5th gear upgrade. .681 success 11% RPM drop

[david_594]

Edit: The important details.... A .70 and a .681 fifth gear sets that should fit the stock 5 speed manual tranny with the TDI were found. The .70 was never tested by anyone and I installed the .681. So now there are both a .681 and a .717 5th gear set that are verified to fit the 02J transmissions of our cars. The .717 provides a 5% reduction in RPM's while the .681 provides an 11% drop in RPM's. Either swap will provide for a much more pleasant highway experience. Rough estimates on the fuel economy savings from either swap is guestimated to be roughly half the drop in RPM's but this is not thourghly verified. If your intersted in doing this swap please read through the rest of the thread.

dave

Original stuff....
The info on the .681 gear is in my last post down this page somewhere.

So its a topic that seemed pretty popular 5 years ago and myself and another club member were considering it a bunch as of lately and found some new information. First off the ALH tranny comes with a .756 5th gear set and the original upgrade was to swap it out for a .717 from older diesel AAZ engined diesel available in canada. This provided an RPM drop of rough 5.16% and the people who did it claimed a small increase in fuel economy. In the old threads on this subject there was mention a few times of a .681 gear set from an Audi which would have provided roughly a 9.92% drop in RPMs, but no one ever provided what vehicle or tranny this was from so for as much as anyone knows it doest exist.

The new news

Doing some searchign, supposidly the new 100hp BEW PD's come with a .74 5th gear ratio with 29/39 teeth. This seems fitting with the added HP of the newer 100hp PD motor. (I got this info from a VW tech who looked it up at work)

Also, a .70 5th gear set(28/40 teeth) was found from a euro eurovan 02A tranny. From whate I have gathered the gears from the 02A and 02J are interchangable so this should be a feasable upgrade for all our A4 TDI's. This would provide a roughly 7.41% drop in RPMs for an ALH tdi or 5.41% drop in RPM's for a PD.

Here are the part numbersfor the .70 eurovan gears.
02A 311 361 AM
02A 311 158 AF

So who wants to be the guina pig? This wont be cheap, probabily somewhere close to $400 as the parts would have to be shipped from europe. But at the same time if you get your original gears out in one piece you should be able to sell them to a gasser for around $150 to recoup some of the cost as our gears is an even larger upgrade for them.


Here is a link to the how-to hosted on the tdiclub pictures server:



Follow the link, login to the pics server, scroll down and click on the image that says "multimedia" and it should download the PDF for you.

Please ignore the numerous typos as I clearly didnt proof read it when I made it. Also take the warnings seriously. When I first wrote this up ~10% of people had major complications when doing this mod.

 

[JettaJake]

Re: 5th gear upgrade. .70 ratio!

group buy?

 

[cevans]

Re: 5th gear upgrade. .70 ratio!

Dave,

Just be the trial subject yourself!

Lets see if we can get a vendor to get a definite price!

cevans

 

[nicklockard]

Re: 5th gear upgrade. .70 ratio!

I second the motion: group buy!

 

[DrSmile]

Re: 5th gear upgrade. .70 ratio!

Excellent research, please let us know the results. At $400, even assuming an optimistic 10% increase in mpg and assuming a $3 a gallon diesel price, it would take 4.5 years or 70K miles to recoup the cost, but I could claim a 50mpg average. Quite a dilemma...

 

[david_594]

Re: 5th gear upgrade. .70 ratio!

My assumtions on the cost/benefits of this was actually a modest 5% increase in economy. Also if you resell your original 5th that puts you at roughly $250 out of pocket. Roughly a 5% savings and you would have to spend 5 grand on fuel before you break even. At current prices of $3/gal were talking 1666 gallons roughly. Figure 50 mpg and your only talking 85k miles or so to pay off this mod.

Its all relative though. There is some cool factor to this also that its hard to put a price on.

Cevans,
Of course I'm planning to do this to my car. But like all my mods im a lazy bum. It could take me a long while to source the parts; then an even longer while to install them. If people want to wait for me to be first on this one, thats cool, if they want to try it before me, thats cool to

.

 

[lumberjackbob]

Re: 5th gear upgrade. .70 ratio!

If someones interested, I know of a salvage yard that has a used 5sp tranny with about 70K for $750. The yard is located in SE Washington. If I didnt have a wedding to pay for I might be all for this.

 

[DrSmile]

Re: 5th gear upgrade. .70 ratio!

You don't need a spare trans. 5th gear on a transaxle sits on top of the case and doesn't even require transmission removal from the car to swap out the gear. Labor is minimal, really the major cost is gears and transmission fluid.

 

[TheCheat]

Re: 5th gear upgrade. .70 ratio!

Someone confirm the gears are indeed interchangeable and I'll pony up in a couple months.

 

[BleachedBora]

Re: 5th gear upgrade. .70 ratio!

Contact TMtuning.com They can get any parts you need--tell them you are interested in a group buy and they will work with you--they like giving me personal deals because I have them listed on my "sources" page

Sounds like fun though--wish it worked on an A3!
-BB

 

[david_594]

Re: 5th gear upgrade. .70 ratio!

