29 Ford/302/C4/29" Rear Tires Getting a new center section. Current one is 8" 2.79. Never had it on a dyno so not sure how much HP I actually have. I'd say somewhere around 300-325. Want some more acceleration/torque but don't want to be screaming at highway speeds. Like something in the middle. Was thinking 3.00 or 3.25. Any advice?
With your current setup, you're around 2250rpm @ 70mph, with 3.0's you'll turn 2450rpm @ 70mph, and with 3.25's you'll turn 2650 @ 70mph.
You'll surely notice it from the seat, but it's not going to be drastic, which is what you're looking for. I had a truck with a similar set up. Mild SBC, TH400, and 2.73 gear with a 28" tire. I swapped the rear out for a 3.08 gear and it felt a little more spicy around town, but the slight increase in highway RPM's didn't bother me. I did change my normal highway cruising speed from 80mph to around 76mph to stay in that sweet spot of RPM's to keep the exhaust from droning. On the flip side, I went from 3.27's to 4.10's on a street car back in high school and it was awful on the highway, but the speed limit was still 55 back then.
Yes, you'll notice a bit of a difference with 3.00 gears. But nothing like you'll get with some real gears...3.70, etc You really need to figure out what you mean by "screaming". I'm usually good with 3000 or so on a little engine like that. A big block, would be happier with a bit less, but 2500 is just fine.
If you’re driving on the freeway occasionally I’d go 3.5-3.7. If more often than not on the freeway I’d go 3.25’s. 8” ratios aren’t as common as the 9” varity, so keep that in mind.
Leave what you have, perfect for freeway driving especially with the small rear tires you are running.
Yes, but not a whole lot. Personally, I'd go for the 3.25; I ran a similar setup only with smaller tires (25" diameter) and while that put 70 MPH at about 3K RPM, I still got 17-18 MPG and the car was very lively at lower speeds. So with your taller tires, mileage should go up a bit and while that will reduce low speed acceleration, it will be much more noticeable compared to the 3 flat gears. To get the same RPM I had with your tires, you'd have to go down to a 3.7 axle ratio. Tire diameter can make a big difference. You may even want to consider a 3.5 ratio, that would put 70 MPH cruise RPM at about 2800. SBFs like RPM to produce power...
In my experience with a light car ( As & 32) and a very stock-ish to mild engine 327 & 350 with 28-29 tall tire , 3:50 gear 3,000 rpm 70ish mph , A 3:43 gear 2,,700 rpm @ 70 ish , 3:20 ish gear 2,400 rpm @70 , Then a 3:70 ish gear was 3,300 rpm @70 . all based on 1 to 1 in drive . My 427 sbc combo I prefer in A or 32 Like a 3:00 , I'm just different with big torque & Hp
Last 8” I ran (similar hp as your sbf) had me work up from my 2.79 starting point to 3.55 and eventually 3.80s before it was snappy enough for some real fun. The big BUT was that I also crept up on tire size as I went (I may have had an issue with keeping tread on my tires when I was younger). Please note that car didn’t see much highway. If it did, I’d probably have stayed with the 3.55 gear set with my 750-16 tires. If you stay in that 29” tire size, I’d probably go the 3.25 gear set. I know a couple guys that run the mid 3 gear sets (one with 820-15 tires in a fender car and one with 700-16 tires on his highboy) and they seem to be pretty happy.
I'd look at the 3.25 to 3.50 if it were me. It'd feel a whole lot more peppy around town and being a small block ford they like too rev. To small to make a bunch of low end torque so compensate with gears. I had a 327 turbo 400 with 4.88 gears and 29" tall tires, it was a beast. A bunch of rpms on the highway but being a small block it didn't mind. Didn't worry about gas milage, after all it was a hot rod not an econo box. ..
My avatar has 3.42 rear gears with a 31" tall rear tire. The overall ratio ends up close to your 29" tire with a 3.25 ratio. I take mine on long road trips with a 455 Buick and it works well. Through Montana, I set the cruise at 75 MPH and just keep it there. Your 302 will live a long and happy life with the 3.25 rear gears and those 29" tall tires. If you want to drive at 85 MPH, get an AOD.
