Hi Everyone,

I noticed in Ecklers latest catalog that they have
rear diffs for C5s with 3.90 gear sets. You can
even get them with hardened shafts for a few
hundred extra.

The price looked pretty damn reasonable compared
to some of the stuff I have seen out there.

Anyone running 3.90?

How many RPM does it turn in 6th at 60MPH?

How does it compare to 3.73?

Thanks!

 

You should get a hit here. In the mean time, do a search in C5 Tech. A guy had one put on a few weeks ago. He posted the RPM's and some preliminary impressions the day he had the work done.

 

I'll have my 4.10's in in about a week. If you're going to go to all that work and expense , I'd go 4.10. I'm going to buy some cores and have them built and have them for sale at a reasonable price if all works out as expected.
With 4.10 and a 26.1" tall tire (that's what my 295-35-18s measure) you will turn :
1500 rpm @ 57 MPH
1600 RPM @ 61 MPH
1700 RPM @ 64 MPH
1800 RPM @ 68 MPH
1900 RPM @ 72 MPH
2000 RPM @ 76 MPH
2100 RPM @ 80 MPH
2200 RPM @ 83 MPH
2300 RPM @ 87 MPH
2400 RPM @ 91 MPH
2500 RPM @ 95 MPH
That's a perfect gear! 6th is actually usable. There's no way that this is too much gear. I can't wait. :yesnod: :yesnod:

 

Thanks,

Ran the search and didn't get any hits.
I think the guy you were thinking of did the 3.73 diff.
I found his.
He seems very happy.

 

4.10!

Now that's a gear!

It may be a little much for me.
Mine is not a track car.
I drive it every day that it's nice out.

Still, I am in no hurry.
Maybe I'll wait a few weeks and see how you like yours.

How much would you want for 4.10 rear diff?

 

Found this one, but I think there is still another one I have not found yet. If my memory is correct, hopefully the owner will step up.
http://forums.corvetteforum.com/zerothread?id=243638

 

We can do 3.90 or 4.10. I'll have to see exactly what all the new bearings and seals etc. cost but I'm thinking around $1200. What I did was sold my 3.42 and bought a 3.15 for a little less and am using that one to build. Saved a few bucks that way. :D

 

The guy with the "first" 3.90's was - Ansel Boyce - but I don't know his username. Look for a post by him, or e-mail me. I'll have 4.10's in my car in a few weeks. I think the A4 with a good converter will really be a "piece" after that.

 

Andy, make sure you post when the 4.10's are ready. I was thinking about going to 3.90's but 4.10's would be a real kick in the butt!

 

Good God man!

4.10's and a Carroll stage III.
The rest of us will need a jet just to stay in your shadow.

That thing would fly off the line.

I think hardened shafts would be a good idea!

 

Andy:

Let us know when you are ready to ship these rearends fully assembled :D

Nitrovette :smash:

 

"hardened shafts " Thats the coolest thing I have heard in a long time. I was always wondering when someone would come out with these. Aparently there is significant problems with the stock shafts breaking under drag conditions, but not street conditions, presumably because street tires are less gripy and will just spin before the shart breaks? Anyway this is really cool. I guess its not a problem anymore!

 

Anyone interseted we have the gears or the complete assy's ready to go. 3.73, 3.90,4.10 call for details. 281-821-1222

 

Paul is right. He is the supplier of these gears. At some point, I'm going to have a few for sale, but Paul has them right now at a reasonable price. That's where I got my gears. As a matter of fact they just got delivered today. I'm getting anxious now to get them in. :smash:

 

I wouldn't suggest 4.10's for your supercharged car. You'll NEVER hook up on the track unless you have slicks. You'll just roast them up. I had a buddy with a supercharged LT1 Trans Am that had 4.10's. He'd get smoked by stock 5.0 mustangs because he'd spin his tires all the way up to 100 MPH :eek: on the street. That's just my opinion though :) :cheers:

 

