40 " V hull

[Bond007]

Just got a fix er up 40" V hull. All fiberglass. What size engine should I start with? 10.5 inches wide.
Have an O.S. .21 on the way for starters, figured if it didn't work out I'd use it on one of the other boats.

[Ron Olson]

For that size hull I'd be putting a 7.5 or 11cc in it.

[Chris LaPanse]

.21 is definitely too small, I'd put in a .46 minimum (7.5cc)

[Bond007]

Thanks for the responses. If I go to a larger nitro, would I be better off with a Gas Zenoah instead? Or will this be too heavy?

[Bond007]

I had chosen the OS .21, because it has 1.7 HP, I figured the horsepower was fine with the low weight.

[Ron Olson]

That's too much. You need a 46" hull minimum for a Zen.

[Bond007]

Ron, thanks for pointing me in the right direction!

[Bond007]

If I should be in the range of a 7.5-11cc engine, what am I looking for? Some 7.5 cc engines put out the same horsepower as the .21 I bought. Most seem to be in the 2.5 HP range. The 11cc engine I was looking at (O.S.) puts out over 4 HP. Looks like I'm in the $300 range now.
Now, HP vs. RPM... There is a wide range of RPM between these engines. I know this has something to do with prop pitch, but any general rules of thumb? Is higher RPM better, with a prop sized accordingly? Or is a low RPM better, and easier on reliability vs. performance?

I'm in this project now, my son is excited about working together to fix this up. I know I could have bought a kit, ready to go and satisfy our intentions. But, now that I have a 40" hunk of fiberglass, I want to make it very nice and have plenty of speed/ agility.

I have a 30" cat (Plastic with two 550 motors), I'm going to try to fit that OS RGMX .21 into it. Or we have my old Miss budweiser hydro, with the same motor deal. (This motor won't rip them in halve or anything will it?)

[Ron Olson]

This area starts to get really technical. Some manufacturers have a habit of fudging numbers but O.S. seems to be really close in theirs. Some have different power curves with their intake and exhaust timing so then you have to find the right pipe length and prop that the boat likes. Fun huh? :)
What is your intentions with the boat? Messing around and/or racing? A good engine in the 7.5/11cc range isn't cheap as you've found out.

[Bond007]

We won't be racing, other than each other. I'd like this to be responsive, jump up on plane and handle slow to agressive speed quickly. More fun than anything else. I would like it to approach 35-40, but I wont' be using a radar gun to check. I don't want something that is slow, or takes forever to plane up.
If the 11 cc engine will be faster and more responsive than the 7.5cc, I will choose the 11cc. I liked the idea of a pull start, which is the main reason I had chosen the .21. But I guess I'll be using a belt starter?
Looks like the running hardware is made by Octura. The rudder is held by two thick solid tubes. I marked all of the positions and then I took everything apart and am cleaning, polishing, and will probably reassemble with new bolting using removable strength loctite.
The stuffing box tube was broken, so I got a new one from a local Hobby store and will trim/bend to fit. I will need a teflon insert as well.
The cable size is 3/16.
It has an open top, guess it used air cooling before, I will be making a top for it as well.

Thanks so much for responding, I am finding it very difficult to get info. I live in Delaware, it seems that this hobby isn't very big here.

[Bond007]

I tried sending some pics, but the file size is too big.

[aquajetruner]

Bond,
I live in delaware, been looking for some friends to run with for a long time. I have gas boats boat it's all good.
Where in DE??

Bill

[Burkey1000]

we have in england a puma hull its only 42 inches we run them with g260s and there fine, and very very quick aswell, think it depends on how good the hull is too.

[Bond007]

Newark DE. There is a pond in front of my house, but will probably try a small lake in Middletown.

So you run Zenoah G260 gas enigines in a 42"? This boat is pretty solid, with some slight modifications I could fit one in.
However, earlier discussions have pointed me to the nitro side, I'm looking at the 11cc OS.

[Burkey1000]

im not saying do it its your choice but it has been done and very well, and very fast, im a gas person, also alot cheaper to run thats all.

[Chris LaPanse]

It is cheaper to run, but with that much weight in that small of a hull, I'd go with the nitro. It would run with the zen, but handling could get to be an issue. I'd say go with the 13cc nitro - cheaper than a zen, similar power to a (stock) zen, and much better sized for that boat. If you can keep it under 10-15lbs, 4hp should easily push it past 40 (I have a 55" 19lb V hull with a 4.5hp zen that'll do 38). It should be very responsive, and looks like a good engine. Overall, I'd go with the O.S. .81 (13cc). As for the rpm, high rpm motors are generally a little better on the top speed (though not much when propped right) and a high torque (like a zen) can spin a large prop, so is better on the acceleration. Either would suit your needs, though, and the .81 has plenty of torque (acceleration would not be a problem).

[Bond007]

Thanks for all of the advice! Going Nitro - I'll reply with how we make out.