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What ratio should I choose?
I am a bit of a newbie to all of this having just bought a Cobra replicar and I love it! One thing though, I find first gear very low in city driving, usually going from 1st to third or second to fourth. On the highway I am looking for fifth at 60 mph (3000 RPM).
This car is a 429 CobraJet with top loader 4 spd, a 9 inch Ford rear end and 3:50 ratio. I have the car in the shop for a number of things right now and am considering changing to a more accomodating ratio ... any suggestions? Thanks guys, Greg. |
3:31 is a typical Jag IRS rear gear selection, something in that range for a 9" should be available. It's what I run with my top loader and find it pretty much perfect all around. My motor, like yours, makes a LOT of torque, the higher rear gear is not a problem.
You probably have the more common "wide ratio" top loader. 1st gear ratio in these transmissions is lower than mine which is a close ratio. I shift into 2nd at about 60 mph. I would figure 50 or so with a wide ratio and the 3:31 rear gear. |
see if you can read the tag #'s off the front passenger side of the tranny. If the tranny is original, you'll be able to tell if it's a wide or close ratio. If it's a wide ratio, then change the rear to 3.07 or 2.88's. If it's a close ratio, then I'd probably leave it the way it is.
http://www.davidkeetoploaders.com/idchart1.htm When you're just cruising on the street, the gears seem spaced too close, bujt when you're racing it, either drag or road racing, they're spaced pretty good, and I wouldn't change it unless you're serious about racing. |
I'm with Ernie, I Love my 3.31 rear gear and close ratio...torque is NO PROBLEM, and 25-30 mph shift from 1-2 is very comfortable...speeds in gears at 3000 rpm for a close ratio with 3.31 rear gears is 31 in first, 43 in second, 56 in third...but you said you're reaching for 4th at 60 right now with the 3.50 gears, so that won't change much...
I think 3.07 or so would be a little to tall for a close ratio, but would likely work with a wide ratio... |
Close Ratio: 2.32,1.69.1.29.1.0
Wide Ratio: 2.78,1.93,1.36,1.0 Quite a bit higher 1st gear with the close ratio. I wouldn't go much beyond the 3:31 ratio if I was running a close ratio because 1st gear would be "uncomfortably" high I would think. To LOW a first gear ratio, often due to to low a rear gear ratio is the NUMBER ONE complaint I hear from replica owners. I hear it all the time, "1st gear is worthless it's so low". Compounding the problem is a Five Speed trans with ULTRA low 1st gear ratio and running a 3:50 rear gear. Now THATS a "stump puller" of a low gear. My Excal (3.50 with 5 speed) was 25 to 30 mph in first with the motor SCREAMING rpm (a veritable joke)! |
If you can, change the transmission to a T56.
Has over drive, a creeper first gear and you can leave the rear alone. Just a suggestion |
I took the number off the transmission (two numbers actually) but I think they are not the numbers I was supposed to get for the chart. Can anyone identify what this tranny is from these numbers?
G70R-7A040-A G8AR-7000-0W-5 Came off the passender side rear of the Bell Housing. |
E, go here to David Kee's website and you'll find the info and form you'll need to ID your tranny...
http://www.davidkeetoploaders.com/idchart1.htm I think it is on a sheet metal tag on the tranny (if not lost in space in the past). |
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http://www.davidkeetoploaders.com/idchart1.htm Another way is to drive your car in first gear exactly at 3000 rpms, and record the mph. Drive your car in 4th at 3000 rpms, and record the mph. Divide the mph in 4th by the mph in 1st, and that should be either 2.32 or 2.78 ratio, or close to that, and that will tell you if you have a close or wide ratio tranny. |
That's a great bit of knowledge Anthony! I'm gonna have to write that down or I'll be looking for it for hours someday! :cool:
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I am trying to recall from memory, but if you ever get the trans out, you can also remove the front bearing retaining collar (the snout) on the front of the trans. Under there, on the shaft, if you see a machine groove then you've got yourself a wide ratio trans. Regards. |
3000 rpm at 60mph is howling! I have 3.54 gears with a TKO 600 and 70mph in 5th is 2600 rpm and that grates on you after a while.
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TKO600 w/ 0.82 fifth, 3.07 rear gears and 17" wheels with 315/35/17 tires.
70mph@~2300 RPM. I hear about an even mix of wind noise and exhaust. DonC |
If you drive on the highway a lot, I would buy a overdive tranny. 3,000 rpm @ 60 mph would be too much for me. I have a Tremec 5 speed with a Ford 9" & 331 gearing and at 60 mph, the rpm is apx. 2,100. City driving is just right.
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