Speculation: What will it take to puch a Stinger 260 beyond 60kts (70mph)?

[lbg]

Hello Stinger friends!

I'm the owner of a Stinger 260 from -88 by the name of Wet'n Wild.
Currently her condition is awful since I haven't had the time to treat her in the way she deserves.   So, she will be repainted, or at least the paint will be removed and the gelcoat condition revealed. Then we'll see if she needs repainting.

Anyway, since I'm going to make an overhaul on the exterior, why not on the interior... And since I'm at it, why not the engines?
Everything won't be done at the same time, of course, one thing at a time. Lets talk about the engines, drives and props.

I started out learning the theory of CSB-tuning and has been reading about it for the last 2 or 3 years. Producing 450-500hp from a naturally aspired Chevy Small Block 350 is doable. The environment and fuel economy is not considered. But, I'm now in doubt... Is it really worth all the money? What will the result be? How will the boat behave? Will the drives be able to handle the power?

A lot of questions and no answers before the money is spent... So I would like to look at the "problem" from a different angle.
Driving a boat in excess of 60kts is not without risk. 70kts... Well... I'm a father of two now and I've got a lot to live for, so lets settle with 60-65kts.

What power will be required?
If i use the highly unscientific formula "current top speed / current hp * new hp" => 46 / 520 * 800 = 70kts. Well, the fact that resistance is increased by the speed to the power of 2 (is that how you say it in English?) and not by 1, the boat might make it to 60kts, i guess... ? Maybe more?
Anyone with experience of a 260 going in 60kts? Or more?

The drives are Volvo SX from 88... Far from the best, but according to a service technician they should be able to handle 600Nm if driven carefully... Whatever that means... Well, I won't run in a race and I want to live, so... Maybe they are strong enough.
Will the shape of the lower unit be a problem? Will it prevent the boat from reaching 60-70kts?

Max rpm will probably be somewhere around 4500... The drive gearing is standard (whatever that is   ).
Currently there are 25" props on (totally wrong), which forces the engines to run on a lower rpm. Currently, max is 3800. Way too low. A sailboat have a better acceleration.  
What prop-pitch is standard on the 260? I'm guessing 21"... So with an increase in power from 260hp to 400hp/450ftlb, a prop-pitch at 23" might be right? Or is 25" the better guess (it would save me some money...) ? Anyway that's a smaller problem since I can test the 25" first and see what happens... maybe a change in gearing will be enough...

Estimated launch year: 2015.

Summary:
1. Power requirements to push a 260 to 60kts or more? (lets skip the "how to increase the power" in this, we can take that in another thread)
2. Volvo SX: Will they break or hold?
3. Prop-pitch at 23" or 25"?

What do the rest of you say?

[stinger390x]

Congrats on getting a great boat!
Check the serial number and make sure it wasn't built in Penatanguishine Ontario. The 84-87 Stingers were famouse as they were GREW hulls and almost bulletproof. The 88-91 were known to be porous and the gell blisters easily on many of these boats.
The US Boats were much better hull-wise...
As for power...you will hear many claims of speed in excess of 60 or 70 mph but these are exceptional and usually embellished. 260's will clip along at 55-58mph with twin small blocks no problem Stock, natually exaspurated engines can produce 260hp and they will push the boat along well. If you have a thick wallet you can make it go faster but the question is WHY???
I have a lot of experience with these boats as I have owned one and my friend did as well and made it go very fast, but it cost him a fortune.
One thing you will notice is that the 260 has what is called the "Stinger HOP" This is an undesirable hop that you get at high speed and is a product of the hull design. It can be trimed out if you get a good set of Keikoffer tabs or something similar but it will always be there in some manner until you trim and plane properly with the correct speed...comes with practice as you will get the feel for the boat. (my 390 does not do this at all but my 260 and 245 both hopped badly)
The 260 is a great family boat and as you have kids you can take them tubing. The boat is not too big for this but does drink fuel! I know...I tubed in the bay often with friends.
The cuddy is a fair size and comfy for two for overnight if your visiting another marina.

One thing you might consider is getting a reverse drive outdrive. They usually come with alpha's and just before I sold mine I was looking inot getting one reverse drive. These are rare but available. They are in high demand. When both drives turn the same way it causes a bit of torque to one side but a reverse drive will even this out.
Props........trial and error. I ran 14x23 tripple stainless. Climbed out of the water well and ran 58mph. The 19's only did about 51mpn but got out of the water much faster and great for waterskiing or tubing. I tired a set of clevers but my x-drive was too low in the water.

Nice boat, sexy lines and always a headturner...ENJOY THE BOAT, have fun next summer.

[lbg]

Oh, I'm afraid it might be one of the bad ones then... I'll check the hull number when I can.
But I'm hoping the paint on the boat has helped to preserve the gelcoat.

