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3:31 vs 3:54
I'm running a 427 in my Unique replica with a 3:54, what's the upside or downside of going to a 3:31 other than lower high end rev ?
Lou |
What trans are you running. Having the 3.31 will make first gear more usable.
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3:54 to 3:31 rear gears
Upside
Higher top speed Better gas mileage Downside Slower acceleration $$$$$ Time to do the swap |
:o Does one really need a top end greater than 160 mph? I prefer the neck snapping hole shots with the 3.54. IMHO
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What cam? Figure out your final drive rpm with each rear ratio and pick which ever best matches the power band of your cam based on the type of driving you do.
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If you spend much time spinning your tires is 2nd.
you will probably go faster, spinning tires is slow and dangereous. I find a 3.08 about perfect for street. With race slicks I would be better off with a 3.55 because only then can the excessive torque be utilized gn |
4Speed, 5speed, OD? I'm running a 3.73 with a Tremec 5 speed. 0.68 OD. It works out to 2.6 overall or so in top gear. If I had it to do all over again I would get a taller gear in the back. Maybe 3.25 or so.
Bob |
Not very swift to leave out the tranny I'm running in the 427......
4speed toploader, had the option for a Tremec 5 speed but I wanted to be like Carroll..... Lou |
I have 325 Gears in the rear. At a 1 to 1 ratio in high gear. 3200 rpms = 80 mph. I had 331 rear gears in my last Cobra and got tierd of people passing me on the freeway. At 80 I was running around 4000 rpms.
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Quote:
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car math
Here is a link that will allow you to figure the differents in gears, tires and trannies. Tires size plays a big part in the overall ratio. You have to decide what you want to do, fast out of the hole, low rpms on the freeway. Or a compromise. Quick away from the red light is good:LOL: I chose a 5 speed to give me a little of both worlds.
http://www.secondstrike.com/Technical/GearCalc.asp Dwight |
For27-which toploader?WR or CR.Makes a big difference.
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With a 4 spd top loader, I had 331 then went to 354 , I think I might try 331 one more time . longer first , unreal 2nd !!! little more normal in 4th . The 354 change I did with the 390FE , later I went with a 427 , so I would like to retry the 331 .
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I have 354 and a Toploader, I'm now looking for a 5 speed:CRY:
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3:31, I'm cruising along about 60 mph on the freeway, and just for kicks, drop it into 2nd and nail it! Eh eh, love doing that 2nd gear thing at freeway speeds, takes off like a rocket! :D
Close ratio top loader, the gear ratios in the trans DO make a difference as to what you can and can't do as well as the rear end ratio. Oh by the way, I got 11.5 mpg with my 427 and DUAL carbs on the last tank of gas. Steady cruising at about 2800 rpm, not bad! Heck my Jeep V8 does only slightly better! |
With the torque in a stong FE, you'll do better overall with the 3.31 rear gearset - it just pulls through first gear and its nice to have a little extra in 4th gear. Most people I know that had 3.54s/FE combo are much happier with 3.31s now. My former car had the 3.08 differential and an FE, and overall I feel the 3.31s are about right, and particularly with the wide-ratio trans Toploader or custom big-Toploader with wide ratio setup. Other friends with SPFs running the rear 3.73 gears have changed to 3.27s and like that much better, but for those running the .68 overdrive they say its a tad too tall if you are running a larger cam.
I'm considering (waffling about) a 5-speed road race trans myself but sure do like the way the Toploader / 3.31 setup runs with a larger camshaft for everything except long highway trips. That .82 5th gear would be nice; which drops from 3,000 rpm higway cruising to 2,450rpms. As others have noted, you need to provide your cam/motors specs too to get a better idea from us. |
With my 400 HP 390 , 4 spd top loader , 331 gears , I got 18 mpg on trips . Now 10 with new set up .
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3:31 vs 3:54
Thanks to all for the great feedback and info. Hey Dwight, that link you passed along was great for sorting out all the possibilities. I decided that the 3:31 with my wide ratio toploader is the way to go. A also received a suggestion to change the pair of 295/50's on the rear to 275/60's to achieve the same results. For sure a cheaper way to go, but I don't think I would have liked the stance of the car and also don't know if the car would have felt as planted as it does now.
Thanks again to all, Lou |
I have a 3.31 rear with 4 speed Toploader. The only downside to this combo is trying to drive the car slow in a parking lot. The car will tend to lurch, lurch, lurch at 5 MPH or less. Other than that, it is really a fine gear setup with the toploader. In first I can get up to about 60MPH. You may not be out of 2nd at all in city traffic. The car will pull well in just about any gear.
You can take off from a dead stop in 2nd. I would never think about changing this combo... unless you wanted to drag race... otherwise, you will be happy with it. |
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