Technical NEED HELP WITH QC REAR END RATIOS FOR FLATHEAD W/ T5 TRANSMISSION

Hi,
I am getting close to final assembly of the QC and time has come for me to select a gear ratio for the rear end. Still far away from driving...
First time trying to figure out ratios and with so many options, I am just lost....Total greenhorn here!
I am hoping to get some help, maybe an advise from someone with a similar set up, but most important, how do I figure it out???

Would like to get a good set of gears, a good starting point, that would give me reasonable RPMs for driving around town and 60 -70 mph on the highway.
I know I can switch gears later one and fine tune. it but where do I start?

I have a freshly rebuilt stock 59AB flathead with an '80s T5 transmission and a Winters V8 quick change. I will be running 16-750 rear tires, so 31" tall. All, in a '31 Model A Roadster.
I am assuming RPM target for a flathead, 2,300-2,500

I've been reading and searching all that I can but the results I am finding are all over the place and no longer know what's right

One of the vendors recommended set #1. 3.78/3.78
Most searches recommended, Set #3, 3.48/4.11
A calculator I found, the only one simple enough for the layman, came up with

2,400 rpm x 31" tire size = 74,400
74,400 ÷ 70 mph = 1,062.85714
1,062.85714 ÷ 336 = 3.16326531 overall ratio
3.16326531 ÷ 0.7 = 4.51 rear end ratio

3.20/4.47, set #4 ??

Yeah, I am lost

Thank for all and any help.

 

This is about as simple of find your rpm for speed, tire size, rear gear ration and trans gear ration as you will ever find. I used it yesterday to figure out that some flathead they showed on FB that allegedly did 101 mph in low gear back in the day would have to have been turning over 14000 rpms to do it.

Calculate RPM for Given Speed(MPH), Rear Gear Ratio, and Trans Gear Ratio (purperformance.com)

This one (don't laugh too quick) is off an electric vehicle page. It is beyond simple and you can plug in three and it will give you the fourth. With an overdrive trans you do have to multiply the trans gear ration by the ring and pinion ratio to get a corrected ratio. It is probably the simplest calculator for finding any of the four items by putting in the other three.
Tire Size, RPM, Speed, and Differential Ratio Calculator (advanced-ev.com)

Other than that, every engine seems to have it's happy spot rolling down the long roads. That rpm that everything just jives and it runs great, gets reasonable fuel mileage and you just cruise.
I haven't had my 8BA on the road yet so I don't know what that will be.

 

This is the guy that knows all about them maybe he can help you out. @GearheadsQCE

 

I’m a simple man, I’d probably run a 3.5-3.9 rear depending on tire size, and let the OD in the T5 do it’s work.

 

No point in getting Set 1 , might as well just have the stock gears and no quickchange. Set 3 is a good starting point but final depends on the original crown wheel and pinion ratio.
The Tremec site has a T5 calculator which just requires your input of the numbers and hit the button.
https://www.tremec.com/calculadora.php
At 2400rpm with a 31 inch tire
3.20 will be 69 in 4th 110 in OD
3.48 ..............63.............100
3.78 ..............59...............93
4.11...............54...............85

 

The 286 flathead in my sedan likes 2,600 RPM best for some reason. I cruise there with my 31.5" tires, 3.78 rear gear, and no overdrive and it's around 65 MPH I think.

If you are going to have an overdrive of 0.7 I'd think you could have a rear gear of 4.11 really easily as a starting point. Then have a couple other sets close by there to fine tune.

My little bro and I just bought a few sets of genuine Halibrand V8 gear changes from Speedway on sale for $40 each. Maybe they have some Winters V8 on sale too?

 

I recommend 3.78 rear gears to all my chassis customers who are running a T5 and Flathead. Most of them are using a 30-31 inch tall tire so the 3.78 works out fine. Done 100's of them.

 

I have set #3 in my Winters Champ, in the 4:11 configuration. 8BA, T-5, 30" tall tires, I run 2000 RPM at 72-73 MPH.

 

I'm running a 3:25 gear 31.5 tire
5 speed .86 overdrive
With a warmed over flat original motor
29 roadster 60 mph is right around maybe 2200 can't remember exactly
Cars runs down road nicely at 60-70 plus
Top speed i ever got out of it was just over 85


Sent from my iPhone using Tapatalk

 

With your flatty and a T5 you want your final drive to be 4.11:1 or a little lower.

Here is my logic on this. I had an '88 S-10 for a while that had a banger and a T5. The final drive was 4.10:1. The banger was as healthy as they came, rated at 195 HP as opposed to the 100 HP rating for your flathead. 2500 LB vehicle. Out on the highway I was down into 4th and sometimes 3rd when I came up to a hill.

