Gear Ratios

Naumoff · #1 (**permalink**) 12-31-2004, 04:17 PM

Why does it seem like Cobra owners don't want to run a tall gear ratio? Is it to loud in the car? It looks like most are under 3.50:1.
In my 63 1/2 427 galaxie daily driver I ran a 4.11:1 and thought it was a good gear for that engine. Your input will be helpful because I am ready to start ordering my kit and all the other goodies.
Thanks Tony

Zoom This · #2 (**permalink**) 12-31-2004, 05:25 PM

The difference between a 1963 Galaxie and a Cobra replica is about 1500 pounds. With a high torque motor - 450-550 ft. lbs. - in a lightweight car you just don't need low gear ratios to get underway. The more time spent shifting is less time accelerating. You'll hear from Cobra guys with "power to burn" motors that just a few shifts through the quarter mile is all that is needed or wanted to turn in a good time slip, i.e., 11's at 120+. I have a 3.73 axel ratio in my SPF with a Tremec 5 speed and I go through the traps at a little over 120 at close to 5.8k rpm.

The 5 speed gives a good rpm while loafing on the freeway at 70-80 mph too. Back in 1970 I had a Hemi-Cuda with 4.10 gears and an automatic. I hated driving on the freeway for any length of time at anything over 55 mph since the motor spun too high for my liking. Some guys really like the new Tremec 600 with the closer ratios, a .82 5th gear mated up to a 3.50 rear end ratio.

Bob In Ct · #3 (**permalink**) 12-31-2004, 05:42 PM

I always thought going from a 4.11 to a 3.50 was going to a "taller" gear. Have I had it backward all my life?

Have to agree with zoom on the gearing. I've got a 3.73 rear, a Tremec 5 speed with a 0.68 fifth, and 275-60-15s in back. At 60 MPH I turn around 1,900 rpms. don't mind those long rides at all, neither does my Windsor.

Bob

ERA Chas · #4 (**permalink**) 12-31-2004, 06:31 PM

Tony,
A "taller" gear is 3.08. A 4.11 is considered a "short" gear.
Zoom and Bob are correct-Cobras are much lighter and generally work better with taller gears, unless you're building for drag racing only.

tpiini · #5 (**permalink**) 12-31-2004, 06:57 PM

I've got a 289 in mine that'll rev to the moon and I'm running 4.57 rear gears and a Tremec 5-spd. I run about 2850 RPM at 70 MPH. I think the gears are good for a high-winding small block, but if I had a lower-revving stroker I'd opt for something more in the 3.42 to 3.73 range.

Naumoff · #6 (**permalink**) 01-01-2005, 04:19 AM

Thanks for all the good info. I can never remember who's tall or who's short. I think of higher RPM and Tall for what I know now is the opposite. You helped me with my choice of gear ratio. A 3.77:1 it is.

trularin · #7 (**permalink**) 01-01-2005, 06:08 AM

It's pretty bad when you are doing 45 on the street and you nail it, the car wants to do a side-ways-shift without your premission.

3:50 is all I would park in the bango. I have a 4:11 if you would like. It has about 300 miles on it. Just to tall or short. I have that same problem with the tall, short thing. Used to remember, age does that to you.

Ron61 · #8 (**permalink**) 01-01-2005, 06:14 AM

Naumoff,

Easy way to remember low versus high gearing is. The higher the ratio number the lower the gear ratio. Example 4:11 is a high number and that is a low gear ratio. 3:00 is a lower number but a much higher gear ratio. Most ford Galaxies in the 60s with automatics used the 3:00 ratio as the stock one. Hope this simplifies it some.

Ron

clayfoushee · #9 (**permalink**) 01-01-2005, 06:53 AM

Tony,

I'd really carefully re-think your gear ratio choice. The comments above regarding a very light car and BB torque are quite accurate. I'm running a 3:31 Jag, with a toploader, and still have difficulty getting it to hook up in first and second.

Your times are likely to be slower with the lower ratio.

BTW my problem was a stuck T-stat (now changed) and all is well.

