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Back pressure is always bad. The issues in exhaust tuning are gas flow velocity and pulse timing. These must be matched with engine speed and cam timing. Look at my dyno chart Stage VI+ NAversus an NA with an ECU upgrade only (i.e. stock intake, exhaust, cams heads, manifolds) NA with ECU only. Many of the mods on my car-intake, straight through mufflers, ported heads-are reputed to reduce low end torque. One of the mods, longer duration cams with an additional 20 degrees overlap, is know to reduce low end torque (and increase high end torque). Headers generally increase mid to high end torque with little effect on low end performance. So, the net effect, combining mythology (intake, exhaust, ported heads) with actual (increased valve overlap) should be a massive loss of low end torque. Frankly, I fail to see it, and it does not appear to exist on the street either. Of course, these dynocharts don't really go below 2000 rpm, but then I rarely get below that in normal driving anyway.
The story behind the NOELF's symbol RECYCLE PAPER - KEEP A TREE FROM BEING PLANTED 208.5 rwhp dynochart
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