Upping the octane for emergency power

NO2 is a great way to scatter an engine all over a transom. Combustion chamber pressures increase dramatically, as does heat, stress and strain. I've blown quite a few NO2 equipped engines. I would never recommend it on anything other then a full race setup, where the engine is built to tolerate the abuse. Simply put, even just a few seconds of a NO2 burst is enough to toss rods, collapsed piston tops and break cranks, if the engine isn't designed to tolerate the loads. Even if using just a small "shot", the loads can be huge. Water or alcohol injection, coupled with a way to advance timing is the reasonable way to go. Both of these run much cooler and produce much less strain on the engine, while still offering an output boost.

If you have a modern engine with electronic controls, you can install a multiple tune on the ECM, so at the push of a button, you can increase output by 20% to 50%, yet return to the normal "tune" after you've crossed the rough patch. On mechanically adjusted engines (like I suspect yours is), you don't have this option, though a twist knob to advance timing could be arranged and possibly another for mixture, offering a rich, advanced setup, for those occasions you need some more power.

As to a magic goo in a can, that can be poured in the tank, well there's really no such thing.

 

PAR, that is the silliest thing I have seen you write. The amount of excess power just depends on how much NOx you allow into the engine, it is no more prone to scattering an engine than your idea reprogramming the ECM or advancing the spark. If you only want a 20 percent boost in power, you just set the output to that. I have seen engines scattered without any increase in power output, anytime someting is overlaoded you risk damage.

Uncontrolled NOx injections is just as sure to damage an engine as anything you might do, but if 50 percent increase will scatter an engine, than it will happen by any means you use. There is no magic formula, but using a NOx injector, throttled to limit the power increase, is the simplest way to to acheive an instand increase in power.

No matter how you do it however, that rasies an interesting question: how much risk are you willing to take on the remaining engine? If you are in a critcal location, and you loose one engine, presuming you will go to full throttle on the remaining engine. If you have your magic switch that would suddenly increase your power out put on the remaining engine, what would happen to your situation should you bundle up your remaining engine? Any increase in power, including just going to full throttle, risks engine damage. Advancing the timing or increasing the fuel mixture, or adding NOX, will increase out put, but also put addtional strain on the engine. Are you really better off with the additional power, vs. risking having no power at all?

They actually do similar tests on military aircraft, where they develop tables for time and throttle settings, where there is a "max continuous power" and a "max military power" with strict limits on how log that can occur before risking permanent damage. In combat or in an emergency, if the risk was loosing the whole aircraft (and possibly crew), vs. drastically reduced engine life, than there are times when that is work doing. But these tables were developed with many many hours of testing, and engine tear downs and inspections.

If you are really at risk of life and vessel with an engine out condition than I would say you have three options: 1) do a lot of extra maintenance/inspections on the engines to make sure they are always at their best, 2) get larger engines and run them at 85 percent, unless you have an engine out condition (it will give you the extra engine out performance you need), or 3) install a third back-up engine.

and of course you also have the option of never exposing yourself to such a condition with careful planning, or get a bigger boat.

Where do you want to choose the line between risk vs. safety? Increasing power output will always add an element of risk to the remaining engine no matter what you do.

 

NOX works great in outboards for short bursts BUT as everyone has learnt you need to inject methanol with the nox not extra fuel which also means you need alcohol resistant oil so that means castor oil.
You also need a cool down mode programmed in.
Not as simple as a 4 stroke.

 

Thanks again for all the advice. I had a feeling this might not be a practical proposition, and so it seems to be. Maybe fitting trim tabs to the boat might help to get it up planing on one engine, flogging it to full throttle for a very short time isn't really a concern, whatever the case the boat will have more headway than it would with auxiliary power. As a very last resort, there is an option of running the bar the way they did in small displacement boats of yesteryear, by watching behind for bigger waves that are likely to break, then turning around 180 degrees to face them, before resuming the inward course. That could happen half a dozen times or more apparently, but was the safest way available. The swells easily outran the boat speed.

 

Lets see, running an engine at WOT then tossing in a 20% NO2 shot. Yeah, you might get away with this for short bursts (30 seconds or less), but do this frequently and you'll stretch something pretty quickly. This is simply because if you have a 100 HP engine, it's innards are designed to tolerate 100 HP forces. A 20% jack isn't much, but with a basic, typically spray bar NO2 setup, it comes on in a violent, very harsh way.

I agree it's a possibility, particularly if throttled in and limited, especially if coordinated with ECM adjustments and alcohol, but these systems are way over the top for the average back yard guy, looking for a quick boost to get over a set of breakers or pass a rough inlet.

With the older 2 stroke he's got and no real on the fly adjustments available, he'd be better with a less harsh and much cooler running setup, like water or alcohol injection, which would be marginal at best, without some way to crank in some advance. This wouldn't be terribly difficult for a technically minded back yard wrench.

 

The owner of the boat is an able mechanic, but I doubt his skills run to alcohol injection, I think he prefers to drink that ! But as you say it would likely be marginal without added spark advance. The more I think about it, trim tabs seems the best alternative, and possibly transom wedges so the motor can be trimmed under further. Like me, this bloke would not dream of radioing up a rescue boat to tow him back in over a bar, that is just putting more people at risk.

 

its 2 stroke under extreme duress, you would be retarding the timing
http://www.nitrousdirect.com/faq.html

 

OK, but on the water, rough conditions maybe, making the adjustment a bit difficult ? Lifting the lid on the engine, having waves splash over it, might finish with both engines out !

 

yes so if you cant do that then your normal setting might be retarded if you want to flog your engine.
Drag race outboard guys actually use a solenoid on the timing stop to shift it backwards and retard the timing when they hit the nitrous