Power...
Why increase? Because I'm a speed junkie... 
And because the boat currently doesn't perform the way it should, something needs to be done.
A stock engine from late 80s is (in my opinion) a fuel drinking, lazy lump of heavy iron. They are quite inefficient and because of that they are also quite easy to tune up and you don't need a fat wallet to do it. It's a matter of how you look at it, I guess...
Currently the engines are taken apart because they started giving off blue smoke and make strange noises. And when I had a look inside them, I saw that the cooling canals are so badly corroded there is no use putting them back together without changing the blocks. And to change a block you need to take everything apart. So why should I put the old stock parts back in, when I just as easily can put in better components that will make the engines produce more power by letting it breath a lot better?
Hence my question: What power will it take to push a 260 to 70mph?

The "Stinger hop" you talked about... At what speed does this occur?

Reverse drive outdrive?
Volvo SX can turn any way you like. Just put on a reverse prop and change the gear cable and you're done. My props turn in opposite directions. It's been that way since I bought it, almost 10 years ago...

Props at 23" pitch on a Stringer 260 and the boat runs 58mph? Nice! You're engines were in good shape compared to mine then. You remember the engines RPM?

In its current condition it is not possible to enjoy the boat next summer, unfortunately.
It is in a desperate need of a serious overhaul. And that is what I'm going to do.

And then a summary update:
Power: Stock engines with 23" props => 58mph (50kts)
With my slightly more scientifically correct formula: stock speed to the power of 2 / stock hp * new hp = new speed to the power of 2 => 50^2 / 520 * 800 = 62^2. So with 800hp (combined) a Stinger would do 62kts (71mph). And with 900hp, 66kts (75mph).
Volvo SX: Break or hold... Well... We'll see. I'll be careful.
Props: As you said, stinger390x, trial and error... But your info on the 14x23 props were really valuable. It would be great to know what RPM the engines ran at...

[stinger390x]

Stinger hop starts just after plane...not too much you can do about it as it is in the hull design and is a factor that you have to live with.
My 23's were turning around 4800 rpm or so at 58mph.
The 19's however turned around 5100 but the3 boat topped out at around 50-51. It did get out of the water much faster and easier but no top end...
As for the Volvo drives I am not familiar with those. I have had many stingers and all have had Merc's except for my 210 that had an OMC (YUK!) Counter rotating drives will give the boat a lot more lateral stability and stop the torque to one side when excellerating.

In a nutshell...to go faster than sixty you need a very thick wallet which will be a small billfold after your done. My friend Chris had a 260 a decade ago and it did 85mph, but he had Bravos on the back and 750hp supercharged small blocks. This boat was insane!!!but he sold it because of the "Stinger Hop" and bought a 38' Cobalt with twin 780's

[Breakaway]

I have an 84' 260 LTD with stock 350's & stock Gen I alpha's(non-counter rotating...yet). My props are SS 15" diameter 25 pitch, she really comes out of the water slow even when loaded light you have to ease her out of the hole or she'll cavatate pretty bad,especially on one side. Once up on plane she does want to hope sometimes in chop but only if you let her. It will always trim out at any speed but sometimes takes a little tweaking especially and seems to be worse at mid range power settings around 50mph. The engines will only turn about 4700-4800rpms flat out in perfect trim but that gives me about 72mph if I'm light(by myself), add 1 200lbs passenger will bring that top speed down to around 68ish flat out. All my speeds are confirmed by a GPS. With just my wife and I onboard full of gas,trimmed out nice at about 3400-3600rpms and 50mph....this seems to be the sweet spot for the engines to unload and sing nicely without gutting or lugging them and seems to give me my best fuel burn to speed ratio. So it is possible to get 70 from the stock engines but you need to keep it light and completely give up any hole shot. 

[stinger390x]

To be perfectly honest with you...if you want to go faster than 50-60 that your doing now, then go to a bigger boat. 36plus feet to 42.
My friend Chris had a Stinger 260 and he dumped a pile of money into it. 750 hp twins with Bravo's and the boat was incredibly fast, however you just can't get away from the dreaded "Stinger Hop".
My advice...and Chris's, is to go to a bigger boat for more speed. Be thankful the 260 does a smooth 55-60mph as you will be spending a fortune on modifications. Chris is a man of means, so this project didn't hurt him, but he regrets spending so much on it and never getting his money back out of it.
That boat incidently was parted out and now the parts are on a bigger boat.

What I'm trying to say is -  have fun with what you have and enjoy the sunny days on the boat. If your serious about going faster choose a hull that will allow this. My 260 did 57 as I said before and it was a great boat!

After re-reading your previous post where you state its sluggish and a gas guzzler you mention your doing in the 3000 range and topping at 4000 and change? This sounds to me like a prop issue as the engine are capable of turning a cool 5200-5300 without problems. I think you should address the props first and try some different ones out, then work your way into the blocks and possibly go injection with new ignition modules perhaps to update the older technology.
just a thought..........