Hotfingrs · #10 (**permalink**) 01-01-2005, 08:46 AM

Another thing to think about, the Galaxie is probably running a taller tire than the Cobra....so the 4:10 in the Galaxie and the 4:10 in the Cobra will have a different final ratio.

niles · #11 (**permalink**) 01-01-2005, 11:45 AM

No one can even start to give you advise without knowing, what size motor? What are power goals? what trans? Do you drag, street ? Are you interested in making a lot of noise and smoke or hooking up and go!
gn

TerrysSPF · #12 (**permalink**) 01-01-2005, 12:23 PM

Naumoff:
I had a 4:11 in my Chevelle w/ 454 and switched it to a 4:56 later on (even thought about a 4:88). Car was strictly for 1/4 mile use, or "light to light" on the street. Never took it on the highway. It would have sounded like a Singer sewing machine! But......that was a heavy car. Got off the line in a HURRY with that 4:56 though!
I have a 3:73 in my SPF w/ a 427SO and TKO trans w/ .68 5th. The .68 5th is great for the highway but I find myself "in between" 4th & 5th a lot on the "street". I think the 3:73 is too much for these light little cars. 1st gear is totally useless and 2nd isn't much better when you're "on it". Unless you're feathering the go pedal, you'll hit the rev limiter (and I DO recommend you get one!) in 1st gear before you can blink. Depending on what trans you go with, I would opt for something in the 3:08 to 3:54 range. I'm hoping to exchange my TKO for a new TKO600 trans (much better 1st gear ratio) and change my 3:73 for something in the 3:50's or maybe even the 3:20's.
-This info is based on me guessing that you are going with an FE.

mpotito · #13 (**permalink**) 01-01-2005, 01:54 PM

I listened to the experts at ERA based on my intennded use which is primairly street use. The motor will put out about 500 horse with about 500 ft lbs of torgue at 3500rpm. I went with a 5 speed Richmond and a 2.88 differential gear. At 1000 rpm the set up goes 8.5 mph in 1st, 13.1 in 2nd, 17.8 in 3rd, 22.7 in 4th and 27.9 in 5th. Ratios: 1st 3.27:1, 2nd 2.13:1, 3rd 1.57:1, 4th 1.23:1, 5th 1:1. With a 3:31 differential gear at 1000 rpm: 7.4 mph in 1st, 11.4 in 2nd, 15.5 in 3rd, 19.7 in 4th and 24.2 in 5th.

A Tremec 3550/TKO 5 speed with a 331 differential gear at 1000 rpm does 7.4 mph in 1st, 12.3 in 2nd, 18.1 in 3rd, 24.3 in 4th and 35.7 in 5th. Raios, 1st 3.27:1, 2nd 1.98:1, 3rd 1.34:1, 4th 1:1, 5th .68:1. Using a 377 differential gear at 100 rpm 1st 6.5 mph, 2nd 10.8 mph, 3rd 15.9 mph, 4th 21.3 mph and 5th 31.3 mph.

Hope this helps with your decision.

decooney · #14 (**permalink**) 01-01-2005, 02:38 PM

Naumoff,
Can't believe it... Prince Fredrick, Md. Eh? Bout fell outta my chair when I saw your inquiry and where you are from... me too for part of my life. People usually say to me "where is that?". Its where my father finished his life out, and where I spent many summers growing up. My cousin and some old friends live there. Sort of felt homesick for a second when I saw your post. Many many memories on the Pautuxent and along the Bay.

Ya ever met Eddie Trail who owned the Trail's Amoco (great mechanic) there for many years? He taught my Father and me many things about building performance stuff... lots of boat fun and racing back then. Eddie now has a private shop and the last I saw him he was still doing some high-end musclecar stuff for people, conversions, etc... He could tell ya a thing or two about gear ratios.

Just wanted to say Hello.

________________________________________________

IMO: Extra light weight performance cars like Cobras don't need low gears (torque multiplication factor) on the street. It does depend on what motor you are building. If its a torque motor, go a bit "Taller" on the axle ratio and you'll see what the phrase "takes off like a slingshot" means. With a 4-speed TL, 9" equipped cars seem to do well with 3.25:1 axle ratio and Jag/Dana rears at 3.31:1, and even better with a 5-speed.

Good Luck!

Excaliber · #15 (**permalink**) 01-01-2005, 02:58 PM

4.11 in a Cobra without slicks would be useless, your only going up in smoke.

