Do I need to change timing in T2 with FI for altitude?

[Spacer101]

Hi,
Going from LA to Colorado to ~9000ft. Do I need to adjust the timing when going higher ?
1975 T2 with 1979 fuel injected engine.

Thanks!!!

[airschooled]

I only do it when I’m staying a while. And I’m fast at that kinda stuff, so like, two days is “a while” for me. I don’t mess if I’m just passing through to Kansas.

You can grande your engine when you go back down if you forget. If you have the 75 or 79 DVDA, pulling the retard hose off the distributor and letting it leak is an easier way to recover your idle quality and throttle response. If you want power back on the high end, reset the timing.

Last time I took seven adults in a 2L type 4 over the Rockies I set 36* max mechanical advance and used premium fuel for the first time. L-Jet does much better at elevation than my single carburetor Type 1…

Robbie
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[Wildthings]

[SGKent]

only if you are moving there permanently and then remember that when you come down in elevation you will have to change it again or burn the engine up due to advanced timing. It won't hurt anything going up but the coming down will get ya if you change it.
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[metahacker]

when you go to higher elevation you're running richer and with less air density/cylinder pressure, so you don't really "need" to do anything

for the other way around, IF you live way up in the mountains AND happen to have a state of tune that matches the not atypical super lame lean/hot stock Jetronic tune (1.0+ lambda, aka "14.7+" in common but technically incorrect-for-ethanol-era-fuel terminology), then you can have problems at sea level if you're running more than the otherwise lame 28º

going in either direction - up or down - the fuel ratios can be off off and noticeably impact idle quality, but that isn't any indicator of a real problem.... real engine damage is about over-advanced timing and/or too-lean fueling (typically coupled with hard-running).

going up in the mountains makes it run richer.....which isnt great for washing oil off cylinder walls once you get way too rich.... but does help absorb some heat before that point

so, a stock bus that runs right, at sea level, can go up in the mountains and be rich and should not hurt itself even if it's not running great

a bus that is perfectly tuned for optimum performance in the mountains can be in danger at sea level

stock tunes leaves excessive safety margin on timing...hence everyone preaching 28º...

if you are perfectly stoic ("14.7" but really lambda 1.0) you end up way rich - low 11's at 8000 ft elevation

so if your bus is rich to begin with at sea level, it could be way too rich at 8000ft.
similarly, a more happy 13.6 would end up being 10.5.... 0.71 lambda is way too rich for a N/A to run all the time, but not the end of the world for a trip .. it is not good for your rings .. but you need a wideband to really make proper decisions with this stuff ... it can really matter though, a rich bus at sea level can easily damage it's rings at really really high elevations.

altitude changes AFR because the typical Jetronic has no compensation mechanism
but it also impacts cylinder pressure with the air density changes

so, the general thinking:
higher elevation = you have to remove fuel and add timing for ideal
lower = add fuel, remove timing

tl;dr version below

if you live at sea level and have passed CA sniffer smog, and have timing at 28º it's reasonably safe to just not worry about anything. you will be running rich, have less power, less mpg. the additional fueling may help you run cooler climbing all those hills :)

if you're tuned really rich at sea level right now, going to very high elevation will be very hard on your rings.

going up in elevation, you can add some more timing if you want but it isn't necessary, and may cause problems coming back down...depending on your state of fuel tune and octane of fuel