jim993

Anybody have experience with 3.73 rear gears, A4 on a road course track?

I track the car a couple of times a year but have developed a whine in the stock 3.15 gears plus broke one or both Bellville preload springs in the differential.

I'm considering going to 3.73 on the new rear end, with a WaveTrac differential.

v98roadie

No track experience, yet but, the 3.73 gears make the A4 perform like it should have from the factory. Acceleration and performance are outstanding yet the car is still a great all around street machine. No downside other than a loss in fuel economy.

jim993

Thanks for that input.

radar502

I think a 390 is even better , not as low as one would think. The 390 will wake up the LS it likes top anyway and puts it right there right now . More bank for the buck and driving about the same but when you gas it goes right now ..

v98roadie

I was running around this weekend and a guy pulls up next to me in a C6. We had a long stretch of flat open road in front of us. He took off and was very surprised an A4 C5 could stay with him. Ultimately I am sure the C6 would have pulled away but the C5 with 3.73 gears will surprise a lot of folks. The 3.90's might be even better for the track. It makes a huge difference.

jim993

Even with the 3.15's, the A4 gains on straights during the time others are shifting their manual transmissions. The A4 keeps pulling right through the shift and that is where I can gain a little. Plus there seems to be no danger of trailing throttle oversteer with the A4.

Top speed is not a factor, I am only just above 110 on the longest straight at Laguna Seca before having to brake for turn 2.

Great for an old guy like me.

On the other hand, I have a DeWitts radiator, auxiliary trans cooler and B&M finned aluminum trans pan just to keep the A4 cool.

Thanks for the input.

BlackbirdXX

I went 373s, yank 3800 Dual Lockup and Sonnex 6 pinion 2.84 instead of the 390s took forever to tune but I really like the combo. Like to hear when and if you decide to use the WaveTrac how you like it. I went with the Dynotech Stage IV Pro who use the Quaife carrier unit, I need to brace it this summer (ran out of cash on the trans/rear upgrades) Personally I would say use the 390's if your A4 is 3.06/1.63