Audi 90 quattro TDI: gearing questions

vtpsd

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Audi 90 quattro TDI: should I tear down the WVO TDI?

Hi All,
I am about to begin putting an AHU tdi into a 1990 audi 90 quattro. I have the physical logistics of the swap pretty well worked out, but my only real question is gearing. There isnt great options for quattro diesel transmission in the US, and I really want to use the stock trans for cost reasons. I live in the mountains and the vast majority of the driving is about 60 miles of backroads a day with 20 miles on the interstate where most people drive 65. So this car would be going 50mph most of the time, sometimes 65. I am one of those guys that drives 65 on the highway on long trips too. That being said, I calculated that the engine would turn about 2800-2900 rpm at 65. I have a 1.6 ecodiesel jetta and it screams on the highway and gets great mpg, have never really driven a tdi. Is this rpm too high? The doner car has a blown clutch, so i cannot experiment with it to see what 2900 rpm crusiing feel/sounds like. Would I expect running at that rpm to negatively effect rpm?
Here is the pretty old girl in question.
 
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Frans

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2800-2900 rpm @ 65 is quite high for a tdi engine. Normally with a tdi quattro it's about 2300 rpm at around 75. What is your current transmission code and diff?
 

vtpsd

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the transmission is an 01a code with a 4.11 final drive. My calculation may not be correct.
Here is the info I have on it
1st-3.545
2nd-2.105
3rd- 1.300
4th-.943
5th- .769
final 4.11:1
 

vtpsd

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checked my calc again assuming 195/60-14 tires (winter size) and i still get the same rpm
 

vtpsd

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i could swap in a 6 speed from an s4 (these are not cheap but are 4.11) and i get the revs down to 2600 ish.
 

oil_me

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I looked deeply into this issue for my swap. One possible option is swapping gearsets 4th & 5th from an 01a TDI trans.; .838 and .659 respectively. Using the tallest tires that will fit in the wheel opening is another angle. With 185/65 14 tires a .789 5th and a 3.89 rear diff (from an Urq) my rpms are about 2800 @ 65mph. I'm living with it for now as I have no high speed travel to get to work. The 01E trannys require tricky shifter mods, drive flange or driveshaft changes.
 

scubagli

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look up oilme, he has an 80 ahu, he used a 2.8 a4 5spd, you should be able to make a 3.89 a4 rear diff work.
 

vtpsd

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I looked deeply into this issue for my swap. One possible option is swapping gearsets 4th & 5th from an 01a TDI trans.; .838 and .659 respectively. Using the tallest tires that will fit in the wheel opening is another angle. With 185/65 14 tires a .789 5th and a 3.89 rear diff (from an Urq) my rpms are about 2800 @ 65mph. I'm living with it for now as I have no high speed travel to get to work. The 01E trannys require tricky shifter mods, drive flange or driveshaft changes.
I wonder how i would get ahold of the gearsets? Seems like that might not be a terrible option if the price wasn't too bad. I am pretty comfortable with the modifications required to swap in an 01e, basically i just want the cheapest solution (dont we all!).
I think I will most likely run the stock transmission first. Most of our driving is pretty unique here. Mostly mountain climbing and 50mph roads with lots of 45mph dirt roads. I figured the rpms at 65 would be the exact same with a stock trans as my ecodiesel jetta. Its not ideal, but it works well for the type of driving we do here.

If the trans is a real problem on a daily basis, then I will need to decide what route to go.
 

vtpsd

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just found the tdi 5th gear. $495 for the set. Might still be the best bargain, but i am going to have to hold off on that for now I think. I think there is a chance the stock trans could work for me.
 

oil_me

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I have many hills & 45mph speed limits where I live in the Catskills which make my gearing tolerable as well. That said; I would love to find cheaper 4th & 5th gearsets, maybe even used. Hey, I can dream.
 

vtpsd

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I have many hills & 45mph speed limits where I live in the Catskills which make my gearing tolerable as well. That said; I would love to find cheaper 4th & 5th gearsets, maybe even used. Hey, I can dream.
cheap tdi quattro parts.....a dream for sure :D
 

vtpsd

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well i got my doner car home last night. It actually runs great even though the car is completely rotted out and ratty. Ran it for half an hour, no codes, no leaks. I think I will go etdi, i like how it runs, and I have everything here to make it work. Now to get that nice audi 90 on the trailer and headed to VT!

