Group buy / order: 0.65 / 0.643 5th for TDI

Okey dokey then, for Dan (and others!), here's a full list of the revs v. speed for the ratios under consideration:

75PS (0.756) 90PS (0.700) 0.681 0.65 0.625

70mph = 2575rpm 2383rpm 2318rpm 2180rpm 2127rpm
60mph = 2205rpm 2042rpm 1987rpm 1867rpm 1822rpm
50mph = 1838rpm 1703rpm 1655rpm 1555rpm 1520rpm
40mph = 1470rpm 1360rpm 1325rpm 1245rpm 1215rpm
30mph = 1103rpm 1020rpm 995rpm 935rpm 912rpm

Also, for information, here are the gear ratios for the 75 and 90, as standard:

Gear 75 90

1st 3.778 3.778
2nd 2.118 2.063
3rd 1.360 1.304
4th 0.971 0.903
5th 0.756 0.700

As you can see, there is a massive jump from 1st to 2nd and then a less severe jump from 2nd to 3rd and a similar smaller jump to 4th and finally a pretty small jump to 5th.

In percentage terms, 2nd is 56% of first, 3rd is 64% of second, 4th is 71% of third and 5th is 78% of fourth. For the standard 75 'box, going to the 90PS cog will result in a 5th to 4th percentage of 72%, or 70% is you opt for the 0.681 ratios. In this light, I'd not recommend the 0.65 ratio for 75PS owners, as it'll be too big a jump (67%).

For the 90PS 'box, the numbers are 55%, 63%, 69% and 78%. Going to 0.65 will change the last number to 72% or 0.625 will yield 69%.

As you can see, the final jump to fifth is not a massive one, but will be a kind of overdrive, depending on what cogs you choose. There is also the option for 90PS owners to sell on their ratios to 75PS owners, which will be of benefit to both parties, as the 90 owner recoups some of the cost of the new cogs and the 75 owner gets a cheaper option than new ratios.

Cheers,

Mike
 
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Good work Mike.

Decisions, decisions - with a remapped 75 I am tempted by the .65. Will now put that all into excel and plot against the dyno readout I got from Stealth.
 
Having read Mike's findings I think I'd better use gear more than 0.65. I have a standard 75 tdi. I could consider buying somebody's cogs from 90 tdi. I'm just thinking how sensible it would be to put old parts in once changing. :confused:
 
Having researched this extensively now, fitting old gears is not a problem, as long as they're in perfect condition and by this I mean no appreciable wear and certainly no chipping.

The chipping occurs mainly when the old cogs are removed and only if you apply too much force with a puller. To avoid this, it is recommended that the gear is heated to around 100celcuis with a heat gun, at which point it'll come off really easily.

An appropriate reduction in price for the item being used is of course to be expected, so as opposed to £85-90 and £130-135, think around the £45-50 and £65-70 mark.

This would of course benefit both the 90PS seller and the 75PS buyer, as we'd all be getting a bargain!

Cheers,

Mike
 
Thanks for your work on this Mike. I obviously missed a detail in my earlier post, apologies.

Count me in for a TDI90 cog if someone is willing to sell me theirs, otherwise I would be interested in a UK sourced 0.681 cog if the price & distribution are sensibly managed. Thanks!
 
Skipton01 said:
An appropriate reduction in price for the item being used is of course to be expected, so as opposed to £85-90 and £130-135
Click to expand...

Sorry Mike I'm a bit lost, what are the two prices for?
Are some gear ratios more expensive than others?
Or are you comparig UK OEM sourced gears to Bret's EU ones?
 
Just to add a little to this post:

Today I've had my 75PS remapped by Stealth - got it to 111, but turned it down a shade to keep emissions perfect -. While there I spoke at length with Vince regarding the .645 & .700 gears.

Vince has advised the .645 would be too long for a 75, even remapped, & is sure there would be unnecessary 5th-to-4th gear shifts, especially on country lanes or d/carriageways with 40 MPH speed limits.

Vince also advised the .700 5th gear ratio felt just about perfect in the 90, so advised if a change was to be made for 75PS engines the .700 was the way to go.

However this was before I read the latest possibility of a .681.

The .681 seems like the perfect ratio, and I'd be interested in a group buy of these gears.

Cheers

Jeff
 
Will said:
Sorry Mike I'm a bit lost, what are the two prices for?
Are some gear ratios more expensive than others?
Or are you comparig UK OEM sourced gears to Bret's EU ones?
Click to expand...

Neither Will!

The conversion 'kit' will comprise 2 cogs: one for the input shaft and one for the output shaft.

