Engine braking

Ctease said:

Interesting question.

Not much difference, I think limiting factor is tire grip since engine braking only affects rear tires. The stock front to rear proportioning of brakes is very conservative so there is room for slightly stronger rear brakes. Engine braking could provide it. On the track you have to downshift while braking or the brakes will overheat. On street I don't see the advantage to downshift-engine-braking over regular engine braking, other than fun and/or practice for track. Engine does produce a lot of braking at high rpm. Trick is rev matching downshift as to not lock the rear tires. I loved my 2-way LSD in my previous car. When I downshifted in factory loose viscous LSD it would make the car squirly. With stiff 2-way, it would lock the diff and create very steady straight braking. Haven't played that hard on my new car.

But it's a great question. I'm interested in the actual results!

Click to expand...

I think you nailed it, Ctease.
Unelss there is a deficit of clamping force for some reason, the brakes are already capable of overwhelming the available traction, even with the best tires on the best surfaces. So the difference wouldn't be anything...unless there was something wrong with the brakes themselves...or if they were already totally heatsoaked or some other extreme situation.

I totally get why some folks would look at the brakes as an afternoon repair job and an engine being a $15k, car crippling disaster...but as others have pointed out, engine braking doesn't seem to add any measurable wear and tear to the motor. The maintenance benefit seems to be in reduced brake wear as it allows you to ease on and off the brakes and still have some deceleration when you're not on the brakes, rather than riding the brakes the whole time.

Maybe someone can refute this thought:
While the engine is making some heat under engine braking by squeezing air (which is how it's bleeding off your kinetic energy and slowing you down) the engine is also making less heat than it would be at the same RPM under power...which means that you're spinning the water pump at a speed that's higher than necessary for the heat generation, thereby giving your motor a cooling benefit while engine-braking.
Maybe? :shrug:

Freedom said:

I can't seem to find any test dedicated to this but, I know that engine braking helps the car slow down.

So 2 tests:
80-0 mph while in neutral and flat on the brake pedal
80-0 mph while downshifting and flat on the brake pedal


What is the difference in length to slow the car down? If someone has done this test/website let me know. I can't seem to find the right keywords. I don't have a car right now to test and the questions been nagging me.

Click to expand...

There will be no difference. Or the engine braking would upset the braking balance of the car so much it would lengthen the stopping distances.

Using the brakes in a 100% ABS stomp mode means the vehicle's brakes are still doing all the work of slowing the vehicle. The brakes slow the vehicle much faster and harder than engine braking, so it could also be theorized that engine braking would actually increase braking distances, as the brakes would also have to over-come the inertia of the rotating mass of the engine.

I think we have to separate normal everyday engine braking. Cruising at 60mph, needing to merge into a slowlane which is traveling 50mph, then hit exit ramp and slow down to 30mph for feeder and finally stopping for intersection. 60 to 50 stay in 6th let of accelerator let engine brake & wind resistance slow you pretty quick to 50 and switch lanes, then repeat braking & wind from 50 to about 40 as you enter the offramp, at that point downshift and engine hits higher rpm which slows you down to 30 quicker, but also lower gear sets you up in case you need to accelerate again, you're off the exit ramp and cruising down feeder, once again let off the accelerator, leaving car in gear to keep engine braking (no wind resistance at this speed) and apply the brake, using the clutch for actual stop).
To recap you don't need actual foot brake on highway if you're driving normal. Wind & engine will slow the car and without downshifting. Don't need to downshift until you're in a position where you might need to accelerate again. And finally use engine & foot brakes to slow to a stop and engage clutch.

That's all normal stuff. You reduce engine & braking wear.

Hardcore downshift engine braking is flying down the back straight at 150mph & 7,500rpm. Slam on the brakes as the brakes & engine rapidly slow the car. You're modulating the brakes to keep the tires on edge of grip. As engine RPMs drop, engine braking power lowers too so you apply more foot brake to ride the edge of tire grip. As engine RPMs drop to lets say 5,000rpm (all happing in a split second) you rotate the heal at tap the accelerator, all while keeping the toe of your foot firmly on foot brake. As you tap accelerator, you're also clutch in and downshifting as fast as you can. If everything goes well you rev match, car goes into lower gear and engine braking rapidly increase as engine revs back upto 7,500rpm. You're basically accelerating in reverse order all while applying the foot brake. Since the engine brake at 7,500rpm is much greater than at 5,000 where you just came from. You must modulate the foot brake as the downshift engages to keep the rear tires from locking up. By the time it's complete you have to repeat for the next downshift. You could drop from 150mph down to 50mph and two gears in 3 seconds. It all happening that quick.

