carwhisperer

Today’s lesson: don’t believe everything you read on the internet. Everybody’s running around putting 4.2s in their boxster, right? Bolts right up, right? Also you can swap a 996 3.4 or 3.6 into a boxster, bolts right up. Renn27 builds V6 powered 996s, bolts right up. You can swap a 4.2 for a 2.7 V6 in any Audi, right? Therefore a 4.2 should bolt right up to a 996 transmission, right? Well, it doesn’t. I bought a 2001 996 tip transmission and a 2004 A8 donor car. Guess what, they aren’t even close to bolting up. The 4.2 bh is way bigger. Here you can see the 4.2 spacer and how it almost swallows the 996 transmission. The 8 bolt pattern on the crank does match. The bolt circle for the A8 is around 14.25” and about 12.5” for the 996. What am I doing wrong? Is it that this particular 4.2 has a bigger bh than d2 or other 4.2s? I heard there was one 4.2 from the S6 that has a bigger bh but I thought all the others were the same. Someone shoot me please

MP4.2+6.0

C5 4.2 or D2 4.2 should be 5HP24A for either A or S versions. Basically the V8 tranny and A = AWD.

2.7T in the C5 A6 2.7T (or probably the S4 cousin of the era) was a 5HP19 or one of its variants. More broadly, the 5HP19 grouping was the typical V6 tranny whether blown or N.A.

No idea in bell housing fitments but the 5HP24 group had higher torque ratings so in turn a larger torque converter and therefore likely a larger bell housing makes sense.

See here for lots of fine print, applications, likely cross fitment, etc.: https://en.wikipedia.org/wiki/ZF_5HP_transmission

I think what a few people may have done is put a 5 speed factory MANUAL from a 2.7T into a 4.2 to go from the mandatory auto in a stock 4.2 to a stick. The final drive ratios have to be dealt with too in any AWD scenario, so those likely got into rear diff transplants alongside. You couldn't drop a 4.2 motor into a 2.7T either because the C5 4.2 was specifically fit with a front clip that was not just 4.2 fender flares but also a 3" stretch to fit the longer V8 block and accessory drives. It has been 15 years since I looked at 4.2 tranny stuff, but IIRC the final drive ratios varied from 2.7T--higher geared overall for the 4.2's IIRC to try to help the fuel economy a bit. Those are asides though; the starting point likely problem is a 5HP24 is just not a 5HP19 and 4.2's and 2.7T's varied in that way.

dvs_dave

They probably do bolt right up to a 996 with a manual transmission, but not an auto. Kind of an important detail to miss…..right?

carwhisperer

ah so you live in a world where an engine from a manual 996 won't bolt up to an automatic 996 transmission. But you don't really know anything relevant, right? I mean "probably" lol

dvs_dave

Yet you’re the one throwing all the parts, time and money before realizing nothing fits or works together. Way to go!

Probably best sticking with hotrods and ZZ Top dreams. Lol

carwhisperer

you are exactly right!