Transmissiion

[klaptrapper]

Has anyone had any work done to "tighten up" the V's transmission?
I love the car, but the tranny seems only one step away from the old Dynaslush buick. It is neat to be able to control the shift points with the selector, but downshifts especially are slow and unpredictable. Upshifts somewhat better.

Thanks,
Rusty

 

[richardyoo]

I've been working with Chuck of Corvettes of Westchester on mine... his first tune was miles better than stock... firmer shifts and significantly less slop between gears... still not quite perfect, but MUCH better.

He's not far from you - you should check him out.

 

[klaptrapper]

Thanks, Richard. When I get back to NY in the spring, I shall schedule time with him, for sure. Please keep me abreast of any further progress you make with the transmissiion. In my opinion the most significant shortcoming of the car.

Rusty

I've been working with Chuck of Corvettes of Westchester on mine... his first tune was miles better than stock... firmer shifts and significantly less slop between gears... still not quite perfect, but MUCH better.

He's not far from you - you should check him out.

 

[richardyoo]

He also does a rear-end 3.42 gear swap that increases power to the wheels with a slight MPG compromise... I'm considering it after seeing this:

http://www.youtube.com/watch?v=AWxWvy76VyE

more here:

http://forums.corvetteforum.com/c6-...-rear-end-a6-attack-package-jump-in-here.html

 

[richardyoo]

Looks like there isn't much of a MPG change after doing some reserach... the RPM is a little higher than before after the 3.42 swap, but since the engine is under less load its probably a wash on mileage... we'll see

 

[klaptrapper]

Gearing

Richard, the rear axle ratio of our cars is 2.56 to 1. Replacing it with a 3.42 would be a 33% increase of rpm per mile. Since speed is linear it would result in a 1/3 reduction in top end, since our top end is limited by the engine management computer, it is hard to tell, but it would yield probably a top end of somewhere near 110 -115 mph. Further our gas mileage would reduce by about 1/3 or be somewhere in the neighborhood of 10 mpg on the highway.
The car would be very fast in the quarter mile and probably red line at the stripe in 5th. But I wouldn't want to drive it on the street.

The corvette probably has a stock ratio in the low 3's, or thereabouts, so the jump to 3.45 isn't so great, yielding the results the article proclaims.
Just be careful to research actual results with our cars, before making such a costly mod.

Just my 2c

Rusty

Looks like there isn't much of a MPG change after doing some reserach... the RPM is a little higher than before after the 3.42 swap, but since the engine is under less load its probably a wash on mileage... we'll see

 

[richardyoo]

Richard, the rear axle ratio of our cars is 2.56 to 1. Replacing it with a 3.42 would be a 33% increase of rpm per mile. Since speed is linear it would result in a 1/3 reduction in top end, since our top end is limited by the engine management computer, it is hard to tell, but it would yield probably a top end of somewhere near 110 -115 mph. Further our gas mileage would reduce by about 1/3 or be somewhere in the neighborhood of 10 mpg on the highway.
The car would be very fast in the quarter mile and probably red line at the stripe in 5th. But I wouldn't want to drive it on the street.

The corvette probably has a stock ratio in the low 3's, or thereabouts, so the jump to 3.45 isn't so great, yielding the results the article proclaims.
Just be careful to research actual results with our cars, before making such a costly mod.

Just my 2c

Rusty

It looks like you have 4 concerns:

1. Reduction in fuel economy
2. Limited top end speed
3. Drivability
4. Cost

I did a significant amount of the research on this - you are technically accurate, but the real world data is not consistent with the math.

** Reduction in fuel economy

First off - gas mileage is not as impacted as you'd think... this was my first assumption as well - great minds think a like. But what I've learned is that since the gearing is lower, there is less load on the engine... In that, with the taller gears it becomes easier to turn the input on the diff... so yes, the RPM is higher, but it uses less fuel to do it... real world expereince from drivers who have 3.42 gears in their A6 vettes all report no change in MPG or slightly improved MPG. Less load on motor equals less fuel used. (which is why when you put the car in neutral and run the engine at 2k rpm it uses less fuel than when you are driving and have the car at 2k rpm with 2 people and a trunk full of luggage... same RPM but different loads on the engine)

This is also why your MPG goes down when you put larger rolling-diameter tires on a car... the drivetrain load increases bringing MPG down despite the fact that RPM went down... put on smaller rolling-diameter tires on and your MPG will increase - despite the face that the RPM goes up...

I agree that its a bit counter-intuitive but thats whats happen in real-world.

** Limited top end speed

The A6 c6 and the XLR have the same A6 transmission... the 4L80e.