So I am going to be order a set of these. I found a guy from the vortex in Europe who is getting them shipped to me. So hopefully we will know in a few weeks.

 

[Mike_M]

5th gear upgrade. .70 ratio!

WOW! Here's some numbers...assuming the ring & pinion (final drive) remains stock. Assumes 2150rpm @ 60 for stock .756 gear.

1900rpm (torque peak): 53mph before, 57.3 after
2000rpm: 55.8mph before, 60.3 after
3000rpm: 83.7 before, 90.4 after!

65mph: 2329rpm before, 2156 after
75mph: 2688 before, 2488 after
85mph: 3046 before, 2820 after!

Huge improvement from just a 5th gear upgrade.

Now, if I have time to go look at my Bentley manual (to find out the stock ALH final drive), I'll be able to calculate if you also swap in watercop's beloved 3.156 final drive...

Mike

 

[david_594]

Re: 5th gear upgrade. .70 ratio!

final drive is 3.389

 

[david_594]

Re: 5th gear upgrade. .70 ratio!

No wife, Im a college student though. Its not just the friction losses you are reducing. The main advantage in terms of economy should be the fact that you are keeping the car closer to its max torque. And the max torque should also be the where the car is nearest its maximum mechanical effeciency. This is what your gains would be from, not friction losses.

 

[VelvetFoot]

Re: 5th gear upgrade. .70 ratio!

perhaps that fellow vw4motion could help.

I wound up chipping a few teeth when i took out the old gearset. Maybe I wouldn't again, but you have to get the right puller.

Is there even a lower 5th gear? http://translate.google.com/translate?hl...6lr%3D%26sa%3DN

 

[david_594]

Re: 5th gear upgrade. .70 ratio!

VF, good find. I'll see what else i can find about the numbers they posted. Maybe that is the fabled .68 gearset you guys were trying to find like 3 years ago.

 

[david_594]

Re: 5th gear upgrade. .681 FOUND!!!

So we found the a .68 that SHOULD fit. Using the link from VF and the Euro ETKA work of SLAB he found this:

93-2003 Transporter Synchro
02D 311 361 (32 tooth)
02D 311 158 (47 tooth)

= 32/47 = 0.681

This tranny has a 5.31 final drive which kinda makes sense that it has a .681 5th. The 4th gear in it is a 1.1 so it makes a big drop from 4th to 5th which kinda worries me.

1st = 4.375
2nd = 2.266
3rd = 1.3
4th = 1.1
5th = .681 (etka lists it as 1.46 which makes me think it was listed backwards)

All the other 5th gear ratios for this tranny begin with the 02A so that is a good sign as to it fitting. So does anybody have any thoughts on this one?

Another thing supporting this possibility is that this transporter tranny is offered with a .74 5th gear and this gearset has the same part numbers as the .74 fifth gear set offered in the 2005 US PD100 Golf 5 speed.

 

[SLAB]

Re: 5th gear upgrade. .681 FOUND!!!

I thought i had found a .063 gearset as well, but it turned out to be a non-02A style transmission.

i would like to buy a set of .681 gears for my Golf.

i will check monday to see if the gearset is in the USA system as some euro-only parts are avaialble if you know who to ask, and where to look.

 

[03_01_TDI]

Re: 5th gear upgrade. .681 FOUND!!!

another good benifit is less engine wear.
But a possible bad side effect is more stress on the clutch.

 

[IndigoBlueWagon]

Re: 5th gear upgrade. .681 FOUND!!!

This is a very tempting upgrade. Why won't it work on the A3 Jettas? That car really needs taller gears.

If there's a group buy on these gears count me in.

 

[david_594]

Re: 5th gear upgrade. .681 FOUND!!!

It wont work in the a3/b4 because you have an 020 tranny(i think).

I'm gonna be the guina pig on this one. Once I get one across the pond and make sure it works, then you guys can get started on the group buys.

 

[Lug_Nut]

Re: 5th gear upgrade. .70 ratio!

No wife, Im a college student though. Its not just the friction losses you are reducing. The main advantage in terms of economy should be the fact that you are keeping the car closer to its max torque. And the max torque should also be the where the car is nearest its maximum mechanical effeciency. This is what your gains would be from, not friction losses.

Your major apparently isn't physics.
Torque is dependent on your right foot's position. It is not possible to have the engine produce more than the 150 lb*ft at 1900, but being at 1900 does NOT mean that 150 is being made. Torque at 1900 rpm can actually be negative during engine braking. This lack of direct correlation between rpm and torque is the main reason that the numerical advantage of gearing does not return an equivalent change in fuel economy.
Humor me and allow that 15 hp are needed to maintain 55 mph. That works out to 1900 rpm with stock gearing. The engine can make up to 150 lb*ft at that engine speed. 150 lb*ft at 1900 rpm is 66 hp. But since only 15 hp are needed the engine is operating at 23% of that rpm's full load capacity.
Change the ratio up 5% and the engine slows to 1800 at 55 mph. The peak torque at 1800 is about 140 lb*ft for a maximum power of 48 hp. Since the same 15 are needed to maintain 55 the engine is at 31% of that rpm's full load capacity.
That's where the fuel economy saving are, operating at a higher percentage of a given rpm's full load capacity. The loss of specific effeciency (HP per gallon per hour) from operating the engine outside of it's best efficiency range cut into the gain a bit so the full 5% improvement isn't realized.

