Nissan 370Z Forum - View Single Post - Greddy Twin Turbo Kit for Nissan 370z

Sharif@Forged · 03-15-2010, 05:32 PM

Quote:

Originally Posted by Phimosis

Something doesn't add up.

Air goes in at one atmosphere (14.7 psia), gets mixed with gas at roughly 11:1 ratio, makes 277whp.

Add turbo & intercooler, add 6.2 psi of 'boost' (20.9 psia), add 42.2% more fuel to match the 42.2% more air (20.9psia / 14.7psia = 1.422) and at same 11.0:1 air/fuel ratio and you should, in theory, get 42.2% more power.

I say in theory, because you end up getting less than that. There are frictional losses from turbulence as flow velocities in intake runners go up, there's losses from backpressure that the turbos create, there's some loss in air density from increase air intake charge temperatures, etc. Regardless, at 6.2 psi boost an otherwise stock 370z should only make 394 whp. Likewise, 8 psig would get you to 428 whp and it should take 9.3 psig to get to 452 whp.

The other ways you can squeeze more power is by more using ignition advance, leaner a/f ratio or modify the engine/intake/exhaust. Using a lean burn or ignition advance will cause detonation and aren't viable in a turboed engine.

So something doesn't add up. Any ideas?

-Phim

Hi Phim,

It's always best to use the mass of air in calculations, rather than pressure. Pressure is dependent on many things, such as temperature and the effeciency of the turbocharger. For instance, a tiny turbocharger making 20 psi might be producing the same amount of airflow as a larger turbo at 10psi. So we also measure the power potential of a turbocharger in lb/min (mass) of air. Each of these 20G turbos can produce about 400lb/min worth of air which you should give about 400hp worth of airflow PER turbo. You also have to factor in the volumetric efficeincy of each engine. For instance, a 350Z at 6psi with this same kit would only produce about 350whp, whereas the 370Z would produce about 400-425whp at the same boost level. (our dyno numbers).