The car is 350 cid, dual demon quads, stock TH350, the kick down has been adjusted.

The dyno torque is 308, hp is 225 at 4200 rpm.

It has the SA 2.73 rear. The tires are 275/60/15 and stand 27 inches tall. Right now it's at 2500 rpm at 70 mph. I do a lot of highway and street driving. It's purpose is not a 1/4 mile but I go to the open nights once a summer at the local track.

I'm back and forth on 3.73 and 3.91. It needs more from a stand still, but I don't want to be rapping out at 4000+ going down the freeway.

Thoughts? Thanks in advance.

 

First, SA is a 2.73:1 gear. If you do a lot of highway there are two good options.
1. 3.08:1 gears are a great compromise
2. Change to 200 4R trans. It has basically the same 1,2,3 gearing as a TH350 but in OD it drops to .67:1 which will really help on the highway.

 

FYI 275 60 15s are 28" tall not 27". 255 60 15s are a 27" tall tire.


Lose the dual quads if you want more performance than show.


My vote is for 3.23 gears if you stay with the 3 speed auto.


3.91s are not available for your 8.5" rear end. Aftermarket 3.90s are. Regardless I would go with them over the 3.73s if you do plan on going to a 4 speed automatic later.

 

X2 on the 3.08 gears with the 200R4 transmission. I did this a couple of years ago and it is by far the best modification I have made to my car. Off the line it is very good and I cruise at about 70 mph and it will be turning about 2200 rpm. I too would lose the dual carbs. It's a bit over kill.

 

Thanks for the input guys.

The tranny swap is not an option. I'll need to pay better attention at cruising speed on the freeway to the rpms at speed right now with the 2.73. I found some gear ratio calculators online. They all seem to tell the same results for rpm at a given speed and gear ratio. Anyone ever gone off of these before to pick a setup?

Also we do a number of car shows in the summer. Like I said I'm not racing the thing on a regular basis at all, just driving as much as I can. You big block guys have a tunnel ram option that isn't available for my small block. That's the only 2x4 available for the 350.

 

Well since transmission swap is out, if you're looking for a better launch either:

1. Go with the 3.08 gears or
2. Change to smaller diameter tires like a 235/60/15. That should give you the equivalent of a gear difference.

You'll likely have to change your driven gear on the transmission so the speedo will calibrate better. If you have GPS you can use for speed monitoring, don't worry about the calibration. I'm guessing you have an accurate tach in the car to monitor your rpm?

 

Yes the tach is newer, I put in myself reading from the MSD. I have found a link for switch speedo gears.

Thanks again all.