the blip on the throttle increases the rpm of the engine so it matches the road speed.
if the rpm of the engine is too low, the engine breaks the car
so if you want to change to 3rd at 40 mph and your revs are at 2k, then the engine will break, so you blip the throttle, so that the rpm is higher to stop the engine slowing the car
but if you change to 3rd when you are going slower, 30mph then your engine being at 2k rpm will not slow the car at all.
that's what i meant
or do i have something confused here?
oh sorry you want the engine to help break...
but won't the engine break you more if it's spinning at lower rpm?
seems like you are trolling again but i'll reply anyway.
Its quite simple, engine braking is caused by the engines compression strokes on the overrun. More rpm = more compression strokes = more braking effect. You would think this would become blatently obvious pretty quickly to anyone who has driven a manual car.
The sudden and large braking effect on downshifts without rpm matching is not really engine braking so to speak, well it is, but it is caused by poor technique. Do that while you are at the limit of the tyres grip in a corner and the sudden braking effect on the driven wheels will cause the tyres to exceed the limit of grip, making the car slide. In a FWD it will tend to induce understeer in most cases. In a RWD it has the same kind of effect as yanking the handbrake, the rear will step out, it is a technique used in drifting known as the shift lock.
As for this
but if you change to 3rd when you are going slower, 30mph then your engine being at 2k rpm will not slow the car at all.
If you slow down more in 4th, when you shift to 3rd there is still an rpm difference which needs to be overcome on the downshift, only it is smaller when at low rpm, you can get away with it on low speed downshifts by slipping the clutch and it gives a smooth transition but it wears out your clutch.
RPM matching on downshifts is beneficial pretty much all the time, heel-toe isn't really necessary for the most part when driving on the road though, but can come in useful from time to time. It isn't hard to do, but you will find it difficult to start with, pressing the brake pedal hard by accident when blipping the throttle for instance, but practise makes perfect. This isn't so much of an issue when you are allready braking very hard though like you would be on track. Anyhow, it is far easier to master than left foot braking
