Hey guys, i have a 68 coupe with a 289 and a C4. From 50-80 this car is a beast. But from 0-50 its not as fast as i'd like for it to be. Im pretty sure it has the original 2.73 gears in the back. Any reccomendations on what to bump it down to? 3.55? 3.73? I do mostly just cruising with an occasional tripon the interstate.

 

I'm going to 3.70's from 4.11's. Either of your choice is good.
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Ask yourself what kind of revs can you live with on the freeway, and choose gears accordingly. For me, with the c4, its a 3.25 -max 3.55. there are plantly on online calculators to let you know what revs you will be pulling at 60.
eg
http://www.wallaceracing.com/gear-speed.php

or this
http://www.wallaceracing.com/calcrgr.php

Cheers

 

I for sure wouldn't go any higher than 3.73's, but I'd recomend 3.50's. It also depends on your tire size though.

 

3.5 or 3.73 would be ideal but if you plan onroad trips or longer highway runs I'd get an overdrive unit. It attaches behind your transmission and you would need a shorter driveshaft to compensate but you wouldn't be wound out in the high rpm range all the time.

 

for a week-end cruiser you could go to like a 3.89:1 for some serious low end grunt. But somewhere between 3.50:1 and 3.73:1 would probably be ideal. I've got 3.50:1 in my car with a slightly beefed 302 and C4 trans - course the car hasn't moved yet but... that's minor details. My dad's camaro has 3.55:1, it launches hard and pulls hard all the way - course it's a big block too... again minor details. I've always thought a 3.73:1 was a really nice place to be, plenty of grunt and doesn't peg the tach on those occasional interstate trips.

 

Heres a really good test you can do to see how 4.11s will feel in your car.
While doing 60MPH, drop it back to 2nd (in yourC4) which is a 1.46 ratio. With your 2.79 diff this works out as the same as having it in top with a 4.07 diff(close enough to a 4.11)
I tried this last night and was shocked that people can drive around like this thinking itis fine, It was reving at approx 3200 RPM at 60, at 75 it was pulling almost 4000 RPM at 75!
If you spend all your cars time at the track, go for it, but for street use, [:'(]
Thats why Im going with a nice 3.25. it gives me 2500 RPM at 60, or just under 3000at 75. I could go to the 3.5, but since I picked up the 3.25 cheap, it will do me fine.

 

could someone explain whats the difference driving with a auto tranny in drive, and 2ed, and 3rd?

 

In drive when you take off from a stop, the auto changes automaticlly from1st to 2nd to 3rd (three speed)
If you put the shifter manually in 1 - it holds first gear
If you put the shifter manually in 2 - it will start in first and change automatically into 2nd.
Is this what you wanted to know?

If you have a 66 or earlier its a little more complicated becuase the valve body is setup to give two drive positions. Thats a whole new topic.

 

oh ok thanks, I was just wondering because my shifter rod is messed up and I cant shift into 1st or 2ed, and I was wondering if I was missing anything