Here is a copy of my original post from December


MessageSubject: New 3.90 Installed

New 3.90 Installed

Today I drove down to West Coast Corvette (WCC) to have the 3.90 gears installed in my 2000 HT. On my way down I thought I would write down some observed speed vs. rpm in each gear for comparison. Here is that observation,

3.42 gears
Gear RPM Speed
1st 2000 17
2nd 2000 26
3rd 2000 35
4th 2000 46
5th 2000 62
6th unable to go fast enough in stop and go traffic
6th 1325 60

I had set up an appointment through Craig for 9 AM. I arrived at WCC at about 8:45 AM, by 9 AM my baby was in the air. The young man assigned to my car was Jason. I watched and took many photographs during the whole operation. This is the first time my Corvette has been worked on by anyone other than me in the two and a half years since it was built by the General. Was I nervous, just a bit! Jason removed the lug nuts by hand but for the rest of the operation it was full tilt impact wrench. Jason mentioned that he has R&R'd over 100 differentials on the C-5. Watching him work I felt he could have done it blind folded. He knew where every nut, bolt and clip was. He was careful and seemed to take pride in his work.

Mind you, I have never been to WCC before and I can only say that I would go back for other work.

As I watched I thought to myself, thank God I didn't try this at home. The entire exhaust system was removed with the exception of the manifolds and the entire rear cross member with the leaf spring was removed. The long cover that is part of the drive train tunnel was removed and the transmission/differential was lowered about 12 inches. My existing 3.42 diff was removed and the new 3.90 diff installed in it's place. Visually there is no difference and as things started going back together I was anxious to be able to give it a try. As luck would have it, there was a rep from the company that is supplying the gear sets to WCC. After Jason took my C-5 around the block to make sure it all worked the rep said to let it set for about 20 minutes. Why you ask? I have no idea but he said they found it was better for them (the diff) then to just jump in and take off.

Now you are wondering how long the whole operation took. By my watch about 2 hours and seven minutes, I'll pass on the seconds. I found everyone courteous and cautious. The work shop was clean and neat and very professional looking. There was a beautiful '61' in the air being worked on and a hot rod shark in the air next to it. If you like Corvettes (silly question), you would enjoy watching these people work, they seem to care about what they are doing.

Ok, on to the good stuff. The 20 minutes has passed and I had paid my bill ( I kept my old diff ) so it was time to hit the road. Pulling out of the parking lot I thought everything feels normal but it's too soon to notice any change. Since this is a new differential I will take it easy for awhile as in 500 to a 1000 miles. Now it's on to the freeway and head for home. Before I arrive at home I did another observed speed vs. rpm in each gear for comparison. Here is what I now show,

3.90 gears
Gear RPM Speed
1st 2000 15
2nd 2000 22
3rd 2000 31
4th 2000 40
5th 2000 54
6th 2000 80
6th 1500 60

Bare in mind there has been no recalibration to the speedometer as my computer was not touched. What I felt as I drove the car was no difference in sound as all was normal. What I did notice was 5th and 6th gear felt a whole lot better on the freeway. Shifting seemed a bit closer and the initial start off in 1st seemed to be a bit easier. In town driving I use 3rd gear a lot now I find myself using 4th. Granted I still need more time to see how I really like it but for now I like it.

There is one down side to this whole thing... This should be an option with GM!

 

if you are really wondering about the RPM vs speed it is going to be almost exactly what a Z06 does. the 3.90 is a cheap way to get the ratios of the z06.

 

For those with 3:73, 3:90, 4:10 gears, what gear are you guys finishing the 1/4 in?

 

With a 4.10, 6600 RPM is 125 MPH in 4th gear.. So I'd have to say 4th. Any thing that will turn faster than 125 in the 1/4 is probably also capable of more RPM than 6600.

 

Thank you. I'm vindicated. I'm considered a walking encyclopedia of car information by my friends (I have about 2000 car magazines going back to 1965). I was really getting discouraged that I could not find your post. :D