Technical Early V8 gear ratios and highway manners

Yes, I've searched, I know there's nearly a phone book of discussion. But how about some real banter of what the wins and losses are of replacing a 3.78 with a 3.25 gear set. With my 30.5 tall rear tires (7.00-16) a 3.78 spins the motor at 2500 to get me 60 MPH. A 3.25 gives me 70 at that RPM. While we're all aware that low speed acceleration suffers with the 3.25s, is it unbearable? Hill climbing would surely demand a downshift but 90% of my use will be highways and rural roads. Not many hills for me. I'd think the worst I'd experience is my annual trek to Hershey where there's pretty long grade on my route. How bad would that be? I don't have the means to install a QC or Columbia, the latter would surely need to have the beloved "bullet proof" treatment requiring even more initial up front capital. My research says about a $5,000 hit from 'A' to 'Z' turn key ready. I can get a Motive brand gear for $350, and they used to be a quality product but that was 30 years ago. Hit me. Wins n losses. Bad move? Love/hate?

Maybe we can take a scenic route into favored long distance flathead RPMs too. I'm not looking to run with modern traffic and yet I also don't want to be in the way of it. I think extended 3,000 RPMs to hit 70 is a bit much. The engine is a fresh stock postwar 59A which will likely see dual carbs and little else beyond tuning to be all it can be. I think 2500 is probably ok but how bad is a 3.25 gonna be to live with? Who's done it?

A final wrinkle, it's quite possible she gets a SBC some day but it's not one of the 10 commandments in the build plan, just a potential reality. I really want to leave it a flatty. Lookin fwd to the inputs, thanks y'all.

 

Well, I don't have a flatty V8. I have gone from a 4.11 to a 3.4 ratio. You can see the engine at left. About 2600 at 65. I am content . And I am often dragging a teardrop along. Start off is a little "slip" sometimes since the low rang is now faster/higher. Second a lot more in town. I am used to it after 13 years.

Overdrive would be best choice but like you, it was not in the budget.

Ben

 

Remind us again on what the rear axle is?

 

My flathead powered roadster had 3.78s, 750x16s, and a column shift 3 speed. I regularly cruised at 80 mph. Easily kept up with a buddy that had 3.25s.

 

39 Ford, stock banjo, 3.78 gears, 30.5 tall tire.

 

You will hate 3.25s with that tall tire and maybe 100.hp.
Tried that with my F 1 pu. What a turd. On a hill it was 2nd gear screaming at 40 mph. Would go 65 on flat ground, no more. Just not in the power band. Flatty s made their peak rated hp at 3600 rpm
Put in a 5 speed and now it's a joy to drive

 

One other thought: The old Ford 3 speeds had two different first gear ratio possibilities. Kind of a wide ratio close ratio option. I wish I could remember the tooth counts of the two different types, but when I went from a 4:11 to a 3.54 in my pickup, I used the "closer to granny gear" first gear wide ratio setup and never looked back. Yes, first gear is kind of low, but seems to work well for city and highway use.

 

^^ I have a Mitchell in my coupe. It’s been good to me as with my 4.11 rear, I have the best of both worlds for in town or highway use. Worth giving the a call as they are very open to talking with customers about their products and experiences. Good people.

 

You need some sort of overdrive.

Changing rear gears just shifts the problem.

 

This is mostly going how I wanted it to go. 65 max MPH seems pretty limp-wristed to me. I expect a big old Packard to start perspiring at 60-65, but most of them tip the scales over 4,500lbs. This car is like 2,800 so my senses thought otherwise. I drove a 34 3W a couple years ago, all stock. It was happy at 55 and had enough zoot to tickle 65 but I couldn't imagine 3 or 4 hours at that pace.

Mitchell, yes, I've had that in mind as well and it seems NOBODY ever sells one or reverses course. Also a left uppercut to the ribs of my wallet with the ante for that game about $4K. The only bad reviews I've seen were in the user's wrong choice of 26 or 36 percent.

Let's shift gears (yes, pun intended). With my get-up as it stands, am I going to hate screaming between 65-70 for hours on end? I know the motors peak at 3600 and I might see that once ot twice but that's not what the car is about. I'm also aware that I've got 3 or 4 decades of "conditioning" to get over, meaning that like most of us we're now accustomed to the MPH/RPM relationship of newer cars where OD is the industry std. My truck has 3.78 gears and tall tires, almost 32". With the locking convertor I can duplicate the ratio relationships in 4th. Yeah, it's up there close to 3K between 65 n 70. It's diesel too so torque is m***ively available, but it's also out of breath at 3500. Did it as a goof on my way in, got me to thinking, "should I change my gear?" So in my best Paul Harvey, "And now you know, the rest of the story."

You guys are great...

 

I am going to do a little comparing apples to oranges but....

I am running a 261 in my 53 Chevy, Corvette 3spd, 57 Chevy rear. I was running a 3:70 rear gear but changed to a 3:50. I have driven it on long trips 3 hour plus!

I live in a rural part of up state NY I have to travel at least 40 minutes to closest interstate and about the same to the closest 4 lane divided state road.

There are many hills on the east coast and with the 3:50s I find myself having to down shift climb them! I spend as much or more time in 2nd then I do in 3rd!

I picked up a rebuilt 3:70 Posi to go back in.

