High altitude carb jetting - trip to sea level

[92saturnsl2]

My wife and I are moving to Kentucky at the beginning of March, and as part of that, we have to drive at least a couple of our vehicles out there beforehand. First to go is my 1985 F-250 w/ a carbureted 460 V8.

When I rebuilt the carb (Holley 4180C 4 bbl) in 2013, I installed jets for 6,000 ft. elevation. The 4180C is a Ford exclusive variant of the Holley 4160, designed to meet mid-80's emissions, so I imagine it runs a bit lean to begin with, even before I installed the jets for high altitude. It'll be an 1100 mile trip-- 600 miles into the trip, I'll be near sea level.

Should I be concerned about driving it with high altitude jetting @ sea level? Truck never knocks or pings, but I've never driven it below 5,000 ft elevation. If it does begin to have issues with spark knock while I'm driving out there, is there a quick remedy I can use, such as retarding the ignition timing to keep the engine happy? Perhaps use high octane fuel? Just trying to dot the i's and cross all the t's before I take this beast on the long drive. Any input would be appreciated.

 

[Ramblejam]

Not a 460 carb expert, so I'll defer to those who are...

Whereabouts in KY are you moving to? New job?

 

[Merkava_4]

High altitude jetting at sea level will cause the carburetor to meter too lean.

 

[Nick1994]

Factoring in the cost of gas, eating out, hotels, other expenses, have you looked into having some of the cars shipped?

 

[spasm3]

Really there is no way to know how lean or rich you are now, without egt( exhaust gas temperature) measurement. so its a guess. If you are ok or slightly rich i think there would be no problem, if you are already a bit lean at 6000ft, there may be an issue.

I'd rather rejet than run lean. Lean is lean wether you back the timing off or not, lean makes the egt go up. If you have a spare carb , jet it and swap them out.

 

[Linctex]

This is impossible to determine without a wideband oxygen sensor installed in the exhaust, to get an accurate baseline to work from.

A LOT of things affect fuel air mixture besides the main jets. Power Valve Channel restrictions are most often ignored, but often have a greater effect. So do air bleeds.

Without knowing if the truck is already running too rich or too lean, as it is right now..... it's very difficult to make a recommendation.

 

[JHZR2]

Originally Posted By: Merkava_4
High altitude jetting at sea level will cause the carburetor to meter too lean.


How did vehicles operate back in the day on cross country and mountains to the sea trips?

 

[mk378]

The very highest point in Kentucky is 4145 feet. Even in the more mountainous regions of the state, you might average about 2000 feet, you could consider it a sea level tune.

 

[Chris142]

It will prolly stumble @ cruise with the high elevation jets in it at sea level. What number did you take out vs put in?

 

[spasm3]

Originally Posted By: JHZR2
Originally Posted By: Merkava_4
High altitude jetting at sea level will cause the carburetor to meter too lean.


How did vehicles operate back in the day on cross country and mountains to the sea trips?


he does not have stock factory jets. he installed smaller jets for high altitude. stock jets are a compromise that would work in most situations.


I think some manufactuers ( in the early carb era) had high altitude options, when you bought the car.

 

[92saturnsl2]

For some reason the 4180C uses different jet sizes than a standard Holley 4160 4 barrel (I think due to the annular boosters and design of the emissions carb) so while they're interchangeable physically, the 4180C uses a smaller jet for the same elevation.

According to Holley's literature, I'm three jet sizes leaner than their sea level jet. They equate each jet size to approx. 2000 feet. The one I took out was what I crudely call a 2000' feet jet. I went two sizes below that (a 62? IIRC) which would configure the carb for 6,000 feet elevation. The truck runs fine with no issues where I live.

Surely, back in the day one did not have to hook their vehicle up to wideband in order to configure it to a given elevation. And I'm reasonably sure people traveled across country with high altitude jetting and vice versa. Most carb'd vehicles intended for sale in this region were equipped for high altitude-- I see them all the time in the junkyard with stickers affixed under the hood that reads something like "This vehicle / emissions system... was equipped from the factory for use at high elevation (> 4000 feet). Read your owners manual for details." Something to that extent. Just curious if there's some remedy for preignition/spark knock (probably the first lean symptom I'll encounter) should I have issues.

Once we get moved, I'll certainly rejet and retune the carb, but I have to get it there first and don't have the time to fiddle with it.

