Carb tuning for altitude

[oz]

This is a bit premature as my bike is not nearly finished but a thought/problem keeps nagging at me
If a bike is set up at sea level with a ram air system it will run rich at low speeds and correct at full speed hopefully if i manage to get it right. I have heard that due to atmospherics at Bonneville O2 can vary between 4000 and 7000 above sea level is there any way to calculate jet sizes or approximate jet sizes as in an equation to determine correct fuel/air ratio or is it trial and error ish.
Altitude shouldn't effect nitrous systems at all should it?

Sorry if this is rudimentary but I have always lived in low lying areas and if you don't ask you will never know!

[Stainless1]

Rich is your friend when using N2O, 
get your tune on it correct, it will override the carb tune anyway.... 

[oz]

I understand that the nitrous will have to be jetted to the correct ratio but that is not influenced by atmospherics or is it?
The nitrous wont be used till higher speeds its the getting to the higher speeds that I am thinking about. it would run real rich at sea level settings. Could try dribbling a bit of nitrous into the air box the nitrous I have is direct injection wet system.

[JackD]

Unlike any other form of MC racing that you have experienced and certainly altitude if you run in the UK. Bonneville requires a richer setting than you would imagine because the duration of the run will build heat that will substantially cut the power or worse hurt a part.
Go with your sea level tune up and get through your license runs with that as you learn to ride all over again also.
Making yourself small and learning to apply the power to match the traction is as important as any horse power you bring to run.
Reading rich plugs is a lot easier on the program than suffering with aluminum packed ones.
"Peak power on a Dyno or extensive experience at a Drag Strip for example is like perfecting your high dive before you know how to swim." (me) 

[oz]

I see where you are coming from don't try and run before you can walk  and it ain't a big problem to re jet a set of carbs I suppose.You know what its like though over excited that's what makes it good, already thinkin about running up the salt and its still a way in the distance.

[jackson]

Home is at 1,300 feet above see level for us.  With gasoline we can tune at home and it runs a little rich off the starting line but seems to be just about right by the end of the run. 

On methanol all bets are off.  It seems like we have to chase it by the hour. 

[JackD]

Looking ahead and thinking ahead helps to keep your head off the wall.
Sitting ant watching is fun, unless you have a broken ride, and then it is the worst.
Pal up with somebody with similar machinery way ahead of time and help each other out as you proceed.
You might have to forget your English and learn a bit of American.  LOL

[Stainless1]

Rich is your friend when using N2O, 
get your tune on it correct, it will override the carb tune anyway.... 

Oz got your PM, Your N2O tune will override anything your carbs deliver.  N2O can run very rich with a minor loss of power, but just a little lean can be catastrophic...Search the site, this has been discussed a lot, my advice, don't trust off the shelf kits, flow everything so you know how many PPM of fuel and N2O you are flowing and do the math.  You will be on the juice longer than the drag race kits will allow.  If you know what is going to happen to the bottle, you can tune for that as well, it just takes a little thought.  Stay liquid and the mix is easier.    

[oz]

Thanks words of wisdom! One question though you say that I will be on the juice longer than Drag race kits allow is that because of quantity of gas  freezing up or line pressure drop. I am carrying 5lb.

[JackD]

Drag race kits are designed for a minimum weight and a duration of 1/4 mile.
LSR is something else again.

[oz]

Hi Thanks again for the info in your PM stainless1 I think I have phrased my question wrongly I only intended on using the N20 in the last 1 1/2 miles of the run not the entire distance so hopefully it will only be in for 20+ seconds at around 40bhp  I know traction will be a problem on a single shot system but a progressive controller should soften the blow slightly.Since talking to a few people I am also thinking it may be advantageous to run the bike in two classes one with juice and one without at least that way I can do my license runs and get used to the surface before hitting the fast forward button. (if you can do this)Suppose thats a question for the Bonneville rules section.

[Seldom Seen Slim]

Oz:  I'm not sure that you'll get away with it -- even if you use a progressive controller.

In a previous setup I ran a Schnitz progressive controller (set for 2 1/2 seconds) AND a dry shot (40hp) into the airbox, therefore making the hit even slower than it otherwise might have been.  I moseyed down the course (about a buck-eighty) running gas only, and hit the button around the 3 1/2.  (wait...wait...here it comes...BAM! WHEELSPIN!)  Yee-hah, boyoboy isn't this cool, as the back end skated around. . .

That's what happened to me -- be aware that it might happen to you so if it does -- you're not surprised too much.

The Schnitz, by the way, was their standard unit -- 20-second cycle then shuts off the nitrous.  By letting up on the button for (I think it was) 2 full seconds it would reset so you could get another 20 seconds -- so I until I replaced the Scnhitz I would have to push the button (for maybe ten seconds or so to build some speed), then let off for a couple of seconds to reset, then mash the button again to get the rest of the speed.  Too much thinking required!  And the Schnitz wasn't adaptable to go to a longer "on" time without more work than I could do at the track -- so I've gone to a different system (which maybe will get some use if the danged crankshaft ever gets built).

As for running two classes -- fuel and gas, but otherwise the same class -- sure, it's common.  Run gas class to get your acclimitisation runs in, then put the bottle on the bike and switch to fuel class.  You're not allowed to have a bottle on the bike when you're in gas class, that's all.

[oz]

Adrenaline is Brown,Time for bicycle clips and a cork by the sound of it. I am pleased about the two classes being common its probably the best thing for me least ways i can check the bike is ok and that I have the nescasarys to handle it.
   

[Sumner]

Adrenaline is Brown,Time for bicycle clips and a cork by the sound of it. I am pleased about the two classes being common its probably the best thing for me least ways i can check the bike is ok and that I have the necessaries to handle it.
   

If you have no intention of running for a "gas" record there is no need to pay to enter two different classes.  If you have nitrous they don't require that you use it on a run and you wouldn't even have to have the bottle on during those runs if you don't want to. 

Remember the only time they will check to see if you are legal is if you actually break a record and end up in impound.  The rest of the checks are for safety, so you should have the bottle on when you go thru tech at the beginning.

c ya,

Sum

[Seldom Seen Slim]

Valid point by Sum.  You don't have to spray during a run if you're registered in a fuel class.  And changing classes costs a few bucks, so there's another reason to not run in both gas and fuel.  If you elect to run on gas while registered for fuel -- then think about having the bottle installed, even if not hooked up or armed, so that the balance and weight and everything are just as if you WERE going to spray.

Also he's right that you need to go through tech equipped for the class in which you'll run.  In gas class -- no bottle.  If you run that way and switch to fuel -- you'll need to go through tech again before you'll get your "re-inspected" sticker.