Turbo Measurements

[Rusty]

This is going to sound extremely newbish but can someone just clear up for me what the difference is between psi and bar? I understand the basic theory of turbos but I am unsure of how they are measured and talked about!

Sorry for starting a thread for such a silly question; a search didn't give me the answer. :down:

 

[crogthomas]

PSI (Pounds per Square Inch) and Bar are both measurements of pressure. Just different units (like pounds or kilograms).
1 Bar is approximately 14.5 PSI.

 

[Ed]

14.7 is actually more commonly used with turbos.

 

[crogthomas]

At the risk of being taunted for being a smart arse. 14.7psi is actually 1 Atmosphere, but is close enough to 1 bar that people often interchange the two when accuracy doesnt matter.

 

[Ed]

Exactly and turbos are based on flow capactity vs pressure ratios, and pressure ratio is atmospheres of pressure where a ratio of 1 is at sea level. I.e. no boost.

 

[kristian]

stoichiometric point, this is also 14.7

For petrol, the ratio
14.7 to 1
air-fuel
is theoetically ideal combustion ratio....

confusion?

 

[Ed]

no lol. Its the combustion ratio for most complete combustion, for most efficient CAT operation. It however is not the ratio for max power

 

[Rusty]

Ok, thanks for clearing that up.

 

[Ed]

Just to add for reference. Most standard Japanese cars run between 0.5 and 0.7 bar boost. This is around 7-10 psi. European cars are similar. Its uncommon to see much more, other than say the high power, high spec more recent metal.
Typically anything above 1.2 bar is considered pretty high boost, anything above 1.6 bar is really quite alot. For even more reference Allens Evo, which I mapped to around 1.6 bar mad about 430bhp@wheels from 2.0 engine. Most of the GTIR's I have mapped make around 300-330bhp @ wheels from around 1.6 bar. The March ST made 110bhp from around 0.7 bar and with my mods made [email protected] bar. My highest ever peak reading on the ST for boost is around 1.8-1.9 bar - I have no power figues for this boost level.