Hot Rods Gear ratios and diff ratios - what's the ideal combination?

I have a 3.50 ring and pinion with a 200 4-R and a 28.5" tall tire. I cruise 70 at 2000 with a 350 SBC. I was getting 20 mpg this last trip. 80 mph was 2500.

My little 283 always like the 3.36 rear gear.

 

Every Monday and Wednesday my drive is about 100 miles each way. About 2500 rpm at 55 but I'm usually running anywhere between 3-4000 rpm.

 

So many good experiences here. I have heard of people getting 23mpg with a 283 sitting around 2200rpm so that's the target rpm I want to go for. I'll need to investigate what cam would work for this. Here's my plan:

283 - rebuilt
Alloy Heads & intake (I want to save weight where ever possible - as the 235s were lighter and I'm running a stock front end with original manual steering box)
Spread bore Quadrajet - small primaries and jets
World Class T5 Box with a .72 or .73 overdrive
3.55 Diff ratio
27" tires

According to the RPM calculator at www.csgnetwork.com/multirpmcalc.html
I will be sitting at 2179rpm at my highest cruising speed (70mph) in 5th with this setup.


The vehicle weighs 1400kgs, rides low to the ground and has a roof chop, so its pretty slippy in the air.

Cams are uncharted territory for me, but this is where I'm at so far.

 

• My OT 66 FE Fairlane had a happy medium and economy at 3.25:1. It cruised well with plenty of acceleration from a dead stop or when rolling, 2,500rpm @ 60mph. 3.89:1 on the contrary on the highway had it at 3,100rpm @ 60mph with 215.70.14 (25.9").
• My 35 has 3.54:1 with 700R and 235.75.15 (27") tyres, cruises at roughly 2,000rpm @ 65mph.
• My DD SUV has 3.73:1 and 235.75.15 tyres, cruises at roughly 1,900rpm @ 60mph

Rule of thumb I go by is engine RPM at cruising speed should be from 1,800rpm to 2,100rpm.

 

Nice to see that move up and away from 2.87 and 3.08.

These old school engines with carburetors need to be at a bare minimum of 2000 Rpm to work.


The alloy heads, what are you planning on there?
You'll need more compression with aluminum heads-Usually at least 1 full point. be mindful of the ports and valve sizes of the heads on your small bore block as well as the port and runner size. Larger port volumes and shrouded valves with the small swept volume of the 283 will drop the velocity thru the port and a loss of velocity kills torque.

 

Hello,

Our little high school group had a bevy of Chevy cars. ( A 55 2 door post, a 56 2 door post, a 57 2 door, Bel Air hardtop, and my 58 Chevy Impala. ) The transmissions and gear ratios were all stock with all cars being stick shift. All v8 motors and all 3 speeds. The 55 was the easiest to drive and just go anywhere with the small v8 and gear ratio of 3:56. The 56 somehow had a 3:56 in it while the 57 had 4:11 gears.

Remember, these cars were all bought used and the former owners did what they did by the time my friends bought their cars. The second owners just used what was there. My new 58 Impala had special order 4:11s in the back. But, my brother and I bought a complete 4:56 third member to make quick exchanges for the drags.

Driving in all of those cars, the easiest car to make long distance drives was the stock 55 2 door post car. The v8 had just enough power and the rear gears were perfect for highway cruising. For some reason, when we changed the 57 from the stock 3 speed to the 4 speed, it became the easiest to drive. There was something in that 4 speed to make it run well in those freeway speeds, despite the dual quads and 4:11 rear.

Now, my 58 Impala was the hardest to drive when it was a 3 speed and when it was changed over to the 4:56 gears for the drags. I was responsible for changing the third member every Thursday for the Friday night drags and the all day Saturday drags at Lions.

Now here is the great part, from 55 to about 64, the third member units were interchangeable between the models. That was one of the reasons my brother and I got our hands on a 56 Chevy complete rear axle set up with 3:70s for gears for our 1960, 40 Willys build. Now, we had a 3:70, 4:11 and 4:56 Chevy third members to play around with for each specific purpose.

During the heyday of 58-59, we used the 58 Impala in the A/Stock car class at Lions Dragstrip. I was responsible for exchanging the 4:11 out for the 4:56 weekly. That went on for those years until we were no longer competitive against cars in the same class with at least 45 more HP from the factory.

Jnaki

What did the 3:70 gears do for the 58 Chevy? (“Absolutely nothing!” to quote a laugh from Seinfeld and song from War/Edwin Starr) You would think that with the power from the 348/280 hp motor, it would pull in all gears. The 57 Bel Air with the dual quads and 3 speed stayed up with me and sometimes would be out in front. Those 3:70 gears did not do anything for us at all, so I gave the whole unit to the owner of the 56 silver 2 door post car (above friend) to make more power for him. It did and he was happy.


Now, the standard street driving rear gear for the 58 Impala was the 4:11 and sometimes the 4:56. But, driving on the street with the 4:56 gears in the Impala was a screamer and long distance driving was not too much fun. A long drive from Long Beach out to Pomona (and back) for the Winternationals was a high pitched drive, that caused some hilarity. But, for those stop lights to stop lights it was outrageous. It also helped tremendously at the Friday night drags and against those more powerful 59 and early 60’s Chevys in A/Stock. As for the Willys in 1960, these 3:70 gears also did “Absolutely nothing !” So, the standard in the Willys was the potent, 4:56 gear ratio.

 

I can't give you much advice, but I can tell you that my '62 Chevy biscayne has a mild cam in a 283 (I don't know what cam.. my grandpa built the engine) and I run a 700r4 which has overdrive. I have a 3.20 rear end and I crank about 2000 rpm at 70. It's absolutely perfect. It tears up the highway


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I have a 355 SBC with a 9.75 CR, Lunati 268/276 Voodoo cam, Dart aluminum heads and dual plane air gap intake, 700 Holley. Rear is a 3.89, I was running a 3.56 rear and it was doggy around town, lugging too much. The 3.89 made it a different car. At 70 RPMs are around 3200, so it seems to be pretty happy. Lunati recommended gears with the cam and they were right.

 

Consider vortec heads, 862 or 706 castings, 1999-2005. Used on 4.8 liter (293 cubic inch), Chevy trucks and SUV.
These are very efficient heads with excellent chambers and should provide the best low rpm port velocity where you need it, you will need a vortec specific intake. 500 cfm carb, maybe even a 2bbl.

Figure out your T5 gearing and set up, a T5 from a camaro sounds right as it was geared for a small V8. Others may chime on with best gear mix and model T5. Look for 3.20 -3.40 range rear. Sounds like you're looking for an existing rear end and not setting it up, use what you can find that about the right range.

Cam it from there, don't need much of a cam, but the tech line can set you up with best mix of lift, duration to put you where you need. Low rpm velocity, with a little kick.

Run a good ignition, I'd say a new quality brand stock HEI, not traditional but reliable, parts readily available. Put in the effort to get the timing and curve dialed in, you can pick up a lot of mpg gain with good tuning.

Very general advice, based on what's available, so there's always tradeoffs.

 

One of the big factors is fuel quality low highway RPM and to much compresson don't work well together. New cars get buy because of electronics.