Tuning my 340 for high elevation...

[firefighter1]

Hi guys,

I have a 70 dodge with a 340 engine, performer intake manifold, 650 cfm edelbrock carburetor, electronic ignition, 727 transmission. I live in the bay area which is below sea level. So my car is tuned for the sea level. Every year when I am in Reno Nevada for hot August nights, my car acts up because of the elevation. I was wondering of anyone knows what to do to get the mixture right for the elevation? Do I just lean out the fuel? Or do I also retard or advance the timing? Thanks.

 

[Leadfoot]

Lean it out an advance the timing just a couple degrees. The rule is supposedly 1 degree for every thousand feet roughly. I also bought a 600 Edelbrock and it ran great out of the box and I'm at 5000 feet give or take.

 

[TrailBeast]

Lean it out an advance the timing just a couple degrees. The rule is supposedly 1 degree for every thousand feet roughly. I also bought a 600 Edelbrock and it ran great out of the box and I'm at 5000 feet give or take.

Me to, about 5000.
Ya need to drop the primary jet size down about 2-3 sizes, then re tune your idle mixture leaner, and advance the timing. (After you are there of course)
I used to drive from Susanville to Reno to Stockton, so I had the opposite problem.

 

[firefighter1]

which way is advance which way is retarded? Clockwise for advance? So if I was at 500 ft above sea level and now I'm at 5500 ft above sea then I have to advance a whole 5 degrees?

 

[70aarcuda]

the rotor turns clockwise..to advance turn the distributor counter clock wise..

only way to get mixture correct is to change the air/fuel ratio....less air at 5000 ft...so I need...????

less fuel...

 

[shanson30]

We used to drop 4 jet sizes on a holly and i think a couple of numbers cooler on spark plugs. Never changed the timing and dont really remember about the plugs. This was for drag racing in denver.

 

[firefighter1]

Less fuel is not the only key. The car still stalls out and runs rough even after I dial back the fuel. I don't have a timeline light here at the show in Reno so I can't acuratly advance the timing. Any other suggestions?

 

[70aarcuda]

once you get over Donner Summit ...you can coast downhill all the way home...lol

 

[MopaR&D]

Less fuel is not the only key. The car still stalls out and runs rough even after I dial back the fuel. I don't have a timeline light here at the show in Reno so I can't acuratly advance the timing. Any other suggestions?

Buy one... lol seriously your engine is starving for timing advance, you might get by advancing it by ear but then you run the risk of going too far and hitting detonation. What are your timing specs at home at sea level?

FWIW my 360 likes 16* initial, 35* total (not including vacuum) at 5500 ft. elevation here in Denver. And that's with Magnum heads and a mild cam, with older open-chamber LA heads your 340 will want even more.