6 Speed MPG

Grahamat

New Member
Hi all,
Can anyone advise me what improvements, if any, have been made in the economy of TDI cars that have had the 6 speed conversion?
I’m seriously considering it as most of my mileage is done on motorways.
Thanks
 

BiggDogg

A2OC Donor
From experience, for the TDI90 with MYP, the difference is marginal, maybe 2mpg and will never pay back.
Going to skinny tyres pumped up to full recommended pressure, solving any existing engine issues, adopting a lower cruising speed and accelerating slowly, taking your foot off the accelerator early (rather than braking later), closing windows, OSS and using ECON are the boring but way more cost effective options IMHO. Matt


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Grahamat

New Member
Thanks for that Matt.
Sadly, my yearly trip to Italy precludes a reduced cruising speed lol. Quite the opposite in fact!
 

timmus

A2OC Donor
On long runs, with suitable exterior temperature, I can get 80mpg from my 6-speed TDI. That's doing 65mph. It's a full-fat beast with lots of heavy optional extras and 205-width tyres.

Adding a 6th gear does improve fuel economy, but it's not necessarily a financially sensible move. When I had my 6th gear added, I calculated that I needed to do 125k miles in 6th gear before it paid for itself in fuel savings. However, there are other savings that are more difficult to quantify; my engine doesn't sit there rev'ing its head off on the motorway, meaning less wear. I also really appreciate the silence whilst cruising along.

Cheers,

Tom
 

Grahamat

New Member
Hi Tom,
Thanks for your input.
I’m not overly worried about getting my money back on the 6 speed as I get car mileage for one thing plus I want a more relaxed motorway experience.
If I can sit at 80 on the French autoroutes using cruise control then I’m sure that I should definately see an improvement in MPG.
The car basically runs non-stop from fuel fill to fuel fill until we get to Italy!
 

bretti_kivi

Member
One of the early CKR adopters on the German forum reported back recently and was disappointed in the lack of fuel savings. Comfort may win out but their numbers were definitely on the side of a negative effect.
Would have to dig out the thread. Difference was of the order of 10% IIRC.

- Bret
 

timmus

A2OC Donor
I want a more relaxed motorway experience.
That you will definitely get.

The graph below shows my gearing setup. You can see that I get 70mph at 1955rpm and 80mph at circa 2250rpm. It's lovely and quiet and just whistles along ...you just need to be careful not to use 6th gear too low down the rev range. High load, low rev scenarios are terrible for your gearbox and engine bearings.



Cheers,

Tom
 

Grahamat

New Member
Ah OK. I get that.
In my case then would just a higher 5th gear work better in my favour do you think?
I have a TDI90
 

timmus

A2OC Donor
but their numbers were definitely on the side of a negative effect.
I don't know the ratios of the CKR 'box, so can't really comment. Perhaps the gearing is too long and that they're stressing the engine? Perhaps they've increased their speed in order to keep the engine in its peak torque area, thus increasing aerodynamic drag significantly? I don't know how scientific they've been about their measurement, but I'd be very disappointed to have fitted a 6-speed 'box and not be getting an efficiency reward. Certainly everyone I know in the UK with a 6-speed 'box (and there must be at least 40 of them now) has seen either an improvement or no change in economy.
I know that I've seen an improvement. With a 5-speed 'box, I struggled to break 72mpg on a long run. I'm now disappointed if I don't get 70mpg on average, and I regularly see 78-80mpg on a long run (assuming the Webasto/aircon isn't running).

Cheers,

Tom
 

timmus

A2OC Donor
Ah OK. I get that.
In my case then would just a higher 5th gear work better in my favour do you think?
I have a TDI90
Here is the equivalent graph for a TDI90, which already has longer gearing from factory. The black lines show the TDI90's standard 5-speed 'box, the red lines show the same gearbox once covered to 6-speed.

So, a TDI90 turns 2407rpm to get 70mph. That's a lot more than the 1955rpm that I turn in my TDI75 in 6th.
Note that these graphs are for 5-speed gearboxes that have been upgraded to 6-speed. You can, however, fit the MYP 6-speed gearbox to a TDI90 and get the equivalent of the graph in Post 7.



Cheers,

Tom
 

Grahamat

New Member
What kind of money would I be looking at for the 6 speed conversion and is a higher 5th gear ratio available for the TDI90?
 

timmus

A2OC Donor
What kind of money would I be looking at for the 6 speed conversion and is a higher 5th gear ratio available for the TDI90?
Yes, you can just change the 5th gear. Changing 5th to a 0.659 ratio on a TDI75 looks like this....



I'd recommend that you fit the 0.622 ratio to a TDI90, as that scales things proportionately. You obviously end up with a big jump between 4th and 5th, but if that's not going to be an issue, it's a much, much cheaper modification than a 6-speed upgrade.

Cheers,

Tom
 

Edwrai

Member
Here is the equivalent graph for a TDI90, which already has longer gearing from factory. The black lines show the TDI90's standard 5-speed 'box, the red lines show the same gearbox once covered to 6-speed.

So, a TDI90 turns 2407rpm to get 70mph. That's a lot more than the 1955rpm that I turn in my TDI75 in 6th.
Note that these graphs are for 5-speed gearboxes that have been upgraded to 6-speed. You can, however, fit the MYP 6-speed gearbox to a TDI90 and get the equivalent of the graph in Post 7.



Cheers,

Tom
I fitted a 6 speed box on a TDi 90 and I don’t think I see much difference mpg to be honest, if anything I think it may be slightly worse.


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Jellybean

Admin Team
I have a 6 speed MYP in my Tdi75 (remapped). First 5 gears are the same as standard, but 6th is like overdrive. It gives an engine speed of 2000rpm at 70mph, rather than about 2600rpm. It certainly makes for relaxed cruising lower noise levels. Stealth Racing fitted the MYP, I sourced from a breaker. Complete with new clutch and oil, installation was about £400 ish. It's not a cost effective conversion, but I really appreciate the longer gearing for motorway cruising.
 

Grahamat

New Member
Hmnn. Very interesting.
That being the case I think that the higher 5th gear with a mildish remap is in order.
That and an upgrade to Bose lol.
 

AndyP

Member
Yes, overall improvement quite small on my daily drive to work, which is probably about 20% max in 6th, but I certianly haven't been driving any slower since it was done either. Overall driving satisfaction and smugness measure high though!
 
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