Headers only help if there is enough HP to GET OUT.
With a 75 HP exhaust on a 69HP engine, you would need 6HP of power adders before needing an exhaust upgrade.
And for real HP, freeflow makes HP up in RPMs and back pressure makes power down lower. Volume plays into it more than pressure tho.
Anyone (into 2strokes) remeber the LRD kinda adjustable pipes? One inch longer or shorter makes the power hit a thousand RMP higher or lower. NOT more power, just where it rolls on.
But in very high HP applications free flow is worth more than volume or pressure.
Thats not an issue unless you have over 12 to 1 CR or lots of boost.
On a built BBC boat with headers and NO exhaust, a set of baffled inserts (mufflers) can cost a guy 500rpm on top.
Searching for power in a toyota is a dead end search. I mean cmon, its pretty much a forklift motor.