The output shaft cog is basically just a straight cog (albeit a piece of precision engineering) but the one on the input shaft has the is a 'change cog' which is actually 2 cogs in one, as it has to mesh with the one on the output shaft and also mesh with the selector mechanism, hence it's higher price.

So, the total price for a kit will be in the region of £210-225 plus fitting.

Jeff, the 0.681 ratio is a good compromise, but I think that the 75PS could take the 0.659 (not sure of the 0.645 ratio - I can't find one that is OE, but that's not to say it doesn't exist), albeit only as a motorway cruiser.

Cheers,

mike
 
bretti_kivi said:
I've just spoken again. He claims to be able to keep the price if 10 sets of cogs from 20 are returned.

OTOH, the price mentioned was €10 higher. I don't quite get what's going on with that, but....

My question: who can deal with this in the UK - cog collection / sending within the UK?
How many sets of cogs will we get back? I presume the discount is around €50 or so for returning them.

That makes it really complex on the maths, but works out like this:
Total: 20 x 130 --> 2600
--> 160 for those who don't want to return --> €190
--> 100 for those who return --> €119

into GBP + VAT that turns to
--> (rate is 1:0.871 right now) £104 / £174

Transport costs should be minimal, even if I was to do this. I don't know what the cogs weigh, but I will try and find out.

At these rates. who is still interested?

Bret
Click to expand...

There's a little bit of a difference Dan, but from the above, it seems that without returning the old cogs, we're looking at £174 plus shipping, so around £40-50 cheaper for the Rosenkranz parts.

If we can get 90 owners paired up with 75 owners (who want to put the 90 ratio on), then the price comes to around £100 for the 75 owner and £125 for the 90 owner, after the 75 owners have bought the old ratios.

Cheers,

mike
 
It's starting to make sense now!

So you need a list of 90 owners
and another equal list of 75 owners

so all that has to be worked out is the labour cost.

wow, the last post finally cleared the mist!
 
Well, from my reckoning, we have the following 90PS owners down for the group buy:

Design Time
Eagle
Mlarner
Skipton01

These four could pair up with 4 75 owners who want the 0.700 gearing, making 8 satisfied owners and leaving 10 others (I believe Arilies has withdrawn), so there could be a two-tier buy going on.

I've also heard back about the cheapo 0.659 gearset (the one at £67 and £88) and apparently it's good for up to 300 foot pounds of torque, so could be an option for the 10 75PS owners who don't pair up.

Like I said before, I have niggling doubts over fitting non-Audi (or non-VW) parts to my car and in view of the comments about Rosenkranz reconditioning old gearsets, this is compounded.

I'll try for a price this week and then hopefully, we can get this moving very soon.

Bretti - I hope I'm not stepping on toes here, it's just that this thread started 10 weeks ago now and we've not even got a firm price. I know that it's difficult for you, especially as you're trying to co-ordinate members from Finland, Germany and the UK, but a lot of UK members are really eager to get this sorted soon.

Cheers,

Mike
 
I will want something geared a bit higher than the 90 but not so high it becomes an overdrive ratio. Based on the thread so far I think the 0.681 ratio seems about right for me with a remapped 75. Will have another read through and confirm!
 
Here's all the data in graphical form (I know I was having trouble visualising things).

The standard 75 stuff is in red, the 90 in blue.

As only the last ratio is being altered by the proposed new gears (0.681, 0.659, 0.625), I've just included these as single green, yellow and black lines.

A2TDiRatios.gif


If you currently change up from 4th at around 2400rpm, then you'll be a new 5th at around 1600rpm - you can work out whether you have the torque to do this comfortably or not.

Cheers,

Mike

PS Click on Open in new tab (or window) to be able to zoom in and see detail
 
Bret - thanks for the groundwork, and sorry but I'm not commiting to the original idea given the new info

Mike - thanks for all the effort!

As I'm planning a remap in April, I am interested in the 0.681 and 0.65 - if any remapped 75 owners can provide a dyno readout to assess the torque available compared to the theoretical revs I could make a decision...

Can anybody post their dyno readout please?
 
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Thanks again Mike, and thanks for the effort to push it forward (edited last post after you replied to say thanks!)
 
Thanks to Brett for getting this idea going and Mike for putting so much work into it this past week. I am sure the research by Mike will be equally applicable to A2 owners in other countries and gives a 'home source' for the upgrade using OE components. I know when i spoke to Mike last week when working on my car he was as keen as me and others to make progress with this. When do you anticipate being in a position to start offering a fitting service Mike? I am happy to be a guinea pig with my '75' once I have finalised the ratio to go for.
 
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