NCLA951

Forgive me if this is a dumb question, but thinking about how a manual boost controller sees boost, I've read around that they will get different boost depending on air temp/density, and that being a reason to go EBC, but doesn't it always see the same air density post turbo compression? I'm setting my boost at ambient LA winter temps (mid 60s), but don't want to take it out on a cold morning and over boost. It's not computing to me that a MBC will not see the ambient air density change but an EBC will, unless the EBC has a temp sensor? Thanks!

Sam

Paulyy

cooler the air the more dense it is, the more air the turbo sucks in. on cold(really cold) days, you'll see ~1psi more probably. I wouldn't be worried. just set the boost with normal average temp in your town.

in summer it'll boost slightly lower. again it's no more than 1psi with a mbc. maybe 2 depending on the turbo. but unlikely.

odonnell

They'll read different boost levels at different air temp densities, that is probably true. But, your air going into the manifold will also be at a different density because of the same phenomenom. So that reflects the MBCs ability to account for different manifold air temperatures.

Willard Bridgham 3

Air density changes both with temperature and elevation.

Turbo works better at cool temperatures and lower elevations where the air is more dense.

NCLA951

Thanks for the replies, I'll set boost 1 or 2 PSI below safe peak just in case. I understand density altitude from pilot training, just thought that the turbo dynamics evens that out by the time it gets to boost controller since compression begets heat etc etc. Thus the turbo advantage at high altitudes, where the boost controller still lets it build max boost since the turbo packs the thin air to the point it's the same as cold low air before opening wastegate. I suppose that would also heavily depend on turbo size and design as well.

CO951

The confusion is that you can measure boost two ways.

Absolute, like the stock 951 gauge, where zero is no pressure, 1 bar is sea level atmosphere and 1.7-1.8 bar stock boost. When I turn my car on the gauge says about .7 bar, because I live at altitude. The car will still boost to roughly the same level even with altitude and temp changes using stock boost control. However, it will build boost quicker on colder days or if I go down in altitude.

Relative, the MBC and many aftermarket boost gauges look at boost relative to your atmospheric pressure which changes with altitude and temp. So if you drive a car with a manual boost controller up into the mountains you will still make the same relative boost compared to atmosphere, but you absolute boost will go down. Likewise, as the air cools, your absolute boost will go up a little, even though the relative boost the MBC sees stays the same.