[lust4speed]

Got the trans ordered this morning and that only leaves ordering out the Dana 60 with a new ratio to best utilize the transmission. Was going with the 3.54 ratio, but after looking over the chart I'm wondering if the larger cam wouldn't be a little happier with the slightly lower 3.73 ratio. Only about 100 RPM difference at 65 MPH so still a nice low cruising RPM. I changed around an excel file to allow me to look at the different RPM ranges and the link to the file is iegtoclub.com/TKO.xls. On my computer a bar appears at the bottom when I click on the link and I just click on opening it. To insert different numbers you just have to enable editing at the top of the excel sheet. You can change tire size, RPM ranges, and gear ratios to suit your own needs. Anything in red can be changed while the black cells are locked because they contain the formulas to compute the results in that cell. For those that don't want to open the file, attached is a photo of the sheet with the 3.54 and 3.73 ratios. The excel file was created by me and is stored on our GTO website that I maintain so it is safe to open.

Anyone running the 3.73 with the TKO-600 or any other trans with about a .64 overdrive ratio?

[b-man]

No experience with that transmission, but I will say that the 3.73 looks like a better match for a large cam.

Crawling along in traffic in first and second will be better with a slightly lower rear end gear. Same for highway running, your big cammed engine will appreciate running another 100 or so RPMs at 65 to 85 mph cruising speeds.

[cdrookie]

I have 4:10's behind my TKO600 with .64 5th gear and 27.5" tires. I run the back roads around my place in 4th and 5th gear.

[Formulajones]

3.73 is my favorite no matter what the camshaft is.

With that said, I'm currently running 3.55's in mine. With a little 302 in front of it using a 254 @ .050 cam I'd say that qualifies as a pretty rambunctious cam given the size of the engine compared to what most run in a much bigger 455 on this forum.

Even so, with some tuning and having the package dialed in nicely, it lugs that 3.55 gear around in 5th gear no problem all the way down to 30 mph and 1,000 rpm and still picks up speed nicely without downshifting. That's with a fat 780 holley on it and it never chugs or complains. Hell I even use 5th gear lugging around town in the 35 mph zones all the time without a problem. If I can do that with a 302 and a large camshaft, even the more race oriented 455's on this forum shouldn't be having an issue.

https://youtu.be/e39e6p7NMY0

[Scarebird]

My 600 has the 0.82 OD gear - a mistake. I initially started with 3.42's but realized that 3.08's make a better all around gear given the high highway speeds around NM. This is with a LS3.

[Formulajones]

Yeah the .82 doesn't offer a bunch of reduction. Usually that's coupled with a steeper first gear so you can drop the rear gear down pretty far, 3.08 like you said. I'd like that deal better if it had a steeper first gear though.

We're in Arizona so like you, highway speeds are 75+ and loooong distances between towns.

Still easily doable with a 3.73 or even a 4.10 rear gear, IF you use the .64 overdrive.

With my 3.55's I'm only spinning 1800-1900 to go 65 mph. I can loaf at 75 and barely be over 2,000 to 2100 rpm. Putting 3.73's in only makes about a 100 rpm difference. Cruising at 80 for the long trips is pretty nice.

[PDC]

The 2.87 First Gear in the TKO 600 is pretty aggressive, when you consider 2.21 is 1st in a ‘close ratio’ Muncie and 2.48 / 2.52 is the 1st gear ion a TH400 / 350 respectively. I know lots of folks end up going with 3.73s behind their .64 OD TKO-600 in order to make OD ‘useful’ at less than 80 mph. But with the 3.73 rear end, your overall reduction in 1st gear with 3.73s is 10.7. That would be like running a 4.33 behind your TH400. That’s pretty darned aggressive in a big displacement, long stroke engine (455 or 460 stroker) that already makes TONS of torque. 1st gear almost becomes a waste - it’s pure wheel spin for a split second before you have to shift.

I had a .64 OD TKO 600 in front of a 3.42 ring gear and I found that I was never happy on the highway. Even though the engine may not have been technically lugging it just felt ‘soft’ at any speeds under 70-75 in OD. I really needed to be going 80+ to feel comfortable in 5th. And then if I did downshift to 4th from that .64 OD the tach would LEAP to match revs. At speeds between 65-75, I felt like I was either whizzing like a sewing machine in 4th or near lugging in 5th.

I ended up re-building the TKO with a .82 main shaft and swapped in a 3.23 ring gear, and I could not possibly be happier. Overall gear reduction in 1st gear is 9.27. That’s even a bit more aggressive than running 4.11s behind the 2.21 first gear in the stock ‘close ratio’ Muncie. In 5th my overall reduction is 2.64 which is plenty comfortable at 75 mph. And if I need to downshift to pass, its a much more comfortable step. I think the TKO-600 with the .82 OD is tailor made for a 3.23 rear end.

