BAN SUVs is correct. If you take the turbo off any factory turbo car, it is going to make fairly pathetic power. Start by looking at a stock 2.5rs then cut off another chunck of power and tahts probably what an STi would have if it ran without a turbo.

 

Can't give you an exact number, but if you have an STi you can simulate non-turbo power pretty easily, and it's rather pathetic.

Here's how, with the engine off the boost gauge should be somewhere near 0, usually just slightly on the vacuum side. This reading is atmospheric pressure, since boost gauges just measure pressure inside the intake manifold, and with the engine not running, it's the same as atmospheric pressure.

Power from an engine is BASICALLY manifold pressure x RPM. A turbo and non-turbo engine will make the same power at the same manifold pressure and RPM (as long as they are both in vacuum since a non-turbo cannot operate in boost.)



Now, normally aspirated cars ALWAYS operate below atmospheric pressure, since they have to suck air into them to burn with fuel. Engines at idle have very low pressures inside, since the engine always tries to suck the same amount of air per revolution BUT the throttle body blocks most of it, less air, less fuel, less power. Now, at full throttle, the manifold pressure will rise, but will always be slightly less than atmospheric, since the engine still is sucking air, (if it was higher, then the engine would spit air out the intake, turbos FORCE the air in at higher pressures, keeping this backflow from happening)

Now that i've explained what you actually see on a boost gauge, to simulate non-turbo power, accelerate and watch the boost gauge, adjust throttle so the boost doesn't go above atmospheric. Throttle position doesn't matter here, the turbo compensates for the partial throttle, and vice versa. You will find that the STi is VERY weak in vacuum situations and it will not take very much throttle to keep the engine just below atmospheric pressure.

Long explanation to show what to do, but I like to explain what's going on and the science behind it.

 

Actually, it is a very good indication, since the engine itself doesn't care about the throttle position, just how much air is available to it, and if the pressure is the same at 1/4 throttle with slight boost (but still a vacuum) as a non-turbo at full throttle, then the power will be the same. Physics is physics, and power from an engine comes from only a few factors, air, fuel, ratio of mixture, timing on spark, and RPM.

Love to continue this, but got this nasty thing called a hurricane comin straight for me....

 

Why couldn't you get a pretty accurate number by looking at the stock dyno graph for torque and HP and boost at each point on the graph and multiplying by the appropriate factor of (boost pressure/2*Atmospheric Pressure). So, for example, if at 6000 rpm, the max HP is 300 and the boost is 14.7 (for ease of math) then it would be 300*(14.7/(2*14.7)) = 300*(14.7/29.4) = 300*(1/2) = 150 HP. The STI makes 300 at 6000 RPM, so what is the boost at 6000 and then that should be close to the amount the engine would make NA. Is this not true or am I off in my thinking?