Tuning carbies - Altitude vs. coast?

[Bogan]

Looking at AFRs and such, specifically related to bikes, but I guess also applicable to cars, if I can't get to a dyno at the coast what would be a reasonable guess as to what mixture/AFR to aim for on a Canberra dyno if I'm going to be wringing the bike's neck at the coast?

Air is thinner up here so tunes will be altered in the denser coastal air, how much I really don't know.

I've burnt an exhaust valve at Bega in the Lancer before, and while I'm not 100% sure it was due to leaning out it would make sense. After that I used to have a spare set of jets one size larger for the Webers and on advice from the tuner I'd put them in when we headed to the coast.

Given that I don't think I'll have the luxury of spare/changing jets how should it be set up in Canberra to be on the safe side (I don't want a super aggressive tune, it's a street bike) when I get to the Island/Creek?

People have told me it will never blow up, but I'm going to spend the money and may not have a jet kit arrive before November.

[mick_dundee]

I think you're clutching at straws frankly, we don't get altitude here in Aus, not even if you live at the top of Kosiousko I reckon. I'm seriously untechnical but IMO it would make so close to fuck all difference it wouldn't bear thinking about.

[jl4049]

I agree, air density here varies more with temperature and humidity than with altitude. If you tune it for the coast, leave it at that, if you aren't riding all out all the time, running a wee bit fat at altitude won't do any harm.

[FONC]

G'day Bogan,

Don't like raining on anyones party but altitude does make a difference. I used to work at Charlottes Pass which is just a few K's from Mt Koscuiszko my old 302 powered Ford ran like a piece of shit up there until I completely removed air filter. Not enough oxygen!

You have 3 choices Set it for Canberra, set it for Bega or go half way between. If you are fuel injected the system can correct itself a bit to compensate through EMS.

The other guys are sort of on the right track about heat and humidity and AFR but in that scenario you can actually be in the same place as the air density changes eg the cooler it gets the air gets more dense so a bit more induction charge a bit like passive supercharging. And even though you are in exactly the same place it is the equivilent of being at a lower altitude hence the denser charge. Cars and bikes always go harder on a good clear night.

Hope this helps!!

[Bogan]

Yeah thanks for that. It didn't get a tune before I went, but it did run fine all day both days at the island.

Probably something to do with me buying it from Maroochydore (coast) and not changing the tune since I've had it up here in NSW Heights, err I mean Canberra.

Might be a trap for if I do get some carb tuning done, but I'll just get the tuner to not place it on the ragged edge of AFR and things should be sweet no matter where in this wide brown land I go.

Thanks for the reply.

[Gosling1]

.....Don't like raining on anyones party but altitude does make a difference. I used to work at Charlottes Pass which is just a few K's from Mt Koscuiszko my old 302 powered Ford ran like a piece of shit up there until I completely removed air filter. Not enough oxygen!.....

you have got to be kidding !

Not enough oxygen ?

If this were *remotely* true, the the sides of the Snowy Mountains HIghway would be full of cars and buses pulled over, all fitting smaller main jets, or ripping off their air-filters so they could drive from Cooma to Smiggins Holes !!

Altitude *does* make a difference - but only where the altitude is of a sufficient difference to actually make a difference in the first place. Some places in the US where the altitude can change upwards of 6-7000ft - yes, they *do* need leaner jetting than the coast...but here in Oz ?? Not on your nelly.

I have lived in Canberra for almost 40 years, driven up to the snow a billion times, and *NEVER ONCE* have had a problem with a single motor vehicle, either car or bike, fuel-injected or a shitty old single-barrel Stromberg on a red 6 - which has required any jetting changes as a result of driving up to the Snowy Mountains (BTW that name is a complete misnomer - they should actually be called the Snowy Slightly Higher Hills Than The Rest of the High Plains...)

What jetting changes would you suggest are correct between the ACT and Bega ???

