Is B8 2.0T 6Spd Quattro Manual Suitable for a Diesel?

[kuso]

I'm planning to diesel swap a b5 a4 quattro, through some previous post I've gathered that the 2.0T transmission from the b7 generation is the most suited (which I have struggled to find.) A wrecked 2009 A4 quattro 6spd 2.0T came up really cheap from marketplace and I'm wondering if it would be suitable gearing wise for a diesel? I've looked around and can not seem to find anything reliable on the gear ratios for either of these transmissions. Thanks folks.

 

[oilhammer]

The longitudinal cars underwent a major design change with regards to the eng/trans mounting, spacing, and steering/suspension. You cannot mix 'n match many parts because of this. They redesigned the gearbox (both manuals and automatics) such that the centerline of the front axle and the outlet flanges on the gearbox are right up against the engine, and the flywheel is actually behind this point.

The 2009 Audi A4 is the later type, so you cannot really use its transmission. It wouldn't easily bolt into the car, and the axle flanges would be in the wrong place.





Upper is the newer type (notice where the drive flange is)... the lower is the older type, with the differential (and thus the output flanges) behind the clutch/flywheel. It is a very different arrangement. At the same time, they also completely changed the way the powertrain mounts to the car, they moved the steering rack down below the powertrain and mounted it to the subframe, whereas previously it was up in a cavity against the firewall.

 

[kuso]

Man, you're a huge help.
I didn't even realize they were totally different designs. That would certainly not work for my application. I will continue my search for the 02x then, it's been a real PITA trying to find a good donor.

 

[kuso]

The longitudinal cars underwent a major design change with regards to the eng/trans mounting, spacing, and steering/suspension. You cannot mix 'n match many parts because of this. They redesigned the gearbox (both manuals and automatics) such that the centerline of the front axle and the outlet flanges on the gearbox are right up against the engine, and the flywheel is actually behind this point.

The 2009 Audi A4 is the later type, so you cannot really use its transmission. It wouldn't easily bolt into the car, and the axle flanges would be in the wrong place.

View attachment 139053

View attachment 139054

Upper is the newer type (notice where the drive flange is)... the lower is the older type, with the differential (and thus the output flanges) behind the clutch/flywheel. It is a very different arrangement. At the same time, they also completely changed the way the powertrain mounts to the car, they moved the steering rack down below the powertrain and mounted it to the subframe, whereas previously it was up in a cavity against the firewall.

Do you have any good sources for gear ratios regarding the 02m diesel and 02x 2.0t? I've searched around and haven't found anything solid. People have pointed me in that direction but I want to cross reference to make sure.

 

[oilhammer]

I sure do not. I can tell you that VAG really did start to address the woefully low gearing of older gasoline fueled cars here starting around the same time the FSI/TSI engines and 6sp manuals started coming around. Even the lowly NCS Jetta S got MUCH taller gears than older cars did with essentially the same basic engine. So chances are, a 6sp manual that was bolted to a BWT 2.0t gas engine in a 2007 Audi A4 sedan is probably going to be geared just fine for most any 4 cyl diesel you'd be wanting to use. And something like that BWT engine, or a BPG from a 2006, will be the same basic architecture as an ALH, BEW, or (most closely) a BHW. Remember, in addition to the transmission, you also need all the diesel-specific bits for a longitudinal application. Which for us here, was JUST the 2004 and 2005 B5 Passat with the BHW.

 

[d24tdi]

Agreed. Got a friend on the other side of the state here who just got a BHW swap on the road in a B7 Avant that was originally powered by a 2.0T (which was dying). He kept the stock 6spd quattro gearbox - 02X I am near certain, GVE code sounds familiar? - and the ratios are very nice for the TDI.

He previously built another B7 that had started life as a 3.2L V6 gasser. The 6MT trans in that car also worked out OK for the diesel but the ratios were a little shorter. 2.0T trans was a better match.

Older gen Audi gasser gearboxes OTOH all seem too short for diesel compatibility, as OH pointed out. The factory 6 speed in my 2001 allroad for example has the 2.7tt buzzing at 3500-4000 rpm in 6th at interstate speeds around here. Factory 1.8T 01A gearboxes in the AWD B5 Passat/A4's and the early B6 A4 are similar. I don't think a TDI would really mind those revs even for sustained periods, and I think some folks on here are overly obsessed with getting cruising RPM down to rock bottom - I would rather spin a 4 banger TDI at more like 2800rpm than lug along at 1800 where there's no advantage - but it seems like you do lose some efficiency once you get much beyond 3000-3200 or so, and spinning at 3500+ all day in anything without balance shafts would be tiresome due to the NVH factors. In other words it's more about the wear and tear on the driver than on the motor, and mega tall gearing isn't necessarily what you want esp in a heavier Audi spinning AWD drivetrain parts and big tires.... but there is a nice sweet spot on there in the high 2000s if you can hit it.

For what it's worth, in the heavy equipment world where I live my day to day, you often run the engines right around governed speed all the time. 7.2L CAT diesel with a fuel cutoff "redline" at 2500 rpm is happy to roar all day at 2450. 5.9 Cummins or 7.3 IH T444E will spin 3k all day long. If those big pistons and rods can do that for 300k miles I'm sure a little lightweight TDI could happily spend its life at 4000+, given good upkeep of course. But it would not be much fun behind the wheel.