What size is the bore of a stock TB then? I'd be surprised if it's restrictive TBH, but without knowing the size, that's pure guesswork on my part.The engine capacity isn't particularly relevent - it's the flow, and you can pretty much tie that directly to the power as well. Low flow means low power, regardless of engine capacity, and vice versa. Funny enough, the topic of TB size was on another fourm I frequent this very morning, so it's probably worth posting the same quote here.This is from Jenvey, who make throttle bodies for a living. Context was single large TB and plenum inlet, just like our engines."It helps to understand the relationship between size and output to consider that a 2L Formula 3 engine produces 200+BHP through a 26mm (531 mm2) restrictor and a 75mm throttle body is eight times larger at 4,418 mm2! Similarly, in an experiment to curb the power of 270 BHP touring car engines, we reduced the size of the single throttle body to less than 44mm (1520 mm2) before there was any noticeable reduction. A 75mm body has three times the flow."