Mate - every weekend we ride from here to the coast and back, sometimes via Brown Mt, sometimes up Mt Darragh, sometimes up the Mac Pass......and the last time anyone ever had a problem with *jetting* when changing 'altitude' between all these places was...........well..........never. Basically the same whenever we ride up the Snowy Mountains highway over summer - up over Adaminaby, Khancoban, etc etc etc.......no-one ever *re-jets* because their bike is running like shit !! Thats because they don't.

In any case, its got *nothing* to do with the amount of oxygen available, and *everything* to do with the atmospheric pressure changes at higher levels, which requires jetting changes in certain locations (ie riding from Rocky Mountains CALIF to LA)

[Rusty]

In any case, its got *nothing* to do with the amount of oxygen available, and *everything* to do with the atmospheric pressure changes at higher levels, which requires jetting changes in certain locations (ie riding from Rocky Mountains CALIF to LA)

To be strictly accurate, it has to do with the lower amount of oxygen pulled into the engine due to the changes in air density/pressure.

[Bogan]

I'd wager unless you're on the ragged edge it's not going to make a pinch of shit difference like Gos says.

I did burn an exhaust valve in the Lancer at Bega one year, possibly (well I think anyway) something to do with not changing jets like I was going to and the thicker air down there leaning it out just that little bit and f*cking up my exhaust valve. Mind you I had it at 6-6.5krpm for the best part of two hours in the forests around Bega and it only started running rough in the last stage:).

Got to the finish alright, but the head needed to come off and we relapped all the valves to be sure.

I don't want a super aggressive tune, so even if it does get dynoed and rejetted I'll leave it at something which can comfortably handle the coast .

Gos I asked on the ABC science nerd forum and they quoted air density differences at a given temperature and pressure (I think) for Canberra and the coast and it was considerable (not significant).

[Rusty]

I'd wager unless you're on the ragged edge it's not going to make a pinch of shit difference like Gos says.

Exactly. I'd argue that you were going to burn that exhaust valve anyway. If it was due to jetting, the jetting was too lean for Canberra, too.

Or you may have got a speck of foreign material in an emulsion tube or something silly like that.

[Wattie]

my kx60 used to run like a pig at Oberon campared to sydney.

but those things can be a bit tempremental anyway...

[FONC]

.....Don't like raining on anyones party but altitude does make a difference. I used to work at Charlottes Pass which is just a few K's from Mt Koscuiszko my old 302 powered Ford ran like a piece of shit up there until I completely removed air filter. Not enough oxygen!.....

you have got to be kidding !

Not enough oxygen ?

If this were *remotely* true, the the sides of the Snowy Mountains HIghway would be full of cars and buses pulled over, all fitting smaller main jets, or ripping off their air-filters so they could drive from Cooma to Smiggins Holes !!

Altitude *does* make a difference - but only where the altitude is of a sufficient difference to actually make a difference in the first place. Some places in the US where the altitude can change upwards of 6-7000ft - yes, they *do* need leaner jetting than the coast...but here in Oz ?? Not on your nelly.

I have lived in Canberra for almost 40 years, driven up to the snow a billion times, and *NEVER ONCE* have had a problem with a single motor vehicle, either car or bike, fuel-injected or a shitty old single-barrel Stromberg on a red 6 - which has required any jetting changes as a result of driving up to the Snowy Mountains (BTW that name is a complete misnomer - they should actually be called the Snowy Slightly Higher Hills Than The Rest of the High Plains...)

What jetting changes would you suggest are correct between the ACT and Bega ???

Mate - every weekend we ride from here to the coast and back, sometimes via Brown Mt, sometimes up Mt Darragh, sometimes up the Mac Pass......and the last time anyone ever had a problem with *jetting* when changing 'altitude' between all these places was...........well..........never. Basically the same whenever we ride up the Snowy Mountains highway over summer - up over Adaminaby, Khancoban, etc etc etc.......no-one ever *re-jets* because their bike is running like shit !! Thats because they don't.

