Altitude effects on a 1406.

[Isaac nickerson]

Probably an already answered question, but I'm gonna be going up to mount hood a lot this winter from 100 feet above see level and up to timberline lodge which is 6000 ft above sea level. Will the truck be able to make it up without too much struggle or will it be far too rich? Stock 350 with manual trans.

 

[AuroraGirl]

HIGH ALTITUDE Altitude has a direct effect on the operation of most carburetors. As the altitude increases, the air becomes less dense so a carburetor, originally calibrated at low altitude (sea level), delivers too much fuel and the engine runs richer. If the preceding tuning procedure is performed, then a proper high altitude calibration will result. If the vehicle was calibrated at lower altitude, however, and is to be driven at high altitude temporarily, it is not necessary to repeat the complete calibration procedure. Instead, use the rule of: “2% leaner per 1500 feet” and the Calibration Reference Chart for your model carburetor. For example, with a #1405 at baseline calibration (location #1 on the chart) and intended operation at 6000 ft. altitude, you would want 6000 divided by 1500 x 2% = 8% leaner calibration. That would be location #24 on the chart which would require only a rod and jet change.

https://edelbrock-instructions-v1.s3.amazonaws.com/edelbrock/carb-tuning-guide.pdf

 

[Bextreme04]

Probably an already answered question, but I'm gonna be going up to mount hood a lot this winter from 100 feet above see level and up to timberline lodge which is 6000 ft above sea level. Will the truck be able to make it up without too much struggle or will it be far too rich? Stock 350 with manual trans.

You'll be fine. It will be rich and down on power, but you will have no problem as long as it is tuned up ok beforehand. The first winter after I got my truck, I decided to hunt the White River area over by Maupin during the General season and pulled my ~3500lb tent trailer over there from Salem. This was with a 350 that had been sitting for 11 years or so and was not in good shape. I had no problem pulling through Government Camp at 45mph plus.

Just make sure you have it tuned right at sea level, lean of peak idle and slightly rich cruise and full throttle will keep you in a totally OK range even at altitude. You'll be down quite a bit of power though. General rule of thumb even for fuel injected engines that are at the right A/F mixture even at altitude is a 3% reduction in HP for every 1,000ft of elevation without forced induction. That means you will be down AT LEAST 15-20% at full throttle, not taking into account loss of power due to it being rich.

A healthy 350 or larger will have plenty of extra ponies available so that you won't really notice unless you are hauling a load. A suped up 350 or larger will have plenty of extra power to not even notice the drop.

 

[AuroraGirl]

You'll be fine. It will be rich and down on power, but you will have no problem as long as it is tuned up ok beforehand. The first winter after I got my truck, I decided to hunt the White River area over by Maupin during the General season and pulled my ~3500lb tent trailer over there from Salem. This was with a 350 that had been sitting for 11 years or so and was not in good shape. I had no problem pulling through Government Camp at 45mph plus.

Just make sure you have it tuned right at sea level, lean of peak idle and slightly rich cruise and full throttle will keep you in a totally OK range even at altitude. You'll be down quite a bit of power though. General rule of thumb even for fuel injected engines that are at the right A/F mixture even at altitude is a 3% reduction in HP for every 1,000ft of elevation without forced induction. That means you will be down AT LEAST 15-20% at full throttle, not taking into account loss of power due to it being rich.

A healthy 350 or larger will have plenty of extra ponies available so that you won't really notice unless you are hauling a load. A suped up 350 or larger will have plenty of extra power to not even notice the drop.

I think he may run into more driveability issues if he doesnt have a regulator. but could he perhaps use a distributor curve set to potentially help the situation? From what I gather, healthy or stock+ smog era 350 would benefit from a advance coming in sooner and having a more set curve, at least the edelbrock tuning pdf made me think that. Lol.

 

[Bextreme04]

I think he may run into more driveability issues if he doesnt have a regulator. but could he perhaps use a distributor curve set to potentially help the situation? From what I gather, healthy or stock+ smog era 350 would benefit from a advance coming in sooner and having a more set curve, at least the edelbrock tuning pdf made me think that. Lol.

Having the distributor and carb tuned properly will definitely help. But that doesn't really have anything to do with his question. Higher altitude will not inherently require anything different in either fuel pressure or timing. The lower power from altitude will require more throttle for an extended time though, which could expose any already present issues. Like I said though, just taking a day trip up the mountain isn't going to be any kind of big deal. The biggest issues I could see might be cold start if he is leaving it in the ski lodge parking lot and hitting the slopes all day. We don't get a lot of really cold weather here, but up on the mountain is a different story. Generally trucks that have had an edelbrock carb swapped on often also have a big open air filter and no heat pipe on it either. That can lead to issues with carb ice and cold start problems. Again, probably not a major issue for his use case, but something to consider.

 

[AuroraGirl]

Having the distributor and carb tuned properly will definitely help. But that doesn't really have anything to do with his question. Higher altitude will not inherently require anything different in either fuel pressure or timing. The lower power from altitude will require more throttle for an extended time though, which could expose any already present issues. Like I said though, just taking a day trip up the mountain isn't going to be any kind of big deal. The biggest issues I could see might be cold start if he is leaving it in the ski lodge parking lot and hitting the slopes all day. We don't get a lot of really cold weather here, but up on the mountain is a different story. Generally trucks that have had an edelbrock carb swapped on often also have a big open air filter and no heat pipe on it either. That can lead to issues with carb ice and cold start problems. Again, probably not a major issue for his use case, but something to consider.

I know he wants to head up there a lot. I guess its a great question if he plans to be parked or not that would be a huge one yeah. But I was thinking if he has a high pressure, and like a lot of edelbrocks, maybe is richer than proper tuned, and then going up where there is a less dense air, I could see that just making it annoying at least, maybe fouly. But i just saw an SAE link of a study from the day, they tinkered a bit and concluded a 1 range hotter plug could be used if consistently driving above 5000 feet. If your truck isnt doing short trips and only goes left to the store and left back home normally, you probably wouldnt have any problems generally with a 1 hotter heat range. The plug gap and all that is not recommended to be toyed with. If your plugs are due or close you may try popping a set in on your second trip maybe see if it has any benefit. it wouldnt be pronounced but it did indicate you would not want to do WOT at sea level if tuned at elevation, but you still would be tuned at sea level.