Pikes Peak trip!

[chaseincats]

1 hour ago, TomoHawk said:

If I did that, I'm pretty sure the engine would stall.  Would you please explain what "any vacuum line unplugged" means?

It just means unplug a vacuum line that goes directly to the intake manifold

[TomoHawk]

There are several vacuum hoses;  one to the brake booster, one to the heater controls, and one to the distributor.

[Racer X]

13 minutes ago, TomoHawk said:

There are several vacuum hoses;  one to the brake booster, one to the heater controls, and one to the distributor.

Pick any one, except the brake booster one. You just want to create a vacuum leak.

 

I'm skeptical that any of this will help at 14,000 feet though. The problem with a normally aspirated engine at high altitude is the air density. There isn't enough oxygen in the air, and the relative air pressure is much lower than at sea level. When the intake valve opens at sea level, the atmospheric air pressure is something like 14 pounds per square inch, so the air/fuel mixture is easily crammed into the cylinder. The relative e air pressure at 14,000 feet is only around 2 pounds per square inch. At such low relative atmospheric pressure it isn't very easy to get the air/fuel mixture into the cylinder, even with the suction created by the rapidly descending pistons.

What a normally aspirated engine needs at high altitude is the addition of an oxidiser. A shot of nitrous oxide might do the trick. Or some aviation gasoline, which has oxidisers added to aid combustion at the altitudes airplanes operate at.

Turbocharged engines aren't affected by the low atmospheric air pressure, as they use waste engine heat to turn an impeller to force the air/fuel mixture into the engine.

Edited November 29, 2020 by Racer X

[chaseincats]

1 hour ago, Racer X said:

Pick any one, except the brake booster one. You just want to create a vacuum leak.

 

I'm skeptical that any of this will help at 14,000 feet though. The problem with a normally aspirated engine at high altitude is the air density. There isn't enough oxygen in the air, and the relative air pressure is much lower than at sea level. When the intake valve opens at sea level, the atmospheric air pressure is something like 14 pounds per square inch, so the air/fuel mixture is easily crammed into the cylinder. The relative e air pressure at 14,000 feet is only around 2 pounds per square inch. At such low relative atmospheric pressure it isn't very easy to get the air/fuel mixture into the cylinder, even with the suction created by the rapidly descending pistons.

What a normally aspirated engine needs at high altitude is the addition of an oxidiser. A shot of nitrous oxide might do the trick. Or some aviation gasoline, which has oxidisers added to aid combustion at the altitudes airplanes operate at.

Turbocharged engines aren't affected by the low atmospheric air pressure, as they use waste engine heat to turn an impeller to force the air/fuel mixture into the engine.

So with this switch on, the air filter off, and an extra vacuum leak added for good measure still wouldn't get enough air into the engine to get it up Pike's?

Edited November 29, 2020 by chaseincats

[Carl Beck]

5 hours ago, Racer X said:

I'm skeptical that any of this will help at 14,000 feet though. The problem with a normally aspirated engine at high altitude is the air density. There isn't enough oxygen in the air, and the relative air pressure is much lower than at sea level. When the intake valve opens at sea level, the atmospheric air pressure is something like 14 pounds per square inch, so the air/fuel mixture is easily crammed into the cylinder. The relative e air pressure at 14,000 feet is only around 2 pounds per square inch. At such low relative atmospheric pressure it isn't very easy to get the air/fuel mixture into the cylinder, even with the suction created by the rapidly descending pistons.

 

Air pressure at 14,000 Ft. would be closer to 8.26 psi.   Still an L28E ruling at factory spec.'s shouldn't have any problem going up Mt Evans even at 60% power.  I've driven a stock 72 240Z up there.  Just thinking out loud - I know nothing about the F.I. on the 280Z.... but for some reason I'm thinking the ECU on the 280Z is an analog computer. 

I'm wondering if that  Gold Canister that @chasincats pictured, with the Blue&Black wires - is a sort of altimeter - that outputs an analog signal of varying strength. So it is not a matter of sending  ON/OFF signal to the ECU - so much as sending an analog signal of the correct strength to the ECU - to adjust the air/fuel mixture for different altitudes. Like a fuel level sender in the tank, or a temperature gauge. Jumping the wires together - might send the opposite signal needed to the ECU and make things worse at higher altitudes.

Does the Factory Service Manual tell you how to test that Gold Canister, or give a signal strength that it should output at Sea Level ? 

 

[chaseincats]

11 hours ago, Carl Beck said:

Air pressure at 14,000 Ft. would be closer to 8.26 psi.   Still an L28E ruling at factory spec.'s shouldn't have any problem going up Mt Evans even at 60% power.  I've driven a stock 72 240Z up there.  Just thinking out loud - I know nothing about the F.I. on the 280Z.... but for some reason I'm thinking the ECU on the 280Z is an analog computer. 

I'm wondering if that  Gold Canister that @chasincats pictured, with the Blue&Black wires - is a sort of altimeter - that outputs an analog signal of varying strength. So it is not a matter of sending  ON/OFF signal to the ECU - so much as sending an analog signal of the correct strength to the ECU - to adjust the air/fuel mixture for different altitudes. Like a fuel level sender in the tank, or a temperature gauge. Jumping the wires together - might send the opposite signal needed to the ECU and make things worse at higher altitudes.

Does the Factory Service Manual tell you how to test that Gold Canister, or give a signal strength that it should output at Sea Level ? 

 

This excerpt from the FSM should explain it a little bit:

Edited November 29, 2020 by chaseincats

[Racer X]

4 hours ago, Carl Beck said:

Air pressure at 14,000 Ft. would be closer to 8.26 psi.   

 

Correct. I made an error in my math, resulting in the 2 psi figure. Sorry, eh?

Still, 8 psi is nearly half that of sea level. Consider an older, high mileage engine that isn't producing the original rated output, then cut that output by nearly half, and you now have a huge deficit.

Time for some NOS.

 

 

[Racer X]

9 hours ago, chaseincats said:

So with this switch on, the air filter off, and an extra vacuum leak added for good measure still wouldn't get enough air into the engine to get it up Pike's?

Unless the air filter is really dirty, removing it probably won't lean the mixture out enough to compensate for the lower air density.

[siteunseen]

Maybe this member will respond with some real life experience? @73str86

Click on "73str86 replied to a topic" he went up the peak to 13,500 ft

 

 

[Carl Beck]

6 hours ago, chaseincats said:

This except from the FSM should explain it a little bit:

 

Thanks- @chaseincats

 

I guess that confirms what I wrote;  “I know nothing about  the F.I. on the 280Z”.  

 

Have to say - even in 1978, I’m surprised they sent the level at 3675ft. - given California is 282ft below sea level in one place and 14,000ft above in others. Perhaps its more an Emission Control thing for Calif. 

[Zed Head]

If you live at 3,500 feet it probably changes with the weather.  That would be annoying.

[chaseincats]

9 minutes ago, Zed Head said:

If you live at 3,500 feet it probably changes with the weather.  That would be annoying.

good point