Engine Braking

[Edges]

Exactly...If you get a good run down the hill in top gear you can use your momentum to keep you going for quite a while.

If you drop down a couple of ratios beforehand though, you'll be on the gas way earlier.

I chuckle every time I see a steep gradient sign with the 'select low gear' warning sign...that may well have had some relevance 40 years ago but now, it's pointless.

On the motorway yes.. But if you're on a speed limit and need to stop/slow at the bottom of the hill after being on them the whole way down, you're gonna have a s**t load of brake fade and not be able to stop

 

[MarkCup]

On the motorway yes.. But if you're on a speed limit and need to stop/slow at the bottom of the hill after being on them the whole way down, you're gonna have a s**t load of brake fade and not be able to stop

I've never once experienced brake fade on the road.

On track, on a standard setup, I need several big (120mph) stops before anything starts to suffer. Maintaining a constant or slowly reducing speed down a gradient on the road isn't going to do the same.

In days gone by when drums all round was the norm, yes, fade would be an issue. In a 42 ton artic I'd imagine it would too.

In a 1 ton hatchback with modern discs/pads? Nah.

 

[GiT]

You achieve the same by leaving the gears alone and braking down the hill. I can't see why you'd change down a couple of gears just so you don't use the brakes. You are still not using any throttle.

Because in neutral, rolling down the hill you are wasting brake pads and fuel. The injectors are still getting fuel to idle the engine. In gear, the engine is spun by the momentum and the ECU cuts the fuel - that's why the MPG gauge goes high.

 

[The Fatty]

Always. ECU's cut fuel to the injectors when you do it. The Road momentum turns the engine.

Same with a big hill, drop a gear or two so you lose no speed and coast down, fuel is cut.

Road momentum is still turning the engine going down a hill without changing down a cog. Your not saving any more fuel than if you left the car in the gear it was in. In fact, you have used more by rev matching it. Also why would you loose speed by staying in 5th?!

 

[The Fatty]

Because in neutral, rolling down the hill you are wasting brake pads and fuel. The injectors are still getting fuel to idle the engine. In gear, the engine is spun by the momentum and the ECU cuts the fuel - that's why the MPG gauge goes high.

the engine isn't at 'idle' though!! It cuts the fuel whenever the car is moving, revs are above idle (900rpm) and your not using the throttle!!

 

[GiT]

the engine isn't at 'idle' though!! It cuts the fuel whenever the car is moving, revs are above idle (900rpm) and your not using the throttle!!

Eh, What? In neutral rolling down the hill... Where do you think the fuel is coming from to keep the 900 revs??? Throttle may be cut but the ECU is still supplying fuel to let it idle mate.

But in say 4th, on a downhill section with no throttle the ECU cuts ALL fuel as the momentum turns the engine and compression effectively slows the car.

 

[Brett]

I used to change down through every gear in my 182 because with a decatted exhaust system the noise is great with the rev match. I also used to ensure I reg matched to prolong the life of the transmission. Now I have a leased diesel Seat Ibiza I don't bother as it has a warranty and doesn't have a chocolate gearbox so I don't see the point, plus it sounds like a Hoover.

 

[Munson]

I think 1500rpm is around where modern engines will start fuelling on a closed throttle.

 

[GiT]

Road momentum is still turning the engine going down a hill without changing down a cog. Your not saving any more fuel than if you left the car in the gear it was in. In fact, you have used more by rev matching it. Also why would you loose speed by staying in 5th?!

Yeah, see what you are say, but you need the gear to match the speed you want don't you? So in 6th the car will still pick up speed (Fuelling is cut) as the compression in the cylinders are less frequent and there is less to slow the car. in 4th say, the revolutions are higher, more instances of compression and the car slows. If that makes sense.

Steeper hill, lower gear.

 

[GiT]

I think 1500rpm is around where modern engines will start fuelling on a closed throttle.

V.A.G and Toyota have both had me on course before where they have explained how this all works... it was as simple as an oscilloscope to the injector wiring and it was 1000rpm odd. Basically where the engine needs fuel to keep it running (Idle to fast idle) it supplies fuel. Otherwise - it cuts it all.

