When will boost change
 

Will elevation change boost? I know when you get better air, your engine will perform better, and this will increase rpm and rpm will increase boost. But -
Example: If you go from 1500 feet to sea level and the air quality is exactly the same, would this change boost levels?:rolleyes:

Alittle bit ,very little at that small change

In talking to NordicHeat last week he said from 4000' to what elevation Havasu is it made a 2 PSI difference. From 5 to 7 lbs.

Does ambient temp have as much effect upon SC engines as NA?

Boost / Altitude
 

Keep in mind that your boost on the gauge will change very little on the gauge at different altitudes unless you’re running more rpm from increased hp. There are some density effects but they appear minor.
It’s the actual, true absolute manifold pressure that you need to see and not gauge.
I have the ability to look into my little black ball (FAST ECU) and confirm this real time, which is very helpful in my high altitude dealings.
When we boat at Havasu (~500 feet) I see 7 lbs of boost on the gauge and a true 7 lbs in the manifold or approximately 150 kPa via my lap top reading from the manifold in absolute pressure and not delta from ambient outside pressure.
So for example when we boat at 4500 feet I still see 7 lbs on the gauge but only 4.5-5 (or ~130 kPa) in the manifold. This is basically because we are starting out ~2-2.5 lbs in the hole already when running here at this altitude. In other words, when the pressure is already down 2-2.5 lbs outside (ambient) at 4500 feet, the gauge reads delta from that so 7 lbs is really only 4.5-5 lbs.
Another example is that when not running and I “key on” at Havasu I read ~100 kPa (14.7 normal, ambient sea level pressure) . When I key on here at home (5000 feet) I read ~82 kPa (or ~12.2 pressure)
This is why we loose so much power at high altitude on naturally aspirated motors. When the naturally aspirated guys from around here go down to sea level it’s like adding a blower with 2.5 lbs of boost. When the sea level guys come here they wonder what the hell happened
At least on supercharged we can drop a little in pulley size and re-coupe a bit if not all of that loss.

Bottom line is what your seeing on the gauge is not representative of what’s really happening. That’s why we can generally run 2 more pounds of boost safely here than you can at sea level.
That just catches us up though ;o)

As far as ambient air temp goes, I think there would be some effect along with the water temp if intercooled.

Hope that wasn’t too confusing; if so, sorry.

Dave

Dave good explaination
 

that's what I though but it's nice to hear it from other lips.

Thanks for taking the time to type, Mike.

Density altitude has a bigger effect than actual elevation change.