berk4422

Two mods on my list that I am considering for my 2007 A6 LS2:
1) Change from 2.56 to 3.15 gears
2) Add LPE Heads to complement a GT11 Cam (+20~25 HP)

Wondering if anyone has any regrets on the Gear swap?

My intended use is for street driving mostly around town and the occasional road trip. Car sees road tracks a few times a year. Currently putting down 400 RWHP.

Keith Tedford

With our 2005 six speed, we are running the stock 3.42 gears and they are great and I have run slightly over 35 mpg (Imperial) over a 200 mile run. If you want to go drag racing. 3.90s are great and would work fine on the street too with the deep sixth gear. Autos may be a little different animal. I put close to 200K miles on my old COPO Chevelle and it had 4.10s and no overdrive. About the only damage the gears did was to my wallet with the amount of gas the car went through. 10-12 mpg (Imperial).

23/C8Z

with a cam change can't go wrong moving up in rear ratio imo.... best of luck. i too would make that change if a 3.15 rear was local to me for decent price..

j_digi454

Looking to do this change as well, hopefully their is some good knowledge/advise on this swap.

dbratten

I changed to 3.15 gears in my '06 C6 A6 four years ago when I decided I needed a better differential than OEM. I had an OSGiken installed and changed the gear ratio at the same time. I made both changes to give me better performance for autox, primarily, and the better diff for HPDE as well.

The 3.15s give me the lower gearing I want to mainly use 2nd gear on smaller autox courses in much the same way as a Z51 M6 car. But, for me, this is all that I gained with the gear change. I don't feel the car is any faster on the street or for HPDE even though the sensation of speed is improved. I am just a gear lower than before.

I always use the paddles to control my gear selection and know that with this change I need to shift more often. First gear is rarely used. For instance, 3rd gear with the 2.56 allows me 129 mph where 3.15 allows only 105 mph.

I do not drag race and cannot say if the gearing makes a verifiable time difference as some have reported.

For autox, I am pleased with the 3.15 gears, but, less so elsewhere.

--Dan

HOXXOH

Pros: quicker acceleration response in the lower gears

Cons: fuel economy, extra wear on transmission

It has been tested/confirmed that a 2.56 to 3.42 swap is good for .10 seconds in the 1/4 mile, so a 3.15 should show about a .07 second improvement.
WOT shifts from 3rd to 4th are the weak link in the transmission. For most people that's not a concern, but those with higher HP mods should be aware and drive accordingly.

For drag racing, a higher stall converter will easily out-perform a gear change and do it for about half the cost.

berk4422

Guys, great responses, makes me glad I decided to seek advice before pulling the trigger. Also, glad I'm not the only one considering the impact of the swap.

Main take-away's from Dan's and HOXXOH's comments, based on my intended use, are:

"The gears won't make the car faster, even though the sensation of speed is improved"
I translate this to my 40 to 80 time will not improve with gears (validation of this assumption would be appreciated).
But also noted, "so a 3.15 should show about a .07 second improvement." I'm assuming this is really a result of the improved 60ft by reaching the power band quicker? So, perhaps my zero to 60mph time may have an imperceptible improvement of less than a 10th of a second?

"2.56 allows me 129 mph where 3.15 allows only 105 mph" & "WOT shifts from 3rd to 4th are the weak link in the transmission."
I translate this to a possible set-up for earlier Transmission failure. My two local tracks have straights that take me up to 130 at WOT. This would require the 3-4 shift at WOT. I could have upwards of 30 of these hard shifts in a single track day. I always heard that the 4L60E was rock solid, maybe not so solid? "those with higher HP mods should be aware and drive accordingly" Currently at 400rwhp, will top out at 430rwhp with current build plan.

"For autox, I am pleased with the 3.15 gears, but, less so elsewhere"
For AutoX at lower speeds you're higher in the powerband, whereas with HPDE and driving around town you just happen to be one gear higher.

I'm getting the signals that the gear swap may be less attractive than doing the heads and getting up to 25 more HP at the rear, with less risk to the transmission.

Thanks again, please correct me if I misinterpreted.

HOXXOH

4L60E was only in '05 and by higher HP, I meant 500+. You can always bump the rev limiter a taste if you're hitting it near the 130 MPH area in 3rd, assuming the cam and springs will handle it.