The A6 C6 cars also have the same diff as the XLR with 2.56 gears (the C6 Z51 also has an uncommoon 2.73 gear option).

The XLR-V and the A6 C6 cars do NOT have the same torque converter. The A6 has an 11inch converter with a single plate TCC... the XLR-V has a 10.5" with a dual-plate TCC. The translates into a different stall rpm and a more durable TCC so it can handle more tq - which makes sense since the XLR-V is blown and has a flat tq curve and the typical A6 C6 is naturally aspiraed with a typical sweeping tq curve.

The vette M6 and the vette A6 do not have the same rear end gearing nor the same gear ratios between shifted gears... additionally the A4 and the A6 do not have the same gearing between shifted gears - they are as follows:

The effective gearing ratio with the various diff gears is the following:

When doing the math, you will see what the RPM speed is at various speeds with stock gears on the A6:

RPM	1st	2nd	3rd	4th	5th	6th
500	3.80	6.47	9.97	13.27	17.95	22.77
600	4.55	7.76	11.97	15.92	21.54	27.33
700	5.31	9.05	13.96	18.58	25.13	31.88
800	6.07	10.34	15.96	21.23	28.72	36.44
900	6.83	11.64	17.95	23.88	32.31	40.99
1000	7.59	12.93	19.95	26.54	35.90	45.55
1100	8.35	14.22	21.94	29.19	39.49	50.10
1200	9.11	15.52	23.94	31.84	43.08	54.66
1300	9.87	16.81	25.93	34.50	46.67	59.21
1400	10.63	18.10	27.92	37.15	50.26	63.77
1500	11.39	19.40	29.92	39.81	53.85	68.32
1600	12.15	20.69	31.91	42.46	57.44	72.88
1700	12.91	21.98	33.91	45.11	61.04	77.43
1800	13.66	23.28	35.90	47.77	64.63	81.99
1900	14.42	24.57	37.90	50.42	68.22	86.54
2000	15.18	25.86	39.89	53.07	71.81	91.10
2100	15.94	27.16	41.89	55.73	75.40	95.65
2200	16.70	28.45	43.88	58.38	78.99	100.21
2300	17.46	29.74	45.88	61.04	82.58	104.76
2400	18.22	31.03	47.87	63.69	86.17	109.32
2500	18.98	32.33	49.87	66.34	89.76	113.87
2600	19.74	33.62	51.86	69.00	93.35	118.43
2700	20.50	34.91	53.85	71.65	96.94	122.98
2800	21.26	36.21	55.85	74.30	100.53	127.54
2900	22.02	37.50	57.84	76.96	104.12	132.09
3000	22.77	38.79	59.84	79.61	107.71	136.65
3100	23.53	40.09	61.83	82.26	111.30	141.20
3200	24.29	41.38	63.83	84.92	114.89	145.76
3300	25.05	42.67	65.82	87.57	118.48	150.31
3400	25.81	43.97	67.82	90.23	122.07	154.87
3500	26.57	45.26	69.81	92.88	125.66	159.42
3600	27.33	46.55	71.81	95.53	129.25	163.98
3700	28.09	47.85	73.80	98.19	132.84	168.53
3800	28.85	49.14	75.80	100.84	136.43	173.08
3900	29.61	50.43	77.79	103.49	140.02	177.64
4000	30.37	51.72	79.78	106.15	143.61	182.19
4100	31.12	53.02	81.78	108.80	147.20	186.75
4200	31.88	54.31	83.77	111.46	150.79	191.30
4300	32.64	55.60	85.77	114.11	154.38	195.86
4400	33.40	56.90	87.76	116.76	157.97	200.41
4500	34.16	58.19	89.76	119.42	161.56	204.97
4600	34.92	59.48	91.75	122.07	165.15	209.52
4700	35.68	60.78	93.75	124.72	168.74	214.08
4800	36.44	62.07	95.74	127.38	172.33	218.63
4900	37.20	63.36	97.74	130.03	175.92	223.19
5000	37.96	64.66	99.73	132.69	179.52	227.74
5100	38.72	65.95	101.73	135.34	183.11	232.30
5200	39.48	67.24	103.72	137.99	186.70	236.85
5300	40.23	68.54	105.71	140.65	190.29	241.41
5400	40.99	69.83	107.71	143.30	193.88	245.96
5500	41.75	71.12	109.70	145.95	197.47	250.52
5600	42.51	72.41	111.70	148.61	201.06	255.07
5700	43.27	73.71	113.69	151.26	204.65	259.63
5800	44.03	75.00	115.69	153.91	208.24	264.18
5900	44.79	76.29	117.68	156.57	211.83	268.74
6000	45.55	77.59	119.68	159.22	215.42	273.29
6100	46.31	78.88	121.67	161.88	219.01	277.85
6200	47.07	80.17	123.67	164.53	222.60	282.40
6300	47.83	81.47	125.66	167.18	226.19	286.96
6400	48.59	82.76	127.66	169.84	229.78	291.51
6500	49.34	84.05	129.65	172.49	233.37	296.07
6600	50.10	85.35	131.64	175.14	236.96	300.62
6700	50.86	86.64	133.64	177.80	240.55	305.18
6800	51.62	87.93	135.63	180.45	244.14	309.73
6900	52.38	89.23	137.63	183.11	247.73	314.29
7000	53.14	90.52	139.62	185.76	251.32	318.84
7100	53.90	91.81	141.62	188.41	254.91	323.40
7200	54.66	93.10	143.61	191.07	258.50	327.95
7300	55.42	94.40	145.61	193.72	262.09	332.50
7400	56.18	95.69	147.60	196.37	265.68	337.06
7500	56.94	96.98	149.60	199.03	269.27	341.61

