leftme4dead

Im trying to decide on what gears I should put into my chevelle. What I really want I cant have, which is lower engine speeds @ a higher mph for cruising on highways and gears for better 1/4 times. Basically, I have a 383 w/a turbo 400 and 2.73 gears. Right now @ 60mph im around 2500-2600 rpm's. If anything I would put 3.73's but I dont want too too high rpm's @ hwy cruising speeds.

Im wondering, based on what I have told you about the car, about how many rpm's do you think I would be pushing @ 60mph if I changed gears to 3.73's? Also, about how many do you think if I changed to 3.42's? Would I see a significant difference between the 3.73's and 3.42's????

1SlowFormula

It depends on you conveter and how loose it is and if it is locking or not, I will assume it is non locking.

Jumping up from 2.73's to 3.73's you will probably rev to about 3200 RPM's @ 60 MPH.
Going up to to 3.42's will put you close to 3000 RPM's @ 60 MPH.

Again however you converter could also effect this...

leftme4dead

I know its a 3800 stall, I just dont know who makes it. I dont think it is locked though. I still dont quite understand the concept of locked or unlocked, and what exactly stalls do other than being able to launch at a higher rpm I guess.

sssalah

Going to 3.73 will put your rpm @ 3500, 3.42 @ 3200. The TH400 doesn't have lockup meaning it'll always have some slippage. Have you considered the gear vendor box or slapping in an overdrive like the 4L80?

leftme4dead

I dont really know anything about the box or the 4l80. I just bought this from a friend last month. All I know if the th400 is built for atleast 900hp. I would consider other tranny's or putting in a nice viper tranny, but I would rather invest the money in other areas of my car for now. I just know the car would be much more killer if I got different gears. Would there be a significant differrence between 3.73's and 3.42's in respect to et's or what not.

GregP

I need to know the gear ratios in your transmission, the tire size (like 275/40R-17 so i can calculate the diameter of the tire when inflated to recommended air pressure), the RPM, and the speed you are going at that RPM. If you tell me what your present diff ratio is I can tell you what RPM you'll turn with another diff ratio in it.

The math isn't too difficult. If anyone is interested I could email the spreadsheet or have the moderator post it in this forum ... assuming he or she would do so.

It is in Microsoft Excel, is accurate, and includes standard formulas from Hot Rod Magazine as well as my own calculation of speed in gears.

leftme4dead

I would have to go look up the gear ratios for the trans and all, I was just looking for a ball park figure, and if I would see a significant difference in 1/4 times between the 3.42's and 3.73's.

GregP

3.73 would give a slightly better time on the quarter mile, but not much. Either ratio would be better than a 2.73. Anything higher than a 3.73 is getting into dedicated drag racing stuff. You cruising gas mileage will go down and the engine will work more.

Nothing WRONG with that, but you'd best expect it.

Personally, I'd say that anything that came with a 2.73 differential .... would warrant investigation into the transmission ratios before changing. The trans might be optimized for a 2.73 ... might not.

The thing is, FIND OUT, before you spend the money.