Originally Posted by THE BULL

The Nismo exhaust can be just as restrictive as the OEM. As for the clogged HFCs (how old are they)

It's possible that HFCs could have deteriorated over time due to running them on a stock tune. Possibility of oil from the Breathers and PCV could have contaminated that bank more than the other.

Numbers are a bit low due to exhaust, if indeed you have an under performing HFC then yes he would not be able to add the necessary timing that they usually take. These 3 degrees would have had you closer to 310whp which is not bad when you take in that Nismo exhaust.

One thing you can do is replace resonators in that exhaust or the muffler section.

At the same time look into the HFC issue. Long tubes might introduce rasp on the Nismo exhaust.