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Junior Charter Member
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Discussion Starter · #1 ·
Which do you prefer?427w 500 fp torque ,355gears.
 

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Former Roadster Owner
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1,861 Posts
Since you have a moderate axle ratio and a ton of torque, I'd go with the .68 unless you're planning on doing some 130+mph road course events. -dan
 

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Premium Member
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18,135 Posts
I have 3.55 rear gears, lots of torque, and a .68 OD. In regular street driving this is a nice combo. I can cruise down I-25 at 80mph at a reasonable rpm (2000'ish). easy to drive, and plenty of torque for hills and passing.

But, on the track, it sucks. Drop it into OD and I might as well throw out a parachute. Can't accelerate much at all. If I were to do it over again, I'd go with .82.
 

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891 Posts
Go with the .82 5th unless you are really in to crusing down the freeway at 1800 RPM. I have a .50 in my T56, 6th gear, with the same rear gear and it is just too high to be fun.
 

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With that much torque and 3.55's, the 0.68 will be fine on the street. If you ever intend to do any open track though, go for the 0.82.
 

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Junior Charter Member
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1,066 Posts
I'm sure I will have the minority opinion on this but here's my take on it. The cam you are running is a big factor. Where does the power band start? I went with a .80 because the power band for my cam is 2400 - 6000. The .68 would have me cruising below the power band. The other factor I considered was the kind of driving I do in the Cobra. I spend very little time on the interstate and a lot of time on back roads. The .80 puts me in a perfect RPM range (2200 - 2700) at 55 - 70 mph on twisty, hilly back roads. I made a spread sheet to assess RPM vs. speed for the various gears and picked the one that would work best for my style and engine. (P.S. I had .68 w/3.55 with a B-cam 5.0 in my MKII and hated it because it lugged the engine in 5th below 70 mph.)

</font>
  • RPM 1 0.8 0.73 0.68 0.63

    1800 37 46 51 54 59
    1900 39 49 53 57 62
    2000 41 51 56 60 65
    2100 43 54 59 63 68
    2200 45 56 62 66 72
    2300 47 59 65 69 75
    2400 49 61 67 72 78
    2500 51 64 70 75 81
    2600 53 67 73 78 85
    2700 55 69 76 81 88
    2800 57 72 79 84 91
    2900 59 74 81 87 94
    3000 61 77 84 90 98
    3100 63 79 87 93 101
    3200 66 82 90 96 104
    3300 68 84 93 99 107
    3400 70 87 95 102 111
    3500 72 90 98 105 114
    3600 74 92 101 108 117
    3700 76 95 104 111 120
    3800 78 97 107 114 124
    3900 80 100 109 117 127
    4000 82 102 112 120 130
    4100 84 105 115 123 133
    4200 86 108 118 127 137
    4300 88 110 121 130 140
    4400 90 113 123 133 143
    4500 92 115 126 136 146
    4600 94 118 129 139 150
    4700 96 120 132 142 153
    4800 98 123 135 145 156
    4900 100 125 137 148 159
    5000 102 128 140 151 163
    5100 104 131 143 154 166
    5200 106 133 146 157 169
    5300 109 136 149 160 172
    5400 111 138 152 163 176
    5500 113 141 154 166 179
    5600 115 143 157 169 182
    5700 117 146 160 172 185
    5800 119 149 163 175 189
    5900 121 151 166 178 192
    6000 123 154 168 181 195
    6100 125 156 171 184 198
    6200 127 159 174 187 202</font>
 

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FFCobra Craftsman
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2,238 Posts
Have 345hp crate motor w/ carb, 275's, 3.55's and a TKO II w/ .83, we have shorter tracks up here and have not yet needed 5th (very close though 4th @ about 5800 - 5900 at the end of the longest straight, with a little more motor I will need the 5th, I think, will have to see what the future brings) on track which makes me wish I had the .62 when I am on the highway running 2700 r's plus to keep up w/ the poky traffic ... depends on your use ... a 6 speed might be even better ????
 

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I have the .83 with 450HP at the flywheel running 3.73 gears. It is nice on the highway but I would rather have the .62 on the track. Accelleration is sluggish in fifth.
 

