random thoughts on an Nos installation

[Vishnuatepork]

I'll start by saying I know nothing.  I had a thought at work today while putting out my 110th Scallop and Prawn with smoked paprika polenta with caramelized shallots and krispy kale.  The stock carbs on my VX800 are a CV type from Mikuni.  The choke circuit isnt really a choke as it is an enrichening circuit.  It got me to wondering; when adding in Nos, how much more fuel do you have to add?

If normally youre running at 14.7:1 afr, do you go down to say 12.5:1 or is it dependent on the size of the shot?  The larger the shot the richer your fuel mixture needs to be.  I would like to learn more about this topic. Are there any web sites that anyone can recommend?...

Cheers
Alan

[Peter Jack]

I know this subject has been looked at extensively in the past including the flowing of nozzles but when I tried a couple of searches I got no results. Can someone else get a result from the search? 

Pete

[55chevr]

If you are running carburators the best solution is a wet system.  One that adds both nitrous oxide and gasoline.  Setting up a dry shot on carbs will result in a fried engine.

[panic]

If normally youre running at 14.7:1 afr,

But you're not. 14.7 is an interesting scientific abstract.

[Dean Los Angeles]

14.7 is an interesting scientific abstract.

It's not an abstract, it's the stochiometric ratio that defines the air/gas ratio IF you have a perfectly vaporized mixture.

12:1 is the more realizable ratio in the non-perfect world of an engine with a carburetor with less than perfect/poor atomization and mixing. The actual ratio isn't as important as the color of the spark plug, or the hole in the piston.

I tried a couple of searches I got no results.

A note to everyone! If you wish to search for anything you must return to the forum home page. If you search for nitrous from here you get no results. Searching from the main forum page gets 16 pages of posts related to nitrous.

[Vishnuatepork]

A note to everyone! If you wish to search for anything you must return to the forum home page. If you search for nitrous from here you get no results. Searching from the main forum page gets 16 pages of posts related to nitrous.
[/quote]

thanks, I had tried the search....and got zero....now I see all the pages.

[Peter Jack]

Thanks Dean, I never realized that. 

Pete

[panic]

Since we're back to playing that schoolyard level?

It's not an abstract, it's the stochiometric ratio that defines the air/gas ratio IF you have a perfectly vaporized mixture.

The ratio defines the ratio? What language is that?

BTW: vaporized has nought to do with it.

[hotrod]

The 14.7 AFR for gasoline is an "assumed value" for typical gasoline.
It is a value that is "close enough" for most calculations but not true for any.

Gasoline is a blend of between 300 and 500 different chemicals each of which has a different stoichiometric fuel air mixture.

Gasoline blends can range from a true stoichiometric fuel air mixture of about 14.6 to about 14.8 but some gasoline components such as toluene which is often used to increase fuel octane in racing gasolines can have higher stoichiometric fuel air mixtures. That is one of the reasons folks sometimes have to change carburetor jetting when switching gasoline blends. As you change fuel blends you change the fuel density viscosity and the true stoichiometric fuel air requirement of the mixture.

14.7 is good "rule of thumb" value for typical pump gasoline but is not an absolute value that is always correct for any blend called gasoline.

For example:

