I was at a show this weekend and parked next to a fellow Shelby owner. He was running about 650 rwhp out of an 07. He said hisbtuner told him not to run long tubes and to keep the manifolds but did not say why. I was under the impression better flow = reduced boost pressure. Better for the engine and more hp. Is the tuner full of it or am I missing something? Any theories please post, always looking for more knowledge.
You are correct, boost is a measure of back pressure on the engine. The lower the boost, the less stress on the motor. I have been running 785 rwhp in my 07 for over 25,000 miles and 3 years now, lt's and cams keep the boost down. I have been told 18 lb's of boost on these engines is the max. I would suggest VMP or Lund for any tunes.
Maybe due to cost vs gains. I run Kooks long tubes on my Procharged Mach 1. Gained 30 HP. There are cheaper & easier ways to gain 30 HP.
But headers are cool & sound good, just pricey for GOOD ones.
That is what I was thinking as he also said he had the traction control and tpms tuned to be off. Guy drove a long ways to get the car tuned so I hope not.
Unless you are looking for sound or to get to a moderate power number easier, the $1500 you can spend on exhaust can be better spent. The factory manifolds are quite good. That said, a set of long tubes and high flow cats will net you 25-30 rwhp at sea level, will run cooler and sound great.
One reason a tuner may mention this is the extra distance for the O2 sensor to pick up its information. Gases may have dilution and or delay. Another is the opportunity for leakage which can cause the same issue of O2 sensors not performing their jobs properly. A properly installed set should not leak but are prone to future leaking. Tuner may be leery of these possibilities.