That type of downshift engine braking causes wear and tear to engine and brakes. You are not technically braking faster than bonsai no engine brake run because no matter what happens, you're limited by tire grip. The reason you go through all that trouble is to save the brakes from overheating.

I don't really like putting all the unnecessary revs on the motor. I do it sometimes but only in moderation and at lower speeds

Tire limited. Abs would be cycling and tires would be at limit of traction so no need to downshift for better braking times.

Downshifting if done correctly with rev matching is harmless to the engine. More strain on motor at full throttle than the "negative" horsepower encountered while slowing.

Once again since I see some people don't understand what engine breaking is. You don't use it instead of breaks in most situations, when you need to stop the car or do the maneuver you just use breaks as a sane person.

Engine breaking is a situational thing, for example when you see the red light far ahead of you or when you're going downhill in the city and there is a speed limit. For example, in my town we have a long downhill with a limit of 50km/h and almost everyone just puts their car in lower gear and cruise down without any need to use brakes at all. You save fuel (injection is completely off in this scenario since the engine is driven by the wheels) and you don't put any wear on brakes. It takes like one minute to go through that hill and there's no need to stay on your brakes during that time and let them produce unnecessary heat because of friction.

The fun of rev matching and downshifting for the cool sounds is different than downshifting and braking simultaneously on a road course to be in the correct gear for maximum drive out of the corner.

I think many people who drive today's big hp cars would greatly benefit from a high performance driving school.

On a road course I've found (and I didn't invent this finding, mind you... just my own development) that my car is more stable when I don't downshift and let off to engine brake immediately, which I figure is the result of keeping brake balance consistent. I'm experimenting here because I am developing this skill set (when to actually brake, when to downshift). Right now I'm being as easy on the engine/clutch as I can muster so I downshift and let it engine brake halfway through the braking zone right around just before I start letting up to balance the car a little better (more weight on the back wheels). Engine braking basically makes the rear wheels have more "braking power" than they would with just the pads, so it becomes a grip issue both in terms of the tire being able to grip and the reduced weight of the car on the rear wheels on account of braking harder. On the street, I engine brake almost always along with pedal braking just because it sounds cool, haha.

FWIW it's against the law to coast down a grade in here in GA. What represents a "grade" is subject to an officer's interpretation.

tom_sprecher said:

FWIW it's against the law to coast down a grade in here in GA. What represents a "grade" is subject to an officer's interpretation.

Click to expand...

It's against the law to not pass in the left lane, but... ya know. Them a-holes be set in cruise control at 65 on the dot riding right next to another car for 20 miles listening to Beyonce and drinking their latte-frapa-lap-ding-dongs. :lol:

R3v said:

Once again since I see some people don't understand what engine breaking is. You don't use it instead of breaks in most situations, when you need to stop the car or do the maneuver you just use breaks as a sane person.

Engine breaking is a situational thing, for example when you see the red light far ahead of you or when you're going downhill in the city and there is a speed limit. For example, in my town we have a long downhill with a limit of 50km/h and almost everyone just puts their car in lower gear and cruise down without any need to use brakes at all. You save fuel (injection is completely off in this scenario since the engine is driven by the wheels) and you don't put any wear on brakes. It takes like one minute to go through that hill and there's no need to stay on your brakes during that time and let them produce unnecessary heat because of friction.

Click to expand...

How can I take you seriously when you spell brakes brakes and breaks.:lol:

wildcatgoal said:

On a road course I've found (and I didn't invent this finding, mind you... just my own development) that my car is more stable when I don't downshift and let off to engine brake immediately, which I figure is the result of keeping brake balance consistent. I'm experimenting here because I am developing this skill set (when to actually brake, when to downshift). Right now I'm being as easy on the engine/clutch as I can muster so I downshift and let it engine brake halfway through the braking zone right around just before I start letting up to balance the car a little better (more weight on the back wheels). Engine braking basically makes the rear wheels have more "braking power" than they would with just the pads, so it becomes a grip issue both in terms of the tire being able to grip and the reduced weight of the car on the rear wheels on account of braking harder. On the street, I engine brake almost always along with pedal braking just because it sounds cool, haha.

Click to expand...

^^^ This pretty much sums up what I do when on track and the street.

I always use engine breaking, I love the pops and gurgles of the exhaust when doing so

Varekai said:

I always use engine breaking, I love the pops and gurgles of the exhaust when doing so

Click to expand...

Same here.

SpaceGhost said:

Brake parts are cheaper than engines.

Click to expand...

Engine braking doesn't wear anything out that is important. It uses the other side of the teeth in the transmission, so you are not going to damage anything or wear anything out faster than things are already being worn out.