Can anyone tell me their impression of having a rear end ratio thatís geared for economy and low revving Vs the usual 3 or 4 series rear?
I have a 3.55 open rear in my 72, and the engine is turning 3200 at 70. Memory is vague, but 30 years ago when I had my previous GTO this didnít seem to bother me too much, but now after driving cars with over drive all these years it seems like the motor screaming.
Not looking to drag race, and want to eventually go to a 5 speed, ($$$$$) but in the mean time I was thinking of swapping rears ($).
Ahhh, 30 years ago....... national speed limit was 55MPH, so you probably did not have a problem with the gears you had. But now, many highways are 65-70 MPH with traffic rolling at 75-80MPH, or more. I personally get uncomfortable revving past 2600RPM's on those long trips, but some don't have a problem with it.
This is all assuming you have an automatic trans.
I have a '76 Lemans with 350CI/TH350, added a Q-jet, and 2.78 gearing. When it was on the road, I did not have a tach, but I could comfortably run 70MPH and the best I could squeeze out of it was almost 20MPG at steady flat road driving. The down side was around town. With that stiff of a gear, and the weight of the car, it requires more gas to get it rolling and up to speed only to be hitting your brakes for the next stop light. Gas mileage went down the tubes and it seemed like I got about 13-14MPG - it burned gas, and most of my driving back then was local and in town.
First, you are not driving a car that is going to get stellar gas mileage - they are not today's cars with the electronics, variable timing, fuel injection, lock-up converters, and overdrives. So my suggestion is to select a gear that satisfies both local and highway driving -short of installing an OD type transmission.
Try one of the online speed/RPM/gear calculators and see what turns up as a needed gear to run 70MPH @ 2500-2600 RPM's. 3.08's are a typical gear for highway cruising, but the 3.23 or 3.36 may be a better all around gear. Still not going to be zippy like 3.55's. You will lose performance with 3.36 through 2.78's. This is where the bigger cubes of a 455 excel as they have more torque to pull these kinds of gears and get the car rolling with less sacrifice in performance.
So there is no magic gear ratio that will give you everything you want. It will have to be a compromise to find some kind of middle ground based on your driving requirements and RPM range of the engine. The OD transmission is really the way to go nowadays, but more work, modifications, and $$$.
Also, I will add this. I have a '73 Plymouth Fury 360/727 trans, 2 Bbl, 2.76 gears. Chrysler offered different stall converters based on the car and engine combo. The '73 Fury with the 360CI got a factory 2500 RPM stall converter. It is a "loose" converter in that it takes a little gas to get the converter up to speed in order to get the car moving. BUT, this really adds to the performance of the car. Even with the stiff gears, it is in my opinion pretty zippy when you nail the gas and the engine goes into its lower power band and starts to pull hard. So around town, I have a little fun with it. On the highway, around here in Charlotte, it'll run 70MPH and not be breathing hard and I have no problem running 80MPH keeping up with the flow of outside lane traffic. At 95MPH its still running great and doesn't feel like it is screaming. Now I probably don't get 15-16MPG's with the car, but I did not buy it for gas mileage, that's why I have a Hyundai. But the point here is that you could consider a compromise between performance & highway cruising by going with a more modern "tight" 2500 stall converter that does not have the slip when taking off using reasonable acceleration, but will zing right on up to 2,500 RPM's when you nail the gas and give you that acceleration performance. Then at highway speeds of 70MPH and above, your engine RPM's will be down to a reasonable cruising speed.