I want to add a 3.23 or 3.27 posi, but i was thinking, i'd lose some top speed if i went higher, but also gain some low end power. So does anyone know how much of a power gain it would be at the low end if i went from 2.92 to 3.23? and for losing MPH i don't care cause it's probably not going to be big enough for me to care. (Unless it's 50 MPH )

 

Top speed, if anything, will go up, because you're getting more power to the ground with the 3.23 gears. I betcha anything your engine isnt going to make enough power to run outta gear with either set though. Aerodynamics and HP will kill your top speed before gears will. You will feel more power from low speed, although not much because its not a massive change of gearing, just because the torque multiplication is greater.

 

Hmmm...what if i went from 2.92 to 3.73? Then what kind of change should i expect in both power and speed?

 

Anyone? I know my car doesn't have the power to have a low gear, then i'd start to take off like a honda, but will a 2.92 to 3.72 and non-posi to posi make a big difference?

 

you would definetly notice an increase in off the line acceleration but you would lose your top end. a non posi is kinda crappy(i have 2 of them) but the increase in gears will let you get up to speed better.

 

How much of my top speed or top end power would i lose? cause i don't want my top speed to be 80 (how slow )

Ok, here's the deal to give you an idea...

2.92 non-posi right now, want to go to 3.42 posi. big time difference? big time speed loss?

 

http://www.f-body.org/gears/



what's your top rpm?

 

3.42 is probably the most popular ratio that gives good acceleration without sacrificing much on the top end. I went from 2.73 dif. to 3.73 posi and I liked it a lot. Also, with the higher ratio, a posi would be a good choice.

To give you a better idea, using the gear calculator, at 4500rpm with my 3.73 gears in OD, theoretically I'd be doing 133mph.

 

wow, if i could still do 133mph with a 3.73 i might do that. cause my 2.92 i have now is a nice fast take off, but it's not firm, it's sloppy and fast, so i want the posi to stiffen it up, then get a bigger gear for even faster take off. all that sound good in theory?

I just checked, it says i should have 131mph at 4500rpm...if my tire radius is 10, i should double check cause i know that ain't right. but otherwise, i got a 2.92 and getting 131mph, would it drop to about 100-110 if i went to 3.73? (i'm asking because i don't trust my ability to use the equations)

 

forget about overdrive right now.
if you had a 245/50/16 tire at 1 to 1 in third gear at 4500 rpm you'd be going 118. if you change to 3.73 youd' be going 92.

50 mph with 2.92 1900rpm
50 mph with 3.73 2400rpm


what's that, about 25 percent increase in fuel consumption?

 

Z28cross-fire,
The tire diameter should be around 26". And when you put in the 3.73 gear and .7 OD, you'll get 133 at 4500rpm.


chesterfield,
I don't think you can forget about overdrive and worry about fuel economy at the same time. When I went from 2.73 to 3.73, I didn't really notice that great of an increase in fuel consumption. It might have been some, but not close to 25%.

 

Ok, thanks. I checked that and yeah, it says i can do 172mph or something with the gear i have now, and 133mph with a 3.73, so i think i'm going to change to the 3.73 because 133mph is fast enough for me. Now i should really get a kick when i floor the pedal . Thanks for the help guys!

 

he was prolly just saying forget about the overdrive cause you cannot make a top speed run in overdrive anyway, anything past half throttle and it kicks down right

 

Well the overdrive isn't measured into the fourth gear, the overdrive is a whole nother gear.

 

No it's not. 4th gear in a 700-R4 is overdrive by definition....the ratio in 4th is .68:1 which means it takes a hair over 2/3 of an engine rotation to turn the driveshaft through a full rotation. In other words, the driveshaft is turning more RPM than the engine......that's what overdrive is.


edit: IMHO 3.42 is the best all-around gear for a 700-R4 car that's driven on the street. More gear causes traction problems and burns more gas, less gear sacrifices acceleration.

 

Hmmm, i didn't know the fourth gear was also overdrive....kinda nifty. And going to a 3.73, that's the point of going to a bigger gear for me, is to get such a good acceleration or an easy burn out when flooring it. instead of my wimpy 2 full spins of the tire with the gear i have now...but yet i still can get up to 60 in probably 6-7 or so seconds....

 

When I had the auto in my car with 3.73's, I could still go a little past 140mph. Now I have the T5 and run out of gear at around 135mph.

Also, my auto would shift to and hold 4th at WOT.
here is a vid running to 130mph,
http://www.transamws6.com/video/130mph.wmv

 

I'm starting to drool now, i really really want 3.73's but....i have no or very little money....maybe i could finally have something to show up to this other guy i know and his 1969, 9 second camaro

 

If you find the right 3rdgen in a junkyard, you might find 3.73 gears. Mine, and all factory L69/5-speed cars had them.

 

Hey I have a 3:73 gear and a GM posi unit for your car i will sell for $125 Good wear pattern on the gear and the posi unit looks brand new

 

$125 for both the posi and gears? could you send pics to scwizzo@yahoo.com then. and i take it the posi unit is a 3 series carrier so it can take that 3.73 right? oh and also is the posi unit a 26 or 28 spline?

 

With the 3,800 rpm diesel governor in my 700r4 mine would shift into and hold OD at WOT. Nothing like going into OD at 90 and 3,800 and then dropping to 2,500 in OD and still pulling.