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Senior Member
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5,559 Posts
Bob G., if your accelleration is sluggish in 5th with .83, then .62 will be even worse! The .83 is closer in ratio to the 1:1 4th, so you lose less rpm's shifting to 5th. For me, the .62 is almost useless under 75-80, unless I'm on a long, flat interstate cruise, in which case, it saves some gas by keeping the car at idle. If I buy a new trans, I'll definitely go for something in the .80 range, as I hardly ever go on long interstate trips.

Brian
 

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Building
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259 Posts
Go with the .82 TKO600.
The .68 is actually a TKO500 and isn't a good combo with your 3:55s.
http://www.ttcautomotive.com/English/products/TKO.asp

I'm going through the same dilemma.
I have a TKO600 with a .64 5th gear so I decided to sell my 3.55s before I put them in and I'm now looking for a set of 3:73s.
The cruising rpm's would be too low for the cam profile I want to use.
 

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It really depends on where/how you will drive .
I have 373's/ 351W/ 15" wheels with .68 OD. It tops out in 4th around 125mph @6200rpm. Three guys in our group went with the .82 5th gear. On road trips with sustained 60-70mph cruising the only ones revving higher at speed than the .82's are the toploaders. With 500fp torque you might enjoy a 2000rpm 60mph cruise now and again.
 

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I chose the .82 with 3.46 in back and 500 for HP and torque. I am quite happy with it. Go to the second strike gearing calculator. Put in both sets of numbers. When I did that, I found that I had multiple different rpm/mph bands where the .82 was reasonable. The .68 was very limited in my driving situations. My motor is happy at 2200 but less so at 1800. I run 2300 and change at 70mph. I am never going to wear this motor out, so I chose the flexibility of the .82.
 

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Master "Gear Head"
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434 Posts
I had Forte recommend that for me when I purchased my TKO600. At the time I had a 408 stroker and he recommended a 3.27 rear gear and the 0.82 OD of the road race version of the TKO. The best thing is to forget the TKO500 and it's 3.27 first gear. The 2.87 of the TKO600 flys by so fast as it is. Certainly with the torque of your motor you can chug around at lower rpms and be fine in terms of power. I find that if you have even a moderately aggresive cam, the lower RPMS are not appreciated by the large strokers. For me, cruising around at 1700-1800 RPM was not tolerable with some bucking and such from the motor/cam combo, so the 0.68 overdrive gear would have been useless. The 0.82 was perfect though. So it depends on what you are looking for and how well your engine will run at those lower RPMS. Don't overlook the fact that your motor might not like chugging around that low. HTH
 

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Cobra Crazy
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845 Posts
I have a BB with the exact same setup (3.55 IRS, TKO 600 and .68) Really the .82 is a better choice. In 5th at 55 mph the motor runs around 1800 rpm and too low for fun driving. When I get on the interstate and can go 80 without getting caught then it's usable at about 2100-2200 rpm. I was doing 115 mph on Roebling Road Racetrack last week in 4th at 4400 rpm. So top end is not a problem, there is plenty of gearing to go fast if you wanted.

What kind of driving are you going to do the most of, back roads at 55 mph or interstate at 70 to 80 mph? That is the real choice. Your choice but if I had to do again I would pick .82 just to get more use out of 5th.

[ November 07, 2006, 10:10 AM: Message edited by: Lowcountry ]
 

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464 Posts
I contacted Tremek and a gentalman named jeff sent me a calculator to figure out rpm's/ and speeds given different gear ratios, rear end ratios and tire sizes. Very helpfull! All of the TKO 500's have a .68 fifth gear. They offer a 600 with either a .82 or a .64 fifth gear.
I appologize, I am not computer savy enough to figure out how to add the calcultor file to this responce. Bottom line is it all depends on what you want out of your car and what you plan on doing with it the most.
 

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Moderator
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12,663 Posts
Originally posted by Wade Chamberlain:
With that much torque and 3.55's, the 0.68 will be fine on the street. If you ever intend to do any open track though, go for the 0.82.
AND the 327 gears.. 3.55 gears Max out at 128 in fourth at 6000 RPM..

IMHO, 327 gears with a .8 OD is the PERFECT combo. ( your milage may vary)


earl
 

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Junior Charter Member
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Discussion Starter · #19 ·
WHAT A WEALTH OF INFO.From what I gather and the type of driveing I hope to someday do,I think the .82 will be my choice.....THANKS TO EVERYONE!!!!!!!!!!!
 
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