4 or 5 speed
Thread Starter
Cruising
Joined: Aug 2016
Posts: 13
Likes: 1
4 or 5 speed
Hi everybody. Taking delivery on my first C3. It's a 72 convertible ,small block, auto. I've got,m20,m21 and an m22s from other builds stored around the shop so the 4 speed is not the question. The question, is a 5 speed ,TKO 500, worth the effort. I would like it to be freeway friendly ultimately. I do plan to separate the body and frame for cosmetic and mechanical repair and or upgrades. The engine will definitely need a bump in compression, cam change to a mild roller and a general rebuild so I guess you can see where this is going. So let the dialog begin. Thanks , Steve.
Race Director
Joined: Mar 2016
Posts: 14,321
Likes: 8,125
From: Napa Valley California
My '73, 454 has the TH400 and 3.36 rear gears. I'm looking at either swapping the TH400 for a 2004R or a TKO600. I am also wondering about the swap and what would be involved in adding the clutch pedal/brake pedal combo. Great timing on this post.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
If you have 3.08 rear gear, keep the 4 speed; 3.36 or steeper, go withthe 5 speed (.66 overdrive). At highway speeds, the engine will purr (instead of 'scream'); fuel mileage will increase about 20+%; and the heat produced under the hood will be much less. Your engine will thank you for it every time you take it out on the highway. 
Drifting
Joined: Oct 2005
Posts: 1,615
Likes: 150
From: Forth Worth TX
Not sure how much you plan on driving your car or what the cost of switching to a 5spd will be, but here's a quick and simple comparison of 4 vs. 5 speed.
4spd - 15mpg x 1k miles =66.6 gallons of gas x $2.00 per gallon = $133 to drive 1000 miles at highway speeds.
5spd - 20mpg x 1k miles = 50 gallons of gas x $2.00 per gallon = $100 to drive 1000 miles at highway speeds.
(An increase from 15mpg to 20mpg would be a 33% increase in fuel economy. Your results will most likely be less.)
A $33 difference for every 1000 miles at highway speeds(4th gear vs. 5th gear). When you drive around town and aren't in 5th gear there's virtually no savings.
If you're driving 20k miles per year, great. If you drive 1k miles per year....well?
4spd - 15mpg x 1k miles =66.6 gallons of gas x $2.00 per gallon = $133 to drive 1000 miles at highway speeds.
5spd - 20mpg x 1k miles = 50 gallons of gas x $2.00 per gallon = $100 to drive 1000 miles at highway speeds.
(An increase from 15mpg to 20mpg would be a 33% increase in fuel economy. Your results will most likely be less.)
A $33 difference for every 1000 miles at highway speeds(4th gear vs. 5th gear). When you drive around town and aren't in 5th gear there's virtually no savings.
If you're driving 20k miles per year, great. If you drive 1k miles per year....well?
Last edited by Revi; Sep 29, 2016 at 08:30 AM.
Instructor
Joined: Sep 2015
Posts: 122
Likes: 17
From: MA
Tko600
So I'm gonna propose a practical question:
Why bother installing a 4 speed, going through all the labor and not install a five speed TKO-600? Problem solved pretty much forever. The TKO 600 can handle just about all the torque most of us will ever drive with, it has a great first gear ratio, and can be upgraded with carbon fiber synchros and brass fork pads. I removed a TH350 and put the TKO-600, including pedals, cross member, and a rear end swap, in my C3 and its amazing.
https://shiftsst.com/
http://www.hurst-drivelines.com/
Why bother installing a 4 speed, going through all the labor and not install a five speed TKO-600? Problem solved pretty much forever. The TKO 600 can handle just about all the torque most of us will ever drive with, it has a great first gear ratio, and can be upgraded with carbon fiber synchros and brass fork pads. I removed a TH350 and put the TKO-600, including pedals, cross member, and a rear end swap, in my C3 and its amazing.
https://shiftsst.com/
http://www.hurst-drivelines.com/
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Race Director
Joined: Jun 2000
Posts: 10,039
Likes: 669
From: FL
TKO-600. Absolutely no doubt in my mind. Shoot for 3.36 to 3.55 rear gears.
I ran a Tremec 3550 (TKO predecessor) for over 10 years. One of the best mods I ever did. My only real grip was the gap between the 1.1 4th and .62 5th. When I swapped to a big block and 3.73 rear, I swapped to a T-56 Magnum with 5th and 6th OD.
I ran a Tremec 3550 (TKO predecessor) for over 10 years. One of the best mods I ever did. My only real grip was the gap between the 1.1 4th and .62 5th. When I swapped to a big block and 3.73 rear, I swapped to a T-56 Magnum with 5th and 6th OD.
