If I live at over 9000ft, do I have to increase my intital timing to compensate for the increase in altitude? Any help would be great....


Brad

 

I'll take a stab at it - if nothing else someone will be compelled to set me straight. I doubt that changing timing alone will do much. I do not remember ever reading a high-elevation timing, different from the regular setting.

The major problem at altitude is there is less air - very profound!

(Because you are posting in the FE engine forum, I assume that you are are carburetted, not fuel injected.) Carburetors are designed and calibrated for sea level operation. At high elevation there is less air per cubic inch drawn in by the engine, so the mixture ends up rich. Not only does this waste fuel, the engine does not operate as well with a non-stochiometric mixture. A good carb shop (at your elevation) can tune the carb (changing main jets & other stuff) to compensate for the high elevation, but you will be lean at lower elevations and that is not good, as in burnt valves & pistons. VW actually had an option on the carb that replaced the main jet with a little bellows unit that slid a tapered metering needle in & out of the main jet as elevation changed.

The next thing to do is more extreme, but if you need a valve job or an engine rebuild anyway, that would be the time to increase your compression ratio. Way back in the '30's Chrysler shipped their 6-cylinder flat-heads to all the Rocky Mountain states with what was known as the "Denver" head. It was a stock head, with smaller combustion chambers to give a higher compression ratio. There are numerous ways to increase compression ratio, especially if you are doing engine work anyway.

If you do not want to do the above, you could install one of the after-market electronic fuel injection (EFI) units. This only makes sense if you drive a LOT of miles and need to do both high and low elevations. It will cost some $2,000 plus, not counting installation.

If you pick one (or more) of these, there is a lot of help for you on these forums. Do some searching and ask more questions in this thread.

 

yeah, I realize the fuel adjustments,I was wondering if it's really o.k to increase intial timing until it pings, than back it off. I am able to increase this intial timing pretty high. I am wondering if this is because of the high altitude?

 

Another way to look at the effect of thin air is that it decreases the effective compression ratio. The mechanical ratio is constant, but if you fill up the cylinder with fewer molecules of air at the bottom of the intake stroke, the temperatures and pressures at the top of the compression stroke will be lower, similar to a lower compression ratio at sea level. This should let you advance the timing, but how much is the question.

If you do advance the timing, keep on top of listening for the sounds of pinging. What works under some conditions may be too much, say when hauling a load.

It might be that advancing the whole distributor would not give you as much benefit as having the distributor re-curved by a pro who is used to tuning for high elevation. You would then complete the tuning by experimenting with what initial advance worked best.

 

That's good thinking, find someone with one of those fancy timing lights to find out what your total is, and how quick it comes in.

FWIW I run my initial at 10* to 12* before TDC, close to 7k feet here. The book specs I have read say to add 1* advance for every 2000 feet above sea level.

Some trivia: Last week I skimmed an article that was talking about different altitudes having different octane requirements. The refiners sell a cheaper grade here because they can.

 

Another way to look at the lower octane offerred in the mountains is that most people do not do the mods, so it would be a waste to offer the higher octane gas. If you are going to push your timing, you might end up pushing into running premium. I am not teasing: you may get enough better gas mileage & performance to justify the extra cost if your engine has a compression ratio that is bordering on needing premium already.

Now that you mention it, my rusty memory validates the 1-degree per 2,000 feet rule. It has been so long since I saw it that I forgot. Thanks, Hypoid, for adding a fact to all this speculation.

Chump; Keep posting so we can all learn from your experience.