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| The exhaust install went very quickly. |
The turbo did spool slightly faster at low rpm but overall the boost levels stayed pretty consistent. As the turbo spooled the air fuel ratio was leaner with a shallower slope as the mixture trended towards full rich at wide open throttle. Full rich did not occur until 4300 rpm or about 700 rpm after maximum boost was reached. This had some implications on the car's state of tune which we will explain a little more next.
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| The exhaust uses all of the stock hangers. |
The early Evo X from 2008-2009 did not have what Mitsubishi programmers call lean spool enabled in the fuel control program. Lean spool is a bit of code that makes the engine run leaner while the boost is building to bump up the exhaust gas temperature for more energy in the exhaust stream which speeds turbo spool up. Many Evo variants have lean spool enabled from the factory and many experienced tuners turn off lean spool to have direct control over the air fuel ratio in the map.
Starting in 2010, Mitsubishi enabled lean spool on the Evo X which has made it much more sensitive to bolt on parts. You can see the results of lean spool being enabled in our datalog. At 3800 rpm we are reaching 22 psi of boost while our air fuel ratio is fairly lean for this level of boost and pump gas, about 12:1. To makes things even more volatile, our Evo X had a lot of timing in the ignition map.
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| The polished muffler can looks good and is fairly tasteful. |
The result of lean spool being enabled was that we could hear some rough combustion and some light knock at wide open throttle and the data log indicated a knock count of 10-12 counts. This probably isn’t enough to cause engine damage on the street but it is on the edge. Track action on a hot day could be a problem.
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| With the intake and exhaust before tuning, we registered a knock count of 14. There was some audible knock and definitely some rough combustion. Under track conditions there is a good possibility of engine damage. Note how much ignition timing the 4B11 runs under boost and high rpm at 20 degrees. This is an unusual amount for an engine on pump gas. |
