Carb vs Fuel Inj

[CG]

I only read a couple of car/truck boards and one of the interesting things I see fairly often is people talking about having to adjust their timing and carbs for altitude. Im not sure but it seems odd to me. Back when all we had was carburation and points did people have to adjust their carbs and timing for road trip driving?

I sure as heck don't remember my dad having to fiddle about with his carbs or ignition when we went back to Minnesota in the summers to visit his family. We had to go through a couple of mountain passes to get there. Was the gas just better so altitude wasn't as much of a thing?

I keep seeing all the builds with newer FI engines, or old engines set up with FITECH or Holley etc etc. Is this really the best way to go if the plan for whatever you are building is to take it on trips?

Cant you build one of our trucks with a carbureted engine and HEI upgraded ignition that would go coast to coast anymore without having to constantly fiddle about with timing and carbs? Build it, dial it in, close the hood and just go. No messing around under the hood until its oil change time?

[powerdriver]

I Believe you can build a " no touch " Carb engine . That being said most guys I know like to fiddle with stuff . Back when everything was a 6 banger and the one barrels which had basically 3 moving parts it was probably a necessity .

[GOPAPA]

My first experience wtih altitude and my carburation was in my 73 chevy when I got to Tuson Arizona ,,the truck acted like it was missing ,,this was 1974

The other time was with my 1980 F truck with a camper on it and I was headed for Arkansas ,,And in heavy traffic in Denver Colorado the truck had no power and I had a hard time getting to the pull off ,,waited awhile and slowly made it into Kansas this was in 1981 since then all my trucks and cars does not seem to be evected with elevation .

[special-K]

Most interstates don't go all that high. It's mostly driving up mountains or extreme altitude changes. I remember being ok most of the time, but once you climb enough you notice the bad tune and it's time to adjust. Most times once down in altitude I was able to keep that tune in the lower country.

[Bigdav160]

Like mentioned, driving though you would just put up with the 'no power'.

If you lived at elevation then you'd go for the tune

['63GENIII]

With my carbureted engines, I would notice the loss of power when going from sea level to 3,500'+ and if I was spending some time at the higher elevation. IMO, a well tuned carb will get you pretty much anywhere you need to get without much fanfare. Although noticeable, the lack of power is more of an irritation to me as I always "want" to fix it.

When Id ride the Shovelhead to Street Vibrations back when, I would always have to stop in Auburn to swap jets. On the way home, swap them back. It was pretty noticeable with that carb. It was pretty crude.

The FI that I have in the truck now is nice though. Turn the key, no pumping the pedal for the choke, decent mileage (for a big block that is) and no real noticeable loss of power wherever I am. Just kind of always runs the same.

Only drawback I can see is if you do have a problem, limping it home is a little more difficult than with a carb. For that reason alone I really like the factory set up. Parts availability.

[Ziegelsteinfaust]

Some carbs like the Q-jet, and the Edelbrock/Carter are typically better with Altitude changes. Then a typical Holley, but a small Holley is not so bad. Something like a 390 will be pretty decent. But all carbs jetted for where I live at sea level start getting pig Rich after 4000, and almost undrivable after 7000.

Holley mechanical secondaries can be horrendous at altitude, but people usually jet them for performance. Not nice road manners.

Higher compression higher vacuum engines tolerate altitude at a much better rate then low compression low vacuum engines. But still by 5000 foot they start really laying over.

20 years ago I drove my 66 Mustang cross country, and drove over the Rockies. Honestly I should of gone around, but my car thankfully made it. It had a 5.0 302 with 10-1 compression, B303 cam, and self ported GT40P heads. It should of been good for 300 hp 325 Tq I think, and was a great all around engine. It was drinking gas, and felt like I pulled two plug wires. A year later I did in a C10 with a crate master engine, and as bad as the 302 was this was epically worse. I tried adjusting the carb with what I had, and it still sucked bad. It failed the plugs, and got 5mpg wheezing over the hump into Denver.

So I can see why people love fuel injection, but my heart still belongs to carbs. I love the look when I pop the hood open. Hopefully in a couple years when I spring for a Holley Terminator classic I will still get that feeling.

