Road cars tend to have lower ratios than race cars. I'd still like to see you outbrake someone who has a car set up for racing. You use engine and they use brakes, see who slows down faster. Hell you can use BOTH and they will slow down faster than you on brakes alone. Not because of skill, but because the car is set up better.
The amount of braking you will gain from using both is pointless, like I said, you can use it when you don't need to use the brakes to slow down, but when you want to realy slow down for a corner you will still have to use the brakes. At which point engine braking, and its comparably lower force, is still going to be negligable when you are slowing down with the brakes. Remember, these guys arn't on a sunday drive, they don't have time to leave it in gear for engine braking to have an effect. they usualy spend as much time in gear as they do out during braking, especialy if they double clutch as they heel-toe.
@h0tz
Please don't make me re-write the whole article about engine braking I had to write in the other thread. I'd link to it, but I can't find it either.
Engine braking is caused by the vacuum of the intake system, because the engine needs to speed up and the throttle is closed, vacuum increases, this increases resistance on the piston face when it lowers on the intake stroke.
If you look at engines the way I do, from a completely physical and mechanical sense you will realize that compression is always paired with a power stroke so it can't possibly be compression, it can't be friction because again, there's always a power stroke happening to counteract that. So whats left? Vacuum in the intake causing the pistons to do more work during the intake stroke.
And I won't even get into diesels and engine brakes, because they are very different.