Engine Braking

nicholas · Post by **nicholas** » Thu Jul 05, 2007 12:21 pm

Hey guys,

Was just reading the heel + toeing discussion and people were saying that engine braking uses more fuel.

I always thought that engine braking worked because no fuel was injected unless the throttle was pressed, so the engine works under vacuum which in turn slows the wheels down (engine braking).

Apparently this isn't true? So can anyone explain how it actually works...

Delvance · Post by **Delvance** » Thu Jul 05, 2007 8:43 pm

Well when you do the heel part of heel and toe, youre using fuel to bring the rpms up. Even without being on the throttle but having a gear engaged, im almost positive it still uses a bit of fuel.

Post by **BorepYano** » Thu Jul 05, 2007 10:42 pm

always thought RPM is directly linked to fuel usage...
i.e. if the RPM goes up it'll burn more fuel, thought when u engine brake, the engine forces extra fuel into it as the RPMs go up.

feel free to correct me, that's just what i always though...

FtoSam · Post by **FtoSam** » Fri Jul 06, 2007 9:58 am

BorepYano wrote:always thought RPM is directly linked to fuel usage...
i.e. if the RPM goes up it'll burn more fuel, thought when u engine brake, the engine forces extra fuel into it as the RPMs go up.

feel free to correct me, that's just what i always though...

Sorry yang, but im pretty sure no...

Starting from the start, You have an Air/Fuel Ration right?

So the more air you consume, the more fuel you consume.

The more you plant your foot, the more air is sucked in...

Thats why a turbo pushed my fuel from 600km/tank to 200km/tank

So thats why city driving can chew your fuel..

You're constantly accelerating with your foot half down between idle and 3,500rpm..

On the highway is another thing, You may be doing 4,000rpm at 120km/h but your only feathering the accelerator.

How far your foot is off the floor is DIRECTLY related to the fuel you'll use..

FtoSam · Post by **FtoSam** » Fri Jul 06, 2007 10:00 am

So everytime you tap your foot on the accelerator, you give the engine a nice squirt of fuel...

It takes a lot more power (fuel) to increase the rpm of an engine than it does to maintain said rpm...

eThix · Post by **eThix** » Fri Jul 06, 2007 11:49 am

Very interesting Sam

thanks for the info

Post by **BorepYano** » Fri Jul 06, 2007 1:47 pm

thanx sam
you know what the stupid thing is?
after reading that i'm like "derrrr, yeah i know that, what the f**k was i on about before" lol

maintaining RPM is pretty much just maintaining speed, which means all u have to do is counter friction as compared to accelerating which means moving the weight of the car... yup yup

still cant get my head around why engine braking uses more fuel though. i guess my question is does the increased RPM when u down gear and engine brake draw extra fuel through the system without u touching the acc pedal?

FtoSam · Post by **FtoSam** » Fri Jul 06, 2007 3:46 pm

Engine breaking will only use a little more fuel...

Maintaining an engine at 1000rpm will use less than at 4k...

so engine breaking only uses a little more fuel...

I presume