Engine braking on diesel vs petrol

Submitted: Tuesday, Apr 15, 2003 at 13:15

ThreadID: 4405 Views:2308 Replies:3 FollowUps:6

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IAMGQ

Has anybody ever tested the difference of engine braking between diesel and petrol engine with same engine capacity (e.g 4.2 diesel vs 4.2 petrol ) ?
I drove a Pajero 2.6 petrol before and it seems that the engine braking is as good as my 4.2 diesel now when going downhill . Probably because of the weight of vehicle ?

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Reply By: Member - Jono (Perth WA) - Tuesday, Apr 15, 2003 at 13:47

Tuesday, Apr 15, 2003 at 13:47

dont forget that the gearbox has a big bearing on engine breaking as well, ie manual/auto 'box. Its not just petrol/diesel.

maybe the Paj has some techno stuff to help it crawl down slopes???Cheers, Jono.

Sorry bout the pic, another one is on its way!!! GO THE SURF!!!!

AnswerID: 17669

Follow Up By: tristjo - Tuesday, Apr 15, 2003 at 13:58

Tuesday, Apr 15, 2003 at 13:58

Hey Jono, don't you mean GO HOME THE SURF!?? hehehe, just kidding. Jonos rite, mate, the gering of a vehicle will have alot to do with its engine braking, its not just to do with the motor, although diesels do have better engine braking out of the box, but you can always do with a lower low range and thats the reason for those rockhopper gearsets that reduce low range gearing to enable incredibly slow crawling speeds for rocks and steep stuff. The give even a moderately modified vehicle greatly enhanced offroad ability, because you can tackle obstacles at a much slower speed, but you probably already knew that.
Tristjo.

FollowupID: 11098

Follow Up By: Member - Jono (Perth WA) - Wednesday, Apr 16, 2003 at 10:51

Wednesday, Apr 16, 2003 at 10:51

GO HOME THE SURF!!!!! I would slap the silly out of you if i could be bothered getting off my arse, hehehehe.

Funny you should say that.....a new truck is on its way, so if anyone wants a surf with bugger all k's on the clock then get in touch with me on dix@iinet.net.auCheers, Jono.

Sorry bout the pic, another one is on its way!!! GO THE SURF!!!!

FollowupID: 11137

Reply By: Voxson (Adelaide) - Tuesday, Apr 15, 2003 at 14:10

Tuesday, Apr 15, 2003 at 14:10

I have done the same downhill grading in a diesel 4.2 patrol and a petrol patrol and the difference is noticable..
Diesel went down the hill at a crawling speed and i felt like accelerating a bit, but the petrol walked down and i felt like a wanted to hit the brakes...Manual gearbox by the way........

Pretty steep hill though..I couldnt walk down it without a hand out behind me..._____________________________________________
Countin the days till July 5th. *Cape York Trip*
_____________________________________________

AnswerID: 17672

Reply By: Rob from Cairns Offroad Training & Tours - Tuesday, Apr 15, 2003 at 16:50

Tuesday, Apr 15, 2003 at 16:50

Engine braking is directly related to the compression of the motor in a manual car. Diesels have significantly more compression therefore far superior engine braking in 2 cars with similar gearing.
Cheers RobCairns Offroad Training & Tours

AnswerID: 17683

Follow Up By: StephenF - Tuesday, Apr 15, 2003 at 17:11

Tuesday, Apr 15, 2003 at 17:11

Not necessarily. The air that was compressed during the compression stroke now acts to push the piston down again, thereby cancelling out most of the effect of the higher compression.

The nett result is not much more engine braking than on a petrol motor. Gearing would have a greater effect than whether the motor is petrol or diesel.

As I said in another thread, I've owned both petrol and diesel versions of the same car and have not noticed a great deal of difference in engine braking between them, and this is with 23:1 compression on the diesel.

Stephen.

FollowupID: 11106

Follow Up By: Rob from Cairns Offroad Training & Tours - Tuesday, Apr 15, 2003 at 19:54

Tuesday, Apr 15, 2003 at 19:54

I also have had both a 4.5lt cruiser and my current 4.2 diesel and there is no question which I would rely on more for its engine braking capabilities. As soon as you are in low range diesels rule IMHO.
Cheers RobCairns Offroad Training & Tours

FollowupID: 11114