up on plane. They're generally not a boat to take off from a dead stop with.

what would happen if I did use one of these motors?

If you under power a hydro it will be slow and might not even get up on plane. That's why I said "perhaps it'll run ok". I should have put emphasis on "perhaps"...

I guess I dont understand I have been talking with other people around here about using one of these motors in this boat.... The boat weighs less than my HPI Savage (a 1/8 scale monster truck) which is where these motors came from and they have enough power to make it flip over backwards so I figured that it would be enough power for this boat. The biggest thing that they are worried about is cavitation since these are high RPM motors. O.S. recently took one of their truck motors as put a marine head on it and they claim that it is a rocket. I was hoping that maybe this might work for my boat. You seem to be very knowledgeable about boats so what kind of prop might I need or should I try with this boat and motor. If I cant find a marine motor in my price range these are what I will be using. I really appriciate your help.. Thanks sorry if I am annoying

Are MDS engines any good? There is a 61 on ebay for 60 right now and 25 to ship

What's an MDS and why does it cost so much to ship it? That's a lot of money for shipping as I've shipped things a lot larger than an engine for $25.00 .

MDS is the brand of the engine it is a glow fuel engine and it costs so much to ship I guess because its in Europe............

Try one of your LHS's, Rider's or Hobby Stop West to see what they have. HSW knows boats better than Rider's.

Does Hobby Stop do a lot of boats I usually go to hobbytown since I am about to work there and I live just down the street from them. I have only been to Hobby Stop once. At least I think I have been to that one where is it at.

You're not being annoying, asking questions is the way one learns. Also, thinking outside the box is the way new things are discovered...

I know a bit about boats, as do others here. The RPM range you cited for the engines isn't going to be a problem. To give you an example, it's been estimated by people who know way more about boats than I do that the .45 MAC engine in my Sport 40 hydro is turning close to 30,000 RPMs when the boat is at the end of a straight. Anyone who has seen this boat run knows that cavitation is not a problem. Boats typically use high RPM engines and are propped accordingly.

It takes significantly more power to propel a boat on water than it takes to run something on land, or even in the air. For example, the Rolls Royce Merlin engine that has been used in unlimited hydros could get them somewhere in the 200 MPH range, give or take some. In a P-51, the same engine could propel the plane at over 400 MPH. Who knows what the engine would do in a properly designed land vehicle?

Adding to the problem is that a hydro has to not only run fast, but be able to get up to speed. There's a balancing act to find a prop that will work at speed, but that's not too big for the engine while getting the boat up on plane. Prop it too big or too small and it won't be able to get up on step. I've seen plenty of hydros plow through the water struggling to get on plane only to end up failing. This is where choosing an appropriate engine is important. If the engine doesn't have adequate torque to spin that big prop while trying to get on step, or it's lacking the RPMs necessary to spin the prop fast enough once the boat is planing, the boat isn't going to run well.

As Ron said, 1/8 scale hydros usually use .67 size engines. Even with those, people I know who run them say the boats tend to be underpowered and under weight. I know if you keep an eye out that you'll see a decent engine in this size range for $200 or less. This year alone I've picked up a CMB .67 with tuned pipe for $215 and a brand new OS .81 for around $200. They're out there...

Thanks for your help I am still looking for a motor I havent given up yet I just missed an OPS 60 for 60 bucks its used but I could have gotten a new piston and sleeve for it I screwed up there but I am still watching the budget is really tight now rent is do soon.........

i have a question about liquid cooled marine engines. how does the water circulate in the head, do they have water pumps on them? i am curious because i think it would be nice to make a liquid monster truck.

There is a water pickup on the back of the boat. Most often this is part of the rudder, but sometimes it's a separate part. When the boat is moving forward the water is forced through the pickup and then into the engine.

MDS is a good engine and are VERY good with a pipe .
And those prices you see ARE good and the seller IS reputable . I personally bought three engines from him and without a single problem .
( ps ... the engines might be your top shelf , BUT ... are a LOT faster than K&B's ) )

MDS Engines
4105 Fieldstone Road
Champaign, IL 61822
Phone: 217/355-9511
Web Site: http://www.mdsengines.com