Hey....im taking my car on a 1200 km trip to a friends farm...the cars in tip top shape..the only question i have is that the carbee...do i need to tune it along the way because this place is around 650 metres above where i am currently..and its cold...so the air would be denser....

thanks

 

Eh, you might, but I wouldn't worry about it too much unless you're there for a long period of time (a month or more). That's really not that much of an elevation difference. If it feels really sluggish, you may need to advance the timing a hair.

 

+1....

Don't mess with it... It will probably run a little rich, but a 2,000 ft elevation change won't really make that much difference, but you will loose some, but not muchperformance regardless of the tune...

Where I live 650 Meters of elevation change are routine even in daily driving, and I never think about re-tuning. Carburetorsby naturedo a better job of compensating for elevation changes than they are given credit for. While the change in air fuel mixture is directlyaffected by changes in atmospheric pressure, but the change in mixture is not proportional to the pressure change, it is quite a bit less.

+ the colder air will partially compensate for the altitude.

 

I drive regularly across a 4,000ft elevation change and run my carb with the same tune for sea level that I do at home, though I do have the carb tuned to favor performance at sea level, it just runs a bit rich around here. You could get one of Pro Systems new Blow through carbs that adjusts to pressure changes. Atmospheric and elevation changes won't affect the AFR, but the carburetorstarts at over $900, still cheaper than EFI, but it's an emulsifier and EFI ain't, so the cost/benefit vs EFI is incredible

 

Thanks guys...yeah i probably wont touch it then...would using a lesser octane fuel be better though? I usually run 98 octane (302 4v)...perhaps if i slide it down to 94 octane on the trip or should i just continue as normal? thanks guys

 

How much compression do you have that you need 98oct?

 

Yeah, you shouldn't need that much on a stock J code engine. You should be able to run it on pump gas.

 

well the only reason i run it on 98 octane or Vpower by shell is because the owners manual said so..[sm=burnout.gif]

 

Owner's manual was written in 1967. Octane ratings where completely different then than they are now. Put some 89 in it, then (very)slowly pour a cup of water down the carb while revving the engine. This should clean all the carbon out of your combustion chambers that has been accumulating there instead of burning off, probably making them bigger and allowing you to run said pump gas

 

IMO keep running what you have been running because it seems to work for you. I am not educated enough on the subject to know the difference between European octane standards and the American standard.

But to more directly answer your question, you do not need to go with a lower octane due to the thinner air.

I had a similar conversation concerning altitude and octane with another member who lives at a higher elevation. He said that the oil companies in America adjust the octane levels for elevation depending on what elevation the gas is to be sold at.

My understanding of this is that the same gassold as 91 octane at 5,000 feet elevation, is a lesser octane if used at a lesser elevation...