Instructor
Joined: Oct 2015
Posts: 189
Likes: 24
From: Herndon VA
IMO a 5 speed is worth it if you are going to spend any significant time on the highway. It will improve drivability and you could consider it prevention as the higher RPMs inflict more wear one the drivetrain. Actually doing the swap to a T56 now.
Burning Brakes
Joined: Apr 2013
Posts: 1,194
Likes: 109
From: Las Vegas NV
As Revi pointed out, you're not doing it because the financial ROI makes sense. It really doesn't. Owning a C3 isn't a sound investment in the first place in most cases anyhow!
I did it mostly for comfort, also for less under hood heat. I live in the southwest where when you leave town people are doing 80-100mph on the freeway. Doing anything over 75mph in 4th gear for an extended period of time was quite uncomfortable for me.
Also my 4-speed broke, so there's that!
I did it mostly for comfort, also for less under hood heat. I live in the southwest where when you leave town people are doing 80-100mph on the freeway. Doing anything over 75mph in 4th gear for an extended period of time was quite uncomfortable for me.
Also my 4-speed broke, so there's that!
Last edited by AboveTheLogic; Sep 29, 2016 at 10:25 AM.
Race Director
Joined: Mar 2016
Posts: 14,321
Likes: 8,125
From: Napa Valley California
My questions are; 1). What is involved in setting up the clutch and brake pedals when swapping from an automatic trans to a manual trans? 2). Are the brackets for the clutch and brake pedals already incorporated into the frame so it would be as simple as swapping pedal mechanisms, or will I need to cut and weld new brackets? 3). Are the trans mounts the same or will I need frame modifications? 4). Does the cross member need to be swapped?
Instructor
Joined: Oct 2015
Posts: 189
Likes: 24
From: Herndon VA
My questions are; 1). What is involved in setting up the clutch and brake pedals when swapping from an automatic trans to a manual trans? 2). Are the brackets for the clutch and brake pedals already incorporated into the frame so it would be as simple as swapping pedal mechanisms, or will I need to cut and weld new brackets? 3). Are the trans mounts the same or will I need frame modifications? 4). Does the cross member need to be swapped?
The pedal box is the same, but you will need new pedals and some springs to make it operational. The automatic brake pedal is far too big anyway. For the clutch you will need to determine if you want a mechanical or hydraulic setup. If you swap to a T56 you will need a new crossmember, but I think it is just an adapter if you go with a TKO 5 speed. Check out some of the swap kits being sold online and you will get a feel of what is needed.
Melting Slicks
Joined: Dec 2015
Posts: 3,181
Likes: 732
From: Texas City, TX Texas
Probably find all you need to know here:
https://www.corvetteforum.com/forums...directory.html
I haven't read it yet personally.
https://www.corvetteforum.com/forums...directory.html
I haven't read it yet personally.
Le Mans Master
Joined: Aug 2005
Posts: 6,521
Likes: 1,956
From: Temple Terrace Florida
Tremec
I have a small block with a 4:10 rear. I installed a Tremec 600 with a .62 overdrive fifth gear. I can now take a long trip on the highway without screaming at my passenger. Next to adding A/C, it is the best upgrade you can make. I would also add a removable cross member while the body is off. Jerry
Race Director
Joined: Jun 2000
Posts: 10,039
Likes: 669
From: FL
On the plus side, if you are starting with an automatic car, the cross member is already removable. You may have to weld a couple of tabs on it for the TKO mounting bracket to bolt to but that is about it.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Just for the sake of discussion:
In my case, I swapped out my THM-400 auto tranny for a 700-R4 O/D auto trans...PRIMARILY to save wear & tear on my factory original SB engine with 216K miles on it. Financially, I couldn't justify the cost or the effort involved for the miles I would put on it during the rest of my lifetime. But, every time I drive the car on the highway, I am VERY glad that I did it. And, I know that the long-term health/life of my engine will be enhanced because I made that swap. The highway driving is also quieter, cooler, and much more enjoyable because of the 2050 rpm engine speed at 70 mph.
In my case, I swapped out my THM-400 auto tranny for a 700-R4 O/D auto trans...PRIMARILY to save wear & tear on my factory original SB engine with 216K miles on it. Financially, I couldn't justify the cost or the effort involved for the miles I would put on it during the rest of my lifetime. But, every time I drive the car on the highway, I am VERY glad that I did it. And, I know that the long-term health/life of my engine will be enhanced because I made that swap. The highway driving is also quieter, cooler, and much more enjoyable because of the 2050 rpm engine speed at 70 mph.