Consider the first gear ratio in relation to what ever rear gear you want to go with.

Close ratio top loader has much higher 1st gear than a Wide ratio top loader does.

Close ratio would be a good choice for a road course, keeping the rpm in the best working range through out the gears.

Wide ratio with it's lower (higher numerically)1st gear ratio would give you a better "hole shot" and thus is generally preffered for drag racing.

No matter what COMBINATION of gear ratios you wind up with: Consider your crusie rpm at cruise speed and build your motor (pick your cam) to work well for that. Cam profile for high rpm max horse power may not work well at a low cruise rpm, for instance.

One thing for sure, replicas are pretty light, traction becomes a HUGE issue. I wouldn't go "to low" (like a 3.90-4.11). Many have found BETTER ET's by launching in SECOND gear as a result of going to low.

The original race Cobras often used a 3.73 rear gear WITH a close ratio. Bear in mind they also used slicks, without them that gear ratio combination is really asking for trouble on "street tires"! MUCH more likely the car will want to spin out or swap ends when you least expect it.

Hanging out the rear to "drift" through the corners was the method used to race Cobras back in the day. Think about it!

Naumoff · #16 (**permalink**) 01-01-2005, 08:25 PM

Wow! Lots to think about. My primary use will be street. I will power the Cobra with a 427 medium riser(not a stroker) I wanted a five speed tremec with fifth being over drive. the power plant is a definite. I just need to match the trans and the gear ratio for my application. A little road racing is in the picture. Slicks are easily put on for that. Are you saying that a shorter gear keeps the engine to much in the power range and those fat tires still can't tame it. Boy O' boy I cant wait!!!!!
Clay I'm glad to hear that about your T-stat. Maybe someday you could show me what you mean about the Cobra hooking up.
Prince Frederick not Frederick!!! Or Fredericksburg!!!! Sound familiar? The Charm Of the Chesapeake Great place But growing like crazy. You wouldn't recognize it.
enough day dreaming!! back to business
A taller gear will keep the engine from revving to quick and make the car travel farther before you have to shift. THe car being so lite will not need as much power to launch the car. I just want to make sure that I don't get beat by a tuner car at the stop light!!!

Excaliber · #17 (**permalink**) 01-01-2005, 09:22 PM

I'm running a close ratio with 3:31 rear gear, 1st is good for about 60-65mph, now THATS a "tall gear"!

Tire spin is STILL a problem and I'm running very sticky bias Goodyear BIG letter tires (like they used in the 60's).

11.90 at 122 or so.

Naumoff · #18 (**permalink**) 01-02-2005, 04:47 AM

This is great!! you all are going to save me from a lot of frustration in setting up my Cobra, so I can enjoy it more. I like to tinker but changing gears and transmissions is costly and time consuming. I want to tinker a little and have fun driving. Turning 11 second 1/4 mile times is what I had in mind. Thanks for all the Info!!!!!!!!. Tony

RICK LAKE · #19 (**permalink**) 01-02-2005, 05:11 AM

Tony I run 3.31 in my rear with 2 different trans. G-Force for racing and a nash 6 speed for cruising. You didn't say what hp and tork you are looking at with your car. Given the cobras weight 3.07-3.54 is the best ratios. Trans with over drives you may want to go to a 3.07 gear. MY FEELINGS on the 2.88 Jag rear is the pininion is too small for this power and if you add a 17" soft tire or slick you make break or strip the gear. What ever you deceide build everything with heavy duty parts and chromemoly. This will save you money in the long run. 1 note 5grand clutch drops are brutial on the drivetrain with soft tires. Put a water sprayer kit in your car if you want to impress without breaking parts. Just a thought Rick Lake

Naumoff · #20 (**permalink**) 01-02-2005, 05:31 AM

I'm looking at building a pretty stock 427 medium riser with a 4x2v webers. So I'm guessing around the 450 HP area. My low riser 2x4 427 with E comp heads, with a Crane blazer economy solid lifter cam was pleny powerful enough to take care of those small block Comeros in high school. And if hooking up is a problem I don't need a monster engine. Stock Is good. Has anyone dyno'd a stock 427 medium riser? what torque and HP did you get?