Does high altitude affect timing? If so, how?

[Journeydog]

Given the engine setup indicated in my signature, will high altitude affect timing, especially TDC offset? If timing was adjusted at essentially sea level and I checked it at 7000', should I expect to see some change in the numbers? Or does the baro sensor input to the PCM allow for altitude accomodation, so that timing will not change? Or...if it does change, is there a fudge factor I can apply...such as, 'x' degrees per thousand feet?

TIA

[gmctd]

PCM compensates from Baro input, but I'm thinking only at crank. I intend to apply varying pressure to check this out, but have not yet done so.

[panchosteam]

What about if you have a 4911 rebuilt on a 96 6.5td and live now on sea level, then later on move to a place where you will be at around 4200 ft above sea level?

1984 sierra classic now with 6.5 td and heath's turbo master

[gmctd]

With less Baro, exhaust will flow easier, allowing some additional Boost, but without pressure-compensating diaphragms, as in the EFI models, you may be doing some manual adjusting to inj pump and turbo.

Carbureted vehicles had factory offsets to jets and vacuum advance mechanisms when shipped to hi alt areas.

Relocating either direction required 'retuning'.

EFI does offer some advantages, don't you know. :cool: