elevation vs. timing - The 1947 - Present Chevrolet & GMC Truck Message Board Network

chevyforever · 03-10-2004, 01:08 AM

i have a question to ask because i have been rattlin this around in my head for a while now
what i am wondering is if elevation changes affects ignition timing. i know that if i tune my carburetor for home(5400 ft elevation) and go to sea level that it will set way too lean because of the more dense air and vice versa, but what if i changed jets to compensate for the elevation change, would i have to adjust my timing also or just leave it alone.

maybe i shouldnt think so much

chevyforever

veedublu · 03-10-2004, 01:36 AM

I have always heard the "advance it 1 degree for every 2000 feet" rule (advancing as you go higher in altitude), but don't have anything to back it up with.

I've done that, and it works well with no pinging

John

stelth2002 · 03-10-2004, 01:41 AM

WOW, someone with a cummins in a chevy 4x4. Ive seen them before and envy you. I wish i had that kinda time. Hows she run? Is it the 12v? I assume your running a divored t/case

veedublu · 03-10-2004, 01:51 AM

My truck is apart right now for paint, and I miss driving it

Yep, I'm running a 12 valve... not one of those new fancy-schmancy computerized "overvalved" engines

Not running a divorced 205, it's married to the NV5600... was almost a direct bolt-up, just a little time spent finding the proper seal

John

stelth2002 · 03-10-2004, 01:55 AM

Care to post some pics. I have been thinking about putting a 4bta in a jeep. I need a cj8 really for the wheel base legnth. But put a 5 speed and such in it. I think it would be a killer outfit. Put some lower compression pistons in there, up the boost, bigger injectors, etc. maybe a wheely bar lol. Not really but when i get done with the 67 its a possibility. jt

veedublu · 03-10-2004, 02:02 AM

No pics yet... when I get it completely "done" I'll post a thread with some pics. Engine is turned up a little bit... injectors, tweaked pump, smaller turbo housing, bumped timing... will smoke the (rather large) tires by just rolling on the throttle in 3rd gear

If fuel prices keep rising, I might have to look into the 3.9 Cummins swaps a little more... I have a rockcrawling 4x4 Toyota that would like to rattle!

John

03-10-2004, 01:08 AM	#1
chevyforever Some like em' long! Join Date: Nov 2002 Location: Grace, Idaho Posts: 69	elevation vs. timing i have a question to ask because i have been rattlin this around in my head for a while now what i am wondering is if elevation changes affects ignition timing. i know that if i tune my carburetor for home(5400 ft elevation) and go to sea level that it will set way too lean because of the more dense air and vice versa, but what if i changed jets to compensate for the elevation change, would i have to adjust my timing also or just leave it alone. maybe i shouldnt think so much chevyforever __________________ 1971 chevy c10 lwb- 300 hp 350 crate motor, soon to be more with ported and polished 62cc chamber 461 double humps, TH400, 3.73 posi, used to be my uncle's truck 1972 chevy k10 lwb- 350,4 spd, old and tired, dad bought brand new and is now mine 1968 chevy c20 lwb- 327, 4 spd, was originally a 50th anniversary truck 1990 GMC K1500-just my runaround truck 1982 Chevy K10 shortbed, new motor and new paint, another project in the mix of the others. IMPORTS SUCK!

03-10-2004, 01:36 AM	#2
veedublu Registered User Join Date: Jul 2001 Location: Colorado Springs Posts: 159	I have always heard the "advance it 1 degree for every 2000 feet" rule (advancing as you go higher in altitude), but don't have anything to back it up with. I've done that, and it works well with no pinging John __________________ 1976 K20 my dad bought new - longbed stepside, just turned 50k miles

03-10-2004, 01:41 AM	#3
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	WOW, someone with a cummins in a chevy 4x4. Ive seen them before and envy you. I wish i had that kinda time. Hows she run? Is it the 12v? I assume your running a divored t/case __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

03-10-2004, 01:51 AM	#4
veedublu Registered User Join Date: Jul 2001 Location: Colorado Springs Posts: 159	My truck is apart right now for paint, and I miss driving it Yep, I'm running a 12 valve... not one of those new fancy-schmancy computerized "overvalved" engines Not running a divorced 205, it's married to the NV5600... was almost a direct bolt-up, just a little time spent finding the proper seal John __________________ 1976 K20 my dad bought new - longbed stepside, just turned 50k miles

03-10-2004, 01:55 AM	#5
stelth2002 Young Gun wth Fast Inline Join Date: Jan 2002 Location: Idaho Posts: 1,475	Care to post some pics. I have been thinking about putting a 4bta in a jeep. I need a cj8 really for the wheel base legnth. But put a 5 speed and such in it. I think it would be a killer outfit. Put some lower compression pistons in there, up the boost, bigger injectors, etc. maybe a wheely bar lol. Not really but when i get done with the 67 its a possibility. jt __________________ 1967 Chevrolet LWB with built 292! 415 ft. lbs of torque, 4 speed :O with 27% overdrive too, 3.73 Posi. Frame and body done... getting painted!!!

03-10-2004, 02:02 AM	#6
veedublu Registered User Join Date: Jul 2001 Location: Colorado Springs Posts: 159	No pics yet... when I get it completely "done" I'll post a thread with some pics. Engine is turned up a little bit... injectors, tweaked pump, smaller turbo housing, bumped timing... will smoke the (rather large) tires by just rolling on the throttle in 3rd gear If fuel prices keep rising, I might have to look into the 3.9 Cummins swaps a little more... I have a rockcrawling 4x4 Toyota that would like to rattle! John __________________ 1976 K20 my dad bought new - longbed stepside, just turned 50k miles



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