26 scarab;

good point about the torque that NOS adds...I don't hit the button until I'm already turning 5500-6000rpm, if you hit it at 3,000 the torque would be MONSTOROUS and the Bravo would likely go BOOM in short order.

Inspectec;
The added fuel for the NOS comes from the spray bar in the plate. The system comes with specific jets for NOS and fuel for different power settings. As long as you have a good seperate fuel pump to supplyt fuel to the plates you should never get lean. Going back to SET-UP, just wire in a 5 psi hobbs switch..that way if fuel pressure drops below 5 the NOS system is killed...added insurance. When the motor turns more R's it will pull more fuel from the main jets in the carb as it normally would.

Checkmate;
You really need a motor that can turn the same prop 500 more rpm without "rev-limiter issues". I turn 6800-7000 on the squeeze, rev limiter is 7200. Obviously I run a solid roller with Jesels etc. You are right about props selection though, you'd need to go up about 2" in pitch if 500 addnl. r's are too much.

Now for a good NOS laugh;

A boater my buddy knows decided he was going to put NOS on his small block Bayliner a few years back. He just 'billy installed the system as follows; put the plate under the carb and ran a braided line from the plate to the bottle valve with the bottle sitting on the floor next to him. No extra fuel...no solonoids...no jets, just straight NOS to the plate. His regulator was how far he cranked open the valve on the bottle. This "crude" regulation worked for about a week. One day there was a little too much NOS introduced with NO ADDL Fuel and the motor went BOOM. He blew the motor so bad the oil caught on fire which in turn caught the entire boat on fire. The guy had to jump out of the boat and swim to shore while watching his dads boat burn all the way down to the waterline before sinking. That Bayliner is still to this day in the lake.

It was either cobramarty or tomcat that went into deep detail about why nitrous was a compromise at best on boats, and you just hit it on the head. The smaller the shot, the less the issue, but you would still be faced with the choice. I would think this would have a somewhat diminishing impact on motors like JDNCA1's where his power peak is plenty wide with the duration cam he is running and rpms are not an issue due to the build of the rest of the engine, but for near stock stuff, I think the window is fairly narrow where the motor gets past it's breathing ability and rev limiter problems. A look at the torque and power curve of the motor before nitrous will give insight as to how many rpms you would really want to add and the impact it will have based on prop choice before shot. Do a search on this, I think it was tomcat due to his simulation software that is able to shed good light.

JDNCA1, do you really see a resdual 3 or 4 miles an hour? That must be due to some aspect of the load curve of your hull at those speeds. I doubt that my tugboat would do that...

Brad;

With a 175 shot I pick up about 9 mph, when I come off the squeeze I lose 4 mph. I have a 26 carrera cat. It is an interesting phenomenon going on. Obviously the hull is packing more air at the higher speed, my theory is that the motor can maintain the addnl 5 mph because the hull is working in its favor...it just needed the extra push to pack more air to get there, so to speak. On V's the impact is less, but the "extra push" helps get the hull up out of the water more which will help reduce drag.

Kind-of-a just get it over the hill and then it will stay on that side kind of thing....

I've heard of such things happening to boats with really screwy torque curves, that they could not reach their intended speed because they could not produce enough torque in the midrange to get past a load hump.

I'm just happy whenever I can get past the getting-on-plane load hump!!

Using nitrous as with anything else it's a matter of how you use it, and what you're looking to acomplish.

If you want to run a few more MPH to impress some buddies, and your engine doesn't turn peak RPM, but you don't want to change props because you like how the boat runs a small shot set up safely will do the trick.

If you want to set your boat up for a kilo run you can do that. We run nitrous on salt flat racers all the time 3 mile passes. You have to take a lot more precautions, but it can be done !!!

How many of us know people who could break an anvil ?!?!?!? These are the same people who do it with N2O, Hot Rods, Boats, etc giving us all a bad name.

Bottom line using N2O on a boat is not bad, it's just not for right for everybodys situation.

The key is to keep the shot down to a reasonable level, and prop some where in the middle. For example, my boat will run 82 @ 4800 with Bravo 28 props, or it will run 83 @ 5500 with Mirage 25 props. For RPM and prop bite reasons I use the 28s. I wouldn't be afraid to spin these engines to 5300 for short periods, which would be 90 mph. A cheap 125 HP system would certainly deliver this extra 8 mph, even in my old boat. That much of a shot is not going to hurt a 500 HP engine, and I have enough fuel pump to handle the nitrous. But I still haven't done it and the reason is it won't help me cruise any faster than I do now (60 mph). I want enough extra HP to cruise at 70 mph which means Bravo 32 props. Never going to do that on nitrous.

I've got a built up 502 that currently makes 532 hp on 89 octane, 32 degrees total timing, 8.0:1 compression, mild Crane hydraulic roller cam. It's got Manley stainless intakes and Inconel exhausts, and JE pistons. Decent stuff, and not too highly stressed. The boat runs mid 80's at 5100. I'd like to add 100 hp, which should push me to 92-93. I've done this before with a 600 hp engine in the boat. I've got a set of props that will give me that speed at 5300 rpm, and the limiter on the current engine is set at 5400.

The engine has Arizona Speed/Marine injection with an oversize (1050cfm) throttle body. ASM felt that 100 hp would be a fairly low-risk proposition for the Radar Shootout that's coming up. Spool it up to 4500 or so, and bring on the gasoline (92 octane) and N2O through an annular-discharge nozzle mountedthrough the front face of the air cleaner, pointing directly back into the throttle body (temporary installation). As long as the fuel pumps will maintain 40-42 psi, it should work with an .052 fuel jet and an .047 nitrous jet. (The two will be mixed as they pass through the nozzle.) Max duration of the shot will be 10 seconds each on two passes.

Any predictions?

All,
Thanks for all the input!!! I am not really sure what I am wanting to accomplish with the NOS I guess just that exta blast to surprise some of the compition. Right now the boat runs low to mid 80's so with the NOS it would be in the 90's. Right now it is the fastest on the lakes that I run. Northern Maine does not have a long boating season so when I came to town with my new machine nobody knew what to think. Again thanks for the info.

Brian

C Spray;

What kind of boat? You should see 5-6mph.

Rumrunner;
well written summary. I know a guy who thinks JE pistons are "junk" because he melted a set running 14 pounds of boost on pump gas..... Oh yea, this guy blows his motor almost every weekend.