And here they are with 3.42 gears:

RPM	1st	2nd	3rd	4th	5th	6th
500	2.84	4.84	7.47	9.93	13.44	17.05
600	3.41	5.81	8.96	11.92	16.12	20.46
700	3.98	6.78	10.45	13.90	18.81	23.87
800	4.55	7.74	11.94	15.89	21.50	27.28
900	5.11	8.71	13.44	17.88	24.19	30.69
1000	5.68	9.68	14.93	19.86	26.87	34.09
1100	6.25	10.65	16.42	21.85	29.56	37.50
1200	6.82	11.62	17.92	23.84	32.25	40.91
1300	7.39	12.58	19.41	25.82	34.94	44.32
1400	7.96	13.55	20.90	27.81	37.62	47.73
1500	8.52	14.52	22.40	29.80	40.31	51.14
1600	9.09	15.49	23.89	31.78	43.00	54.55
1700	9.66	16.46	25.38	33.77	45.69	57.96
1800	10.23	17.42	26.87	35.76	48.37	61.37
1900	10.80	18.39	28.37	37.74	51.06	64.78
2000	11.36	19.36	29.86	39.73	53.75	68.19
2100	11.93	20.33	31.35	41.71	56.44	71.60
2200	12.50	21.29	32.85	43.70	59.12	75.01
2300	13.07	22.26	34.34	45.69	61.81	78.42
2400	13.64	23.23	35.83	47.67	64.50	81.83
2500	14.21	24.20	37.33	49.66	67.19	85.24
2600	14.77	25.17	38.82	51.65	69.87	88.65
2700	15.34	26.13	40.31	53.63	72.56	92.06
2800	15.91	27.10	41.81	55.62	75.25	95.47
2900	16.48	28.07	43.30	57.61	77.94	98.88
3000	17.05	29.04	44.79	59.59	80.62	102.28
3100	17.62	30.01	46.28	61.58	83.31	105.69
3200	18.18	30.97	47.78	63.56	86.00	109.10
3300	18.75	31.94	49.27	65.55	88.69	112.51
3400	19.32	32.91	50.76	67.54	91.37	115.92
3500	19.89	33.88	52.26	69.52	94.06	119.33
3600	20.46	34.85	53.75	71.51	96.75	122.74
3700	21.03	35.81	55.24	73.50	99.44	126.15
3800	21.59	36.78	56.74	75.48	102.12	129.56
3900	22.16	37.75	58.23	77.47	104.81	132.97
4000	22.73	38.72	59.72	79.46	107.50	136.38
4100	23.30	39.69	61.21	81.44	110.19	139.79
4200	23.87	40.65	62.71	83.43	112.87	143.20
4300	24.43	41.62	64.20	85.42	115.56	146.61
4400	25.00	42.59	65.69	87.40	118.25	150.02
4500	25.57	43.56	67.19	89.39	120.94	153.43
4600	26.14	44.53	68.68	91.37	123.62	156.84
4700	26.71	45.49	70.17	93.36	126.31	160.25
4800	27.28	46.46	71.67	95.35	129.00	163.66
4900	27.84	47.43	73.16	97.33	131.69	167.06
5000	28.41	48.40	74.65	99.32	134.37	170.47
5100	28.98	49.37	76.15	101.31	137.06	173.88
5200	29.55	50.33	77.64	103.29	139.75	177.29
5300	30.12	51.30	79.13	105.28	142.44	180.70
5400	30.69	52.27	80.62	107.27	145.12	184.11
5500	31.25	53.24	82.12	109.25	147.81	187.52
5600	31.82	54.21	83.61	111.24	150.50	190.93
5700	32.39	55.17	85.10	113.22	153.19	194.34
5800	32.96	56.14	86.60	115.21	155.87	197.75
5900	33.53	57.11	88.09	117.20	158.56	201.16
6000	34.09	58.08	89.58	119.18	161.25	204.57
6100	34.66	59.04	91.08	121.17	163.94	207.98
6200	35.23	60.01	92.57	123.16	166.62	211.39
6300	35.80	60.98	94.06	125.14	169.31	214.80
6400	36.37	61.95	95.55	127.13	172.00	218.21
6500	36.94	62.92	97.05	129.12	174.69	221.62
6600	37.50	63.88	98.54	131.10	177.37	225.03
6700	38.07	64.85	100.03	133.09	180.06	228.44
6800	38.64	65.82	101.53	135.08	182.75	231.85
6900	39.21	66.79	103.02	137.06	185.44	235.25
7000	39.78	67.76	104.51	139.05	188.12	238.66
7100	40.35	68.72	106.01	141.03	190.81	242.07
7200	40.91	69.69	107.50	143.02	193.50	245.48
7300	41.48	70.66	108.99	145.01	196.19	248.89
7400	42.05	71.63	110.49	146.99	198.87	252.30
7500	42.62	72.60	111.98	148.98	201.56	255.71