 

[david_594]

Re: 5th gear upgrade. .70 ratio!

JB,

You slipped up in your math 1900 RPMs x 150 ft-lbs = 54.3 hp.

So operating at 1900 you would be at 27.6% of full load capacity.
Going with your numbers you are saying that at 55 mph and 1900 RPMs that the engine would be producing 41.4 ft-lbs of torque. At 1800 though it would take 43.7 ft-lbs of torque to drive the same load. So its either a 27.6% loading at 1900 versus a 31.2% loading.

What we need to see is are the graphs of torque versus fuel injected.

This is what matters in this case. The explanation of this graph is in this thread

In short, it shows the amount of fuel required(black lines) at a specific RPM for a specific load. The read lines are constant power across the RPM band so you would compare any points on the same line.

 

[03_01_TDI]

Re: 5th gear upgrade. .70 ratio!

so the theroy is to reduce RPMS err allowing the ECU to inject less fuel. making less torque. Wouldn't any easier, cleaner, and cheaper mod just to get a some dyno time with a rocketchip or the aligator and tune the ECU to create just the right amount of torque at a given speed range.

 

[VelvetFoot]

Re: 5th gear upgrade. .70 ratio!

If the gear set could be obtained at a reasonable price it might be worth a shot. Another consideration is a comfortable rpm drop from gear to gear. 4th to 5th might be a little steeper than before, hopefully

so you might have to rev it more in 4th.

 

[GoFaster]

Re: 5th gear upgrade. .70 ratio!

so the theroy is to reduce RPMS err allowing the ECU to inject less fuel. making less torque. Wouldn't any easier, cleaner, and cheaper mod just to get a some dyno time with a rocketchip or the aligator and tune the ECU to create just the right amount of torque at a given speed range.

That's not the way it works. At part load, the amount of fuel injected is whatever it takes to make the power required to run the car down the road. Doesn't matter whose chip program is in there. If the RPM is the same then the friction losses will be the same and you won't change where it is on the BSFC chart (diagram above).

Using taller gearing lets the engine run at a higher amount of load but a lower speed. This is generally a bit more efficient because there's less friction and parasitic losses due to the lower engine RPM. The previously-known tallest gears weren't a big difference from stock, but with 0.681, now we're talking.

Keep in mind that there is always a compromise. You'll lose some top-gear acceleration with taller gearing, and you might have to use 4th to a higher road speed before shifting to 5th to avoid lugging in 5th.

By the way, this should work on an A3 or B4 as well. We have an 02A transmission (not an 02O). There's not a whole lot of difference between an 02A and an 02J.

 

[jackbombay]

Re: 5th gear upgrade. .70 ratio!

You don't need a spare trans. 5th gear on a transaxle sits on top of the case and doesn't even require transmission removal from the car to swap out the gear. Labor is minimal, really the major cost is gears and transmission fluid.

That makes tis mod far more likley to happen, I bet it takes a special tool or 2 though. Would a VW specialty shop (Hillside?) most likley be able to do this swap? Anyone have any idea on cost?

 

[Rammstein]

Re: 5th gear upgrade. .70 ratio!

Jonathan, do you remember the discussion we had about gears at TDIfest.

I found some "taller gears" on Audi's....

 

[jackbombay]

Re: 5th gear upgrade. .70 ratio!

No wife, Im a college student though. Its not just the friction losses you are reducing. The main advantage in terms of economy should be the fact that you are keeping the car closer to its max torque. And the max torque should also be the where the car is nearest its maximum mechanical effeciency. This is what your gains would be from, not friction losses.

Your major apparently isn't physics.
Torque is dependent on your right foot's position. It is not possible to have the engine produce more than the 150 lb*ft at 1900, but being at 1900 does NOT mean that 150 is being made...

Lug Nut, I think you misunderstood the poster you quoted. He, IMO, is saying that driving at peak torque RPM, regardless of right foot position will make HP more efficiently than any other RPM, thus the gains from this mod are more than lower friction, but also more efficient production of any given amount of HP due to operating closer to the peak torque output RPM.

 

[Mike_M]

Re: 5th gear upgrade. .70 ratio!

final drive is 3.389

Thanks, David! Given that info and the discovery of the .681 5th, here's my updated spreadsheet:

Not quite as tall as a Euro 6-speed (that'll do 69mph at 2000rpm in 6th), but pretty darn effective, I'd say.

Mike