Fuel pump remains active to keep the pressure up, but the injector remains shut


There we go http://en.wikipedia.org/wiki/Engine_braking

 

[The Fatty]

Eh, What? In neutral rolling down the hill... Where do you think the fuel is coming from to keep the 900 revs??? Throttle may be cut but the ECU is still supplying fuel to let it idle mate.

But in say 4th, on a downhill section with no throttle the ECU cuts ALL fuel as the momentum turns the engine and compression effectively slows the car.

I missed your 'In neutral'! I thought you were on about leaving it in 5th!! Silly me not re-reading it first!

 

[GiT]

I missed your 'In neutral'! I thought you were on about leaving it in 5th!!

I thought you had lol. We be both on the same page squire

 

[Munson]

Coolio.

BTW IMO it's bad to use the brakes to maintain speed down an incline. I'm not talking 8000rpm in second down a 45% hill, but using a lower gear to control road speed down an incline is better than unnecessarily wearing out your brakes. It's not like you're otherwise going to use the excessive speed you gained on the hill to save some fuel coasting at the bottom.

Downhill at speed limit using brakes = no fuel used, hot and worn brakes.
Downhill at speed limit in low gear = no fuel used, cold and unaffected brakes.

 

[The Fatty]

I thought you had lol. We be both on the same page squire

yep, my apologies!

 

[GiT]

yep, my apologies!

No need to mate lol. It's all good

 

[GiT]

Coolio.

BTW IMO it's bad to use the brakes to maintain speed down an incline. I'm not talking 8000rpm in second down a 45% hill, but using a lower gear to control road speed down an incline is better than unnecessarily wearing out your brakes. It's not like you're otherwise going to use the excessive speed you gained on the hill to save some fuel coasting at the bottom.

Downhill at speed limit using brakes = no fuel used, hot and worn brakes.
Downhill at speed limit in low gear = no fuel used, cold and unaffected brakes.

Bang on the money... You can add one to this too.

Downhill at speed limit using brakes in neutral = Fuel used and hot / worn / fade prone brakes.

 

[Munson]

No, that's just retarded lol.

 

[GiT]

No, that's just retarded lol.

That be true lol

 

[The Fatty]

Downhill at speed limit using brakes = no fuel used, hot and worn brakes.
Downhill at speed limit in low gear = fuel used for initial rev match, cold and unaffected brakes.

EFA

 

[Chip-mk1]

Coolio.

BTW IMO it's bad to use the brakes to maintain speed down an incline. I'm not talking 8000rpm in second down a 45% hill, but using a lower gear to control road speed down an incline is better than unnecessarily wearing out your brakes. It's not like you're otherwise going to use the excessive speed you gained on the hill to save some fuel coasting at the bottom.

Downhill at speed limit using brakes = no fuel used, hot and worn brakes.
Downhill at speed limit in low gear = no fuel used, cold and unaffected brakes.

Gets my vote, I often change down a gear on steep descents to avoid the car accelerating to a speed greater than the one I have chosen to be doing.

Some of the twisty hills in somerset you would really be wearing out your pads for no reason to do anything else TBH as the bends simply wont let you carry the amount mph the declines would let you reach!

 

[MarkCup]

Gets my vote, I often change down a gear on steep descents to avoid the car accelerating to a speed greater than the one I have chosen to be doing.

Some of the twisty hills in somerset you would really be wearing out your pads for no reason to do anything else TBH as the bends simply wont let you carry the amount mph the declines would let you reach!

What about having enough momentum to carry you for next mile and a half with no additional throttle at all? My commute has a few sections like this, so long as there's nothing ahead that could cause me to brake I just roll in sixth for miles. It does get a bit lively at the top though.

 

[BoatNonce]

Never brake. Ever. Use other cars as your brakes.

Braking is a sign of weakness.

 

[Munson]

Fatty, I'm not personally obsessed with rev-matching. I might dabble in some heel and toe if pressing on, but here I'm talking about normal road driving. The single gear change requires the clutch to be disengaged for probably 500ms. I suppose the engine might use a picolitre of fuel during that time. Better to unnecessarily wear your brakes out? Nah.

