So, I've done some research and found out that my Shelly has 3.40:1 6 3/4" rear end mated up to the standard 1976 4spd.
i read another thread that someone swapped a 2.73:1 and put a 3.40:1 in its place and had excellent results for acceleration and power under speeds of 75mph!
however... my car already has that rear end and i am rather unsatisfied with the performance from a stand still, on hill, etc... I'm contemplating finding an 8" rear end for the car from a similar time period (VERY hard to come by out here). is there a better ratio i could choose from to improve the poor performance my Shelly has?
also, if a v8 swap is a possibility, would a T5 from a v8 or a 2.3L be a better choice?
the reason i am contemplating the switch is because if i change to an 8", that's just one step closer to the all important v8 swap that am leaning more and more towards everyday. ;D
please keep in mind, these parts are either extremely rare or outrageously expensive out here :mad: and i don't plan on buying two of anything if at all possible
also.. would i be able to use the same 4 lug axles in a pumpkin like this?
http://cgi.ebay.com/ebaymotors/FORD-MUSTANG-8-EIGHT-INCH-GEAR-TRAC-LOC-POSI-FORD-9-/150576340160?pt=Motors_Car_Truck_Parts_Accessories&hash=item230f0c9cc0#ht_500wt_868 (http://cgi.ebay.com/ebaymotors/FORD-MUSTANG-8-EIGHT-INCH-GEAR-TRAC-LOC-POSI-FORD-9-/150576340160?pt=Motors_Car_Truck_Parts_Accessories&hash=item230f0c9cc0#ht_500wt_868)
Hello,
First I would like to say that the problem is far more the engine than the rear end gear ratio. You have a mid 70's, 4 cylinder car with a very anemic engine. Going numerically higher might (and I do mean might) give the impression of fast acceleration. But..., because of the lack of torque at higher RPM's (called horsepower) the car falls on its face as you get up there in the RPM's.
There are a number of factors in maximizing your engine/car and even here "intended purpose" must be considered.
1. What is the RPM capability of your engine?
2. Where is the maximum torque of your engine (and how far is the spread).
3. What is the weight of your car.
4. From here you can then calculate the divetrain factors.
5. The beginning ratio (1st gear) and the ending ratio (typically 4th or 5th gear ar considered).
6. The spread between the gears (all) become a factor.
7. Tire size is a factor*.
8. Then lastly the rear end ratio become a factor.
*Please note that changing tire size as listed in point #7 is the same as changing rear end ratios.
That said, it is my opinion that the best ratio that considers performance, engine durability and fuel economy is 3.25. I say they from the perspective of having a Turbo 2.3 with a T-5, 3.97 first gear and 3.00 rear end gears. Unfortunately I have been told that Ford only used the 3.25 gears in very specialized and limited application.
If you go looking for an 8" rear end you will likely find 3.00 and 3.55. While they do offer a 3.40 in the 8" I have found it not to be common. Other ratios would have to be aftermarket gears.
Regarding a T-5; the 2.3 T-5 will not fit, nor will it hold up under a V-8. You will need the V-8 T-5. And surprise, with a V-8 I would recommend the 3.40 gears with tall tires (15"-up) or 3.00 gears with short 13" tires. Again these would be compromise ratios over the mentioned 3.25. Living in Hawaii you must pay dearly for the rising price of gas. Using the lowest (numerical) practical ratio possible would be in your best financial interest.
As a final note of reference to what I have stated; I have a 1973 Datsun 510. I put 215-50-13" tires on it. These are very short tires. With the stock 3.90 rear end the car had no presence of acceleration. I would be shifting into 3rd gear before crossing an intersection. I replaced the rear end with a 240Z 3.36 rear end. Now the car felt like it had some acceleration! Why? Because that ratio took the best advantage of the torque the engine developed at a low RPM. It was also nice not to be going 60 MPH on the freeway at 4,000 RPM.
So, it is all about the torque, how broad its curve is, then tire size, tranny, then rear end ratios.
Tom
Jippah, I think you are referring to my 78 Sedan.
Keep in mind that my motor has been rebuilt and the cylinders bored out .024 of an inch. I run a 92 mustang roller camshaft as well. While all of that may not be relative to how the 3.40 axle affects my acceleration, it possibly could (I don't know for sure).
Take into account that my original axle is a 2.73 gear ratio. Going from the high ratio of 2.73 to one as low as 3.40 is a enormous jump. My 78 with the original axle was slower than a turtle from a stop and with the 3.40 I can actually keep up my my 07 Saturn ion under normal acceleration.
I have never in my live driven a muscle or sports car, so I have no idea what it is like to drive a small car with a good amount of power. The closest I have gotten to that was my friends 75 304 V8 Jeep. It sat for 30 years and we got it running. The carb isn't tuned and it has never had any motor, head, or carb work done to it. With the stock 3spd transmission it really HAULS!
Update since my 78 now has an 8" axle with 3.00 gears in it.
The car doesn't drive any differently aside from acceleration time. It isn't as jumpy to get up and go as it was with the 3.40 gears, but it definitely is nicer to drive on the freeway at 65 and 75 mph speeds!
Before, with the 3.40 gears, I was going 65MPH at nearly 3500RPM. Now with the 3.00 gears it's almost at 3k RPM, but that difference is very noticeable when it comes to engine noise.
I set my red line on my tachometer to 4k RPM. I know that the 2.3 loves to rev, but I baby the car. It was my mothers since it was new, and has lasted 33 years now and only two owners (me being the second). I don't plan to transfer ownership until my daughter learns to drive, and drive safely. It's a family heirloom!
With my v8 swap, I found a Fairmont 3rd member with 2.79 ratio. It is tall and I do not need to shift under power into 4th (only have a 4 speed) until past 80. On the freeway, I can cruise at 75 turning only 1700 rpms. I have been tracking one of those posi units and will get one with 3.00 gearing since my 351 has enough torque to motivate it down the street just fine. First gear is almost useless, but can still be fun