Quote:
Whereabouts in KY are you moving to? New job?


Actually this is my first move where a job isn't dictating where I'm going. Time to slow life down a little and get out of the hectic, expensive mess that is the Front Range area of Colorado these days. My wife has family in Elizabethtown, so we are moving to Hardin County or one of the surrounding counties. We've been there on vacation plenty of times and like the area. We can buy a house there for half what we can here, so that's our plan. We'll stay with the folks until we find a nice house in a good area with good schools, and of course reasonable commuting distance to where I find work.

 

[Alex_V]

Welcome from Campbellsville, 40 miles from E-town. I moved here 2 1/2 years ago from Missouri and really like it - but be warned, the humidity will take getting used to. I don't see you running into a problem with your jetting that premium fuel or a slight timing adjustment won't mitigate until you can retune it. IIRC we're at just shy of 1,000 feet.

If you need somebody that knows the region between here and there to drive a vehicle back for you, you know where the PM button is.

 

[Ramblejam]

Originally Posted By: 92saturnsl2
Actually this is my first move where a job isn't dictating where I'm going. Time to slow life down a little and get out of the hectic, expensive mess that is the Front Range area of Colorado these days. My wife has family in Elizabethtown, so we are moving to Hardin County or one of the surrounding counties. We've been there on vacation plenty of times and like the area. We can buy a house there for half what we can here, so that's our plan. We'll stay with the folks until we find a nice house in a good area with good schools, and of course reasonable commuting distance to where I find work.

I can see the appeal of Etown; small enough for lower property values, though plenty big enough for everything you'd need on a daily/weekly basis. Plus, being right by the interstate, you're only a short hop to Louisville or Bowling Green, and can run right up the BG to Lexington.

What's going on in Colorado these days? Have some family out there on the Front Range who are always singing the praises.

 

[CR94]

My '81 Mazda had an altitude-compensation gizmo attached to the carburetor. I assume it, or some equivalent measure, was required by emissions regulations. Ford got by without altitude compensation 4 years later?

 

[92saturnsl2]

Originally Posted By: CR94
My '81 Mazda had an altitude-compensation gizmo attached to the carburetor. I assume it, or some equivalent measure, was required by emissions regulations. Ford got by without altitude compensation 4 years later?


Anything with a >8600 lb. GVWR gives it a "heavy duty" distinction which makes it exempt from most of the emissions requirements of the day. This truck isn't even equipped with a cat-- just a couple air injection pumps and the ultra low compression that was the norm back then.

The light duty F250s and F150s had the feedback carburetors and all that jazz, even the 5.0L had fuel injection as an option.

 

[92saturnsl2]

Originally Posted By: Ramblejam
What's going on in Colorado these days? Have some family out there on the Front Range who are always singing the praises.


Nothing wrong with Colorado, it has its pluses and minuses just like any other locale. Land value in Colorado, if you want to be anywhere near the Front Range (where the jobs and money are) is pretty nauseating. If you're okay with a nice house on a postage stamp sized parcel of land, you'll love it. That's not to say you can't get a few acres somewhere within driving distance to a decent job, just that it's outside what my family can afford. The closer you get to the major cities, the worse it gets.

Our immediate goal is to buy a larger home with a fair bit of land on it, in a community close enough to a decent sized urban center, and E-town sure fits the bill. My in-laws live there, and it puts me dead center between my own immediate family who live in Colorado and northern New England. I've lived in the St. Louis area before, so I'm at least reasonable familiar with the climate. I'll sure miss the mountains and the recreation Colorado offers (a decent winter season especially), but I can always go back and visit. I am however, looking forward to decent spring that starts in March instead of June!

I drove the truck out last weekend and made it there with only having to turn a wrench once. Averaged 12mpg (best ever) for half the trip, but evened out to the normal 10mpg after. Once I reached the Kansas turnpike between Topeka and Kansas City, I noticed a fair bit of spark knock, pinging on acceleration while getting up to speed on an on-ramp. I retarded the ignition timing a bit and it went away. Other than that, nothing unusual, except the truck has a ton more low end torque at sea level. Never have to go above around 2k rpm before shifting, though I wasn't pushing it. I'll do a thorough tune-up and carb re-jet before driving it again, I'm curious to see how it feels at sea level WOT with all four barrels opened up..