 

[GiT]

What about having enough momentum to carry you for next mile and a half with no additional throttle at all? My commute has a few sections like this, so long as there's nothing ahead that could cause me to brake I just roll in sixth for miles. It does get a bit lively at the top though.

Well, several ways to do this... but I personal would use the hill in a gear to use no fuel and keep the speed at the limt, once it starts to flatten out, chuck it into a high gear and feather the throttle if it begins to slow too much.

In an ST220 where MPG is horrific - you practice this LOTS lol

 

[Chip-mk1]

What about having enough momentum to carry you for next mile and a half with no additional throttle at all? My commute has a few sections like this, so long as there's nothing ahead that could cause me to brake I just roll in sixth for miles. It does get a bit lively at the top though.

As I said, when you are talking twisty hilly roads, which most of the stuff I am used to driving is, carrying 80mph along just isnt an option, in fact in places 20mph isnt possible so if you arent in a low gear your brakes are going to really got hot, in fact when younger and not having the sense to use my gears properly I have ended up smelling my brakes on those sort of roads where they have had to work so hard.

A lower gear makes perfect sense IMHO if a higher one is going to result in too much speed.
If however its a totally open bit of road and no camera then I wont mind ending up at 80, so its situation dependant in that respect.

 

[Adam G]

Don't think I'd want to be in 5th coming down Porlock Hill.

 

[105e]

I don't have a fixed regime, I just do what conditions dictate,

 

[Chip-mk1]

Don't think I'd want to be in 5th coming down Porlock Hill.

Exactly!

Even 3rd is the gear of the brave and the stupid around those parts, lol.

 

[Kazumz]

I got into the habit of blipping down everywhere I went just because I liked the gurgle the car made, but this way is what I like to do now.



A friend of mine does this and it scares the s**t out of me.
This is a bad habit you need to kill. We'll have the VXR forum linking to us and laughing at us now.

VXR's are a joke anyway and I'm already laughing at them for just existing.

My mates 1.2 Corsa with '85' BHP is the slowest peice of poop I've ever driven in my life. Felt like 13 seconds to 60, a bus is quicker. The VXR has been proven to be better in the straights but that's just the turbo. Has nothing on a 2.0 Mk2 Clio.

 

[Edges]

VXR's are a joke anyway and I'm already laughing at them for just existing.

My mates 1.2 Corsa with '85' BHP is the slowest peice of poop I've ever driven in my life. Felt like 13 seconds to 60, a bus is quicker. The VXR has been proven to be better in the straights but that's just the turbo. Has nothing on a 2.0 Mk2 Clio.

Whats any of that got to do with engine braking or heel and toe'ing?

 

[Kazumz]

Whats any of that got to do with engine braking or heel and toe'ing?

Read what I quoted please.

 

[J.B.]

Because in neutral, rolling down the hill you are wasting brake pads and fuel. The injectors are still getting fuel to idle the engine. In gear, the engine is spun by the momentum and the ECU cuts the fuel - that's why the MPG gauge goes high.

Have you quoted the wrong post?

I didn't say put it in neutral; I said there is little point changing into a lower gear to go down a hill. I am saying you should leave it whatever gear you're in already. Not sure why you're explaining it to me as I completely understand in-gear down a hill is best. I'm not the person who said they change to neutral down a hill. Any RS Clio is capable of maintaining speed down a reasonable hill in 5th gear, and my car will maintain speed on most hills in 6th.

*"reasonable" i.e. not something like a 1:3.

 

[...]

Most decent modern cars that run fly by wire throttle cut the throttle signal via the brake light switch hence why bother trying to heal and toe ..... brake and block.change , its far far less transmision stress far better way to drive .......
And the heel and toe because racecar driver is b****cks too .... nowadays you would be using a seqential box you wont hear any heal and toe (just ecu programed blips maybe)

 

[Munson]

This thread is chock full of misinformation and misunderstanding.

 

[Adam G]

This thread is chock full of misinformation and misunderstanding.

Clio is to Pagani as Dino is to Ferrari iirc.