Transmission variance between petrol and diesel

[Paachi]

I was perusing the UK brochure and something just struck me. The petrol and diesel have different ZF 8HP variants. The petrol gets a 8HP51 (500 Nm peak torque) whereas the diesel gets the beefier 8HP76 (750 Nm peak torque). 
https://blog.fcpeuro.com/zf-8-speed-transmission-guide-8hp45-specs-common-problems-diagnostics-maintenance?hs_amp=true


https://en.m.wikipedia.org/wiki/ZF_8HP_transmission
The 51 is used in cars like Supra, Z4 and G20 3 series. The 76 is used in the torquier Alpina B7,  Gulia and Gladiator Diesel. 
Now what’s noteworthy here is that the headroom capacity in each transmission for tuning and general hi rev abuse. The Petrol transmission literally will run at 90% of peak, at base engine tune in high load conditions. Whereas the diesel will still have a about 25% headroom under peak loads. That’s definitely disappointing. 
I wasn’t planning to tuning the engine for more power/ torque but don’t like the fact that the transmission wasn’t beefed up more. 
I know ZFs are generally considered bulletproof transmissions. But am I missing something here??

 

[stickshifter]

I saw the same thing. I had assumed they’d pair the 76 with both engines - given the emphasis on heavy duty durability. Be nice to have more room to tune the gasser with confidence in the tranny. I suppose it saves a little weight and maybe cost?

 

[DaveB]

I bet there is a fair safety margin built into those peak torque figures.

 

[Paachi]

True. I was perusing the Supra forums and folks have been pushing this transmission to higher numbers without catastrophic failures plus there are kits to beef it up. 
Still not happy that they went for a cost (I’m guessing) management route. Plus I think the 8HP76 is a longer transmission which means parts like shafts won’t be interchangeable 

 

[Stu_Barnes]

topic moved

 

[Ferrugenfish]

Thank you for sharing that and bringing it up as I had been wondering about headroom for tuning.  90% for the petrol - which is will be the only option in the U.S. where I live - might as well be 100% If you're towing anything uphill. I can understand the dilemma for them though... most people won't be using the vehicle above it's spec, so why make it cost more by pre-upgrading the gasser?  Simultaneously I'd definitely like to have built-in head room for a tune, as I'd like more HP/torque out of the gasser since it's my only option. Upgrade kits for the tranny are assumedly expensive to put in, and my skills are with wood, not trannies, so I'd be paying labor. All in all we'll just have to wait several years before we see whether the gasser tranny generally has a short life.  Fortunately they chose a very well-known and proven tranny to begin with, so while we can wish for more headroom, we have no room to complain. I'm just glad they went with a proven, smooth tranny to begin with.   

 

[Stu_Barnes]

https://www.puredrivetrainsolutions.com/bmw-transmissions/zf-8hp70-75-76-stage-2-package

A bargain price for increased hp and torque. 

 

[stickshifter]

Respectfully, I disagree that $10,000 to upgrade the transmission in the B58 is a bargain. Here is why:

In the IG gas (B58 engine), you get the 8HP51 transmission.

In the IG diesel (B57 engine) you get the stronger 8HP76 transmission. In addition, you have a much more complicated engine, with EGR and DEF systems.

Here in the U.S. if you opt for the diesel variant in the same model vehicle you are looking at an extra $4,000-$6,000 for a mid-size or full-size truck, and if you are shopping for a Super Duty truck, the cost increase is $10,000 to get the 6.7 liter diesel engine over the standard gas engine. You have to pay more for the diesel because of all the extra emission systems, a stronger transmission, etc. But if you have the option of buying the IG with the diesel, it is the same price as the gas option (at least this is true in Australia - not sure about other markets).

So if you buy the gas Grenadier (and that is the only option in North America), and you want the same transmission that comes stock in the diesel Grenadier, you have to pay an additional $10,000 to do an aftermarket upgrade? Sorry, but from my perspective, that is ass-backwards.

With a cheaper transmission, and without EGR and DEF, the gas version of the Grenadier should be quite a bit cheaper than the diesel version. Then, with that savings, a person - should they so choose - could upgrade their transmission.

