No power at 7000 feet

[LVJJJ]

Right now towing (94 k1500) from way up in Blaine WA to Flagsaff AZ. Been many mountain passes and up and down hills. So going from sea level to 7000 feet. as we climed the 383 began losing power and much lower gas mileage, which I know happens. In the old days (w/carburetor) we would just change the jets. I'm wondering if I should be changing the timing? Advanced, get pinging, retarding lose power, maybe answering my own question? Down here in Arizona the regular is 85 octane. Maybe I should be buying higher octane gas?

 

[HotWheelsBurban]

Right now towing (94 k1500) from way up in Blaine WA to Flagsaff AZ. Been many mountain passes and up and down hills. So going from sea level to 7000 feet. as we climed the 383 began losing power and much lower gas mileage, which I know happens. In the old days (w/carburetor) we would just change the jets. I'm wondering if I should be changing the timing? Advanced, get pinging, retarding lose power, maybe answering my own question? Down here in Arizona the regular is 85 octane. Maybe I should be buying higher octane gas?

I thought the 383s were supposed to run on at least mid grade 89 octane?

 

[0xDEADBEEF]

It's just a function of less oxygen, that power ain't coming back no matter what you do with timing.

 

[L31MaxExpress]

If the tuning in the chip is set up correctly the TBI computer adds spark advance and reduces fuel as the MAP decreases. The altitude compensation is already built in. The only thing you can do to help without a supercharger/turbocharger is get as much cool ram air to the air cleaner as possible to help offset the density loss.

I set up a GMC motorhome with a 500 CID Cadillac Eldarado engine a couple of decades ago. Back then there was a company that built a ram air box for a 14x4 air cleaner. It had dual 4" snorkels. I used a pair of square body air inlets on the core support to 4" ducts to the air cleaner of that 500. It ran noticeably stronger everywhere. The 500 had the GM port fuel injection on it using a later TPI computer. Ran good even up the Ike pass. It lost power as it went up but nowhere near as badly as when it was breathing hot air from the engine compartment.

 

[GoToGuy]

Higher altitude equals less oxygen per cubic foot. The PCM adjusts fuel proportions, timing, for best burn. 8 % less oxygen = a proportional amount less power. That's at " standard rate " . Then if you add it's 95° F , then the density altitude could be 10,000 feet rather than the 8,000 feet above sea level the sign at the top of the pass.
To recover the lost power, as the earlier post said " stuff more oxygen and fuel in ".

 

[LVJJJ]

Thanks guys. Thot so. nice to have confirmation. I do have 2 cold air intakes. Got rid of the orignal intake box and hose. Ran a 4" smooth aluminum drier duct directly from the fender to the air cleaner. Wrapped it in insulation so it wouldn't get too hot. Took out all the stuff that was in the air cleaner funnel, so the air has a fairly smooth passage into the TBI. Then cut a hole on the other side of the cleaner, glued the original corregated funnel into that hole, ran a 3" corregated rubber pipe down thru the splash guard out into the wheel well. so, have probably done all I can for cold air.

 

[Bob2650]

Changing the timing won't help.
Power loss at 7,000 feet is normal. Going over the continental divide on I-70 will take you over 11,000 feet. The power loss on those steep slopes will really get your attention. Any kind of computer controlled fuel injection including our throttle body system compensates for the altitude but still lose much of their power because there is less air to work with. Turbochargers are very good for maintaining sea level performance at altitude. Carburetors are nothing but trouble in the mountains blowing clouds of black smoke and depositing carbon in the heads. A bigger problem can be overheating. The thin air greatly reduces radiator effectiveness. But the biggest problem of all can be overheating the brakes.
I live in Texas now but I am no flat-lander. I lived in Colorado a long time and hauled heavy trailers all over the mountains.

 

[wb292]

Thanks guys. Thot so. nice to have confirmation. I do have 2 cold air intakes. Got rid of the orignal intake box and hose. Ran a 4" smooth aluminum drier duct directly from the fender to the air cleaner. Wrapped it in insulation so it wouldn't get too hot. Took out all the stuff that was in the air cleaner funnel, so the air has a fairly smooth passage into the TBI. Then cut a hole on the other side of the cleaner, glued the original corregated funnel into that hole, ran a 3" corregated rubber pipe down thru the splash guard out into the wheel well. so, have probably done all I can for cold air.

I’m about 2 hours west of you along IH40. We go to Williams and Flag quite frequently. I have 4 TBI trucks. They all loose power when in town.
I have however gotten better power results from 14X4 open air filters. It never gets hot enough in Flag to try cold air intakes. I’ve also found that reducing exhaust back pressure helps even more.