Just curious to know if anyone knows how bad of a hit my hopped up big block is going to take in HP when I move to Denver next year? Going to have to re-jet my Holley double pumper, probably going richer but am preparing for a mild disappointment in throttle performance.

 

My house is at 5000 feet. You can look up the actual loss, but it is somewhere around 10% reduction. What really kills you is a hot day where the Air Density altitude soars to 9000 feet.

but anyway the way my carb is setup is that I go two jet sizes bigger front and rear for when I go down to sea level. You did not say your carb size, but bigger jet number size would only require 1ish jet size change.

Less oxygen slows the burn rate so you might bump the timing a couple of degrees

 

It's roughly a 3% loss for every 1,000 feet of elevation from everything I have read.

 

Drop a message to Lars,he is actually in Colorado and should be able to point you in the right direction as for jet sizing and timing for the mountains.

 

When I moved to Denver from Houston...my mid 11 sec 427 Camaro lost nearly .9 tenths in the 1/4 mile. I kept looking at the tach saying "C'mon...you can do it!" as I watched it climb at a much slower rate.

Normal driving it will feel fine...but when you go WOT you'll notice.

Added compression and timing are your friends.


JIM

 

I raced up at Bandamere Raceway in Denver once. All the classes looked like they moved several years back in their performance levels. It was the first time the sanction I was racing in had run there. Of course we were lucky enough for there to be record high temps and the adjusted altitude was over 9500 feet.

 

Too bad no one makes a supercharger kit for a C3 that fits under the hood. Maybe it's not possible to get a blower under the hood. My C6 looks like a tight underhood situation, but in fact a centrifugal supercharger fits right in and looks like factory.

A supercharger is an advantage at high altitudes...particularly the Eisenhower tunnel at 10,000 feet.

 

I live in Denver Metro area and my 1977 Vette runs fine on the 85 Octane Fuels but what does suck when we park the car for winter is 10% Ethanol in the fuel will attract water when sitting.

Accually at the higher Alittude you wil need to run leaner fuel mixture you will find out here we have lower octane fuels at higher Altitudes. Here we run 10 % Ethanol and lower Octanes than other states.

Richer mix will not be good leaner mix is the key despite what you think. Out here we have lower Octane levels and running richer mix is just wasting fuel and causing problems It is a different world at over 5000 above sea level. Too rich and not enough oxygen which is way if you look at less fuel less oxygen cleaner burn. I can provides proof on this.

You might still need to run our highest Octane at 91 but I bet you can you can run the 85 or 87 Octane without a knock. You have to run a leaner mix up here instead of richer. Less oxygen require leaner fuel mixture since there is less oxygen the fuel requires less octane and it sucks the engine produces less power. Strange I know but the lowest grade is 85 instead of 87. I had to adjust and I run 85 Octane in my 1977 without any problems at all.

 

I live in Denver and i do have a bit of an issue with a ping when it's hot but otherwise all seems fine. Any ideas on a hot day ping? I run 91 octane.

 

The horsepower loss from sea level to Denver is actually almost 20% on a normally aspirated car. You can minimize the loss through proper timing and tuning, but there is nothing short of supercharging that will get the power back. NHRA correction factors for ¼-mile times here in Denver are .9 to correct for sea level.

You can make slight advances in timing, but the gas available here at altitude is lower octane, so you can’t “cheat it” without getting into detonation.

Jetting changes needed are minimal. A carb is actually self-leaning, since it meters air based on mass-flow through the carb’s Bernoulli Tube venturi: As air mass decreases, delta-P decreases, and the carb leans out. I find that most cars are set up somewhat lean for sea level operations, and they end up being right where they should be by the time you get up here. If you were actually jetted correctly at sea level, you can drop jetting by about 2 sizes for better fuel economy, but power will not be greatly affected.

Once you get here, feel free stop by the Viking Lounge and Corvette Workshop for a setup check and a beer…

You can put a supercharger under the hood of a C3 – there is no “kit” available to do it, so you have to fabricate it yourself. Here is a Vortech system I just finished up on a ’71, and it all went under the hood. 670hp on pump gas in Denver:

 

Jetting changes needed are minimal. A carb is actually self-leaning, since it meters air based on mass-flow through the carb’s Bernoulli Tube venturi: As air mass decreases, delta-P decreases, and the carb leans out. I find that most cars are set up somewhat lean for sea level operations, and they end up being right where they should be by the time you get up here. If you were actually jetted correctly at sea level, you can drop jetting by about 2 sizes for better fuel economy, but power will not be greatly affected.

That is so true. When I lived there I used to scarf up deals on carbs at the swap meets. Folks would "tune" on them because of all the things they had read or heard and really screw up a perfectly good carb. I would go back to the Holley literature and put them back to stock as a baseline. Sometimes this was easy...sometimes hard... because folks would start drilling air bleeds and fuel passages. You had to look at things closely. But once you got them back to a good baseline, it was pretty easy to make minor tweaks to account for altitude.

The Viking Lounge is always a good place to hang out!!

JIM

 

[QUOTE=lars;1585163803]The horsepower loss from sea level to Denver is actually almost 20% on a normally aspirated car. You can minimize the loss through proper timing and tuning, but there is nothing short of supercharging that will get the power back. NHRA correction factors for ¼-mile times here in Denver are .9 to correct for sea level.

You can make slight advances in timing, but the gas available here at altitude is lower octane, so you can’t “cheat it” without getting into detonation.

Jetting changes needed are minimal. A carb is actually self-leaning, since it meters air based on mass-flow through the carb’s Bernoulli Tube venturi: As air mass decreases, delta-P decreases, and the carb leans out. I find that most cars are set up somewhat lean for sea level operations, and they end up being right where they should be by the time you get up here. If you were actually jetted correctly at sea level, you can drop jetting by about 2 sizes for better fuel economy, but power will not be greatly affected.

Once you get here, feel free stop by the Viking Lounge and Corvette Workshop for a setup check and a beer…



You can put a supercharger under the hood of a C3 – there is no “kit” available to do it, so you have to fabricate it yourself. Here is a Vortech system I just finished up on a ’71, and it all went under the hood. 670hp on pump gas in Denver:

Ok thanks for the tips, we should moving in July or August. Little bit concerned now, it sounds like more of a drop than expected. I'll to think of some extra HP tricks to pull.!!

 

I see the same carbs with the same "tricks" done to them. As you noted, the only "trick" is to undo and identify all the mods and travesties performed by the previous owner, get the carb set up back to spec, and make mild tuning adjustment from that point based on what the engine needs. On the dyno up here, we actually see that a Holley carb in its "stock" sea-level setup is almost always jetted right on the money, and needs very little other than a precise setup with primary/secondary throttle blade opening balance and float level/squirter setup. They are jetted lean at sea level, but run right on the numbers here at 5,000 feet.

The Viking Lounge is always well-equipped, and you will see the Texas State Flag still proudly displayed behind the tap. Your signature, however, has faded, so I need to give you a better felt marker for the autograph next time you're through Denver..!





Lars

 

Glad to see it's still proudly displayed! My daughter lives in Longmont...and I'm about to buy a new lift...for the new shop...and it looks like Denver may be the nearest dealer to me ( I moved to Salt Lake City area a few months ago). I may need to plan a road trip over soon!

See ya,


JIM

 

Like stated above,only a slight advancement in timing will be needed.You will for sure feel a loss in performance.

 

Might have to hook up with a touch of nitrous? Don't have it installed but it might be an idea we'll see.