 

[Ferrugenfish]

[QUOTE username=stickshifter userid=8617054 postid=1332855316]Respectfully, I disagree that $10,000 to upgrade the transmission in the B58 is a bargain. [/QUOTE]

With respect to that perspective, I think a delineation can be made between "good deal" and "worthwhile alteration". I make the distinction because the price of uninstalling an existing tyranny, upgrading then reinstalling accounts for lots of labor and room for profit. Whereas when Ineos installs it from the assembly line it's basically the same cost as installing the weaker of the two. That doesn't mean that a third party selling and upgrading our tranny should charge less. They're separate. Personally I'm pretty allergic to a $10k charge to beef up my U.S. petrol-only rig when I don't have the diesel torque to load it, so it's not a worthwhile alteration, to me.

That said, another thing on my Ineos wish list is for them to make the upgraded yranny an option for gassers off the production line so that I we can benefit from the low cost of just paying for the parts instead of being relegated to aftermarket uninstall+reinstall. This would allow us to tune the gasser engine, deal with bigger tire torque etc.

 

[stickshifter]

[QUOTE username=Ferrugenfish userid=9004165 postid=1332855749]

With respect to that perspective, I think a delineation can be made between "good deal" and "worthwhile alteration". I make the distinction because the price of uninstalling an existing tyranny, upgrading then reinstalling accounts for lots of labor and room for profit. Whereas when Ineos installs it from the assembly line it's basically the same cost as installing the weaker of the two. That doesn't mean that a third party selling and upgrading our tranny should charge less. They're separate. Personally I'm pretty allergic to a $10k charge to beef up my U.S. petrol-only rig when I don't have the diesel torque to load it, so it's not a worthwhile alteration, to me.

That said, another thing on my Ineos wish list is for them to make the upgraded yranny an option for gassers off the production line so that I we can benefit from the low cost of just paying for the parts instead of being relegated to aftermarket uninstall+reinstall. This would allow us to tune the gasser engine, deal with bigger tire torque etc.[/QUOTE]

I totally agree that Ineos should provide the option to buy the 8HP76 when one buys the gas (B58) Grenadier. For those happy with the power output of the Grenadier's version of the B58 (281 HP / 332 lb-ft), they can stick with the 8HP51. For those who want to tune-up the Grenadier's B58, or for those just looking for an 'overbuilt' transmission for their vehicle, they could opt for the 8HP76 - for a modest price increase. Modest, because, as you point out, the only additional cost when it comes from the factory is the cost difference of the transmission (there is no additional labor or other costs when installing an off-the-shelf transmission at the factory). I would be happy to pay some additional cost for an 8HP76, installed from the factory. I don't know the price difference between the 8HP51 and the 8HP76; I would guess not more than $1,000 (just a wild guess).

My personal choice: there is no way I'm going to spend $10,000 on an aftermarket kit to upgrade the 8HP51 if that is the transmission I get when I buy the gas Grenadier. My choice would be shaped by both the cost of the kit, but also by the recognition that I'd be spending $10,000 for something that is really valued at closer to $1,000 (and that wouldn't sit well with me). Of course, if I were a billionaire, I wouldn't care about the 10K.

Lastly, I recognize that other people will make different decisions than I make, and that's all good. ?

 

[ADVAW8S]

Here are two videos that has been shared on the LR forum from a guy i respect around the ZF transmission.  The same transmission that is going into the Petrol IG is in the L663.  

https://www.youtube.com/watch?v=HhkH3Zc0-Dc&t=373s

https://youtu.be/FqyPizRyphQ

 

[DCPU]

I think the link above makes reference to this mod:

"xHP Flashtool is the worldwide first and complete Tuning solution for BMW’s with ZF6HP and ZF8HP automatic transmissions."

xHP ZF Gearbox Tuning - WG Motorworks

At WG Motorworks we are a official dealer for xHP, with advanced unrivaled software for the ZF gearboxes it is a no brainer for us to offer tunes that have had extensive research and development to complement our ECU mapping services for that complete enhanced experience. Which the benefits are...

www.wgmotorworks.co.uk

Just reading through it and noticed a few words, that whilst seem perfectly obvious, might be worth noting here:

"S and M modes are designed to facilitate sporty and fun driving. Shift times are cut and clutches get applied more aggressive. Use these modes when necessary and not as standard. The TCU records the amount of time you spend in each mode. BMW uses this data to judge on warranty cases."

