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Old 01-27-2015, 10:20 PM
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Default TKO600 OD question

I think I have no choice now but to swap out my TH400 auto for a TKO 5 speed manual. I'm concerned about the overdrive ratios so I'd like to ask you guys your opinions.

With my 3.36 rear end ratio, at 75 MPH I'm turning 3100 RPM now.
With .82 OD, I'll be turning 2540 RPM, a difference of 558 RPM.
With .64 OD, I'll be turning 1984 RPM, a difference of 1116.

The 36% difference of the .64 OD seems pretty steep and I wonder how often I would be able to use it, yet the 18% percent difference of the .82 OD isn't a whole lot, especially running higher speeds.

Which do you prefer for highway driving?

My new 383 is built for low & midrange torque rather than high RPM but I'd still hate to lug it. Yeah, the T56 6 speed would be nice but damn it's pricey. And no, I'm not going to go to junkyards and piece it all together. I will buy a kit.
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Old 01-28-2015, 02:50 PM
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JPhil, As a point of reference, I installed the TKO-500 in RamJet (502) a number of years ago. It has the .68 OD ratio with 3.08 rear gears. I run 245x45x17's for tires. That equates to around 1925 rpm at 70mph using the calculator. My Tach reading is actually around 2000 +/- a few rpm's. Tolerance errors I guess.

I have no problem tooling down the highway at 70. I however usually drive 5 mph over. I do get frustrated when caravaning with the Sharks when the lead dog likes to putz along at 65. Feels a little like it starts to lug the engine.

I just installed the Tko 600 in the 69 Blue Angle vert with the 750 hp Dart Engine. We will see how that works this spring. Right now I still have the 4.11's in it, but plan to switch to 3.70's
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Old 01-28-2015, 02:53 PM
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IROC Camaros lugged along at 1600 rpm at 65 - motors generally have no trouble running there forever. With that said, you're right to verify that your cam, carb and intake are designed for that range. 2000 rpm in my C3 would be misery (I've a pretty radical cam, single plane intake, and large carb).

With that said, I had a 2006 GTO with a 6 speed manual, and I rarely used 6th gear (3.42 rear) and found that I tended to get better fuel economy in 5th unless the road was table-flat....

generally the decision point of 5 speed vs. 6 is how much cutting you have to do to put the 6 speed in...

and don't get me started on the Wilcox "upgrade".... when I had my ez efi in the car, I'd compare the tach displays and the stock/wilcox one was always way off..

Last edited by SuperBuickGuy; 01-28-2015 at 02:55 PM..
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Old 01-28-2015, 04:37 PM
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I seldom use 6th in my z06. I don't like lugging the engine.

Under 2000 rpm seems too slow for your sbc to me.
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Old 01-28-2015, 07:45 PM
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i have the ROD 6 in my car with a 3:08 rear... torque is not an issue with the big ramjet...
so 50 mph in 6th gear has 500+ lbft available

Around town i usually shift 1-3-5 its just fine... I used excel and did some math...
I think i still have the spread sheet somewhere pm me with email if you want me to forward you a copy so u can put your own numbers in,,,


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Old 01-29-2015, 02:30 AM
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I have the TKO with the .64 overdrive and on the highway it is simply awesome, 70mph at roughly 2000rpm..... My 383 is not really happy at that low rpm, my cam is 230/236 (don't remember lift but I think it's around .510/.520)... Rear gears are 3.55
The step between 4th and 5th gear is what I really don't like, if I ever do this again I'd get the .82 overdrive

With a milder cam both OD options are great, if you don't spend too much time on the highway going 70+ mph get the steeper .82 overdrive...... Wait, just re-read and saw you have 3.36 gears..... Yup..... .82 it is......
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Old 01-29-2015, 03:05 AM
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I've been using calculators till I'm blue in the face, through all the different trans options and all the gears in them.

I'm leaning toward the .82 OD if I go with the TKO 5 speed. That gives me a 2.75 final drive ratio which is nice cruising. The highways here generally run 75-85 MPH, and I doubt I'll ever run the Sandhills Open Road Challenge.

And after sleeping on it, I think my plan is this:

I will have the builder balance the rotating assembly with both the TH400 flex plate and a flywheel he has in stock, which I will buy. Then I will reinstall the TH400 and run it through the season and make the 5-speed my next years project. This will also give me time to make a more informed & researched decision about the whole package, rather than an impulsive purchase which is where I'm at now.

The debacle with my wheels last spring, plus the 350" build from only 3 years ago that I hated, and now the current rebuild, have set me back on funds available for the car for now so I want to be cautious about dropping another wad like this so soon. But it will happen---the car really needs it now. It is the next step required.

Last edited by JPhil; 01-29-2015 at 09:58 PM..
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Old 01-31-2015, 01:11 PM
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I have a TKO II with the .82 overdrive and a 3:24(?) rear gear behind a 383 stroker. I love the .82 overdrive on the highway. I cruise at 70 mph at just a hair over 2000 rpm. Noise levels are much lower and there is still plenty of power when cruising, though dropping down a gear and punching the throttle can be habit forming.
I also played with the gear calculator for several days before I finally decided I was happy with the numbers. I think you are making a good choice.
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Old 02-01-2015, 01:44 AM
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Looks like .82 it shall be!
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Old 04-07-2015, 11:08 PM
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Default Look what the Easter Bunny brought



TKO 600 .82 OD
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