Has anyone else tried boring out the throttle body? I had the throttle body bored out from 55mm to 58mm, per a friend's recommendation as he did it to his Prius. The change in air flow is minor enough for the ECU to adjust, and the additional air flow helps the car keep up on the highway. Boring helps make the Prius C a little less boring.
I've done it on other cars. Yes, fuel economy would decrease, especially since you are driving as if in a race car. Can also run into computer re-tuning issues. OP is stating a more responsive Prius at highway speeds, no tuning issues and their fun has increased. I can't comment on that. One can inspect their current throttle body to look for metal/ flashings smoothing improvements that could be made. That is what I would do...I would not bore and increase its size. FWIW however, with a Prius restrictive intake channel I think this TB mod is a waste, better money spent in other areas such as car stereo, chassis, rattle and sound proofing even home furnishings. Modding can be a fun hobby!!!
Modding is fun, no doubt about it. Personally though, I want to buy a Prius for the extreme fuel economy. If I had another car, I would find it fun to improve performance, but isn't a Prius all about economy? But, to each his own of course!
That's why I got a Prius C, and I'm really happy with it. But I've found that it's a gateway drug - running with the gas engine turned off is so satisfying-but-frustrating because the car fires up the engine back up at the slightest provocation. So now I'm waiting for the Chevy Bolt EV to come out so I can eliminate gas altogether.
Fuel economy is approximately the same. The coolant wasn't bypassed, so the air isn't as dense as compared to before to impact fuel economy. Although it consumes more fuel accelerating and under load, when cruising it is able to maintain high fuel economy. Avg mpg is 50+ mpg for long trips on the highway. It is a minor mod to improve throttle response and helps when on the highway. Don't expect it to help you overtake many more cars or any cars as compared to before.
