Transmission variance between petrol and diesel

[inky_black]

I really don't have a clue (and chose the diesel anyway ;-) ), but:

Maybe there is no differerence in terms of "strength" of the 2 transmission variants at all? Simply the ratios are different?

Going back to basic physics: Power = Torque x 2 x pi x Rev
If the petrol delivers its power at (roughly!) 4000/min and 450Nm, the diesel (less power!) at 3000/min and 550Nm, for the same top speed the ratio for the petrol would be 33% higher compared to the diesel. For the same transmitted power (I guess that's the starting point determining the design ratings of a transmission) the transmission for the diesel must support an equivalently larger input torque. That means: Only different gear ratio, not different "strength".

That's the consideration for the torque converter locked. Not taking into account torque boost with unlocked converter, second order effects like torque ripple etc.

But of course I could be wrong...

The ZF 8HP76 which is installed in the diesel is really designed for the higher torque and characteristics of the diesel engine. They don't differ at all in how they work. I already had both gearboxes in front of me and was able to compare the components directly with each other. The ZF 8HP76 is more robust than the ZF 8HP51, e.g. the components are larger and stronger

 

[TD5-90]

The ZF 8HP76 which is installed in the diesel is really designed for the higher torque and characteristics of the diesel engine. They don't differ at all in how they work. I already had both gearboxes in front of me and was able to compare the components directly with each other. The ZF 8HP76 is more robust than the ZF 8HP51, e.g. the components are larger and stronger

You are talking "input torque", right? Not transferrable power, as I suggested.

In general, transmissions with same POWER rating, but lower input torque spec and consequently higher input rpm spec are constructed differently. They in fact have smaller components, and in sum are more lightweight for the same transmitted power. BUT that does NOT mean that they are less robust!

 

[TD5-90]

How about an empty wallet?

Beats me!

The twinkle smilie should indicate that I'm not totally serious

 

[Jean Mercier]

How about an empty wallet?

Work, work harder, and work still more

 

[TD5-90]

Work, work harder, and work still more

Believe it or not, I indeed should be working right now (quoting on developing a new ultra high efficiency power supply). But get distracted every minute

 

[DaveB]

Full ack Dave! Especially on your selection of the diesel!

However, I prefer the engineering approach to technical problems if possible ;-)
As an engineer, I generally believe that there's an engineering solution to _any_ kind of problem

yes
Funny as a tradesman we generally say don't let the engineer touch any tools
I often have engineers(customers) tell me that they have done the maths and this should be possible.
The fact is that it is often not practical or probable.
Not all engineers are the same however, some do have experience and common sense
Architects on the other hand....

 

[Jean Mercier]

.... But get distracted every minute

I apologize ... I am not working now, but drinking a beer (Duvel - Belgian)

 

[TD5-90]

yes
Funny as a tradesman we generally say don't let the engineer touch any tools
I often have engineers(customers) tell me that they have done the maths and this should be possible.
The fact is that it is often not practical or probable.
Not all engineers are the same however, some do have experience and common sense
Architects on the other hand....

That's why I (rather: we, my colleagues and I) do the maths and do the proof ourselves.
And don't accept "help" from our customers (often tradesmen )

 

[DaveB]

Believe it or not, I indeed should be working right now (quoting on developing a new ultra high efficiency power supply). But get distracted every minute

7am here and my first day back to work today after holidays .
First job is to resolve some issues with supply and performance of Lithium Thionyl Chloride battery packs and Lithium Thionyl hybrid pulse capacitors in battery powered magnetic flowmeters

 

[DaveB]

I apologize ... I am not working now, but drinking a beer (Duvel - Belgian)

One of my favourite beers
Also Chimay

 

[Jean Mercier]

yes
Funny as a tradesman we generally say don't let the engineer touch any tools
I often have engineers(customers) tell me that they have done the maths and this should be possible.

Don't generalize, but indeed, if an engineer only uses the theoretical knowledge it means he never used a tool ...
I am an engineer, worse, I was a consultant

 

[DaveB]

That's why I (rather: we, my colleagues and I) do the maths and do the proof ourselves.
And don't accept "help" from our customers (often tradesmen )

I have a foot in both camps and after my trade I did my electrical and electronics engineering certificate

 

[TD5-90]

7am here and my first day back to work today after holidays .
First job is to resolve some issues with supply and performance of Lithium Thionyl Chloride battery packs and Lithium Thionyl hybrid pulse capacitors in battery powered magnetic flowmeters

Sounds like a supply problem with heavy engineering background...

 

[TD5-90]

I have a foot in both camps and after my trade I did my electrical and electronics engineering certificate

All thumbs up!!
Focusing on engineering only is very often the right thing to do, but not always...

 

[stickshifter]

As posted elsewhere on the forum:

The gas engine (B58) gets the 8HP51 version of the ZF 8-speed, which has a max torque rating of 500 Nm or 369 lb. ft. of torque.

The diesel engine (B57) gets the 8HP76 version of the ZF 8-speed, which has a max torque rating of 750 Nm, or 553 lb. ft. of torque.

From the UK brochure:



The lower torque rating of the 8HP51 becomes a concern for some people, who have expressed concern about the power of the B58 in the Grenadier, which is 282 HP and 332 lb. ft of torque; the Grenadier is heavy (5,875 pounds for the gas version), and some people feel that it might be under-powered. Note that concerns around this topic vary considerably based on the elevation a person lives at, the intended use for the vehicle, and a person's expectations. A common solution with a forced induction engine is to tune it for more power (it is typically very easy to tune forced induction engines). However, the max torque rating of the 8HP51 is just 11% higher than the existing torque output of the B58, so there isn't much headroom there. Many people are not concerned about the power of the B58 in the Grenadier, and so are not concerned about the difference between the two transmissions. That's a synopsis of multiple discussions on this forum on this topic.

See table below for a summary of the ZF 8-speed transmissions and their applications:

 

[TD5-90]

I apologize ... I am not working now, but drinking a beer (Duvel - Belgian)

Thanks, I feel even more motivated

 

[inky_black]

You are talking "input torque", right? Not transferrable power, as I suggested.

In general, transmissions with same POWER rating, but lower input torque spec and consequently higher input rpm spec are constructed differently. They in fact have smaller components, and in sum are more lightweight for the same transmitted power. BUT that does NOT mean that they are less robust!

You're right i'm talking about the input torque, but the transmittable power and transmittable torque is also higher with the ZF 8HP76. I assume that this is also more robust than the "smaller" ZF 8HP51.

 

[DaveB]

Sounds like a supply problem with heavy engineering background...

Batteries are made in Israel, instruments are made in Cernay, France, we are in Australia
We airfreight 90% of our products in and you can't airfreight the batteries on commercial flights and only as dangerous goods on freighters.
The batteries have severe life reduction under 0 degrees and over 40 degrees ambient but what does severe mean?
In our desert locations you can have 50 degrees in the day and below zero at night
Fun and games

 

[TD5-90]

You're right i'm talking about the input torque, but the transmittable power and transmittable torque is also higher with the ZF 8HP76. I assume that this is also more robust than the "smaller" ZF 8HP51.

Do you have a source for that data? I wasn't able to find anything....
Thanks!!

 

[stickshifter]

Do you have a source for that data? I wasn't able to find anything....
Thanks!!

See post #35, or google "ZF 8HP" - plenty of info on these transmissions. As the numbers of the variant go up (8HP51, 8HP55, 8HP70, etc.) they are built to handle more power. I think we can trust Wikipedia on this, but there are other sources if you look.

ZF 8HP transmission - Wikipedia

en.wikipedia.org