.64 or .82 TKO overdrive?
Thread Starter
Instructor
Joined: Dec 2002
Posts: 115
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From: pinehurst nc
.64 or .82 TKO overdrive?
Need some advice from those of you out there that have already installed your transmissions. I have 3.55 gears and my cam runs in the 1800-5800 rpm range. Trying to decide on which overdrive I should put in. I am worried that my cruising RPM will be too low for the .64 (1800 at 62 mph) on the smaller highways but seems as if the RPM for highway cruising will be too high (2800 at 75 mph) if I go with the .82. The engine is a 496 BBC. Majority of my driving will be around town but would like to take long trips now and then.
Anyone out there with a similar combination?
Anyone out there with a similar combination?
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
You have plenty of torque with a 496 motor. I would go with the .64 OD. If you are a road racer the .82 is a better chooice. If you arelike me and use the 1st 4 gears most of the time and just use OD for the highway the .64 is good.
Melting Slicks
Joined: May 2004
Posts: 2,743
Likes: 845
From: Gulf of America
2023 C7 of the Year Finalist - Unmodified
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I'm running the TKO600/.64 with 3:36 gears and the overdrive selection was my biggest concern. My smallblock is more of a torque engine and it pulls the .64 OD gear just fine. It will pull from 40-45 mph in 5th if need be. In town I run the first 4 gears and when on the highway, drop it into 5th. I've been on 4 Hot Rod Power Tours now and it's just great to slam it into 5th gear on the interstate and cruise with other traffic at 80+ mph with the tac just ticking over.
Melting Slicks
Joined: Jul 2006
Posts: 2,291
Likes: 493
From: Salmon Arm, BC
I have a 406 with a .64od and 3.36 gears my cam is set up just like yours 1800-5800 range, and it works wonderfully. I even pull out to pass in 5th and it accelerates just fine (much better in 4th but 5th is good too.)
With your extra cubes you'll have no troubles at all.....and a .64 5th will give you good milage
With your extra cubes you'll have no troubles at all.....and a .64 5th will give you good milage
Le Mans Master
Joined: Dec 2003
Posts: 5,727
Likes: 38
From: Fremont CA
TKO600 with 0.80 overdrive, 27" tall tires and 2200RPM 65MPH cruising speed with my 70 LT-1. If you Vette has EFI I could see running it below 2000RPM like all the late model Vettes but, if you have a regular carb, I would want the RPMs above 2000 for proper fuel atomization. The 70 LT-1 knocks down about 20MPG with a factory Holley 4bbl carb.
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
Not to be glib but that's the reason for the 4 lower gears besides the 5th overdrive. I would have no problem with the .64 OD with 3.70 gears in my mostly stock L-82 on the highway and would use 4th for the 45-60 MPH range on small back roads. With the motors mentioned above, I would totally be comfortable with the .64 OD especially since my engine pulls pretty effortlessly from 1,500 RPM in 4th gear with my engine with 3.70 gears. With the horsepower you guys have, it would be a no brainer. 1:1 4th with my 3.70 gears is 2,860 RPM with the OEM diameter tires (255/60/15 or 225/70/15).
Last edited by jb78L-82; Nov 28, 2009 at 07:26 AM.
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Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
If you had a 3.08 [or lower] rear gear, the .82 would be your best choice. With a 3.36 or higher, the .64 would be your best option. Who needs "performance" when running in overdrive mode??? 
Le Mans Master
Joined: Nov 2008
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From: columbus oh
Thread Starter
Instructor
Joined: Dec 2002
Posts: 115
Likes: 0
From: pinehurst nc
Thanks for the input. Looks like there are plenty of folks out there running big blocks that are happy with the .64. Looks like that is what I am going with as I really want the OD for the highway driving. Now does anyone know if Keisler is gonna have a sale anytime soon? Need to tell santa when to buy.
Le Mans Master
Joined: Aug 2000
Posts: 6,273
Likes: 14
From: Austin TX
Suggest you consider your torque curve and cruising RPM when selecting OD ratio. You want this combo to put the RPM just up on the torque curve so that when you need speed to pass, you don't have to downshift.
This approach worked great for my 383 with 430lb-ft (prob close to your BB).
This approach worked great for my 383 with 430lb-ft (prob close to your BB).
Le Mans Master
Joined: Oct 2007
Posts: 7,455
Likes: 977
From: RI, Now Franklin/Nashville TN
Overdrives are exactly as the name suggests, to significantly lower and engines revs to save fuel, make cruising comfortable, and to save engine wear and tear. An OD is not an acceleration gear. Most people are looking for a 5/6 speed manual transmission for the reasons above. The first 4 gears are for accelerating and the 5th gear is for cruisng on the highway. Obviously, a good example is the C5/C6 manual transmissions-notice where the engine revs in 5th or 6th. Want to accelerate hard, then you need to downshift That's the beauty of the 5 speed transmissions-you still have the acceleration or better than the OEM 4 speed, but you can snick into 5th when you have had enough for relaxed cruising.
Le Mans Master
Joined: Aug 2000
Posts: 6,273
Likes: 14
From: Austin TX
Overdrives are exactly as the name suggests, to significantly lower and engines revs to save fuel, make cruising comfortable, and to save engine wear and tear. An OD is not an acceleration gear. Most people are looking for a 5/6 speed manual transmission for the reasons above. The first 4 gears are for accelerating and the 5th gear is for cruisng on the highway. Obviously, a good example is the C5/C6 manual transmissions-notice where the engine revs in 5th or 6th. Want to accelerate hard, then you need to downshift That's the beauty of the 5 speed transmissions-you still have the acceleration or better than the OEM 4 speed, but you can snick into 5th when you have had enough for relaxed cruising.
For hard acceleration, downshifting is necessary.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
If my math is right, you'll be around 1825 RPM at 60 MPH with a 26" tire with the .64 OD. At 70, you'll be at 2125.
With the .82 OD you'll be doing 2335 at 60 and 2610 at 70.
Honestly, if it were me it'd be a toss up.
Do a test. Get on the highway and drive her with whatever 1:1 final drive tranny you have in her now. Then cruise around at those RPM levels and find which will suit your tastes; noise level, engine comfort, etc. I agree, 1800 at 60 may be a bit low. You're not over 2000 RPM (my threshold) until about 66 MPH with the .64 OD.
Let us know which way you go.
With the .82 OD you'll be doing 2335 at 60 and 2610 at 70.
Honestly, if it were me it'd be a toss up.
Do a test. Get on the highway and drive her with whatever 1:1 final drive tranny you have in her now. Then cruise around at those RPM levels and find which will suit your tastes; noise level, engine comfort, etc. I agree, 1800 at 60 may be a bit low. You're not over 2000 RPM (my threshold) until about 66 MPH with the .64 OD.
Let us know which way you go.
Last edited by 73, Dark Blue 454; Dec 1, 2009 at 01:00 AM.
