anyone running 700r4 with stock '81 rear gears?

[Sensei]

With overdrive as such a popular mod, I was wondering what the result was like with the '81's highway rear gearing (around 2.8). I am thinking of doing this in the future and actually am leaning toward the 2004r, but am pretty sure I would need to change the rear gearing to be able to use it around town. The 700r4 might work better if I don't change the rear gears, but if I will be unsatisfied with that set up, I might as well wait and do the rear end and the 2004r. So if you have an '81 with overdrive, let me know how it is working for you. Thanks and God bless, Sensei

 

[KANE]

With overdrive as such a popular mod, I was wondering what the result was like with the '81's highway rear gearing (around 2.8). I am thinking of doing this in the future and actually am leaning toward the 2004r, but am pretty sure I would need to change the rear gearing to be able to use it around town. The 700r4 might work better if I don't change the rear gears, but if I will be unsatisfied with that set up, I might as well wait and do the rear end and the 2004r. So if you have an '81 with overdrive, let me know how it is working for you. Thanks and God bless, Sensei

I had a 3.08 tied to my '78's 700R4. My 78 may as well have been like your 81- it was a three-speed auto when I started to build it.

I would have gone with a 3.73 to really launch the car in the future, had I not sold it.

 

[Peer81]

I have a 81 with a 90 corvette 700r4. I don't know how it will run because i'm still working on the body off.
Remember the 200R4 is the correct size to shift with the TH350. The 700r4 is longer so you'll need to change the drive shaft, change the crossmember and change some small things to let the lock up work.
I still don't know if the 81 ECM will also power the lock up of a 700R4 because that is what i want to go for.

Groeten Peter.

 

[Bob Chadwick]

I just put the 2004R in a 77 with 3:08 rear gears. I like the highway RPM's but will be putting a larger rear gear in the diff when I rebuild it as it needs more get up and go.

 

[bossvette]

I've got a 700R4 with 3:10's in my YT and it works for me its too recent a rebuild to beat on too much but it gets out of low real quick and moves that ole farm truck down the road.

 

[Sensei]

I am aware of the differences in the transmissions and the nuances involved in installation. I'm also sure either one would be fine from a start, I can spin the tires with my th350, either overdrive will give me an even lower 1st gear. What I'm really after is this, will shifting into 4th at say 40-45 mph (in town) cause problems with rpms too low? God bless, Sensei

 

[Evolution1980]

I am aware of the differences in the transmissions and the nuances involved in installation. I'm also sure either one would be fine from a start, I can spin the tires with my th350, either overdrive will give me an even lower 1st gear. What I'm really after is this, will shifting into 4th at say 40-45 mph (in town) cause problems with rpms too low? God bless, Sensei

You can more or less set the shift points by adjusting the TV cable and the governor springs in the trans. If the automatic is functioning properly, the car won't shift into a higher gear if the engine is going to lug. You shouldn't have any problems whatsoever. if you're happy with the current gearing setup in first gear, then you can save yourself a lot of hassle by going with the 200R4.

 

[Evolution1980]

*** START OF THREAD HIJACK ***

... (I) will be putting a larger rear gear in the diff when I rebuild it as it needs more get up and go.

I believe when driving my car, your words were, "Oh yeah, I can tell that I need a ZZ4 now..."
:L :L
Save a couple more bones and just get the ZZ383. Unless you want to buy mine. Of course, I'll give you a deal on it. It's already broken in and ready to go!
*** END OF THREAD HIJACK ***

 

[kiwi vet]

Hey Sensei

My L81 has the stock 2.78 rear end, and a 700R tranny added.
It's hardly standard engine, puts out reasonable power, but the result of this gearing can be described in one word = SLOOOOOOOOW!!!!!!.

It wont even keep up with my 3 litre Lexus or the wife's 1600cc VTec Honda, and at 60mph its spinning @ about 1400rpm, very lazy.

I agree with DarkShark, go for the 3.73 if you want a quicker steetable car, thats my plan anyway once I get the thing to handle properly.

Also, if you go to the BowTie Overdrive site, they have an RPM calculator to check your ratios, trannies and tire section sizes to calculate your final result = rpm/speed etc. Also some other helpful calculating programs for comparing the transmission etc, well worth the look.

My thoughts for what it's worth, a quick car is way more fun than a fast car!

Good Luck
Grant

 

[Twin_Turbo]

I still don't know if the 81 ECM will also power the lock up of a 700R4 because that is what i want to go for.

Groeten Peter.

Yes it will, same TCC system (TH350C)

A 700 & a 3.73 gearing makes for a too small 1st IMO.

 

[Evolution1980]

A 700 & a 3.73 gearing makes for a too small 1st IMO.

Easy to say when you've got sufficient power, such as one might find with TWIN TURBOS!!! :eyerole

 

[bossvette]

Yes it will, same TCC system (TH350C)

A 700 & a 3.73 gearing makes for a too small 1st IMO.

Yup a 3:08-3:15 is about right for a 700R4 unless you are running a 283-302-327 and making the power high up

 

[kiwi vet]

Horses for Courses

Yup a 3:08-3:15 is about right for a 700R4 unless you are running a 283-302-327 and making the power high up

I guess it depends what your looking for?, a highway cruiser or a quick sports car

A 3.73/700R still cruises @ 1950rpm @ 60mph with a 255/60/15 rear, as opposed to 1457rpm for stock 2.78/700R (so 500 rpm) & 1730rpm for 3.15/700R, so really not a lot in it.

On our type of roads, most attempted kills (nothing illegal of course ) are really over by 100 - 120mph so you need to get there quick.

Which is hardly the word I would use to describe the current acceleration!

Just my $0.02 worth
Grant

 

[Peer81]

Hello Sensei,

Did you make a decision yet?
Currently I have the 2.87 stock gears but I'm thinking about changing them to 3.08 in the future. But I still didn't drive my vette.

Groeten Peter.

 

[Sensei]

I just ordered a 700r4 from bowtie overdrives. I'll post my opinion of the results as I form them. God bless, Sensei

 

[Barry08]

I just ordered a 700r4 from bowtie overdrives. I'll post my opinion of the results as I form them. God bless, Sensei

How is that 700r4 working with the 2.87 gearing Sensei?

Barry

 

[Sensei]

I have it installed and it works fine with the 2.87 rear end, although a lower rear gearing would probably be better (I'm thinking 3.31). I was originally worried that the stock gearing would be incompatible with the overdrive, but have recently found out that the stock rear gearing on an '82, which came with a 700r4, was also 2.78. Bottom line: it works. If anyone wants more info and tips on doing this install, let me know and I can probably save you some trouble and money. God bless, Sensei