| I have produced the dynocharts in comparative format for the stock TBs and the 60mm units using SAE correction and the charts reflect the conditions of the environment and the calculated SAE factor applied. The initial test with the stock TBs was done in more favorable conditions as the temperature was a few degrees cooler and with around 10-15% less humidity. You can see the difference in the SAE factor of around 2% between the compared runs. 1.4bar:
 1.5bar:
 1.6bar:
 1.65bar
 1.8bar:
The car was precision tuned with the 50mm units and the same tune was used with the 60mm test with the exception of a little bit of fuel trimming around 5000RPM to 6500RPM to equalize the mixture. All other aspects were equal (timing, fuel type, ignition dwell, etc etc)
It is apparent that the difference in temperature and humidity played in at about 2% but unfortunately the SAE correction factor does not properly account for turbocharged and intercooled systems. The rise in temperature and humidity has a larger affect on a FI/IC system than the SAE CF gives credit for and given that some fuel trimming was required through the upper midrange, I am under the impression that there was more of a difference than what the dynomometer is telling us but we still aren't talking about more than 7-10HP/TQ. Regardless, there are minimal gains in peak numbers or area under the curve with the 60MM throttlebody upgrade no matter how you want to split the hairs.
Simply stating, there are some marginal gains with the 60mm units although the dynomometer wouldn't suggest it. This is due to the inadequacy of the SAE factor with FI/IC systems (if you question this, I would be happy to send you the mathematical explanation as to why this is the case). Regardless of the independent results, our goal was to quantify the upgrade as accurately as possible and although there were no appreciable gains observed, we did achieve our goal of showing what the differences are and hope this may help others in their decision making process.
It is quite apparent that the throttlebodies are not the largest bottleneck in the systems immediately surrounding the Throttlebodies. It is speculated that the intake manifold itself is constraining the next greatest source of power/torque potential and given a different manifold design we may find that the 60mm units would be more beneficial over the OEM units.... especially if you have 2.5" intake piping, it would seem only logical to use a throttlebody of similar size as the pipe feeding it.
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