Let's say we have a non supercharged engine that reaches it's HP peak at 6000 rpm.Suppose we move this vehicle up to a moderate elevation like 4000 feet.Of course there will be a loss of power,but will the HP that's left still peak at 6000 rpm?
Elevation effect on HP peak
- Thread starter Truckedup
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Well at 0 ft above sea level the atmospheric pressure is about 14.7psi. You would need to look up what the typical atmospheric pressure for that given altitude is.
Rule of thumb for NA motors is 3% per 1000ft above sea level. So at 4000 ft, you'd be down about 12%.
Rule of thumb for NA motors is 3% per 1000ft above sea level. So at 4000 ft, you'd be down about 12%.
Yes, loss of power is uniform for a N/A car.
Originally Posted By: randomhero439
Yes, loss of power is uniform for a N/A car.
I didn't ask about power loss,I asked if the power still peaks at the same RPM.
Yes, loss of power is uniform for a N/A car.
I didn't ask about power loss,I asked if the power still peaks at the same RPM.
Originally Posted By: Truckedup
Originally Posted By: randomhero439
Yes, loss of power is uniform for a N/A car.
I didn't ask about power loss,I asked if the power still peaks at the same RPM.
Yes lol
Originally Posted By: randomhero439
Yes, loss of power is uniform for a N/A car.
I didn't ask about power loss,I asked if the power still peaks at the same RPM.
Yes lol
Why would the peak power point change by much? The engine internals and tuning are identical.
Altitude change doesn't change the camshaft profile, so the amount of valve lift and air intake will still be the same.
The real differences come from the air to fuel mixture.
Since there is less oxygen content in air at higher altitudes, the ECU has to change the fuel mixture (assuming we're talking about fuel injected vehicles with feedback control) to try and keep it in the programmed range.
Wide open throttle at high rpms tends to go into an open loop map in the ECU, which them just dumps in a preset amount of fuel for the amount of air traveling past the MAF sensor. That means you're running even richer under those conditions at higher altitudes.
Hence, why some vehicles feel like they make more power at part throttle here in Denver and higher altitudes than they do with the throttle mashed to the floor.
BC.
The real differences come from the air to fuel mixture.
Since there is less oxygen content in air at higher altitudes, the ECU has to change the fuel mixture (assuming we're talking about fuel injected vehicles with feedback control) to try and keep it in the programmed range.
Wide open throttle at high rpms tends to go into an open loop map in the ECU, which them just dumps in a preset amount of fuel for the amount of air traveling past the MAF sensor. That means you're running even richer under those conditions at higher altitudes.
Hence, why some vehicles feel like they make more power at part throttle here in Denver and higher altitudes than they do with the throttle mashed to the floor.
BC.
Yes, the engine characteristics will remain the same all the way up to insane altitudes.
In the aviation world, we generally consider the lapse rate (HP loss at altitude) to be 3% per 1000 feet.
There is a "however" in this equation though. Sometimes, excessively restrictive intake and exhaust plumbing becomes slightly more efficient at lower pressures. In other words, the exhaust scavenges slightly better, and a restrictive filter becomes slightly less restrictive (by percentage) . In this case, the lapse rate may be slightly less than 3%.
In the aviation world, we generally consider the lapse rate (HP loss at altitude) to be 3% per 1000 feet.
There is a "however" in this equation though. Sometimes, excessively restrictive intake and exhaust plumbing becomes slightly more efficient at lower pressures. In other words, the exhaust scavenges slightly better, and a restrictive filter becomes slightly less restrictive (by percentage) . In this case, the lapse rate may be slightly less than 3%.
There could very easily be some change in where the peak HP is.
The less dense air Has less inertia for 'ram tuning',resonates in the intake differently,and the exhaust will flow differently.
The less dense air Has less inertia for 'ram tuning',resonates in the intake differently,and the exhaust will flow differently.
Thanks,this engine is a vintage Triumph motorcycle racing engine,with carburetors of course. I'll be racing at higher elevations than usual this summer.There be a loss of power despite tuning changes,but I need to consider gearing changes.
You probably should jet leaner for extended use in high altitudes.
Originally Posted By: Cujet
Yes, the engine characteristics will remain the same all the way up to insane altitudes.
In the aviation world, we generally consider the lapse rate (HP loss at altitude) to be 3% per 1000 feet.
There is a "however" in this equation though. Sometimes, excessively restrictive intake and exhaust plumbing becomes slightly more efficient at lower pressures. In other words, the exhaust scavenges slightly better, and a restrictive filter becomes slightly less restrictive (by percentage) . In this case, the lapse rate may be slightly less than 3%.
Thanks......I'll be running slightly larger carburetors than usual to deal with the thinner air at Bonneville(4000 ft ).The exhaust is a consideration too.I'll be out there for the early October meet when it's cooler.
Yes, the engine characteristics will remain the same all the way up to insane altitudes.
In the aviation world, we generally consider the lapse rate (HP loss at altitude) to be 3% per 1000 feet.
There is a "however" in this equation though. Sometimes, excessively restrictive intake and exhaust plumbing becomes slightly more efficient at lower pressures. In other words, the exhaust scavenges slightly better, and a restrictive filter becomes slightly less restrictive (by percentage) . In this case, the lapse rate may be slightly less than 3%.
Thanks......I'll be running slightly larger carburetors than usual to deal with the thinner air at Bonneville(4000 ft ).The exhaust is a consideration too.I'll be out there for the early October meet when it's cooler.
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