H-Unit,
An exhaust will give you about 8ish at the wheels, and the back pressure reduction will help highway MPG slightly. B&B/SMA's exhaust elmininates the resonator. Magnaflow's and Borla's have their own resonantor to replace the stock piece.
You can port match/contour your K&N kit to help flow slightly. You can alos help the K&N get more cold air and less hot engine compartment air which will help ~1% power increase range.
Also, the throttle body can use some "light work" to clean it up and flow better - there's easily 4-5 HP in this. The TB is worse than the LS1's. The intake manifold needs some work in the TB area - if you feel like a challenge.
There are some electronic mods that I haven't done yet: modify the IAT to put the PCM on a more aggressive timing table, alter the MAF output frequency signal to lean out the WOT A/F ratio, etc.
Remember in Truck Trend's 2nd annual ultimate challenge, the H3 took second because of power, and perhaps it could have taken 1st with some of the bolt-on power adders. Also, it may have got a better run for the hill climb with the mods and an auto.
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