[tom s]

Im running a 3.90 with a 29in tire with 434 CI and a old faithful cam.I would like a touch taller,only thing I can find is a 3.42,pretty sure it can pull it.If I could find a 3.64 I know it would work forsure.Tom

[72LuxuryLeMansLa.]

Originally Posted by tom s

Im running a 3.90 with a 29in tire with 434 CI and a old faithful cam.I would like a touch taller,only thing I can find is a 3.42,pretty sure it can pull it.If I could find a 3.64 I know it would work forsure.Tom

Tom,
What rim and tire are you running? I ask because my '72 came with 14" rims and 26" 70 tires.

To add to this I'm building a 433 with Dave's Stump Puller.

[Formulajones]

I would sure hope your 434 would pull it Tom. My 302 pulls a 3.55 just fine all over the mountains here..

Matter of fact I was cruising at 65 with my father in tow, and it climbed the mountain going from near sea level to up over 7,000 feet in a distance of 6 miles (yeah it's a steep grade) I never left 5th gear and it climbed and accelerated when needed without complaint and was passing other cars.

[Tim john]

I run a 3:73 with a TKO-600 and have done so on a couple different Pontiacs and to me it is an ideal choice. Excellent from a first gear start to highway cruising. 26" tall rear tire on 14" wheels.

Tim john---

[tom s]

Its a 63 421 Lemans.My 69 bird has a 455 with a SP and has 3.31s with a TKO 500 and it is EZ.The 63 has 15x7s,as does the 69 bird but the birds tires are shorter.Tom

[Formulajones]

Originally Posted by PDC

I think the TKO-600 with the .82 OD is tailor made for a 3.23 rear end.

Only problem with that is you're really cutting yourself short on the overdrive idea. You're still turning 2500-2600 rpm to go 75 mph. Don't need an overdrive to do that.

May as well save your self a bunch of money and stick a ST-10 in the car with a 3.42 first gear ratio, stick a 2.73 rear out back, and do essentially the same thing for a whole lot less.

[64speed]

I’m running a 9 inch with a 26 inch tire. I have had the rare opportunity to match the cam to the trans to the rear gear. With my 467 with the TKO with .64 overdrive I put 3.70 in the rear. Should work out perfectly for any type of driving

[Formulajones]

To take that even a step further. We ran a couple of cars here with the T56 that has a .50 overdrive 6th gear. Used that with 3.42's out back in 2 different cars and it worked beautifully. Would cruise under 2,000 rpm and keep up with highway traffic.
I eventually changed one of them to 3.73's. Mainly to improve the first gear multiplication with it's 2.66 first gear. Still went to sleep in 6th and knocked down 26-27 mpg highway.

Did 3 TKO swaps for the same customer, all of them .64 overdrives. 2 cars had 3.70's and one had a 3.50 gear. Driving them really wasn't much difference between them. Hardly noticeable really. The gear change really isn't enough to see more than 100 rpm on the tach and not enough to affect mpg either. After several months of driving the owner had no preference one way or the other.

[PDC]

Originally Posted by Formulajones

Only problem with that is you're really cutting yourself short on the overdrive idea. You're still turning 2500-2600 rpm to go 75 mph. Don't need an overdrive to do that.

May as well save your self a bunch of money and stick a ST-10 in the car with a 3.42 first gear ratio, stick a 2.73 rear out back, and do essentially the same thing for a whole lot less.

I just got tired of the significant drop between 4th and 5th with the .64 OD. Anything between 70 and 80 felt like ‘no mans land’ where 4th was spinning faster than I cared for and .64 od felt soft. Not trying to start an argument here. Just saying what worked for me. P.S. - How big is the drop between gears with the ST-10 If 1st Gear is 3.42? The gear spread with the TKO 6 is quite a bit more functional and a 2.64 final drive in 5th is still a bit calmer than 1:1 with a 2.73 out back.

[jwcfbd]

I'm another one that's running 3.73 and a TKO600. It's a great match in my opinion.

[tom s]

With the TQ of our engines I just have not had a issue with the drop from 4th to 5th.Tom

[GOAT WHORE]

I started out with 3.55:1 rear with my .64 TKO 600. Switched out to a 3.73 rear gear and I believe it's much better. I've done multiple long distance trips with this car and love it.

[lust4speed]

Lots of great first-hand information. Sure looks like the 3.73 ratio will work just fine for me.

Did I mention that Strange has their Black Friday sale on all their rear ends and accessories with 10% off the entire order and free shipping? Sale is on until midnight Monday, 12-2-19. I won't be able to afford any more good deals for a long time after the trans and rear end.