In any case, its got *nothing* to do with the amount of oxygen available, and *everything* to do with the atmospheric pressure changes at higher levels, which requires jetting changes in certain locations (ie riding from Rocky Mountains CALIF to LA)

Yeah good on you Gos Mt Kosciusko is 7310 feet above sea level or 2228 meters
And if you keep running "kerosene" in your bike you will always be at the back of the pack!!!
Sorry you have had to live in Canberra for 40 years, another 59 years and your lease will be up!!!
The higher you go the more rarefied the air go and ask any good tuner. Why do race teams rejet at tracks when they are at the same altitude???
Atmospheric pressure does and can change at sea level!! Go back and have another read no one stated that you should change your jetting as you drive along.
Oh yeah this is AUSTRALIA mate not US!! Who gives a fuck about the US???
Finally would seem you are a bit of an exaggerator "a billion times in 40 years seems a lot of times!!

[Rusty]

The higher you go the more rarefied the air go and ask any good tuner. Why do race teams rejet at tracks when they are at the same altitude???
Atmospheric pressure does and can change at sea level!!

Don't think anyone's arguing that there's not less air up high.

Why do they rejet? Because they're chasing power. 3 hp might make a difference at the track, but it sure isn't going to affect me on the road when the bike's putting out at least 130. A safe tune at Canberra will be a safe tune on the coast. Car or bike.

Yes, atmospheric pressure changes, which only weakens your argument, not Gos's.

[FONC]

The higher you go the more rarefied the air go and ask any good tuner. Why do race teams rejet at tracks when they are at the same altitude???
Atmospheric pressure does and can change at sea level!!

Don't think anyone's arguing that there's not less air up high.

Why do they rejet? Because they're chasing power. 3 hp might make a difference at the track, but it sure isn't going to affect me on the road when the bike's putting out at least 130. A safe tune at Canberra will be a safe tune on the coast. Car or bike.

Yes, atmospheric pressure changes, which only weakens your argument, not Gos's.

G'day Rusty,
I would just say please show me in my two posts where I said everybody had to rejet??
I fully understand why people rejet at the track I was not asking myself why!
The original question was from someone (Bogan) who was going to run on a track day at PI or EC!
So I would personally be looking for power if I was racing!!!
Canberra's altitude is 550 mtrs above sea level and I agree would make little difference to most standard vehicles but that was not the original question!
Gos said atmospheric pressure changes at "higher levels" well that is bullshit it changes at any level from below sea level to well and truely above sea level!

[Bogan]

From here:

http://www.denysschen.com/catalogue/density.asp

Air density at Canberra = 0.0684 pounds per cubic foot.

Coast is 0.0731 (6.8% more dense)

Kosciusko is 0.0558 (18.4% less dense).

Cars should still run though yeah?

At Kosciusko I'll be running rich and at the coast slightly more lean, but it will still run .

[Rusty]

I would just say please show me in my two posts where I said everybody had to rejet??

Please show me where I said that you said that.

I fully understand why people rejet at the track I was not asking myself why!

Oh, good. Glad you cleared that up.

The original question was from someone (Bogan) who was going to run on a track day at PI or EC!
So I would personally be looking for power if I was racing!!!
Canberra's altitude is 550 mtrs above sea level and I agree would make little difference to most standard vehicles but that was not the original question!

Allow me to quote from the original post:

I don't want a super aggressive tune, it's a street bike

I took the original post as wondering whether he should rejet so he wouldn't burn a valve or piston. So, yes, that was the original question. It was a track day, not a race. He was simply looking after his bike.

Gos said atmospheric pressure changes at "higher levels" well that is bullshit it changes at any level from below sea level to well and truely above sea level!

You are aware that density and pressure are related? You don't change one without changing the other. In a given volume, if you increase the mass of air (increase density) you also get a corresponding increase of pressure. That's the concept behind forced induction (among other things, as I'm sure you're aware). So you see, pressure DOES decrease as you go up, because the density of the air is less. So Gos wasn't wrong, but probably neither were you when you said your 302 wasn't getting enough oxygen.