Stock LFX-A6 optimum rearend ratio for drag racing

[67-LS1]

I’ve got an LFX/A6 from a 2013 Camaro in my 66 Chevelle and I’m getting ready to replace the original 3.07 rearend. The old one howls and it’s not posi.

I recently ran it in the quarter mile to see what it would do and I got a severely traction plagued 15.3 @ 96.83 mph. 60’ was 2.7. Quite embarrassing trying to get off the line with one tire spinning away.

My car weighs 3200 lbs (3400 with me in it), 1/2 tank, ready to run. I think I’d like to get a little deeper gear set but keep in mind I drive this everyday.

So what do you guys think would be a good ratio choice? The new rearend will be a 9” Ford.

And at what RPM should I be aiming for at the finish line? Current rear tires are 26.6” diameter.

[AlanRubin]

4.10s all the way, and LSD; or a locker if you're just dragging it. You can also try
and find a lunch-box locker for semi-daily. I am putting one in my Mustang. I only
run it 2-days a week, so...

I mean, you can go 4.50 gears+, but you won't be happy on the highways. You
won't be too happy with 4.10s either.

We can't know the RPM to aim for at the finish line. However, you don't
want to be too far past the toque peak, as it drops, then falls flat
at 6500 or so. The reason I say we really can't select a target RPM
is, tuned? Not tuned? So many factors will vary what your RPMs
will be at the finish line.

[67-LS1]

It’s bone stock other than being in a Chevelle. No tune. Street tires with a 400 compound. It probably has better a intake than a Camaro because I had lots of room to put an insulated CAI off in a corner. Probably better exhaust too since I’m running only 1 Cat per side. And I’m pretty light compared to a Camaro.
Wow, I would not have guessed 4.10. I was thinking of stepping up to 3.35 or 3.50. On my traction plagued run I never made it out of 3rd gear. I think the posi will help the most. I would definitely use 4th gear with 4.10s.
I’m ordering the rearend as soon as I get home in 12 days.
Decisions, decisions.
Am I correct in assuming that I don’t want to hit 5th gear (OD) in the 1/4 mile?
Unrelated to the rear end, I’m super hesitant about getting a tune. I don’t know anyone near me and I’ve heard stories of guys really screwing things up. How much power is there to be gained? And what should a complete tune cost and should it be done with a Dyno?
Thanks

[AlanRubin]

For street use, you usually go up 10% of what the current ratio is.
So, 3.07 + .37 is 3.54, well, since there probably isn't one, you'd go 3.50 to 3.73

If you are using the 6L50, you run it through every gear to the finish. There is
no OVER DRIVE, just 1-6. Also, the V6 trans has a steep 1st gear for launching.
You at least want the 3.27 gearing that the 10-11 Camaro V6 has. However,
your title specifically says DRAG RACING, so 4.10 would be that go to gear for
DRAG racing.

With the 6L50, lockup is used from 2 all the way to 6, so you will have no slip
in the trans when you are accelerating. You won't need to limit any gear, just
floor it and go.

You'll want an LSD in that car's diff, for posi traction.

As far as tuning; if you're looking for every bit if HP you can squeeze out of it, then
it's worth it. CAI will also help with the tune. hand held tuners with the built in ones
won't give you the best results.

Also, the LFX Engine uses the Delphi ECU, easier to tune than the 10-11 with that
shit Bosch ECU. You can also increase shift firmness with the tuner.

How are you running the A6 in this car without a tuner now? The gear ratio is wrong
for that transmission, and it should not be running anyway. Not sure exactly what you
are doing to keep the car from going into limp mode with the wrong rear gearing.
It's not an issue for the M6, but is for the A6...

