? about going from 3.08 to 3.42 and LSD

[Jaymatic]

I was just reading the Gears and Differential section under Modifications Encyclopedia and was a little confused about something. I am thinking about going from 3.08 gears to 3.42, and an LSD.

Question 1:
Will the 3.42 gears get worse gas mileage than the 3.08? Also, will the 3.42 output more power at the wheels than the 3.08 or just have better acceleration?

Question 2:
Will the LSD get worse gas mileage than the stocks one wheel wonder? Will LSD output more power at the wheels than the stock or just accelerate better? Can I run an LSD with 3.08 gears?

[Justin Kirkham]

General consensus is that your gas mileage will not be affected much, if at all, for either the gears or the LSD.

Second, the new gears will not add 20 hp or anything like that. They will simply increase acceleration. If you see an increase in HP, it is more likely due to weather than the gears.

Given all this, the gears and LSD will be a huge performance upgrade for you.

-Justin

[93camaro_zzz]

In a way you get more hp and torque. In a way. In first gear compared to the 3.08s, the 3.42's are multiplying more torque, than the 3.08s. but once you get out of 1st gear it doesnt matter. But for example, if you go dyno your car, they would be EXACTLY the same, because the dyno divides by your rear end gear. And in my opinion, the LSD does only good things. No gas mileage loss, and alot more traction, especially noticeable in the rain. Good luck.

[Jaymatic]

Thanks man. I think I'll do it. But I have another question. Say I get a Differential off a Z-28, does anything have to be re-programmed or recalibrated? Or anything else need to be done? Or should I try a search?

[mjparme]

Searching can be good at times but with a gear swap searching can sometimes make people more confused.

Do you have an automatic?

I just did the 3.08->3.42 swap on my A4 and if you have an automatic make sure you have some sort of programming set up to recalibrate your speedometer and shift points. The shift points on an automatic will be totally screwed up and your performance will decrease until you get those shift points corrected.

On a manual you will only have to worry about your speedo being off. There are devices that will do that for you at a couple of places (a search will get those for you, I don't have my bookmarks handy or I would give you some links).

If you have an automatic your options for shift point correction are custom programing (which I don't believe is available for a 96) or getting a VIN from a car with the Y87 option and trying to find a dealer that will flash your PCM with it.

I think people with a manual have a easier/cheaper time after a gear swap. Something I didn't realize until it was done :(

[AlienInv8r]

the gears aren't going to change how much horsepower you have, it's going to change how it is applied.

Try this for an analogy:
Lets say you're going to race someone on your bicycle. You have your rear derailer with all it's gears, we'll say that's like your transmission.
Now let's say during your race you can only choose one chain ring from your front derailler- those are like your gears. You have the big chain ring, which is like 3.08 gears, it's harder to get started with that one, but once you get going it's gets ok acceleration and you can ride a little bit faster for your top speed. Now what I would choose would be the middle chain ring; it gets good acceleration from the start, and still has a nice top end with it also. It is very versatile since it has nice low end and nice top end, those are like your 3.42 gears.
Now if you went with the smallest chain ring, you'd have excellent speed out of the hole, but would need to change gears way too often and run out of steam really quick on an extended ride. Also, you lose a lot of top end with this ring - that is like 4.10 gears or so.

That's how I understand gears and how they work. 3.42 gears are great all around since they are nice out of the hole, and still maintain a decent top end. The gear ratio is how it's applying your power; On a bike you can apply the same pedal power (engine power/rpms/hp), but depending on which chain ring (gear ratio) you are in it is going to change how fast you jump out of the hole and accelerate with that same amount of power. Hopefully that makes sense.

[Jaymatic]

Thanks a lot guys. I understand all this much better. Yea I do have an automatic so I will have to have it reprogramed. Hope it won't cost too much. But thanks so much guys for taking the time to explain this to me.

-Jay

[Jaymatic]

Oh, and, I don't race or anything. My car is just my car. Just drive around and cruising. So would 3.42's not be worth it if I don't race or anything? I still want to get the LSD though.

[AlienInv8r]

I don't race a whole lot, the combination of the two just make the car a lot more fun to drive. It gives it that little extra kick that'll make it feel more like a sports car, but not affect daily driving any either.
I haven't reprogrammed mine since my gear swap, it's just off by like 5 mph. And shift points havent changed since the speedo/computer still thinks it has 3.08s, and shifts at the same spot. You may as well get the gears done while you're doing the LSD, the combination of the two will drastically change your launches.

[Jaymatic]

ok, thanks.

[mjparme]

I haven't reprogrammed mine since my gear swap, it's just off by like 5 mph. And shift points haven't changed since the speedo/computer still thinks it has 3.08s, and shifts at the same spot.

The speedometer will be off 10% when you go from 3.08->3.42. Your speedo will show you going faster than you are. If the speedo shows you doing 80 you are doing 72. If it shows you going 50 you are going 45, etc.

I suppose every car is different but after my gear swap (3.08->3.42) my 99 A4 had horrible performance because it felt like the computer was holding back power because it was confused. If you do some searching there is enough anecdotal evidence that this is fairly common.

[AlienInv8r]

When you swap gears, the speedo definitely is off by about the 10%; I should rephrase and say that mine is reading 50 or so when I'm going 45, so it's 5 off in average city driving(hence the 10% difference). I know that gap increases slightly as my speed does by a factor of 10%. But when you swap gears, your tach remains correct. So if your computer has an uncorrected speedo, it is still going to shift your car at the same rpm. It's when you recalibrate just your speedo and not the shift points that you run into problems. That's when your computer starts short shifting because the speedo isn't lining up with it's programmed shift point speeds and starts short shifting; I do believe our pcm shifts the tranny based on speed set shift points. So if you dont calibrate anything after the swap, you will still have correct shift points, but incorrect speedo. Recalibrate and you face correct speedo, but incorrect shift points. It sucks having a 98-99 since we dont get hypertech benefits to fix both for us, hopefully HP Tuners software will come out soon enough to tackle that problem. I choose to deal with the incorrect speedo so that my shift points would still be the same.

[Jaymatic]

I have a 96

[Camarorulz]

No, not quite. The shift points are going to be off because the computer uses RPM AND SPEED to determine when to shift gears.

[jc Kyle]

Originally posted by Camarorulz:
No, not quite. The shift points are going to be off because the computer uses RPM AND SPEED to determine when to shift gears.

good call [img]smile.gif[/img]