English to Polish Tech/Engineering Automotive / Cars & Trucks

The next one down though is our exhaust pressure, we can see this is exactly what I was talking about. At the start of the run we're at our ambient or barometric pressure, about 96 kPa, you can see that as we first come up on boost pressure, about 154 PSI of boost, 118 kPa of exhaust pressure. As I move through the run though, we get to a point at around about 6,500 RPM where our exhaust manifold pressure just starts to overtake our boost pressure, and our exhaust manifold pressure peaks at 180 kPa. So that translates into our IMAP divided by EMAP calculation, remember it simply is that easy. We're looking at the inlet manifold pressure and dividing that by the exhaust manifold pressure to calculate a pressure ratio across the engine, and that's what we've got here, remember, it is uniquely named here as engine load normalized.

Let's not do that, let's just make a little bit more room so we can see exactly what that does. So you can see, when we're sitting at full throttle, 2,000 RPM and just settling the engine prior to the run, our engine load normalized where our pressure ratio's 1.15. We've got more inlet manifold pressure than we have exhaust manifold pressure. We get up to a peak here around about 1.3, 1.32 where we've got our exhaust manifold pressure has come up a little bit, but obviously our boost pressure is much higher, and then we can see what I was talking about, our pressure ratio starts to drop away, and by the time we get up to our rev limit, 7,500 RPM, our pressure ratio has dropped down to 0.91 because our exhaust manifold pressure is now above our inlet manifold pressure. Okay, so let's just have a look at what that means to our table here.

I'll just shut that down. So at 3,000 RPM this is the area that we're operating in, around about that 1.3, 1.32 pressure ratio, and if we move across to the right-hand side, by the time we get to 7,500 RPM we are down here. So the advantage, or reasoning behind using pressure ratio as a load axis is that it, to a degree, automatically compensates whereabouts, it's looking in that table as our pressure ratio changes. Now at a fixed altitude that's not particularly significant, but what we are going to find is that if we take the same engine and we now drive it up Pikes Peak, if we're maintaining a fixed inlet manifold pressure, then our pressure ratio is going to change by virtue of our exhaust manifold pressure increasing. So if we've correctly calibrated our IMAP over EMAP volumetric efficiency table, in that case we're going to theoretically end up with a much more stable tune as our altitude and our barometric pressure varies.