Gears for twin screw September 22, 2009, 10:29:21 PM So since I need my bearings all replaced in my differential, I'm trying to decide keep the 3.55's or use the 3.08's I have. I plan on putting on a Kenne Bell 2.1L as it'll play more nicely with the stock block and 4r70w than trying to spin to 6k with a centrifugal sc. I lost both city and highway when going from the 2.73's to the rearend with 3.55's (I'm seeing myself down both 2 city and 6 highway) so I'm thinking of using the 3.08's which are in the middle of the road (13% more gearing than 2.73's while the 3.55's are 15% more gearing than the 3.08's).Suggestions? I'll post the 3.55, 3.08, and 2.73 comparison graphs that will help show in which speeds each has an advantage with acceleration over another. I would assume I'd be back around 20/30 mpg with 3.08's where I seem to get 18/27 with the 3.55's (I blame my foot for the city...) and 20/33 with the 2.73's. This car isn't a track car - it's a semi-daily driver with emphasis on longer drives/traveling.I will also add that I get no traction below 20mph if I floor it right now and the 1-2 shift at 40mph causes a second of traction loss also. I fear a supercharger may be too much for 225's. Quote Selected
Gears for twin screw Reply #1 – September 23, 2009, 01:37:20 AM Your car now should be too much for 225's. I can spin my tires on occasion, and I have a miss at idle. I would go with 3.27's or 3.08's. Just from what all the mustang guys recommend. The 3.27's will still give you alittle bit more grunt, but 3.08 feel just like stock to me.How drastic was the seat of the pants from 2.73's to 3.55's? My rear end is starting to go, and I want to swap in a 3.73 7.5 I have had at my dad's for the last couple of years. Quote Selected
Gears for twin screw Reply #2 – September 23, 2009, 08:22:21 AM Quote from: Haystack;292278How drastic was the seat of the pants from 2.73's to 3.55's? My rear end is starting to go, and I want to swap in a 3.73 7.5 I have had at my dad's for the last couple of years.I went from stock 3.08 to a 3.55 TC rear and noticed a drastic seat-o-the-pants improvement. In my V8 Ranger I swapped from 3.23's to 3.55's and could hardly tell a difference. Quote Selected
Gears for twin screw Reply #3 – September 23, 2009, 08:24:18 AM Got 3.73s in my supercharged 302 tc and let me tell ya it's a wild ride. Quote Selected
Gears for twin screw Reply #4 – September 23, 2009, 09:15:47 AM At WOT, the transmission downshifts hard into a low gear for a split second and is then forced to upshift near immediately due to the much quicker acceleration, which is in turn hard and causes the rear to break loose before again accelerating much more quickly. It will push me back in the seat a little although I don't expect miracles without having 500+ fwhp. This initial downshift and quick acceleration makes passing people take no time at all. 3.55's do great for passing in the 20~40mph range (2.84 1st gear in the transmission) and 55~70mph range (1.55 second gear). Other gears do better here and there but are not as useful on the street for passing people. 2.73's accelerate better between 45-55 and 75-105 as per graphs I made up some time ago.The above numbers are based of 5k shift points which will cause the trans to shift closer to around 5400 on 1-2 and 5200 on 2-3 due to hydraulic delays with the action sent at 5k.3.55's can become expensive, both on gas and tires. I just wish transmissions, besides 6 speed manuals, had wider ratios. I'd be happy with a single .6 overdrive instead of .7 in an auto. Quote Selected
Gears for twin screw Reply #5 – September 23, 2009, 04:27:25 PM What is the stall speed on your converter? For example my stock stall speed (1800 rpm) converter in my AOD will let me burn the tires and leave some 10-15 foot long black marks with 3.73 gears in the back. I'm wondering how the 225s will hold up when I get a 2600 rpm converter in the spring:hick:A 2400-2600 rpm converter and 3.55s will destroy pretty much any tires short of slicks in the back. I'd go with 3.08s if I were you. I have 3.73s because I don't care about gas mileage or destroying tires Quote Selected
Gears for twin screw Reply #6 – September 23, 2009, 05:06:14 PM Quote from: thunderjet302;292323What is the stall speed on your converter? For example my stock stall speed (1800 rpm) converter in my AOD will let me burn the tires and leave some 10-15 foot long black marks with 3.73 gears in the back. I'm wondering how the 225s will hold up when I get a 2600 rpm converter in the spring:hick:A 2400-2600 rpm converter and 3.55s will destroy pretty much any tires short of slicks in the back. I'd go with 3.08s if I were you. I have 3.73s because I don't care about gas mileage or destroying tires Stock from a 2003 v6 Mustang - it begins to grab hard around 2200 so I assume it's stalling to around 23-2400. Being stock though, it doesn't like 5500 and higher so I've got it set to start shifting at 5k. It acts weird with lockup at lower speeds with closed throttle and lower fluid pressures (stock calibration that came with the transmission controller) but works fine with a slight closed throttle pressure boost. I'd like to get a decent one that can handle more rpm. Quote Selected
Gears for twin screw Reply #7 – September 27, 2009, 08:00:23 PM Okay, so the rearend got 3.08's (couldn't find 3.27's local except a used set for $85...). The car can still break the rear tires loose on the 1-2 shift at 45mph. Acceleration has obviously suffered a little though - it is slower to rev. I guess I'll see how these work in the coming months. I will be keeping an eye out for another used Kenne Bell (A 2.1L just sold for $1600 on eBay - I would have bid but I have enough bills this month).I still hear occasional weird sounds out back with gear changes though. I think I should just get an aluminum driveshaft made and get some new ujoints on there. Quote Selected
Gears for twin screw Reply #8 – September 28, 2009, 06:47:23 PM I bet the KB will take car of the lost acceleration Quote Selected
Gears for twin screw Reply #9 – September 29, 2009, 11:04:24 AM I'm sure it will. I figure 50% more rwhp should be about right on the street and likely in the safe zone, especially with lower rpm's, on the stock block. Quote Selected
Gears for twin screw Reply #10 – September 30, 2009, 12:27:44 AM I went from 3.73's to 3.55's and it's still slipery-slidey without drag radials. 3.27's would have been ideal with an auto IMO, I guess you'll have to see how well you like the 3.08's. Quote Selected
Gears for twin screw Reply #11 – September 30, 2009, 10:47:20 AM Perhaps but the lower first and second gears help immensely over an aod. It will still do 80 in 2nd, which is only like 2-3% higher than 3.27's on a 1.47 2nd gear ratio, so it is negligible. Quote Selected
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