I need to decide on gears to put in a posi but I don't know a good ratio for somthing streetable and with some highway cruizes. Any suggestions?
I have a 5.7L 5500 rpm cam with 500 lift 240 dur. and a tci streetfighter th400 with 2500 stall and 28" tires

 

What engine and trans do you have? Auto trans usually like to run lower gearing then manuals. If you are not looking for great numbers on the 1/4 mile, I would use something in the 3.00 to 3.60 range for an auto and 3.4 to 3.7 for a manual.

Massey

 

Choose your gear ratio depending on your engine build. Engines with aftermarket cams react differently then stock engines to cruising rpms. If you have a dyno sheet that gives you lower rpm horsepower and torque you use that to determine what cruising rpm you need. Try to keep your engine at the lower end of your power-band. Also take into account whether or not you have a stall converter installed. If you have a 3500 stall and your cruise rpm is 2200 you can create a lot of heat in the trans. Other than that a little carb tuning may be in order, once again dependent on your engine build.

Here are the gear ratios for GM auto trans:
1st 2nd 3rd 4th Reverse

Powerglide 1.76 1.00 1.76
TH350 2.52 1.52 1.00 1.93
TH400 2.48 1.48 1.00 2.00
200r4 2.74 1.57 1.00 0.67 2.07
700r4 3.06 1.62 1.00 0.70 2.29
4L60E 3.06 1.62 1.00 0.70 2.29
4L80E 2.48 1.48 1.00 0.75 2.08

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

Enter your info and it will calculate the unknowns for you.
If you want a more comprehensive calculator, the guys at Tremec gave me a spreadsheet I have on my comp at work. It will generate graphs and charts.
Let me know if you want it, I will post it tomorrow.

 

I have a 5500 rpm cam with 500 lift 240 dur. and a tci streetfighter th400 with 2500 stall and 28" tires

 

I would run 3.42s. There very common in out cars. If you want a more aggressive set up 3.73. I have 3.73s and will have a 26" tire. So it will be buzzing if I take it on the highway. I think your 28s will be marginal. 3.42s would probably be perfect.

 

I'm running 3.42 with a pretty tall 28" tire, but my big block makes peak HP at a lower rpm range. On my Austin I'm running a smallblock with 3.73 gears and also a tall tire of 29.5" so it isn't so tight at freeway speeds as a smaller 26" tire would be.

 

29.5??? WOW lol Are they Super Swampers or Boggers?

 

I run 4:11 with 30" tires. I can do 65, but 75 is out.
I would not go taller the 3:73. I like aggressive cars.

You said Sunday driver so it isnt a daily driver and you are not concerned with gas milage. My C10 has 3:73 and it will do 75. It is very happy at 65, pulling a trailer.

My friends Nova has 3:73 and he drives it the hour drive on the hwy to the race track.

All 3 vehicles have TH350

If you want an aggressive car, 3:43 are a waste of time. You wont be happy. 4:11 take a certain type of gear head to like. There are clearly low gears and suck on the highway. But my car will do 60. I just stay on the smaller hwys.

 

Mickey Thompson Sportsmans:

 

Just pokin fun Val. I still wanna drive it. I bet with a transbrake it would need wheely bars.