Best choice: 3:42 or 3:73??

[dochidalgo]

Well, the original ring and pinion are shot after change the oil plus slip additive, no track ,no launches...
The gas/mileage ratio is a good issue to count on here in Mexico: bad quality gasoline= poor G/M ratio
My car is an A4 GU5 RPO: 3:23
Thanks in advance for your imput
Doc

[hotwhip9]

what seems to be the general consensus, since this topic has been covered many times on here is to go with the 3.73s. Do a search on the forum and you will be able to find the various discussions on it.

[dochidalgo]

Thanks hotwhip9, you're right...I'll do some search.
Take care
Doc

[hotwhip9]

3.73 or 4.10 thread

[dochidalgo]

You "da man"..thanks a lot.
Take care Doc

[Joe 1320]

Doc, 3.73s are great for performance, but if you do quite a bit of highway driving, the 3.42s will give you better mileage. I lost about 15% in mileage going from 3.23s to 3.73s. For city and overall combined performance, 3.73s will put a smile on your face.

[dochidalgo]

Thanks Joe your comment is what I was looking for.....I drive in highway 20 miles every day and 270 miles each 15 days (my "kids" are in college).
3:42 is a Corvette set up right?
Take care
Doc

[Mr Nice Guy]

I have 3.42s in my Z and it is huge difference from my old 95 formula with the 2.73s. If you drive on the highway much I'd get 3.42s. The 3.73s will be better at the strip but in my opinion the 3.42s are a good compromise between performance and mileage. Either one will wake the car up though. Oh yeah and get ready for traction problems or tire-smoking fun depending on how ya look at it .......Later

[Joe 1320]

3.42s are stock M6 rear gears. If I remember correct, vettes were 3.45s for stick, 3.08 for autos with the performance axle option. The f-body gets 2.73s with automatics unless the 3.23 performance axle option is checked, stick cars all got 3.42s.

Doc, there are a few times that I wish I had 3.42s, especially when cruising at higher than 60 mph on the back roads. I've since set the car aside for "occational" use, not long distance commuting. The car will do it just fine, it's just my gas mileage went south. The boost from the 3.73s though is tough to argue with. The car is much more pleasant to drive in town, it pulls away from other traffic with authority and quickly is up to speed at part throttle. I think a 3.55 gear would be ideal, but that ratio doesn't appear to be available for our cars.

If you do 20 miles a day with the occational 270 mile trip, you should be fine with 3.73s as long as you aren't trying to cruise at over 65 mph. That's where the drop in mileage starts to accelerate. I used to get as high as 27 mpg when babied at 55 mph, about 24 mpg at 65-70 mph. Now I get about 21 mpg at 65 mph. The other thing to consider is that deeper than 3.42s, the odds of additional noise increases. Hope this helps.....

[02Z28]

correct me if i'm wrong, but the 3.73 gears should actually help gas mileage in the city, as it doesn't take as much throttle to get the job done (assuming you don't start having too much fun with the extra acceleration... ). highway mileage and top speed will drop slightly as a result, though.

make the compromise that best suits your driving needs....if most of your driving is in the city, then i'd definitely go with the 3.73's.

even if i did do mostly highway driving, i would still get the 3.73's if mine were an A4, because the extra highway mileage wouldn't be enough to offset the extra performance that i would want from the car

but that's just me....

[dochidalgo]

Thanks guys, let me tell you my situation:
I have a "heavy feet" on gas pedal, I mean, here in Mexico I drive at 90-95 miles per hour on highways (reckless driving?) depending the road & traffic condition, I'm not a kakimaze, but I really like to feel the car in that speed range. That's why I've invested a lot of mods on suspension,brakes (with the kind help from this awesome forum) & manteniance to get a car in premium condition.
I live in a small town, so 40 miles/hr is the standard speed.
The "93 octanes" gas named "premium" is a garbage here in Mexico, so the mileage is very poor, so as, I have to take on count it to decide the right gear for my car. I'm anal with the noises, first time I took the car with the mechanic, he did not listened the gear noise!!!.
With your comments here, seems to me the 3:42:1 is the right one.
I really appreciate your information and your experiences shared with me and any extra imput will be welcomed.
You're awesome people!!
Best regards
Doc

[Kevin - Blown 95 TA]

I took a good hard look at this as well, and built my 10 bolt with 3.42 gears based on the rpms that I thought I could live with at 70 mph where I do most of my highway driving. I had it like that a while and when I bought the Moser 12 bolt, I kept the 3.42 ratio. I think it is the ideal gear for a car that only gets to the track occasionally. And when at the track, I trap just before shifting 3-4 and have traction trouble anyway, so it seems right for my setup. With slicks, it might be a different story, and most of the racers I know with automatics have 3.55, 3.73, or 4.10, and some of them are running bigger tires than stock. My rule with building this car was to stop one step short of best performance on each mod (cam, heads, gear ratio, etc.) to keep it streetable. So I got a mild cam, decent gears, decent heads, and the car is still pretty nice to drive & gets decent mileage although not as good as stock. When I go to the track, I can still lay down a decent time for a street car.

[dochidalgo]

Kevin,that's exactly my point of view about my car mods. My car has not been in tracks, is my daily driving car. The engine has not been modified, but if it's necessary (like the heads...were polished and ported, thinner head gaskets and I regret I did not replace RR,rings with 1.6) I'll do it.
Thanks a lot for your comment.
Take care
Doc

[fastTa]

Using the formula: RPM = (Trans Ratio * MPH * 336 * Rear Gear Ratio) / (Tire Diameter) we can determine RPM's with a given final trans ratio, rear axle ratio, MPH, and overall tire diameter.

Using a stock 26" tire and the .7 OD gear in a 4L60E as a reference point, at 70 mph with 3.42's you're looking at 2166 RPM's. Step up to a 3.73 and you're looking at 2362 RPM's. This is a measly 196 RPM difference. Even at your crusing speed of 90 mph, you are only looking at a difference of 253 RPM's going from a 3.42 to a 3.73. This is absolutely nothing to worry about given the substantial performance gain attributed to the 3.73:1 ratio.

I had 4.10's with a 4L60E in my 97 WS6 and still got 18-19 mpg in the city and 20-22 on the highway. And I also cruise everywhere I go at about 90 mph.

No offense, but I am fairly certain gas mileage was NOT your primary focus of concern when you purchased your LT1 powered TA.

Go with the 3.73's, you will love them I promise!!

[Joe 1320]

Since he has 3.23s, there is going to be more of a differance jumping to 3.73s. The 3.42s are a split the difference choice. There is enough of a spread between 3.23s and 3.73s that may make people think twice if they do alot of higher speed cruising. It's not like an M6 with the double overdrive, autos really could use an extra gear.