As you can see - given enough power, the A6 trans with 3.42 gears an easily go north of 200mph.

As for the ECM limiting speed - my XLR-V had that removed years ago... but once the TCM and ECM are recalibrated with the diff gear swap (which you is required) the computers will have no problem with the new gears, even if you still have the 155mph limiter in place.

** Drivability

From everything I've researched - driveability hasn't changed much... in fact, most people (if not all) did not even notice a difference going from the 2.53 gears to the 3.15... and everyone suggests not bothering with a 2.53 -> 3.15 swap and just going directly to a 3.42...

Everyone describes the 3.42 swap as incredibly fun to drive... but really insignificant at the track - since going to a 4.10 or higher gear is really where you get significant improved #'s at the track.

So if doing a 3.15 swap yields not much of a difference, I can only believe that the 3.42 will also not change the driving characteristic much.

** Cost

People are also reporting lower failure rates with a diff-swap vs any other performance improvements. Mainly do to the fact that:

1. It lowers engine load so the engine, torque converter, and transmission are all under less stress
2. Its an incredibly simple modification - its just a gear swap... no high boosting the engine, no larger fuel injectors, etc...

Additionally, I can't think of anything else that is really less than a couple of grand in terms of cost when doing a major upgrade... Even the Corsa cat-back exhaust is about $1500 - and the dyno proved that I didn't get much for it... The Stage 2 intake kit from D3 also isn't cheap - let alone their one-thousand dollar pulley swap they have... Hell, I spent more on new tires than what this gear swap will cost (buying and mounting Michelin PS2's aren't cheap )

So in relative terms this upgrade isn't all that expensive.

So you get a quick power upgrade with no additional stress on your engine. Sounds like a win-win to me.

I'm open to hearing any more feedback - but all signals point to GO on this... but I'd love to hear something to the contrary - I'd hate to get a case of buyers remorse after the fact.

 

[klaptrapper]

Gearing

Wow! I am impressed by the amount of research you have done on this issue.
Let me add just one more set of facts, which were imperically derived.

I had a '90 ZR-1 for 10 years (My son has it now). The car came with 3.45 gears. My typical 1/4 mile times were 13.5 secs at 108 MPH in 3rd gear at the stripe with those gears and scuff street tires. My interstate fuel mileage was 28 mpg down I-95 from Virginia to Florida. Corsa and injector housing cleanup the only perf. mods. The downside was 6th gear was unuseable, except on the freeway. The LT5 engine is superbly tractable, but 6th is a long stretch from 5th with that ZF trans.

I swapped the rear gearset to Dana 44's at 4.11. .(Viper gears) This required a shift to 4th in the quarter mile, and the 200 ms shift time yielded the exact same trap times +/-. my interstate fuel mileage dropped to 23, same trip (an annual migration). I never tried max speed comparison, but I've been told top speed drops from 178 mph to 156 mph. 6th will still not pull higher speed with an essentially stock motor. 6th gear on that car is a looooooooooooong reach from 5th. That is why the 24 hour record that car held for 10 years was done in 5th gear. That was averaging 176 mph for 24 hours all stops included, for fuel, etc.
But with the 4.11's, 6th gear was now useable and enjoyable at local highway speeds.
3.45 to 4.11 is 19% ; 28 mpg to 23 mpg is 17.8 % Close enough for gvt work...........ha.