[dieseldawg142]

never fiddled around with the 1850 Holley on my old '68 910, and i too live in the pacific northwest CG, surrounded by big 'ol mountains.
never noticed power drops up 7-8000 ft hills, but 20 or 30 horse from 375 was not really noticeable..
i did fi on the bb in my '85, best thing about it is the "driveabilty" factor now. as mentioned, no pumping or choking, just reach in and turn the key, runs the same at home or up at 7000 or upside down..

[special-K]

I recall resetting timing more so than carb adjustment

[blazer2007]

I never fiddled much with anything much until I joined this forum.

[truckster]

I've never had to do much adjustment with Quadrajets, although living at 4800 feet I do advance the initial timing a bit.

It was a different story with my old Honda Elsinore 250. I'd get to a certain elevation (seems it was around 7000 or so) and it would just refuse to move until I adjusted the carburetor.

[Stormin08]

tune that dude for an 89 octane should be able to find that anywhere....

a 93 tune, may be limiting.

but overall, a carb'd engine does make slightly more power than most port injected efi setups. now, tbi setups, may be a lot closer.

[1976gmc20]

Originally Posted by special-K

I recall resetting timing more so than carb adjustment

Yeah, I used to live at eight to ten thousand feet elevation (and drove up to 13K!) and I never messed with my stock carbs, but the timing needs to be advanced for higher altitudes.

An even somewhat dirty air filter will cause a lot of problems at higher elevations. We sold a lot of air filters when I used to work at a service station in a high mountain tourist town. Always answering the same three questions:

1) where's the bathroom?
2) how do I get to Aspen from here?
3) how come my car runs so bad?

['63GENIII]

Originally Posted by dieseldawg142

runs the same at home or up at 7000 or upside down..

Ive heard the upside down thing before. The rock crawler crowd really likes the FI. I'll take everyones word on that point.

Originally Posted by blazer2007

I never fiddled much with anything much until I joined this forum.

And there is the answer to all of the questions that have nothing to do with EFI or carbs!

[67 twins]

runs the same at home or up at 7000 or upside down..[/QUOTE]

The fuel injection may work upside down, but how about your oil pump? Personally I would want it to stop running if I'm upside down. Lol

[special-K]

This thread times out with thoughts I've been having while driving my '72 K2500. My other vehicle is a '95 K2500 Suburban. Both have 350/auto/4.10s/same tire size. I was thinking how nice my '72 would drive with the TBI/4L80E. It's a very practical easy cheap swap. TBIs just go and they can handle a decent amount of HP from factory. The transmission gets into more, as usual. I like the trucks as they are, but for a driver I'd like to go that route. I'd like to build something from scratch so I can leave my '72 alone

[1976gmc20]

I guess back in the "old days" we never knew any different.

We just assumed you would start your truck and let it warm up a while before trying to go anywhere, even on a summer morning.

But my experience is that a carb with a working choke is more likely to start on a really sub-zero morning. It seems like the EFI processor takes too long to figure things out and your battery runs down by then. I've had carb/choke trucks start on the second or third "grunt" from the starter at minus thirty or forty, after having sat for days.

[davischevy]

In 1967 my parents bought a new Chevy car in the Kremmling or Steamboat Springs CO area. It ran fine but got less than desirable fuel mileage in the mountains. We moved back to Arkansas that winter and the car began to get great gas mileage.


I assume it was tuned for the high elevation, and when it was at lower elevation ran leaner.


In 1972 I bought a new Cheyenne. In the spring of 1973 we took a trip out west. As we left west out of Denver and over Berthoud Pass the truck really struggled.

[davischevy]

We have been researching FI units lately.

I am thinking more and more about putting an LS engine in the 67 short bed I am building.

I drive a carbureted truck every day, and get along just fine, but the computer controlled engines are the future.

[Boog]

Oh no. You are being pulled over to..................... the dark side. FI and all things electronic.
I am still strong, so far, in my preference for no new fangled 'lectronics on my 69. I admit every time I start it up I hate the exhaust fumes it emits though...

[Andy4639]

I love the EFI in my vehicles. My 71 has the 6.0 LS with 4L80E over drive. The 14:1 ratio is why you don't have to mess with EFI. It doesn't matter what elevation your at it knows already and compensates for it.
This is one of the main things why GM,Ford Dodge all have to keep in mind. The general public doesn't wrench on their own vehicles so they make it simple for them to drive anywhere no matter what area your in.

