Back at the Dyno

I know I haven't posted anything new on the exhaust yet, or on the Maserati Club International event in Assen, but I'm getting 'round to them.

In the meantime, I've been back to the dyno and to prove it I made a very short video.


The dyno results are below, with the bold lines the new results overlaying the previous results.


As you can see, I've dropped the boost pressure a little which results in a lower peak torque and less agressive ramp up. However, as a result I now have a longer flat section from 4000 rpm to about 5,500 rpm.

Overall performance can be determined by calculating the area beneath the curves... in mathematical terms, if you integrate the curve you'll calculate the actual work done. So although the new curve is not as peaky, across the rev range it's more effective, which should translate as being quicker on the road.

I think there's still some scope to tweak the inlet pressure a little, but it won't yield any big improvements. There's something fundamental preventing me from getting more power out of this engine and I can't quite put my finger on it. Fuelling is not the issue... if anything it's running too rich at the top end, but the chip tuner prefers this since it's much less likely that the engine is going to fail. But it shows that the current injectors are more than up to the job.

So if there's enough fuel, is there enough air? Air supply to the compressors is not the issue, since last time I was at the tuners I did a run with no air filters and there was hardly any difference (so I think the air filters I have fitted are more than good enough). So, maybe I'm getting a significant amount of pressure leak between the compressors and the inlet manifold? To check this I'll need to place a pressure gauge near to the outlet of the compressor and compare this with the pressure at the plenum chamber. It could be that the turbos are having to work very hard to maintain 1.20 bar, which is effecting their efficiency.

Another simple thing to try is to connect the stock boost solenoid... although it won't be controlling the inlet pressure, it's absense may be alerting the ECU and knocking it into safe mode. I don't think the Ghibli ECU has an error check circuit for this like modern cars, but I don't know, so it's worth checking it.

If it's not air supply then it has to come down to timing. I certainly think this is what is preventing me going above 1.20 bar, but I think I should be getting better performance at 1.20 bar, so I'm not going to go down this route yet. I think I should be able to get 360 hp out of this engine at 1.20 bar, so I need to find out what's preventing this before looking at changing out the distribution system.

So... the sooner I install the PLX data logger the better I think.