If the plan is to stay auto....

Grabbing a used diff with 3.42s and running it is the cost effective move.

Absolutely follow the advice above about also installing a new converter. But have it spec'd by a shop that knows how you are going to drive the car and what power combo you will run.

Then blower. The best of all worlds I had was a stock longblock and 10psi. Easy as stock to drive around town (M6 btw) and enough power on tap to have fun. A small cam can wake that combination right up too.

Sidebar.... when it is all done, start setting aside funds for a transmission rebuild when the inevitable happens. Hopefully a long, long time from now.

 

thanks for the reply, yea originally I wanted an rpm unit, but you are right the cost effective way is a used one on ebay, assuming you get a good one, i haven't decided if I want a converter or not though...guess I have to do more research

 

Absolutely, in fact I would argue, swapping the gears in an A4 (assuming you have a 2.73), will make the car more fun and will support what ever power adder path you go with in the future. Only thing, if you are paying to have it done, there's some labor there to drop the cradle to do the swap and then you'll need to re-tune. You can drive the car after the swap but you need to stay below ~1/2 throttle until you get it re-tuned as the WOT shift points and such will be all outta cal for the new rear end ratio until you get your tune adjusted.

 

thanks, yes I have the 2.73 gears....I do have a shop ready to do the work, I have contemplated doing it myself, but we will see... i may just let them do it..
i still need to decideif i want to swap out the converter, guess that will be the next question for me going forward..... but thanks for the reply .

 

Honestly, why are you trying to go cheap on a rear gear. A stage 2 RPM is 2300 dollars. Your talking about supercharger and tune, 10,000 dollars, mild cam and supporting mods, heck throw some cylinder heads in there too. I don’t get it, you’re saving a 1,000 on a used 20+ year old rear diff, why???

And yes, if you’re doing a diff, most get a converter. They sell converters specifically for NA cars or supercharger cars or nitrous cars. You probably want a 3,000RPM converter with a supercharger. And you probably would want a 3.42 gear with a supercharger, any more gear then that and you might be blowing tires off through first and second gear.

Buy all new parts
Buy once, cry once.

 

Yea good point not really saving much, it would be good to know it's all new parts. .not sure if I will ever go the supercharger route once I do get the gears, but ya never know....I just want it to have a stock like feel, but I have never been in a car with a higher than stock converter so I have nothing to compare to.....maybe others can chime in on their brand and stall, and driving characteristics.

 

Modern day converters are nothing like they used to be. My yank SS3200 really drives like stock with the 3.73 gear. There is zero converter whine. I even road course my car once in a while, and the converter has no effect from a roll. From a dig, slamming my right foot through the floor, I’m instantly 3,000 RPM, that’s called flashing the converter. Or you can brake stall it, my combo doesn’t brake stall really well, car wants to go right away when you step on the gas.

As far as reliability, I think the yank3200 is by far the most reliable. People have been running that converter for 10+ years like @grinder11.

Top converter brands are
precision industries
Yank
Circle D

Most converters are around 1,000 dollars. Stick with a converter for a supercharger car around 3,000-3200RPM just in case you go that right in the future.

If your close to northern IL, you can check my car out if you want.

 

Thanks, thats great information...

 

I put 4.11's in my car before i supercharged. They were great, but the super is by far and away far, far, far better.

 

You could do this build a different route. Get the supercharger first, keep the 2.73 gears and stock converter and see how you like it.

Then go from there…

 

I was thinking about this originally but when Andy with A&A recommended the gears over the supercharger, which is wht their specialty is, it had me thinking......wondering if anyone out there has just done that mod with those gears and was extremely happy....

 

Blowers are more fun.

Anything preventing you from selling the car to get a stick model to build?
​​​​

 

It was a gift from my parents, thats the main reason,

 

I know that feeling, my auto was also inherited from my parents. I however cannot stand an auto to the point I am swapping it for a manual. That said gearing will make a HUGE difference especially running 2.73's. Mine has the optional 3.15 gears and it is a different animal than a 2.73 model. If not going FI I would go with 3.73's and the mentioned converter. Andy gave me the same advice BTW.

 

When changing the diff have them replace the shift cable and the fuel filter. When I did my mine 2002 I replace those parts super easy to get to when changing the diff.
I went from 2.73 to 3.15 and felt a nice change, looking back 3.42 if i did it again. At 82 mph my RPM is 2300 before the swap it was around 1900 at 82 mph.
So 3.42 would have given me better performance and still kept it nice on the highway.

 

 

sounds about right with the 3.15. At that speed with the 3.73, I think I’m at 2700-2800 rpm. I went 3.15 to 3.73. The 3.73 is so much fun, 1st and 2nd just rip. Wonder what a 3.90 with a 3600 stall would feel like???

 

@Dads2kconvertible actually it's the opposite! Lol!

I've run 4.11, 3.90 and 3.42 but all with manual transmission. I grenaded my second 4.11 diff and that was my deciding factor to go FI. Now my car has a 3.42 back in it with the supercharger. I have a spare 3.90 diff in my garage that needs clutch packs and my hardened output shafts installed. If I ever get around to it, the 3.90 is going back in the car. The 3.42 has really long legs in an M6 car. Which still sucks cruising out of my neighborhood and around town but a blessing when driving spiritedly.

If I were the OP in an A4 I'd do the diff swap to 3.42. Although I don't have an A4, I know many that do. And the 3.42 is a great upgrade when paired with a 2800 to 3200 converter. Especially if you'll mostly be street driving with an occasional trip to the drag strip.

Then once that becomes a snooze fest, which it will, drop the $ on the supercharger. Hopefully you don't get bored as quickly as I do. Or break parts like I used to. Both can get expensive quick. As mentioned above just bank some money for trans rebuild or replacement for when your A4 gives up the ghost. Until then enjoy the gear and much improved driving experience.

When you love your C5 and/or simply have sentimental value in it, like many of us do, modifying it is inevitable to peak continuous interest and pacify the desire for enjoyable power. Especially when many cars made today are wicked quick. But those other options likely won't be another gift from your parents.

 

this is a great response thank you for sharing your experiences, i thought i had made up my mind on the gears, but i think the supercharger is a one and done. I have alot to think about.....

 

IMO, get the 3.73 gear, so much fun, 1st and 2nd just rip, and my 3rd gear goes to 125mph with a 26.1 inch tire. Perfect drag gear.