[btirthankar]

I have a Toyota Innova D4D. I previously used toi drive a petrol Astra so am used to its engine braking.

Of late I have realised I am using more brakes and less downshifting in my Innova as the engine does not provide adequate braking.

I know that engine braking is all about how much vacuum the pistons have to produce.

My one question. Is the engine braking less in my innova due to the turbo after-revvs? Is it because that it does not have a device to stop the air during intake stroke at the same ytime when the turbo is pumping in air?

[Vid6639]

I had read somewhere on t-bhp that Diesel engines don't have good engine braking. I don't know the technicality behind it but I'm sure some expert will be able to provide more details.

[reignofchaos]

Diesel engines have very little engine braking as they are unthrottled. Thats the reason that heavy trucks come with specialized devices like a Jacobs Brake (also called a jake brake). However these devices are noisy and banned at many places.

[DirtyDan]

Originally Posted by reignofchaos

Diesel engines have very little engine braking as they are unthrottled.

Yes, let me rephrase that, diesel engines have very little engine braking when you get off the throttle. They have little compression when not under throttle. Also, you will notice that when you take your foot off the throttle of a diesel that it will go to idle speed right away. So fast, in fact, that inexperienced diesel drivers sometimes have a little trouble shifting because the engine revs drop immediately and the engine is turning much slower than the rest of the drive train between shifts. This is why you hear some big trucks rev their engines between shifts, to bring their engines up to speed.

[reignofchaos]

Thank you for the correction. I basically meant the same thing.

[btirthankar]

Originally Posted by DirtyDan

Yes, let me rephrase that, diesel engines have very little engine braking when you get off the throttle. They have little compression when not under throttle. Also, you will notice that when you take your foot off the throttle of a diesel that it will go to idle speed right away. So fast, in fact, that inexperienced diesel drivers sometimes have a little trouble shifting because the engine revs drop immediately and the engine is turning much slower than the rest of the drive train between shifts. This is why you hear some big trucks rev their engines between shifts, to bring their engines up to speed.

But does the turbo has anything to do with it?

[condor]

Engine braking in diesels would also be affected by gearing I guess. My 3rd is versatile. But 2nd is what I would use when I want to 'engine brake'.

[CrAzY dRiVeR]

I feel its also got to do with the torque offered by these diesels. The first time i drove the Swift diesel, i was expecting it to slow down with foot off the accelerator pedal, and it just kept pulling!

Originally Posted by DirtyDan

This is why you hear some big trucks rev their engines between shifts, to bring their engines up to speed.

Isn't that for matching the speed to shift into a lower gear?

[ravibhat]

Yes I can see that when compared with my Petrol Innova, My new driver who has experience of driving trucks in NH17 entire stretch and more areas told me this Petrol Innova's foot off the accelerator itself is one brake! even if he is in 5th gear.

Technically speaking Petrol vehicles have such more advantages except Diesel vehicles feel more peppy in City driving.

Regards,

Ravi.

[dadu]

I agree, same with me, perhaps the gear ratio's in Innova allow for lesser engine braking.

Originally Posted by condor

Engine braking in diesels would also be affected by gearing I guess. My 3rd is versatile. But 2nd is what I would use when I want to 'engine brake'.

[alpha1]

Originally Posted by ravibhat

Yes I can see that when compared with my Petrol Innova, My new driver who has experience of driving trucks in NH17 entire stretch and more areas told me this Petrol Innova's foot off the accelerator itself is one brake! even if he is in 5th gear.

Technically speaking Petrol vehicles have such more advantages except Diesel vehicles feel more peppy in City driving.

Regards,

Ravi.

But that peppyness is very shortlived, as the diesel hits the redline pretty soon, and you need to upshift.

I recenty had a Test drive of Scorpio mHawk, and was not at all please with the short rev life that engine had, compared to Swift and Vtec which I've driven.

[Akshay1234]

Originally Posted by alpha1

But that peppyness is very shortlived, as the diesel hits the redline pretty soon, and you need to upshift.

I recenty had a Test drive of Scorpio mHawk, and was not at all please with the short rev life that engine had, compared to Swift and Vtec which I've driven.

lets not get into this here. both have their advantages. there are enough threads to discuss this.

[androdev]

Originally Posted by DirtyDan

They have little compression when not under throttle.

You mean lesser compression losses? Compression ration remains constant.

Originally Posted by condor

Engine braking in diesels would also be affected by gearing I guess. My 3rd is versatile. But 2nd is what I would use when I want to 'engine brake'.

They are transmission/frictional losses and not engine braking/compression losses.

Originally Posted by ravibhat

Technically speaking Petrol vehicles have such more advantages except Diesel vehicles feel more peppy in City driving.

No comments on petrol vs diesel topic. But <b> engine braking is not always a good thing </b> for the following reasons:

It transfers wear and tear to transmission and engine parts that are an order of magnitude more expensive and difficult to replace than brake parts.

Dramatically increase in engine RPM is bad for engine and FE (in cars without fuel cutoffs)

[greatmana2000]

well, i feel it is because diesel engines have a low rpm compared to petrols .diesel engines rely on torque rather than rpm to power the car . In diesels the torque is still there ,but the rpm only goes down and , even if the car is in the top gear , you might still be able to drive the car ,but in petrol you will have to downshift due to the low rpm of the engine in top gear