Elevation Changes - What's the best way to temporarily tune for it?

[JoesEdge]

So this past weekend I attended a car show up in the local mountains (Big Bear, CA). It was a great car show, although my Duster didn't like going from 118 feet of altitude to 7,000 feet of altitude.

Obviously, it was super rich when I was up there and kept stalling out on me which was annoying. It climbed the mountain just great though.

So, what do you guys suggest to do (other than going EFI, which I have been thinking about) to temporarily tune for the altitude change? How can I anticipate what jets/rods I would need?

Do I really need to practically tear the carburetor apart or is there some sort quick fix that I can do when I'm up there, that I can undo when on the way back?

I currently have and Edelbrock 650 AVS on the engine. I usually run a Holley, but the fuel log was leaking so I swapped it out for now. I have the Edelbrock tune close to perfect when I'm in my home town of Downey, CA.

I added a shot of the Duster by Big Bear Lake.

Thanks!

 

[318willrun]

In the eddy, you might get away with leaning the main jets with the rods, but they need to be leaned out. You can also lean the idle mixture too. No matter how you tune, you are going to be missing some power up that high...

 

[JoesEdge]

In the eddy, you might get away with leaning the main jets with the rods, but they need to be leaned out. You can also lean the idle mixture too. No matter how you tune, you are going to be missing some power up that high...

Any idea of how calculate for the right rod to use though?

 

[318willrun]

edelbrock has a chart.

 

[TrailBeast]

Any idea of how calculate for the right rod to use though?

A 6,800 foot lift for testing?
Seriously though, it would be a trial and error, but the rods would be your best bet for ease of changes since it takes like 2 min to change them.
I live at 5,500 elevation and could tell you what jets and rods I run, but don't know how it would relate to your motor and carb.

 

[JoesEdge]

A 6,800 foot lift for testing?
Seriously though, it would be a trial and error, but the rods would be your best bet for ease of changes since it takes like 2 min to change them.
I live at 5,500 elevation and could tell you what jets and rods I run, but don't know how it would relate to your motor and carb.

Thanks! I think it would be helpful to know in order to get some sort of idea of where I should be. My engine specs are on my signature to give you and idea of my engine build.

I was Googling to see if I could find some sort of calculator but no luck. I did see somewhere that said for ever 2,000 ft of change you adjust the jets by one size. That was for a Holley though. I need to get that leak fixed so I an put it back on.

 

[TrailBeast]

Thanks! I think it would be helpful to know in order to get some sort of idea of where I should be. My engine specs are on my signature to give you and idea of my engine build.

I was Googling to see if I could find some sort of calculator but no luck. I did see somewhere that said for ever 2,000 ft of change you adjust the jets by one size. That was for a Holley though. I need to get that leak fixed so I an put it back on.

I would think 1 size for each 2k of elevation would probably relate to other carbs fairly closely.
I'm running a mild 5.9 Magnum, Eddie 600 with .098 main jets and AHH crap we are remodeling and I can't find my calibration kit to know the needles.
I'll find out by pulling one and get back to you in a bit here.
I know it still runs good at 7k feet as I drive up the mountain occasionally.

 

[TrailBeast]

Thanks! I think it would be helpful to know in order to get some sort of idea of where I should be. My engine specs are on my signature to give you and idea of my engine build.

I was Googling to see if I could find some sort of calculator but no luck. I did see somewhere that said for ever 2,000 ft of change you adjust the jets by one size. That was for a Holley though. I need to get that leak fixed so I an put it back on.

Ok so my motor is REALLY close to the same including the heads.
.098 mains and secondary jets with 7347 metering rods.
At 5.5k feet it runs right about 13.8-14.5 AFR at normal cruise speeds and at about 12.5 or so when stepping on it.
At 7k feet you could probably go one more step up on the rod sizes and be pretty close.
You will still go rich when you get into the secondaries though because the only way to fix that is jets.
It takes me about 10 min to change jets so it's not too bad if you went that far into changing it for the 7k elevation.

 

[JoesEdge]

I would think 1 size for each 2k of elevation would probably relate to other carbs fairly closely.
I'm running a mild 5.9 Magnum, Eddie 600 with .098 main jets and AHH crap we are remodeling and I can't find my calibration kit to know the needles.
I'll find out by pulling one and get back to you in a bit here.
I know it still runs good at 7k feet as I drive up the mountain occasionally.

I have .098's up front too and if I remember right, I have the .073 x .037 metering rods.

 

[TrailBeast]

I have .098's up front too and if I remember right, I have the .073 x .037 metering rods.

That sounds like about what should be in it for your elevation.
I know my car kicks A** in Phoenix at about 2k elevation and in CA when we go over there to the coast and runs about 2 full points leaner on the AFR.
I'd bet bigger rods would help a lot at 7k.

If you really wanted to mess with it you could get smaller jets and smaller rods for where you are now, and then just swap the rods for larger ones at the higher elevations.

 

[yellow rose]

Can't say with the edelbrock deal, but as a rule it's 2 jet sizes down for every 2000-2500 feet in elevation, plus 2 degrees more timing.

Every 4000 feet needs 1 range hotter plug.

I tuned guys who went from sea level to a corrected 7000 feet and they only lost .2 and the cars were much more consistent.

 

[TrailBeast]

Can't say with the edelbrock deal, but as a rule it's 2 jet sizes down for every 2000-2500 feet in elevation, plus 2 degrees more timing.

Every 4000 feet needs 1 range hotter plug.

I tuned guys who went from sea level to a corrected 7000 feet and they only lost .2 and the cars were much more consistent.

Thanks for confirming some of those numbers.
I didn't even think about advancing the timing just for a quick trip.

 

[mvh]

Hmm. The super six setup didn't seem to need any adjustment at 7000 feet. Maybe if I lived up there I could optimize for it, but for an extended weekend of up-and-down, I scarcely noticed the altitude. It was also 100º+... I guess if you don't have any power to start with it's not a problem...