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All one needs to do is pull an exhaust valve out and look at the seat and port. What were they thinking? I looks like they cast the head, then decided to use a smaller valve afterwards. My best guess was they built the engine, then realized it had more RPM potential than they wanted, so they took the easy route to choke the thing off..it couldn't have been for improved mileage, that doesn't work. Efficency is what improves mileage.
EB


That's interesting! If your guess is right maybe that was Toyota's way of putting a speed limiter on the truck. That could possibly save them money on warranty claims by discouraging racing the motor.

93 4X4 ext-cab, auto, SR5, 3.4 V6, supercharged, 2.1" pulley, URD fuel mods, Aquamist WI, IPT valve body mod, dual cases, 4" superlift, Alcan springs, 33 BFG MT, ARB locked front & rear, 5.29 US Gears, RB 1" BL, 1.5" BJ spacers, TJM T-17, Warn m8000.