I was in the 2,500 R.P.M. range at 55 and 3,000 at 65 with the 3:70s

 

If you plan on driving long distance often, I'd spring for an OD of some sort. For occasional use, I'd leave it as is.
Extended 3000 rpm runs shouldn't hurt it, but might increase wear, heat, fuel and possibly oil consumption. Sweet spot for most stockish flatheads is around 2500 rpm IMO

 

Never heard of one until now.

 

While futzing around with OT project, I quickly realized what a dog the thing would be with bigger tires. Not to mention the engine would be screaming at 3K at Hwy speeds. That’s why when I started my flathead powered speedster build, I decided on a T5 right away.

 

I’m running 16-700s with 4:10 gear in my roadster, it’s quick but won’t really spin the tires.
It has a 41 Lincoln Zepher 3speed with a Borg Warner R11, @ 60 mph it’s turning 1825 rpm
They’re out there, May bolt right up to your current ******. All of the components and wire harnesses are available.

also it would be era correct

 

I think it’s probably fine as is. You’re not going to hurt anything letting it cruise at three grand it’s not a new Toyota. I’ve been behind @flatout51 going 80mph for hundreds of miles and he was having zero trouble.

3:25’s and a 700:16 around town isn’t going to be sluggish enough to bother you with a stick shift.

 

Leave the rear alone and put a T170 Toploader [TOD] in between.
You end up with almost stock ratios 1-2-3 and a 0.73 O/D in 4th [and all 4 gears are syncro]

Plenty of people convert the tails to Torque tube [Model A's] so it shouldn't be too difficult
https://www.jalopyjournal.com/forum/threads/flathead-to-t170-rts-adapter.1174598/

 

I was told by Brandon at Eastbay Speed and Custom not to run 3.25s with a basically stock flathead or even a mild one. He runs 3.25s but has a built 276" engine. Personally the 3.78s are perfect for a light car.

 

I had 3.54s with 750 16s behind an SBC and found it to be a great all around gear. Good off the line and not winding out on the highway. I didn’t have a tach but at 70 it was 2700 or so according to an rpm calculator

 

You have several choices to consider.
3.78 rear and an overdrive transmission. Open drive is usually required, though a torque tube adapter is/was available.
3.54 or 3.25 rear, you can keep the 3 speed and torque tube.
Here's a calculator for estimating choices.
RPM Calculator - Engine Speed vs. Vehicle Speed

 

I would think him running the shorter tire with the taller gear would probably even out

 

With the 7.00s and 3.25s it puts you at 2500 at 70. With the 7.50s and 3.25s that's 2,428. With 7.50s and 3.78s it's 2,800 at 70. I've ran mine at 80 which is over 3,200 rpm. Im flathead is also stroked, stock bore, ported, relieved, with 2 carbs. Not sure how a stock flathead would do. My dad's 48 four door has a stock flathead with 6.00x16s and he runs 70 all day with 3.78s. He will be doing 80+ when he gets his columbia working.

 

Obviously im a big fan of 3.78s if I were to change to anything it would be the 3.54s not the 3.25s

 

I suppose a stock postwar 239 would be happy enough with 3.54s. Even if I warmed it a little it won't be much added power. 2 carbs, good ignition, dual ex, that's it. Who knows, the clouds may part and I find a smokin deal on a Columbia...

 

My honest opinion is if the rear end you have is good and just needs brakes and such I would try the 3.78s. You can always order gears and do a weekend swap. That would save you money for now that you could use towards the intake and carbs.

 

While a bit spendy (I get that), some of the other advantages of a Mitchell overdrive includes gear splitting (you now have a 6sp), and the ability to put the Mitchell into neutral while rolling, thereby allowing the Ford trans to be shifted into first gear without the need for rev matching, double clutching and holding your tongue just so, while grinding your way into 1st (with the Mitchell in neutral, the Ford trans doesn't know the car is rolling).

My buddy has one in his '32 stock flathead with dual carbs equipped roadster...and loves it. He regularly pulls a tear drop travel trailer and long hauls the car. His is the first in the row.

 

Clever!

 

Not just overdrive, but double and triple overdrive eight and ten speed transmissions with turbo fours tuning 1800 RPM @ 75 MPH.

We have the same problem over on the Studebaker forum. Everyone loves the look of old cars/trucks, but hates the reality that a 85hp-100hp flathead was never designed for 70-80 MPH freeway cruising.

But yes, trying to fix a three-speed problem by changing the rear gears is akin to making a string longer by cutting a piece off one end and tying it onto the other. Whatever is gained in one place, the same or more is lost in another.

So yes, bottom line, any improvement I could live with would have to be accomplished with an overdrive or a 5-speed.

Bonus tip; any change which loads the engine heavier at a lower RPM should be accompanied by an O2 meter rejetting and a distributor recurving.

jack vines

P.S. it's worth remembering the SBC never had main bearing problems as long as it was revving free and easy. Once GM went to the 700R4 overdrive and computer controls, this allowed the engine to be held in lockup in hard pulls at low RPM, more throttle opening and more load; result was main bearing failures.

jv

 

I've got a 41 Ford with the stock 378 rear end and a stock rebuilt 50 Mercury Flathead and the trans is new and it's got 670/15 tires. I'm building a banjo with 325 gears to see what I can get out of it. I've driven this thing to Vegas and back which is three plus hours and I'm turning about 3,100 the whole way. I'd like to knock it down a few hundred RPM would be nice. I don't think it'll hurt me around town as the first gear is pretty deep