in the process of swapping out my 300/st300 in my 65 skylark with a 430/200-4R. Currently has the stock 2.78 in it. What would be a good ratio to run? I do a lot of highway driving with the car. Also running 275/60/R15 tires out back
3.08 is the ultimate compromise. You can also fine tune things with tire height. Gear ratios for A bodies are usually based on a stock tire height of 26.6". A taller tire numerically reduces the gear, shorter tires do the opposite. As an example, I run 3.73 gears out back with a P275/60R-15 which is 28" tall. Since tire circumference varies directly with tire diameter, a simple proportion lets you figure out final drive. Stock tire height/new tire height X ratio = Final Drive, 26.6/28 X 3.73 = 3.54. If you want to run a 3.23, you can run a 28" tire on the street and get 3.07 final drive, and a 26" Drag Radial at the track and have 3.30s.
I vote a 308. If you cruise a lot on the highway, you will have the torque to pull away from/pass those pesky fords, at 85+ mph. They will look at you cross eyed when you finally give them a break and let them catch up.
I stayed on the conservative side. He could run the 3:42 during the whole metamorphosis and have a great combination in the end. He could get a 3:55 with that 8.2”. That is would be ideal.
When I build rears for guys that are running overdrives,I will use a 3:42-3:73 for big blocks,and 3:73-4:10 for small blocks. He is running a big block and mentioned a LOT of highway driving. You also need to consider that today’s speed limits are higher. When the 80’s G-bodies were built,the speed limits were still around 55. Now,most are 70 or more. Another difference in rpm. Another issue is that some of the older AC compressor clutches will disengage once the rpms get too high,so you could be buzzing down the highway,on a hot day,with no AC. He is running a 28” tall rear tire,so a 3:55 would still be a safe bet.
I run a 275 60 15 with a 200 4r trans. 3.55 gear 2000 rpms is 70 mph 2500 rpm is 85 mph With converter in lockup. I live in the country where roads are 35 to 45 mph. Most of the time i leave the car in 3rd until i get up over 50 mph. I use a 2800 stall converter so low speed driving is still fun but on long road trips fuel mileage is managable and rpms are tame in lockup.
x2. Even with a 3.73, your final ratio in OD will be a 2.50. Anything much lower than that will lug the engine at lower rpm. I run a 4.10 in mine.
Yes on the highway miles. When I’m home my commute is 60 miles one way. All highway. I LOVE driving my car and try to do it a few times a week in the summer. (And it saves miles on my lease vehicle) The car will never see the track. That’s why I’m staying with a stock 430. Which I’m sure will feel like a rocket ship after driving it with the 300.
I thought maybe you missed that last night when I seen your reply. Just didn’t get a chance to respond.
Well that is all great BUT...but... there is no 3.42 in that rear, only 3.36 or 3.55 in that year rear. (64-67 BOP) I would taker the 3.55 gears I hd them in with a over drive for 5-6 years and loved the all around good performance with the OVER DRIVE 700r4 rear. 26.5 tall tires 295 50 15 tires. Jim J D
