Ok Ok i know that changing the 2.77 gears to 3.42 will increase acceleration greatly. But my question is how? Will my car shift at higher rpms then it does now? or lower rpms. Somebody talk to me hear Id like to understand how this whole gearing thing really works. I have a 700r4 w/overdrive.

 

Gear ratio changes how many times the engine turns, for each revolution of the wheel.

Going from 2.77 to 3.42 would almost be like adding a "0th" gear below your current 1st, and taking away your highest gear. You will be amazed at how much more "jump" the car will have from a stop.

You know how hard a time your engine has accelerating the car if you're doing, say, 45 mph in high gear, and give it some gas; and then how much better it accelerates when it shifts down; making a 20% change in your rear gear will produce just about the same difference, except it's like that all the time.

 

i am thinking about the doing the same thing. i currently have 2.77 and want to go to a 4th gen rear 3.42. you will also need to change your speedo gear. i'm not sure what speedo gear to use though........

 

Hey Right now I have an 87 iroc 350 with I think 2.77's or 2.73's. My car had a posi unit in it when I bought it, I wanted to know though DId those come stock in any year during the 80's? Becuase Im trying to figure out if I need 7.5' or 8.5' or what? theres so many different sizes and makes of the same ratio. Do you have some more answers for me haha. thanks

 

The 2.77 is a 9 bolt ratio. Ratio up to 4.10 are available, but require a series 3 carrier for 3.23/3.27 to 4.10. More info is available at www.9bolt.com

Miles
Diff Solutions
www.9bolt.com

 

i did the 2.73 swap to the 3.42 swap over the winter.... and on the SOTP meeter... the car is definately a little peppier... no track times yet though... hopefully soon...

 

When I did this swap, and my track times went from a 15.1 to 14.7 and the only reason I didn't go faster was I had one bald tire from when I had my pegleg, so I believe the swap was worth .5sec. But I didn't have posi, so your gain won't probably be that durastic, but you will definitely enjoy your car more. My 60' times have dipped from 2.4 to around 2.1, and this is with basically stock suspension, so my acceleration off the line has improved. On another note, I lost maybe 1mpg with this swap, so it's not bad in that case either.

 

I went from 2.73 to 3.23 and it was a very noticeable change.
Then I went from 3.23 to 3.42 and it was noticeable too, just not as much.

 

I went from 2.73 open to 3.73 posi, feels like a totally different car, wish I had done this on all the other cars I've owned, I only lost about 3-4 MPG and since I started at 27 MPG freeway, now I stil have about 23-24 MPG

 

I just swapped out to 3.42 gears...I have not had a chance to drive the car yet as I am painting it also...give me a month or so and I will definitely know! Sounds like there is quite a difference.

 

Just this weekend I went from 3.23 to 3.42's(changed out the posi unit) and there was quite a difference, I wish it was the first thing I did to the car.

 

Have any before and after track times by any chance?