Get some 5.38's, an AOD and stick a Gear Vendors on the back of the trans. That should let you run mid 8's in the quarter while also giving you a top speed somewhere north of 314 mph ... if my math is corretc
What are your plans for the car? I once had two identical small block ford powered cars, one with 373 and one with 273 gears. The 373 gear car had lots of acceleration and was a blast to drive, but annoying on the highway with a cherry bomb muffler. The 273 gear car was a great cruiser but lazy off the line. Now I have one with 308 gears and it’s the best of both worlds. however that 273 geared car was the king of smoky burnouts because you could get so much wheel speed in 1st gear!
The best way to "have your cake and eat it" is to swap in a 3.7:1 to 4.1:1 rear ratio THEN put an AOD trans in front of it. 4.1 rear x 0.67 AOD o/d = 2.5:1 At 70mph your car will cruise at 2228 rpm with those tyres And it will wake up in the lower gears
Give some honest thought to your driving style and how many trips you will actually take. Do you do most driving around town and the surrounding, less populated country roads where you can chirp the tires "just because"? (This means you prioritize having fun getting feedback from a responsive throttle.) Or do you think that you will do a major share of your miles on the 70+ interstates? (This means you want to arrive at the end of your drive somewhat refreshed and not feeling like you need to lie down in a quiet place for a little while.) If it turns out that you picked wrong, you can still play some minor games within reason with your tire size, depending on how willing you are to mess with that perfect, picturebook stance you are so proud of. (I'm talking minor size changes but 'minor' tire changes still cost you money.) Ultimately, you have to pick your poison. We can only tell you which poison tastes good to us.
If you want more acceleration from the stop sign, add a modern higher stall torque converter, if you have the stock Ford converter! You will really notice some difference, with your high geared rear end and will still have good freeway performance! Bones
These links are to a couple of speed, tire size gear ratio, rpm calculators that I refer to quite a bit. The first one, you put in speed, tire size rear gear ratio and get rpm as the result PH), Rear Gear Ratio, and Trans Gear Ratio (purperformance.com) This one you put in three factors and get the fourth but if you have an overdrive tran you have to multiply the od ratio of the trans by the rear end ratio to get "gear ratio" for the gear ratio input. Tire Size, RPM, Speed, and Differential Ratio Calculator (advanced-ev.com)
You ain't give us enough info....... Is it snotty? Small convertor? What's it weigh? Around town(to the shows)? Freeway cruiser? Trac-loc rear end? Like to do burnouts(or are you sane?!) Gas mileage impotent? What kind of mufflers you got? All ^^^ goes into the figger'n ! 6sally6
Find someone with a set of 27" tires and try them out, that will be pretty close to 3.08 gear with your tires and rear gear. 25" tires will get you close to a 3.23.
Been there since the days of 2-speed autos and 3-speed manuals. Small blocks benefit from lotsa gears. If you're a real Hamburger, maybe find a 3-speed overdrive. If you're in the closet, consider a 5-speed or an AOD. Again, back in the day, cruisin' at 3,000-plus was the order of the day. In this wimp century, we're conditioned to double-overdrive trannys which cruise at 2,000 RPM @ 80 MPH. Some Hamburgers have ears to tolerate high-R cruisin', some don't. Your money, your build, your decision. jack vines
funny thing is I just got back from a 3k mile trip with my wife in her new (2023) sporty car, no overdrive, over 3k rpm most of the time. And it was fine. I do the same in the old cars....planning to take a 5k mile trip next month with 3.08 gears behind a Muncie and a 327, it's sweet spot on the highway is 75 at just under 3000 rpm.
Engines are fine running around the 3000 rpm mark at cruise speed. The whole low rev at cruise thing is all about fuel efficiency and emission control.
I would go with a 3.55. That gets you just out of the timing curve in the distributor for stability, plus it'll be noticeably more fun.
As a few mentioned, a pair of wheels and tires are cheaper and easier to swap out and try out. Once you have the gearing where you like it, then decide on what tires you like best and plug those numbers into one of the calculators to pick your gears.
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