 

[Logsplitter]

Everything seems to be recorded and monitored these days. I had a 2012 Mitsubishi L200 Barbarian (U.K. spec).
Well looked after never abused, serviced at main dealers, and I don’t speed. At 5yrs old and only 50k miles on the clock. The head gasket failed at 70mph on the A34 in U.K. loss of power so pulled off at slip road which was 200m ahead and into service station. Cut a long story short But Mitsubishi bought the vehicle back off me although out of warranty as they could read ecu and confirm never thrashed, as it was a known problem with Mitsubishi in U.K. at the time, head gasket failure leading catastrophic engine failure.
Moral of the story is , when it comes to a warranty claim the manufacturer can tell how the vehicle has been used.

 

[stickshifter]

I think the link above makes reference to this mod:

"xHP Flashtool is the worldwide first and complete Tuning solution for BMW’s with ZF6HP and ZF8HP automatic transmissions."

xHP ZF Gearbox Tuning - WG Motorworks

At WG Motorworks we are a official dealer for xHP, with advanced unrivaled software for the ZF gearboxes it is a no brainer for us to offer tunes that have had extensive research and development to complement our ECU mapping services for that complete enhanced experience. Which the benefits are...

www.wgmotorworks.co.uk

Just reading through it and noticed a few words, that whilst seem perfectly obvious, might be worth noting here:

"S and M modes are designed to facilitate sporty and fun driving. Shift times are cut and clutches get applied more aggressive. Use these modes when necessary and not as standard. The TCU records the amount of time you spend in each mode. BMW uses this data to judge on warranty cases."

I'm trying to decide how I feel about this, approaching it from a rational perspective, but my initial reaction is "I'm going to hackers camp so I can learn how to hack that TCU."

 

[Shaky]

This has been discussed on the forum quite a bit over several threads about the beefier transmission in the diesel and the fact it allows for more scope when “tuning”

I am no expert in this sort of stuff and will be one of the owners with the “inferior” transmission. It won’t bother me as any tuning I ever have done will be to try and eek out more MPG not more HP.

I would prefer the more heftier box that’s for sure but I live in hope that BMW know the score and have paired these two up nicely. I can’t imagine the IA would build in such a weak link knowingly, if it can be considered that.

 

[TD5-90]

This has been discussed on the forum quite a bit over several threads about the beefier transmission in the diesel and the fact it allows for more scope when “tuning”

I am no expert in this sort of stuff and will be one of the owners with the “inferior” transmission. It won’t bother me as any tuning I ever have done will be to try and eek out more MPG not more HP.

I would prefer the more heftier box that’s for sure but I live in hope that BMW know the score and have paired these two up nicely. I can’t imagine the IA would build in such a weak link knowingly, if it can be considered that.

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...

 

[TD5-90]

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...

Maybe it would rationalize the debate if one would look into the transmission(s) from the back: Latest at the input to the transfer case (which apparently has the same ratio for diesel and petrol) torque and rpm have to be approximately identical. So the "strength" (i.e. _power_ transfer capability) of the 2 variants could be best compared when considering the max. _output_(!) torque(s).

 

[DaveB]

Another way to look at it is that the petrol engine comes with gearbox A and the diesel engine comes with gearbox B
They both come with a 5 year warranty
Magna, ZF & BMW have all approved them to work together on the Grenadier in it's intended use.
I am 99.99999% confident that none of them are going to change that just because Dave has concerns.
Which I don't anyway because I have chosen the diesel. (sorry to our NA friends)

 

[TD5-90]

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

 

[Tazzieman]

As an engineer, I generally believe that there's an engineering solution to _any_ kind of problem

How about an empty wallet?