Side note: will the AHU injection pump pull fuel from the tank or do i need a feed pump? It would be nice to bypass the external audi pump and run without one.
 

bbob203

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well i got my doner car home last night. It actually runs great even though the car is completely rotted out and ratty. Ran it for half an hour, no codes, no leaks. I think I will go etdi, i like how it runs, and I have everything here to make it work. Now to get that nice audi 90 on the trailer and headed to VT!

Side note: will the AHU injection pump pull fuel from the tank or do i need a feed pump? It would be nice to bypass the external audi pump and run without one.
like all ve rotary pumps they have a vane pump built into them Though running a lift pump is never a bad idea! :D The fuel pump under the rear floor cant be used at all. The one in the tank some have used as a lift pump but some have reported it causes air to get into the fuel i opted for a lift pump under the floor board.
 

vtpsd

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i think i will try no lift pump for simplicity sake. Should be able to "straight pipe" the section where the pump is.
 

bbob203

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i think i will try no lift pump for simplicity sake. Should be able to "straight pipe" the section where the pump is.
exactly what i did and the guy who helped me do my conversion has been running one for better than 10 years with not problems. Only problem you can have is drainback but just get a nice brass check valve and your good to go.
 

vtpsd

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Project is starting off a bit slow, having trouble getting a shipper booked for the car and the fall is very busy getting firewood in the shed and picking all the apples for this years hard cider!
I did start a bit of playing with the doner car, removing the WVO setup to sell. I am wondering if I should tear the engine down to inspect and clean just based on the fact that it ran WVO for an undetermined amount of mileage. It runs great, but it does smoke more than it should just sitting and running in neutral. Usually i opt to leave an engine together if it runs well. I have rebuilt several engines successfully in the past, but I do think its really nice to have a factory assembled engine if possible. Any thoughts on this? Am I being too paranoid? We have all seen those horror show pictures from the inside of WVO engines.
 

vtpsd

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will do, hoping to make some in the next month or so. Once winter sets in, i will have much more time to mess with it.
 

vtpsd

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finally my car is on a trailer and headed toward VT. Anxious to get my hands on it.
 

Scott_DeWitt

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5 speed tdi quattro transmission are fairly rare, there are much more 01E tdi transmission out there than 5 speeds.

I do have a 5th gear for the 01A, that mates well to a V6 01A found in Us junkyards.



Advanced Automotion 01A tdi 5th gear.


There is also a European 3.70 final drive and matching rear diff available. It makes for really nice diesel ratios I'm doing a A4 conversion with that transmission and diff.
 

vtpsd

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I did find those on your website. For now I am going to *try* the stock trans. I think if it could work for any type of driving it would be for us in the hills of vt. There is very little interstate and lots of 50mph hilly roads....Probably just kidding myself and being too cheap here. The fact that my ecodiesel has almost the exact same final ratio as this setup gives me hope that i can live with the stock 01a trans.
 

vtpsd

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This project is not dead, got my hard cider up, woodshed full, and daily driver cars ready for winter,, so i finally got a bit of time this afternoon and pulled the motor out and cleaned it up a bit.

 

vtpsd

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I'm getting back into this project again. Went through a breakup from a 7 year relationship. Needless to say that derailed me for a while. I got the harness pulled from the mk3 yesterday and started thinking a bit more about the specifics of the swap.



I was looking at the pedal cluster. Doesn't look like a nice easy way to integrate with the 90 pedal cluster. Do you think the throttle pot could survive under the hood? I could see making up a bracket to mount it and use the 90's throttle cable to actuate it. The throw looks about right. Bad idea to mount this thing under the hood? I know people have done it before, but that doesn't mean its a good idea ;)
 

vtpsd

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is that different from the mk3 setup? The mk3 throttle pot looks pretty easy to adapt to usage with the factory audi throttle cable.
 

bbob203

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is that different from the mk3 setup? The mk3 throttle pot looks pretty easy to adapt to usage with the factory audi throttle cable.

Are you saying use the throttle cable to actuate the pot??? I guess that would work. The mk4 dbw pedal takes up a lot less space and you could easily adapt it to bolt up to the audi firewall Im sure.
 
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