 

Totally agree and this can't be overstated.
Tall tires and depending on your choice of S10 T5, will dictate rear gears.
The early T5 with its 4.03 1st gear and .86 5th might not like 4.11s though. The 1st gear would be like granny stumper low.
The later T5 with 3.76 1st gear and .72 5th will like 4.11 gears and 31 inch tires.
Cruising at 2000 RPM might not be great, more like 2400 to 2600 as mentioned above. Heck these older engines don't go down the highway happy at 1600 RPM like my RAM...lol

 

A lot of what I see on the HAMB is OD combined with tall tires and tall gears and these guys are getting lousy fuel mileage as well and not being able to pull an old sick woman off a bed pan. You got to keep your cruising RPM in your power band.

Here is one that you will appreciate. One of the fellas here was using my 355 backed up by a 200R and a 2.8 gear with 30" tires (maybe 31s). My motor makes plenty of torque but keeping it at its sweet spot of 3K he got a ticket for running 135+. The cost of gears would have been way less then the ticket. LOL

 

I'm with Krylon32 on this one. 3.78s are what I chose. S10 1985 NWC T5, Winters QC, and 33" tires.

 

I question your speedo or tach, as your speed should be closer to 60 mph with 4:11s, 30" tires and 2000 rpm in OD. That's what my '32 speed/rpm was with 31" tires before I switched to 4:30s because of a cam change.

 

So about what hp does a stock or mildly modified flathead make at 2000/2200 rpm?

 

Dang !

 

3.78 gear, .69 overdrive will give 1978 rpm at 70 mph.

 

Thank all for your feedback. Wow! A lot of info to digest.
The more I read and the more I am leaning towards buying additional set from the get go and start doing dome tests.

Again, thank you! Keep any info coming. Would like to learn all I can.

 

I was wondering when someone was going to bring up the wide variety of ratios a T-5 might have. Particularly 1st and 5th. Might want to check that out. Having had the proper rear end ratio for cruising, I had a 3+ something first, and had to shift to second in the Safeway parking lot.

 

Assuming I have a stock S10 T5, is there an easy way to know what ratios it has, without having to open the transmission?

 

Shift it into whatever gear you are wondering about, put a mark on the input and outputs, turn the input a whole turn or ten, and count the output rotations. Then divide that fraction.

 

There is only .8 and .69 OD in T5s

 

Bingo

 

I bought a set of gears that didnt change the ratio of the rear end to start with, like 21-21 gears..I might be wrong on 21-21....Then i bougt another set for racing...I still havent used the second set

 

@97 and @krylon32 are right. There is no need for a #1 set as no matter which gear is on top you still have a final drive that is the same as the ring & pinion. A 3.78 with aT5 will be very close to optimum with a flathead.
The only thing you didn't mention was the R&P of the Winters. Depending on which "V8" center you have, the R&P could be 3.78 or 4.11. That will make a difference.

A bit of added information:
The helical gear set selection is very limited. you don't have many good choices for a street rod with 4.11.
Halibrand and Winters (and everyone else's) 6 spline gear sets are interchangeable. Just be sure you have the right thickness. Most are 1 3/8" wide but some are only 1".

 

A bit of added information:
The helical gear set selection is very limited. you don't have many good choices for a street rod with 4.11.
Halibrand and Winters (and everyone else's) 6 spline gear sets are interchangeable. Just be sure you have the right thickness. Most are 1 3/8" wide but some are only 1".[/QUOTE]

R&P in my Winters is 3.78

Do helical gears make a big difference when it comes to reducing noise?
I plan to run silencers inside lakesters mufflers, so I figure that and with it being a roadster that I probably won't hear the noise from straight cut gears

 

Helical gears do make a substantial difference in noise level. Be sure you get the shim pack to reduce the end clearance. Also, getting the backlash and carrier preload right makes a BIG difference.

Message me if you need more help.

Bruce

 

I don't understand why you'd run a quickchange with a T5.
With a stock rear end, you have desirable performance from a standing start for an engine that is designed to run at that rev range around the street, and with the T5's overdrive you have the legs to prevent running over the desired rev range at YOUR desired Freeway speed.
A quickchange with a three speed transmission - well that's a different story.
To me, there's no need for an infinite number of gear ratios to run on the frereway, but then again, that's just my opinion!
And yes, I do like the look of a quickchange under a hot rod, just as much as any other true-blooded hot rodder.
I just don't see the need for both a quickie and a T5.

 

All I know is that its nice to cruise in my wifes 4 cyl SUV at 80 mph, appx 2000 rpms, and knock down well over 25 mpg........and it ain't really a slouch getting on the on ramps. Gears are our friends.

We used to make a hydraulic pump in our machine shop. It had what looked similar in shape to the cylinders on a revolver. Instead of putting bullets in it, it had small pistons. At one end slightly away from the cylinders, was a plate that could be tilted to various angles. The plate had small connecting rods attached in a ball socket. The other end of the connecting rod attached to the pistons .....also in a ball socket. As the unit rotated, changing the angle of the plate changed how deeply the pistons went into the cylinders. Basically it was an infinitely variable ratio. I always thought that someday automobiles would tend to run the engine at its best/most efficient rpm and then just vary the transmission ratio to suit it. Of course there would need to be a manual over ride (gas pedal), but the trans would then adjust to the requested rpm.....infinitely. Always the perfect ratio for the moment.

 

some GM a/c compressors were like that.