[71 Automatic] Question about timing and altitude

[Braeska]

Howdy, So I just got my car shipped to Salt Lake City from The Bay Area, (now at ~4,000 ft above sea level compared to basically at sea level) And I've re-tuned the carbs and everything best I can and its running okay, but I've noticed its a bit under-powered from what it used to be like, especially going uphill. Also my transmission shifts just a bit harsher with a slight jolt which was unnoticeable beforehand. I've come to observe that my car is SUPER picky with timing when it comes to a smooth shift in the past. (for what reason I still don't quite understand but trust me). So my question is would such a change in altitude affect my timing? I've seen some people say yes and some say no, I'm assuming if it does I shouldn't have to adjust it very much, but if I do would I want to retard or advance it?

It's a shame because I had my timing set so perfect for so long XD. But oh well. I'm running dual 34 ICT Webers and the original fuel injection distributor with vacuum advance and pertronix electronic ignition (i'm too lazy to go look up the exact model # sorry)
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|| groovy baby yeaaa ||
'71 Squareback (Eileen)

[sjbartnik]

Altitude does affect what your timing can be in the sense that an increase in altitude is an effective reduction in compression ratio. So you can advance the timing more than you could at sea level.

Do some google research, but for some reason the axiom of advance it one degree for each 4000 feet above sea level is sticking in my head, but don't take my word for it.

You may have to re-jet your carbs for altitude, as they may be too rich now if they were initially jetted for sea level. At altitude you're just not getting as much air into the cylinders so there will be a reduction in power.
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1965 Volkswagen 1500 Variant S
2000 Kawasaki W650

[Braeska]

Just updating this for anyone who might come across it sometime. I'm by no means an expert in any of this so take it with a grain of salt, but it fixed my shifting issue.

After some trial and error and doing the math, I've found that for an automatic type 3 with vacuum advance, every 900 ft. (+/- 100) in elevation you climb, you can advance the timing by 1 degree.

Don't know if this will be consistent with everyone but it worked for me without re-jetting my carbs. Cheers!
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|| groovy baby yeaaa ||
'71 Squareback (Eileen)

[KTPhil]

Another argument for late D-Jet FI... automatic altitude compensation!

[Braeska]

[Bobnotch]

[Braeska]

[gt1953]

Elevation does take its toll on HP and torque. Running at 6500 feet the majority of the time, like I do jetting and timing have to be adjusted. Some other thing came mind;
As a general rule, a naturally aspirated combustion engine will lose 3% of its power for every 1,000 ft of elevation gain.
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Volkswagen: We tune what we drive.
Numbers Matching VW's are getting harder to find. Source out the most Stock vehicle and keep that way. You will be glad you did.

72 type 1
72 Squareback
({59 Euro bug, 62, 63, 67, 68, 69, 73 type ones 68 & 69 type two, 68 Ghia all sold})

[Multi69s]

[Braeska]

Sorry I may have misspoke, my transmission isn't quite slipping, it changes gears immediately like it should and stays in gear, but it's just proceed by a slight jerk, most noticeably between gear 1 and 2. 2 and 3 is smoother. I believe my vacuum comes from two hoses connected to the intake manifolds under the carbs. But like I said it seems like my timing is what determines weather or not the transmission shifts smoothly (which I don't quite understand, and i'm sure that's not how it's supposed to be, but it's what I've noticed). A few months ago when I set my timing with a light for the first time it took away that jerk for me but when I shipped my car up to higher elevation it came back. So I was able to smooth it out a bit by advancing my timing but I still have it come back when driving every now and then, mostly when i'm accelerating hard from a stop. If I don't give it as much gas from a dead stop though it shifts smoother.

Where can I actually find the modulator on the transmission?
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|| groovy baby yeaaa ||
'71 Squareback (Eileen)