Close Ratio / Wide Ratio Opinions 427 Cobra

[dmb496]

I've owned a replica Cobra big block for 29 years.  There have been 2 Toploader transmissions in my car, both wide ratio.  Rear end ratio is 3.70, but I also ran a 3.50 rear for a number of years.  The current transmission is a David Kee-built aluminum body unit with a big input shaft and small output shaft.

The 1st gear ratio in my car is just right for pulling away from a stop, engine speed slightly above idle and normal clutch engagement.  I state that because I know a Cobra owner with a big block, 3.54 rear end ratio, and a close ratio Toploader.  Each time he pulls out from a stop it's obvious he has to raise his rpm's and slip his clutch more than I do.  I once asked him about what I was hearing and he became defensive and said "It's fine like it is."

[FL SAAC]

I've owned a replica Cobra big block for 29 years.  There have been 2 Toploader transmissions in my car, both wide ratio.  Rear end ratio is 3.70, but I also ran a 3.50 rear for a number of years.  The current transmission is a David Kee-built aluminum body unit with a big input shaft and small output shaft.

The 1st gear ratio in my car is just right for pulling away from a stop, engine speed slightly above idle and normal clutch engagement.  I state that because I know a Cobra owner with a big block, 3.54 rear end ratio, and a close ratio Toploader.  Each time he pulls out from a stop it's obvious he has to raise his rpm's and slip his clutch more than I do.  I once asked him about what I was hearing and he became defensive and said "It's fine like it is."

+ 1

[brandosaac]

Thanks for the replies.

But a 3.70 rear gear, with a wide ratio,  in a somewhat lightweight car with a big block with tons of torque?
On paper that sounds like 1st gear would be extremely aggressive ? and almost un usable ?

[dmb496]

A 3.70 isn't the quantum leap above a 3.50 as you may think.  I stated I previously had a 3.50 rear end in my Cobra so you could buy into my overall evaluation of a wide ratio Toploader. 

Unusable?  It doesn't matter if you have a wide or close ratio, a 3.50 or a 3.70 rear in a Cobra that has substantial horsepower.  That's why prudent use of the right foot is so important when driving a Cobra.  I never stab the throttle, I 'tip in' to reduce the surprise factor.

The last gentleman I took for a power ride, remarked after we ran through 1st, 2nd and 3rd gears that he thought the car's rear tires were almost breaking traction.  I grinned and said the tires were actually roasting rubber for the majority of the sprint.

[brandosaac]

In my opinion ................,

3.70 rear with 2.78 wide ratio 1st , seems extremely aggressive with a big block cobra,
you could loose it pretty fast under partial throttle

[shelbydoug]

Well, you asked for opinions and you definitely are getting that here. There are a variety of experiences and none are wrong.



The 427 Cobra transmission that I had was a big input, small output, 24", close ratio.

I do not think that there was ever a wide ratio box ever made by Ford for that application?

If you look down the list that David Key has posted, any original displacement larger then the 390 that he knows of is a big input, close ratio box.
The 390 applications are small inputs, like the 289's.

There are wide ratio 390 transmissions but are small inputs.



With Ford, it seems there is always a rare combination they made that was never made in mass quantities but did exist somewhere, somehow mostly unknown to even experienced Ford appliers?

I do believe though that in the original CSX 3000 cars, the most common, if not all applications was a 3.31 rear with a close ratio (2.32 first gear), 24" long, 1-3/8" big input and small (28 spline) output. So in my OPINION, that would be an original 427COBRA application.



One of the considerations on close v. wide ratio that is not mentioned here, is the smoothness the close ratio gives as you accelerate through the gears v. the wide ratio. You need to consider the wear and tear on the drive line because of the torque loading of the larger displacements.

The 427 Cobra is very sensitive to throttle input but more specifically, to torque inputs. You want to be as smooth as you can when driving it spiritedly.

You shouldn't compare another vehicle such as a big block "Mustang" to the Cobra application. They are not the same. They are beyond apples and oranges.

Many Cobra "kit" cars are not using IRS Cobra rear suspensions but solid axle "Mustang" variants. That changes the equation somewhat as well.



Initially, the 427 Cobra was subject to what was described as "snap steer". What was happening was that the balance of front to rear steering was not right initially.
I'm not sure of the EXACT formula that came to be for stabilizing the car but there was work involved which included a smooth transition of power to the car, which does include the transmission and rear gearing.