Sunoco Green E15 gasoline has a stoichiometric fuel air mixture of 13.8, it is a 5.6% oxygenated fuel
SUNOCO 260 GTX RACING GASOLINE a non-oxygenated racing gasoline has a stoichiometric fuel air mixture of 14.4
SUNOCO 260 GT UNLEADED RACING GASOLINE a 3.3% oxygenated gasoline has a stoichiometric fuel air mixture of 13.9
SUNOCO 260 GT PLUS UNLEADED RACING GASOLINE a 4.8% oxygenated gasoline has a stoichiometric fuel air mixture of 13.7
SUNOCO STANDARD RACING GASOLINE a non-oxygenated gasoline has a stoichiometric fuel air mixture of 14.9
SUNOCO SUPREME RACING GASOLINE a non-oxygenated gasoline has a stoichiometric fuel air mixture of 14.9
SUNOCO HCR PLUS RACING GASOLINE a non-oxygenated gasoline has a stoichiometric fuel air mixture of 14.8
SUNOCO MAXIMAL RACING GASOLINE  a non-oxygenated gasoline has a stoichiometric fuel air mixture of 15.0
SUNOCO MO2X a 2.7% oxygenated gasoline for motorcycles has a stoichiometric fuel air mixture of 14.5
SUNOCO MaxNOS GASOLINE a non-oxygenated gasoline has a stoichiometric fuel air mixture of 14.9
SUNOCO FR GASOLINE a 3.7% oxygenated gasoline blended for use in Europe has a stoichiometric fuel air mixture of 14.5

As you can see from the above from only one manufactures straight gasoline blends without oxygenation range from 14.4 - 15.0 stoichiometric fuel air mixtures.

I bet if you asked Rick Gold he could provide you the exact stoichiometric fuel air mixture of each of his blends used at Bonneville.

Larry

[wobblywalrus]

Alan, as I recall your bike is a modern Suzuki.  Some of the newer bikes have combustion chamber shapes and other things that make them different than the typical engine.  They run best on leaner mixtures.  Sometimes it is a good idea to put the bike on a dyno and to try different fuel air ratios with gasoline and see what happens.  This way, you are working from a known baseline when you add the gas.

[Vishnuatepork]

Larry,

thankyou for that info.  Everytime I come here I learn something.  I had no idea (but it makes sense) that each gas has its own stochiometeric ratio.

Having had a day to mull over my question and understanding where I may have been vague, I'll try to ask it again, by being more specific.

When running Nos, how much more fuel has to be added?
The bigger the shot the richer the ratio, before the NOS?
eg: a 10hp shot would need a pre NOS ratio of say 13.5 and a 50 hp would need a pre NOS ratio of 12.2 (the numbers listed are just to provide an example, not to be taken as a guess nor as gospel).
And to clarify; I was only  thinking of adding a 10hp shot, if it could be done with my "choke". I am not interested in making mondo hp...

Wobbly,

Exactly as I was thinking....
And yes you are right, the combustion chamber is relatively modern, it has Suzuki's first Gen TSCC.

[Dean Los Angeles]

BTW: vaporized has nought to do with it.

The reason 12:1 ends up as the realistic ratio is the excess fuel you have to put in due to the incomplete mixing in the chamber.

This is a chemical reaction between the gasoline molecule and the air molecule. If you don't get the mixture vaporized then you are trying to ignite large multi-molecule gasoline droplets. The fuel is either not ignited at all or delayed and that is not contributing  to the power stroke.

[RansomT]

Vishnuatepork, here you go.  About mid page.  While this isn't absolute, it gets you in the ball park.  Just remember you need to start at the AFR you want with Nitrous.  11.5:1 is a safe starting point, always use good fuel.  On the well designed new sport bikes, I aim for 12:1 with nitrous and then add a touch of fuel more.

http://www.schnitzracing.com/technical_corner.htm

[Vishnuatepork]

RansomT,

Thankyou!  The whole page is awesome! Its full of tech info.

Muchly appreciated.

Cheers
Alan

[Stainless1]

Vishnuatepork, here you go.  About mid page.  While this isn't absolute, it gets you in the ball park.  Just remember you need to start at the AFR you want with Nitrous.  11.5:1 is a safe starting point, always use good fuel.  On the well designed new sport bikes, I aim for 12:1 with nitrous and then add a touch of fuel more.

http://www.schnitzracing.com/technical_corner.htm

Yep, should be able to get some new pistons if you dry nitrous your carbureted bike.  If you are doing a wet system, 1 lb of gas for every 5 lbs of N20 is a good starting point.  The amount of gas you get from those jets is dependent on fuel pressure, just like the amount of N20 you get depends on the temperature of the nitrous.