Diesel Exhaust Brake

Guru Meditation · Unread post by **Guru Meditation** » 01 Oct 2003, 18:36

http://www.bankspower.com/tech_howexhaustbrakeworks.cfm
I thought diesels had meaty engine braking due to the high compression. In 1st gear my zx td has pretty hefty engine braking-not as much as my 205 gti mind-accelerate hard in 1st in the gti, lift off suddenly you were virtually thrown through the wind screen.

NiSk · Unread post by **NiSk** » 01 Oct 2003, 18:41

Diesels also have very low final drive ratios, thus defeating all that extra compression!
//NiSk

rossd · Unread post by **rossd** » 01 Oct 2003, 20:19

Diesels also don't have throttles; I was always led to believe that a petrol had more engine braking as with the throttle closed a vacuum is created between the descending piston andd the throttle butterfly.
Just a thought [:)]
Ross

BonceChops · Unread post by **BonceChops** » 01 Oct 2003, 20:31

The butterfly theory is what I always thought. My diesels have always had less engine braking than petrols - unless you can fit jake brakes to XUD's [:D]

Guru Meditation · Unread post by **Guru Meditation** » 01 Oct 2003, 21:36

Yeah, having read the technical explanation it makes sense why diesels don't engine brake so much as the equivalent petrol, no throttle butterfly to create the vacuum pumping effect and also the low final drive ratio negates the increased compression. S'pose it only really becomes an issue when you've got 30+ tonnes of cargo on a steep descent, cursing the lack of engine braking, doesn't matter so much on our little cits.

NiSk · Unread post by **NiSk** » 01 Oct 2003, 22:26

A ha! if you're talking about engine braking on HGV's, that's another thing altogether. These large diesels have exhaust brakes, where the exhaust is closed off to give the same effect as a closed butterfly valve on a petrol engine. They often have retarders fitted to the gearboxes as well. Decending an alpine road with 40 tonnes behind you is not the time to learn about cadance braking!
//NiSk

BonceChops · Unread post by **BonceChops** » 01 Oct 2003, 23:43

That is how "jake brakes" work - they act on the exhaust valves if I remember correctly

ghostrider · Unread post by **ghostrider** » 02 Oct 2003, 00:36

I seem to remember that the anti stall adjustment on the injection pump also affects the amount of engine braking you get
Pete
________
Plymouth Expresso History