Hey yall. Im building a Model A Tudor and need a bit of help/insight in choosing the right rear Axle. Plan is 312 YBlock, T10 wide ratio 4speed, 750-16 rear tires. need a rear axle insight. What gear ratio? Thanks!
@LarsL In my opinion, 3.25 ish to 3.50 ish…….the wide ratio trans has a fairly low first gear (2.54 I think) to handle your larger diameter rear tires and your car will be light enough to cruise easily with maximum of mid 3’s ratio. Ray
Figure out where you want to be, RPM wise.. say at 65 mph and then Google “RPM calculator “. There’s a bunch out there. You plug in your tire size, rear end ratio, and tranny fourth gear and it’ll figure it out for you.
http://users.erols.com/srweiss/calcrgr.htm I am running a T10 wide ratio, similar tire and a 3.70 rear gear for 3000 RPM at 70 MPH in my Tudor.
I don’t think that y block will be happy at 3000 rpm cruise speed for long. I’m thinking somewhere around 3.30.
Google is your fiend..! No secrets here... As mentioned, RPM/gear ratio calculators are abound in the net. Input your tire diameter, 1 to 1 final drive, pick an RPM you want...it'll spit out the gear ratio..! Mike
It might be that he doesn't know how to pick an RPM. I think Ray is right, 3.25 to 3.5 should work pretty well. Of course the only way to know if it's perfect for you, is to drive it for a while.
Nothing wrong with 3000 rom..! I've driven my ol 259 Stude at 3000/3200 rpm for hours at a time, several times going to out of town races. I sold the car with 93K miles and still running just fine. Personally, 3.50 would be my minimum for good performance in both in town and freeway driving. Mike
the only recent Y block experience I have is an Edsel, stock 292, kind of heavy car, 3 speed (they're wide ratio) with OD that quit half way through a long trip. It had 3.55 gears and kind of short 14" tires. It liked cruising 75 when the overdrive worked, but it still managed 70 or so without it. So, with taller tires, 3.5 would be decent. A lighter car, and more transmission gears available, would be easier on the engine. I know we used to cruise down the highway at 3000 plus RPM in the old days, and everything was fine...but today, most folks seem to think you're torturing the engine by doing that, so the trend is to go mild on the rear gearing, or add OD.
Your tires are taller and your car is lighter and I have 2.74’s behind my y-block. 70mph is 2200 rpm.. I didn’t like the 3.21’s on the highway. I use a site called gearcalc but there are others if you know the diameter of the tires.
Your tires are almost 32 inches in diameter. I would use one of the online gear-ratio calculators, like Strange, starting with a 3.50 axle ratio. If you spend much time on the highway, pick a cruising rpm that will work with your cam, but not as big an issue with manual transmissions, particularly in a light car. A numerically higher gear ratio will be more fun, except on the highway. A y-block won't have more trouble cruising at 3000 rpm than any other engine, but I prefer 2200.
X-2! I doubt you're gonna do any more than 'cruise-it' so think more about fuel mileage. Lower RPM also means less noisy(or music!) when on the freeway going TO the shows. IMHO 6sally6
I can cruise 3000 rpm's with a SBC too, and it has no problem doing it. But I sure don't enjoy hearing it singing along at 3000 rpm's! And a Y block doesn't like that rpm steadily as easily as a SBC does. If it was mine I'd stick with the 3.25 gears too. In a vehicle that light you wont have bad performance with 3.25's and the engine will like a little less rpm's at freeway speeds a lot more.
First question should be “ do you want a cruiser or a stop light rocket?” It makes a huge difference in rear end ratios as to what you do with your car the most. Like mentioned 3000 rpm down the highway is well with in the Y-blocks capabilities , but not real pleasant for hundreds of miles. 2000/2200 would be better for that. But if your car never sees the interstate, a lower gear would be in order. Also the 312 will pull that light car very good with relatively high gears! Bones
For a non overdrive transmission this EV as in electric vehicle speed, rpm tire size final gear ration calculator is about as easy to use as you will find Tire Size, RPM, Speed, and Differential Ratio Calculator (advanced-ev.com) Plug in three quantities and get the fourth. Here with a 29.29 inch tall Coker 700 15 widewhite, 70 mph and a 3.45 gear you are running 2770 rpm down the highway.
LarsL, you'll be looking at approximately 2400 rpm at 65 mph/105 km with 3.50 gears. I think that's a good compromise.
15 posts to get to what is the crux of the question. We all have different needs and expectations of what our rods should do. Cruise rpm versus acceleration capability. What you gain at one end, you lose at the other (unless you go to an OD transmission, but that is not the case here). To give relevent advice, @LarsL needs to tell us what his happy driving situation is............ Here is a good calculator to use. https://spicerparts.com/calculators/engine-rpm-calculator
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