OK, I got my 172 remapped to use higher octane fuel. Nothing else. The people who remapped it said 10% more power. It was hard to notice the extra power, because even 10% more at the top end doesn't feel that much different, despite what some people would tell you. Whatever I got in extra torque at useful revs was noticeable though. Not huge, but noticeable. Enough to make me consider it was worth it.
I don't know whether that 10% was real, but when I took it out to the drag strip I did a 15.0 on the first run. That's better than any magazine road test I've seen for a 172 by about 0.3 seconds.
So what should I have gotten if I really had 10% more horsepower. There's an equation. It says that all else being equal 10% more horsepower should have cut the car's standing 400 metre time by 0.375 seconds. So I may not have exactly precisely 10% more power, but that drag strip time indicated its in that ballpark. Maybe about 8%.
Now at the end of that 400 metres I was doing 92 mph. That's about 40 metres/second. So if I got there 0.3 seconds earlier I was 12 metres further down the road at that point than a standard car would have been. That's about 3 car lengths.
A panel filter would get you nil measurable extra horsepower. Ie, less than the variation between runs on a dyno. A cat-back might get you an additional 5% with a remap to suit. So re-do the arithmetic, and you get around 0.5 seconds quicker down the 400 metres, and that puts you 20 metres, 5 car lengths, ahead of a standard car.
You'll note that the 13% total horsepower increase I estimated isn't much less than the 25 bhp MarkM said you'd get. I'm less confident that you'd see anything like 30 lb/ft extra torque. That's a lot.
If I do the arithmetic to translate that into an improvement in 0-100 mph time I get about half what MarkM says. About 1.15 seconds. Which would put you about 50 metres, yes, 50 metres, ahead of a standard car.
To get the 2.5 second improvement in 0-100 mph time MarkM says you'd need a lot more than 25 extra horsepower. More like 50. I don't think anyone seriously believes you could get 50 bhp extra, 220+ bhp, out of a Clio Sport just with a remap, induction and exhaust. That requires separate throttle bodies and/or cams. I'm suggesting you be getting about 195 bhp, based on the fact that a 182 starts with about 173 bhp.