When you build your own Cobra, you are varying from the Shelby factories solution. You need to be aware that this is at your own risk and you are applying your own solutions which may need some testing to verify the car is stable even under normal driving not to mention track characteristics.


All vehicles with weight bias front to rear with the majority of that weight is on the rear, 40% front, 60% rear, are extremely susceptible to the rear suddenly steering the car. That IS involved in the "snap steer" issue.

One thing that you must insure is that the rear tires have noticeable toe in. Somewhere in the 3/16" to 1/4" vicinity. With an IRS rear that is adjustable. With a solid rear, it is not.

Someone asked here before, what are the factory suspension settings for a "Comp/SC Cobra". All they could find were stock 427 street settings. The reason for that is that each car needs to be set up individually according to it's track reactions. So therefore there is no specific setting, you just start with a street setting and work from there.

Why do I mention that here? Gearing of the car is involved in that. When you step off of the throttle, you don't want excessive rear end steer because of the braking effect of taller gears.



Honestly though, the only way that YOU are going to be able to determine the best setting is for YOU to experiment with these combinations.

Picking the gearing profile you like is probably close to trying to pick a camshaft profile that YOU will like rather then what was recommended to you by others. Simply put, each is going to have their own interpretation of what is streetable, what idles well and what pulls the best, not what others tell you.

Gearing is very similar. That's why people like Miles were at the "tracks" so often testing combinations. I'd go with his picks they put originally in the Cobras.


Again, this is my opinion. Others certainly have taken different avenues and likely may disagree.

[FL SAAC]

What he said :

There is never enough horsepower......just not enough traction.

Carroll Shelby

[S7MS427]

I'll add my 2 cents here.  I've driven the same car with both a close ratio 2.32 to 1 first gear toploader as well as a wide ratio 2.78 to 1st gear.  I much preferred the the 2.78 gearbox on the street.

If you wish to convert a close ration box to a wide ration these are the parts you'll be swapping: 2nd gear, 3rd gear, the cluster gear, and the input shaft.  There are no factory 2.78 big spline 1st gear inputs, you'll have to have it made which requires two inputs, the original big spline input and a donor wide ratio input.  Liberty Gear in Michigan used to do that kind of work but I don't know if they still offer that service.  I was very happy with the work they did for me and it would still be in the car except I switched to a TKO600 (happy with that transmission too).

[FL SAAC]

I'll add my 2 cents here.  I've driven the same car with both a close ratio 2.32 to 1 first gear toploader as well as a wide ratio 2.78 to 1st gear.  I much preferred the the 2.78 gearbox on the street.

If you wish to convert a close ration box to a wide ration these are the parts you'll be swapping: 2nd gear, 3rd gear, the cluster gear, and the input shaft.  There are no factory 2.78 big spline 1st gear inputs, you'll have to have it made which requires two inputs, the original big spline input and a donor wide ratio input.  Liberty Gear in Michigan used to do that kind of work but I don't know if they still offer that service.  I was very happy with the work they did for me and it would still be in the car except I switched to a TKO600 (happy with that transmission too).

+ 1 actually your 2 cents in real life is worth 1 dollar, that's how I felt when I experienced the difference

Same cars, same motors,  same 3.5 rear, just different 1st gears on toploader......wooooosh!

[430dragpack]

I'll add my 2 cents here.  I've driven the same car with both a close ratio 2.32 to 1 first gear toploader as well as a wide ratio 2.78 to 1st gear.  I much preferred the the 2.78 gearbox on the street.

If you wish to convert a close ration box to a wide ration these are the parts you'll be swapping: 2nd gear, 3rd gear, the cluster gear, and the input shaft.  There are no factory 2.78 big spline 1st gear inputs, you'll have to have it made which requires two inputs, the original big spline input and a donor wide ratio input.  Liberty Gear in Michigan used to do that kind of work but I don't know if they still offer that service.  I was very happy with the work they did for me and it would still be in the car except I switched to a TKO600 (happy with that transmission too).

New, one piece, 2.78 large input shafts are available through David Kee and other drivetrain parts places.  They even make the longer version, big input for a small block.   

[FL SAAC]

Dan Williams Toploaders