I agree the old school carbs I never knew my dad to get out and adjust them when we went on vacation to the mountains.
It's like racers adjusting for cool air are hot muggy air. The carb can't adjust to it but EFI can by the computer.

I'm thinking real hard on the sniper system for my daughters 68 now.

['63GENIII]

Originally Posted by davischevy

We have been researching FI units lately.

I am thinking more and more about putting an LS engine in the 67 short bed I am building.

I drive a carbureted truck every day, and get along just fine, but the computer controlled engines are the future.

If and when I wear out the L29 in the red truck, I think Ill go the LS route as well. In fact I almost did with an LQ9 that I traded for the big block.

The LS platform has more than earned its place I think. Something for everyone from 4.8 to 427 factory engines, NA, nitrous, turbo, you name it. Trucks to Corvettes. Just a very versatile piece of engineering.

Originally Posted by Andy4639

I love the EFI in my vehicles. My 71 has the 6.0 LS with 4L80E over drive. The 14:1 ratio is why you don't have to mess with EFI. It doesn't matter what elevation your at it knows already and compensates for it.
This is one of the main things why GM,Ford Dodge all have to keep in mind. The general public doesn't wrench on their own vehicles so they make it simple for them to drive anywhere no matter what area your in.

I agree the old school carbs I never knew my dad to get out and adjust them when we went on vacation to the mountains.
It's like racers adjusting for cool air are hot muggy air. The carb can't adjust to it but EFI can by the computer.

I'm thinking real hard on the sniper system for my daughters 68 now.

So true about the majority of car buyers not "working" on their vehicles. They really do make 'em dummy proof nowadays.

Funny thing is that the "hot rodders" of today get more out of the factory combos by opening a laptop instead of the hood. All of that data logging and open source tuning is completely lost on me but very interesting and impressive nonetheless.

[theastronaut]

I've driven my '64 VW with twin Dellorto carbs from around 600 feet to a little over 5,000 feet and it ran the same with no noticeable difference in power. It also has an AFR gauge and I didn't see it get outside of it's normal range.

I've also driven my '89 Festiva with a Weber two barrel conversion from SC to AZ (700-7000 ft) twice and I've noticed less power at high elevation, mostly noticeable over 4500-5000 ft. It only weights 1800 pounds and makes about 75hp and the car was loaded down to 2240 pounds with all the extras for the race track, tools, and luggage so any missing power was really noticeable. From google searching, 75 hp at sea level is down to about 59-60 hp at 7000 feet. If they have the track event in AZ again next year and I'm able to go I'll throw my AFR gauge in to see how it's affected.

[Matt Man]

When I moved to Idaho back in 2018 I towed a trailer that weighed about 4500 pounds with my 81 k10 4bbl Qjet. Where I used to live was at about 500 feet above sea level. Throughout the 900 mile drive to Idaho the elevation peaks at 8000 feet before getting into Ely, Nevada. Most of the drive after Ely to the Idaho border is 6000 plus feet. Never had a issue besides the power loss from the elevation increase. This route is pretty tough on semi's and towing in general I was surprised how well the Qjet performed as I just did this trip again last month towing to California and back.

[1976gmc20]

Originally Posted by Matt Man

When I moved to Idaho back in 2018 I towed a trailer that weighed about 4500 pounds with my 81 k10 4bbl Qjet. Where I used to live was at about 500 feet above sea level. Throughout the 900 mile drive to Idaho the elevation peaks at 8000 feet before getting into Ely, Nevada. Most of the drive after Ely to the Idaho border is 6000 plus feet. Never had a issue besides the power loss from the elevation increase. This route is pretty tough on semi's and towing in general I was surprised how well the Qjet performed as I just did this trip again last month towing to California and back.

The only trouble that I ever had with a Qjet from 13K' down to sea level was that stupid little fuel filter where the gas line comes in. Well, and sometimes the automatic choke.

I pulled a little Cat on pretty heavy tandem equipment trailer over 11K+' Monarch Pass with my 1981 K10 350/465. It went right up no problem but coming down was interesting. I'm guessing my Cat and the trailer weighed about 15K# combined.