will work the best for my effie with a 302 and c4. i'm not looking for a tire smoker just a respectable around town rear gear that also will cruise along at 55 to 65 mph on the open road . thanks

 

Good question I have same setup. Bought a 9 inch from another member with 3.89 gears and thinking they will be too high for highway cruising.

 

thanks ,i am looking at a 9in that has 2.75s but i think that it would be gutless for low end torque .

 

I think a happy medium with a little grunt(behind) to it would be a 3.25 ratio

 

the best cruising gear ration range is 2.75-3.50 depending of course on your engine/trans combo IMHO. This is a cruising set we're looking for right ?? so we want lower rpms at cruise and better gas mileage.

There are formula's out there on the net where you can figure your engine cruise rpm based on your tire diameter and gear ratio, etc.

A 302/C4 (unless it's built strong) isn't going to have the low end torque of a big block... so I'd look on the higher end of the range 3.25 or 3.5.

A big block with a 3.5 will smoke a set of tires pretty much at will... so 2.75 or 3.25 would work better.

if it were me ??? I'd look for a 3.5 posi unit. This will of course be argued through probably 40-50 posts and then you can take the average


55-65 ???? Grandma's gonna run you over on the freeway !!!

later
John

 

thanks john , you haven't steered me wrong in the past . yeah my 302 is pretty much stock and your right granny will most likely run me over but i live in vermont state where 55 is the max. posted speed limit except on a very few roads that will allow 65 . it works out for me though cause i'm an ole fart lol.

 

I have the same setup 302/C4 I had a WER 2:47 from a Ford Granada it was pretty good on the highway however, trying to spin the tires took some doing. I replaced it with a 3:55 from an explorer I can tell the difference in the sound of the engine (higher RPMs) when I'm on the interstate. It has a pretty quick take-off and will easily spin the tires. I think my gas mileage was better with the 2:47.

 

Given the speeds you want to cruise and the hp you have to play with, a 3.50:1 would be perfect. If you want to smoke the tires, just get a standard "one legged" 9-inch and you'll peel the right rear tire at will. I run a 3.50:1 posi behind my warmed-up 351C and it provides a great hole shot. Cruising at 70 wrings the motor out some, (3200 rpm) but 55-65 would be a piece of cake. A 3.25:1 might be a nice compromise, but with your motor, it won't be very exciting. If you go to a 3.0:1, you'll be pretty gutless off the line, but cruise with good economy. A 2.75:1 or lower will be very disappointing, IMHO.

 

Depends on tire size, too. Tall truck tires or low profile Dubs? There is a downloadable RPM calculator here:
http://www.btc-bci.com/~billben/rpmtire.htm

Don't forget your C-4 will have slip in the torque converter, so if you gear it too tall (low number) it will just slip more in the t.c. IMO 3.50 is the way to go if you're not going over 55.

 

I had a 1974 F100 with 302, 3 on the tree manual, and open 3.25:1 9" rear. That truck was the most fun highway cruiser I ever had. Tromp the pedal and it would MOVE!! 65mph was no problem. That said, with the C4, I'd suggest going to the 3.50:1'ish gears, or try the 3.25's first. My guess is that the more likely one you'll find in the JY, is a 3.25:1 rear anyway.

 

I'm going with the 3.50's for now. I'll swap it out if I don't like it, but I think I'm going to be good..

 

3.25 to 3.50 would probably be a good choice I have the 3.25 with my 5 speed

 

Sorry to resurrect an old thread but here it goes. I have a rebuilt and warmed up Y-block with three speed manual and 3.70 gears in the 9 inch differential. I don't have a tachometer yet but 55 MPH is a comfortable cruise, 65 MPH sounds like the pistons are going to shoot through the hood and I've not found the courage to over 70 MPH. I am considering a gear change to 2.92:1, 3.00:1 or 3.07-ish:1 to bring the engine RPM down so I can keep up with the 70+ MPH on the freeways around here. I don't want to smoke the tires. I just want a well mannered daily driver with reasonable gas milage. I want to keep the 3-speed for now so a transmission swap is out. Gearvendors doesn't have a bolt-on product for the 3-speed.

The Y-block has a 500 cfm Edelbrock sitting on a Blue Thunder intake, 264 degee cam, 95# valve springs and ramhorm dual exhaust. I'm pretty sure the motor has enough horsepower and torque to pull mountain grades of 8% at 65 MPH with the 3.00:1. I just wonder if anybody has some experience that would help me out and keep me from making a big mistake like breaking the transmission.

Thanks, Dave

 

I would use a 3:00 open depending on the height on the tire. If you are running a tall tire go with a 3:25. Exit the exhaust in front of the rear tires and that thing will sound sweet to your ears at about 70 mph. You can also google something like
tire size vs gear ratios and imput your info and research it that way. You want it running around 2500 rpms at 70 mph IMO.

 

There has been several post on this subject in the past. I'm running a 289 with a C4, basically the same setup. I have a 9 inch Ford and was running 3.50 gears. Around town it was great, on highway, I could drive 55 maybe 60 and was taching 3200 RPM. I'm running 28 inch tires. I switched to 2.75 for highway driving and it made a huge difference on the highway and I tached about 2100 rpm at 65 and 70. Very relaxing. The 2.75's are bit gutless on the street. I'm running nearly 300 horsepower so the still comes on strong on the street, but no where near the 3.50 gears. Most people I know are running 3.00 gears for both street and highway. I can switch out the gears to 3.50's but I'm leaving the 2.75 in due to the high gas prices. Not to many people hitting the pedal to the floor with $4.00 a gallon of gas. BTW- the 3.5 gears, I got 14 mpg on highway. The 2.75's I'm getting 21 mpg.