You might consider LS3 heads as a low priced alternative. IIRC, they're around $600 new, including valves. Check with your local dealer.

j_digi454

Thanks!

el es tu

what about a 3.75?

Youd have about a 200mph top speed in 6th and would maximize acceleration in all gears.

Some folks say the car wont hook up but all youd do is change the engine torque management profiles per gear to limit the torque (VERY easy to do) so the car isnt spinning tires through the first 3 gears... you can do this by gear and rpm, so you could limit the torque at lower rpm and bring it up through the rev band as you please. Then you could raise the torque profile as you go higher up in gears.

While I havent regeared my car yet, I have played with these profiles and you can even make it work like a crude launch control. Also if you like driving without active handling (which requires you to disable the traction control first) but want some traction control for the rain this will work for that too. This is a technique used in various forms of motorsport including formula 1.

Ragtop 99

^^^ Drive around in 5th gear for a while on the highway and see if you are ok with the higher rpms. 6th gear with 3.73s would turn slightly higher RPMs than 5th gear with 2.56 gears. Around town the car will be more responsive, but it may not be as pleasant on a long road trip.

subfloor@centurytrans

Please elaborate on what you're referring to with "change the engine torque management profiles per gear to limit the torque" as I'm almost positive it can't be done.

subfloor@centurytrans

Uhh, not quite.

The car will feel faster with a higher gear ratio because it is faster. While I don't autocross my car, I've got plenty of timeslips from the dragstrip to back this up.

As for higher gears putting more stress on the transmission I'm not quite sure where that myth comes from but it's not true. The only minor exception to this is regarding the 3-4 shift at WOT because of those particular clutches being the weak link in the 6L80, but if the transmission is tuned properly and you stay under 550rwhp it'll last quite a while. Apart from that, higher gears won't have any effect on the transmission.

I speak from direct experience with this because I bought my friend's 2007 that had a cammed LS2, 3.42 Z06 diff, 3600 stall and would run 10.8's without fail, all the while with torque management having been turned off for almost 50K miles. Even with over 80K on the transmission it still shifted perfectly every time and it wasn't until I swapped in an LS7 that it started acting up on me. Deciding to play it safe since racing season was almost over at the time, I went ahead and had it rebuilt with upgraded Alto clutch packs. The tech who tore it down for me was surprised at how well everything had held up, especially given the miles and several hundred passes at the track.

el es tu

The tables on the upper left hand side of the engine torque management tab. There's one set of tables that only go to 3000 rpm and then one table that includes the entire rev range for each gear.

You can really manipulate how the car takes off with adjusting this to the tires you're running or even weather if you wanted to run separate tunes to get the most out if it...

subfloor@centurytrans

Been there, done that - in theory it should work but in practice it does not.

Just like sooooo many other things in HP Tuners that simply don't work as expected, this too falls into that category. I experimented with this a few years ago and had zero success with it no matter what I set any of the values to.

I even tried setting all the Brake Torque Limit to almost zero values once (which in theory should have acted as launch control) but ended up being able to launch at whatever RPM I wanted to, up to the limit of what my front brakes would hold.

el es tu

As a test I scaled it down to a max 250 on 1st, drove it for a day, and could tell it felt extremely bogged down so I know there's got to be something to it...

As far as launch control goes it really just helps the car take off cleaner; still going to have to pick an rpm and torque value to hold it to before moving

Maybe it only works with certain tables and within a certain range of torque values (ie no extremes)?

I'm going to have to look at retesting it with no engine tqmgmt again.

HOXXOH

Did you buy Mike G's car? If so, I guess calling him to go to Sacramento this winter won't have a good result.

subfloor@centurytrans

Yeah, back around Easter. The LS2 gave up the second time I took it to the track so I put in one of my "spare" LS7s and then had the transmission rebuilt.

He talks about coming up here to race with it so you might talk him into it.

dbratten

I am interested to know how much you gained with just the gear change. Do you have times comparing the 2:56 vs. 3:15 with that being the only modification? I can't really tell as I also put in the OSG diff with the 3:15s and I expect most of my improvement came for that.

--Dan

subfloor@centurytrans

Yeah, I've gone from 3.42 to 2.56 and then back again on two separate occasions. In both cases the ET difference was right around a tenth. The gains you see from the gear change are partially offset by having to make the 3-4 shift, which you don't have to do with 2.56s.