[67-LS1]

Well I guess I am a little “tuned”. I should have stated no “performance tuning”. I did have a guy change the rear end ratio and delete all the faults that would turn on the MIL that were not applicable to my car. Things like fuel tank pressure, traction control, etc. I’m not even sure of them all.
But he never saw the car. I just shipped the ECM to him.
I have to assume that any mph data the ECM receives is from the transmission because I have no speedo and nothing else that measures road speed. Had I not had the ratio corrected what issues would I have experienced? I can’t think of any use for mph data other than internal for the ECM.
I assume when I change rear end ratios I’ll have to send it back to the same guy? Which is a pain because he’s in New York and I’m in California. I’ve heard that only one guy can tune it once it’s been tuned the first time? Is this true?
So my question was what’s the optimal ratio for drag racing and I appreciate the 4.10 answer. I’ll probably go with the 3.50 though. I couldn’t of imagined it being that high and it is a daily driver first with a very occasional trip to the strip.
I also didn’t realize the 6L50 locked up in 2-6. Good to know. I thought I should avoid the OD gears for being weaker and dropping any torque multiplication even lower.

[AlanRubin]

Yep, Lockup starts in 2nd:

If you change the gear ratio, yes it will need tuned again.

You could say that O/D begins in 5th, but there is no O/D selector, or
method to turn it off. In my Mustang, I have an O/D switch, the Camaro
does not.

You will get solid acceleration from 1-6 at WOT on the highway.

These have a separate TCM, built into the solenoid pack.

ALL communications between the TCM and ECU is GMLAN.




The way the TCC is applied, you don't even notice it. However, you can
if it's cold, if you're holding a gear. Then, once the car reaches operating
temp, you will see the RPM drop when the TCC is applied. I run mine ALL
year. So, when I leave the house, I will be in 4th going up the highway,
slight incline, then the RPMs will drop while still in 4th. Right there is when
the TCC was applied.

Also, you can hold the gear easier in "M" with the paddle shifters, but I
know the car well, so I know when the TCC applies when it's warmed up.
From then on, you don't even notice it.

[67-LS1]

I’m getting way off topic here and it may be better in another post where interested people might more easily find it but here goes…

I do not have paddle shifters. I don’t even have manual control of the transmission. Just P-R-N-D. There is one more click back with the shifter but I’ve never used it. It’s from the original Powerglide with the stroke (throw) modified to match the 6L50.

Everything works great for my daily driving but I would like to be able to control the transmission manually. But I’m not running a BCM and I’m under the impression that the manual control of the transmission goes through the BCM. Is that correct? It looks like it might be pin 7 on the transmission plug. This must be the GMLAN from the BCM through the ECM to the TCM.
Are you aware of any work arounds? Someone told me you could download a certain vintage Corvette calibration but that may not be applicable with my V6.

[AlanRubin]

You would not have manual control over the trans without the paddle shifters.
One more click down for the 6L50 is "M"anual mode. Originally, in that Chevelle, was
"L".

Yeah, the paddles go to the BCM:
Left switch has one resister.
Right switch has two resisters.
->The resistance values are what determines UP and DOWN shift.
Both switch outputs go to pin 21 on the X3 BCM connector...
BCM is on GLMAN, so the transmission TCM will get those signals from there.


Page 410 of the Camaro PDF service manual.
https://kvisit.com/Qg/ub8B

[67-LS1]

I have to ask, where are you getting these drawings? I bought the 2013 Camaro service manual from Helms. It’s 4 volumes each about 2” thick and there are no drawings as clear as these.
I might have heard that the 2013 manual set was so bad because it was a transition year between two formats. I’m not 100% sure of that but it’s not an intuitive manual. The few drawings you have provided are much more clear.

[AlanRubin]

I have a PDF for 10-11, but it's mostly the same from then on. There are very little
changes from 12 to 13, and 14 to 15 is cosmetic. There is nothing that you can't
use between the model years, on older years. The Chassis is the same, and the
rear cradle is the same, and the front K-member is the same. I am almost all 2015
suspension now. In fact, I just bought a 2015 SS rear cradle with EVERYTHING
except the Brembo calipers. So I will have plenty suspension parts to sell once
it's on. All I need now, is the rear section of the SS or any manual drive-shaft.

I also have the ATSG 6L50 Manual.

[67-LS1]

I’ll have to see if I can find a set of 10-12 manuals to compare because the 13 set I have are a disaster.

[AlanRubin]

The link to that PDF is in the forums somewhere, that is how I downloaded
it.