Anyway, Let us all know how you likem after you getem!! Always interested in improvements.

Rusty

 

[richardyoo]

Wow! I am impressed by the amount of research you have done on this issue.
Let me add just one more set of facts, which were imperically derived.

I had a '90 ZR-1 for 10 years (My son has it now). The car came with 3.45 gears. My typical 1/4 mile times were 13.5 secs at 108 MPH in 3rd gear at the stripe with those gears and scuff street tires. My interstate fuel mileage was 28 mpg down I-95 from Virginia to Florida. Corsa and injector housing cleanup the only perf. mods. The downside was 6th gear was unuseable, except on the freeway. The LT5 engine is superbly tractable, but 6th is a long stretch from 5th with that ZF trans.

I swapped the rear gearset to Dana 44's at 4.11. .(Viper gears) This required a shift to 4th in the quarter mile, and the 200 ms shift time yielded the exact same trap times +/-. my interstate fuel mileage dropped to 23, same trip (an annual migration). I never tried max speed comparison, but I've been told top speed drops from 178 mph to 156 mph. 6th will still not pull higher speed with an essentially stock motor. 6th gear on that car is a looooooooooooong reach from 5th. That is why the 24 hour record that car held for 10 years was done in 5th gear. That was averaging 176 mph for 24 hours all stops included, for fuel, etc.
But with the 4.11's, 6th gear was now useable and enjoyable at local highway speeds.
3.45 to 4.11 is 19% ; 28 mpg to 23 mpg is 17.8 % Close enough for gvt work...........ha.

Anyway, Let us all know how you likem after you getem!! Always interested in improvements.

Rusty

Thats interesting data.

Well - some things to note in difference is that first we're talking about the XLR's A6 here... not manual... and you were moving from 3.45 to a 4.10... whereas we're moving from 2.56 to a 3.43... So really we're moving closer to your stock 90 ZR1 config - not going beyond it...

One could also argue that the gear shiftpoints on the C4 ZR1 are very different than they are on the A6... if we assume that the C4 ZR1 gearing is similar to the C6 ZR1 - then you're 1:1 at 4th... but on the A6 at 4th you're at 1:1.15 when the TCC is locked up... So really the ZR1's 3rd gear at 1:1.20 is closer to the A6's 4th gear at 1:1.15... so you'd really be in 5th gear on the A6 when you're in 4th on the Zr1... and the A6's 5th is 1:0.85..

So even if the diffs had the same 3.42 gears on the C4 ZR1 vs the A6 XLR - the XLR would be spinning slower since you'll be one gear ahead on the A6. Right?

The final drive on a 1:1 would be 3.42 wheel revs per single crank rev...
The final drive on a 1:0.85 would be 3.93 wheel revs per single crank rev...

But thats neither here nor there... since thats a manual vs a automatic... there so many variables its not a reasonable comparison (torque converter slip, toque multiplication at the the converter, lockup points, gears, etc, etc, etc...)

So I think the right thing to do is do a A6 w/2.53 vs A6 w/ 3.42 comparison... which is what I have been researching - and nobody who as done this mod has said their MPG was worse... but everyone who doesn't have it suggests that the MPG will go down... Even Chuck over at CoW swears that the MPG won't suffer - and if it does, it only becuase of a driving style change - in that you'll enjoy mashing the gas more since the car will be so much fun to drive.

 

[klaptrapper]

gearing

My only remaining question..............When Richard????

 

[richardyoo]

My only remaining question..............When Richard????

Hah - funny.

Turns out Chuck is visiting Houston doing a Vararam event - so I'm scheduling with him right now to get it down while he's in town... so looks like the weekend of the 26th in March - so in 4 weeks.

http://forums.corvetteforum.com/c6-...vararam-in-texas-march-24-27-sign-up-now.html

 

[klaptrapper]

gearing

If it works out well, I'll be right behind you for the transmission work and the gears.

Rusty



a

Hah - funny.

Turns out Chuck is visiting Houston doing a Vararam event - so I'm scheduling with him right now to get it down while he's in town... so looks like the weekend of the 26th in March - so in 4 weeks.

http://forums.corvetteforum.com/c6-...vararam-in-texas-march-24-27-sign-up-now.html

 

[GizmoQ]

Well I'm impressed already!

 

[cam99]

Any updates on this?

 

[WB6BBZ]

Hey Richard,
I'm in the process of replacing my tranny and am considering changing the rear end gears to 3.42.
How about some feedback from you!

Tnx,

 

[richardyoo]

No news - never ended up getting it done... Chuck didn't make it to Houston as they cancelled the event... I'm still on standby, in case he comes nearby