Time for Overdrive in a 1970 Chevelle
Posted by Chev_hell@reddit | projectcar | View on Reddit | 43 comments
As title states I have a 1970 BBC Chevelle and really want to go overdrive. And get some modern performance.
Current setup:
454, Holley Terminator EFI (HP ECU)
TH350 built for that motor, upgraded sprag, clutches etc. has been behind this motor since 2011. Works fine just no overdrive
Rear diff is a 12 bolt with 3.42 and posi
Would like to go on longer cruises, maybe auto-x. Would like to get my rpms down on the freeway and get some drone out the cab. I've held off changing the exhaust until I get the transmission ironed out.
Options:
TKX would probably run 6-7k and would be the most labor intensive since just about everything would change.
4L80E is about the same by the time you buy the trans, tcu, and torque converter but would be the most straight forward installation.
200-4r / 700r4 could be built for this as well, would just require a TV cable setup. A 200-4r is probably a direct swap.
Gear Vendors Overdrive - not a cheap unit but would leave existing trans in place. Probably my least favorite option.
Just curious if anyone has started where I am and made the change and they would recommend it.
MCXL@reddit
The gear vendors units are popular and robust, the guys on Roadkill etc put them on personal cars, and if you're happy with the current transmission why mess with it?
Chev_hell@reddit (OP)
I would like lower rpm at freeway speed, and would a little more breathing room hp/tq wise if I make some engine changes. I think I'm at the limits of my th350. Now that I'm unsure if a 4L80E will fit, a GV unit might just be my best move
MCXL@reddit
The Gear Vendors i believe can be moved from a 350 to a 400 with the different mounting parts, but I could be wrong. Regardless, the split shifting feature of the GV units turning your transmission into a 6 speed auto is pretty trick.
chuck-u-farley-@reddit
I take my Camaro on the freeway …. Blown big block, 4:11 posi rear…..
3500 at 70 mph…. Let er eat man
Chev_hell@reddit (OP)
I love in So-Cal and hit the freeway every time I take it out for a good rip. 70mph is about 3000rpm for me. Not horrible but would like to do better. That's a beautiful Camaro!
TEAMTRASHCAN@reddit
3k is prob where you wanna be> Rpm does not have much to do with fuel econ< like 4 cyls spin faster than that at those speeds> you want to be well within your cam specs for rpm band for efficency
SD_CA@reddit
This isn't true. Yes of course you want to be in your power range. But lower RPMs means less friction on the pistons. And less resistance on the crank in the oil. And of course fuel has to enter the engine on every rpm.
You can test this theory in an manual car. Just drive in 4th instead of 5th or 6th. Or take your over drive trans out of overdrive. If you can.
TEAMTRASHCAN@reddit
The friction of the pistons is funny. Rpm doesn’t have direct correlation to fuel entering the engine. When you are at peak efficiency you are also at peak vacuum, which is the absence of air and relationally, fuel. This happens at higher rpm than most think with a fancy cam
MCXL@reddit
This is more complex than you are saying, but you are correct that being too far down will actually hurt fuel economy as the engine efficiency tumbles, and that problem is worse with larger cams. However the speed at which that is true is not 2500 rpm.
SD_CA@reddit
You think your fuel delivery system. Will deliver less fuel at 2x the RPMs?
TEAMTRASHCAN@reddit
At twice the vac, yes
chuck-u-farley-@reddit
Likewise with that Chevelle….
Lookin tough
1968RR@reddit
At the risk of seeming pedantic, it’s 4.11:1, not 4:11.
chmod-77@reddit
What a stupid comment.
When someone types any number such as 9, it can still be 9/1. It could be 18/2.
Do you really think people were confused and thought he meant a ratio of 4.11:3?
NVM. I'll just block and move on.
chuck-u-farley-@reddit
That’s exactly what I did……
chuck-u-farley-@reddit
You are absolutely correct but you knew 100% what i was talking anout so your point? You have to go around fact correcting on a constant basis?
Squidking1000@reddit
I'm running 1600rpm at 70mph, 2000rpm at 84mph with a Viper T56 behind a 465" Pontiac with 3.73 gears in my GTO. I was running 1750@70mph with 4.11's but 1st gear was so useless I dropped my ratio's. 0.50 OD is something LOL.
Funderstruck@reddit
I had a 4L80e in a ‘72 Skylark.It’s basically a TH400 with overdrive. The trans tunnel is not big enough for it and you’ll have to cut out a good chunk of it.
The TKX shouldn’t require that, I was under the impression it was basically designed to avoid that.
Holley Terminator should be able to control it though. At least the newer ones can. That’s what controlled mine
Chev_hell@reddit (OP)
That's crazy you had to do surgery.. was your car lowered a substantial amount? Everywhere I've posted I've been told a 4L80E should fit as long as my body mounts were toast.
Funderstruck@reddit
I personally only had to cut out around the cooler lines, but that’s because I had a LS with motor mounts that pushed the engine further forward, so that a lot of it cleared.
With a big block, chances are you’d probably have to cut out a good chunk of the tunnel. The 4L80 is both longer and wider than the TH400.
Chev_hell@reddit (OP)
That makes sense. LS don't have that flange on the back like sbc and BBC. So at a minimum your going forward probably 1/2" or so. I run a mech fan as well so going forward for me isn't an option without making more changes
Funderstruck@reddit
I had specific motor mounts that moved the engine further forward to help it fit, otherwise it has the same issue.
Lucreth2@reddit
Unless the floor of a 70 is substantially different than a 69, my understanding is a 4L80E won't fit without modification. It does somewhat depend on what engine you are running though as they sit differently in the motor compartment and impact trans positioning.
Chev_hell@reddit (OP)
My understanding was the area around the servo and the cooler lines may need some massaging, but not tunnel surgery required. 68-72 Chevelles should be mostly the same. Not sure if that applies to the BOP A bodies as well but I assume it would
Lucreth2@reddit
I messaged a friend and did a tiny bit of digging. AI and a few top results spit out that it fits but with no evidence. Deeper results agree with what my friend said in that 4l60 will fit without modifications but 4l80 will require, at minimum, some beating and banging. Depending on what engine you're running and what motor mounts are being used, fitment only gets worse from there with several companies offering full replacement tunnels specifically for that swap. I don't believe that product would exist if it wasn't a real issue.
It's possible the results offering positive feedback mislabeled 4l60s, or perhaps the motor mounts vary an enormous amount from car to car, company to company, etc.
And finally..... Frankly these cars weren't built to exacting standards and I wouldn't be surprised if there's a quarter inch or more in variation between vehicles. Hell even a half inch or more wouldn't surprise me.
v8packard@reddit
Do not use a Gear Vendors OD without a lockup converter. With any kind of high performance torque converter and the 4.11 gears you are going to be using gasoline to heat ATF. It will slip significantly at cruise speed, and it's only about a 22% OD ratio. By comparison the 4L80 is 25% and TKX is 32%. A TH350 can be done with a lock up converter, but it may not be your best choice.
I am a TH400/4L80 guy from way back. I would put them in anything. I have used GM stand alone diesel computers, other GM computers, and aftermarket controllers for the 4L80. I have even dabbled in making the 4L80 into a 6 speed. The 4L80 is big, but manageable in a Chevelle (barely). They are not cheap but can be reasonable enough. If I am being honest, the big disadvantage of the TH400 and 4L80 are gear ratios. They have gearing stock that is based on 1950s ideas and powerbands. Not a huge deal when you have a big block, but not ideal for a hot street car either.
I was reluctant to give the modern 6, 8, and 10 speed autos a fair shot. I was wrong. Now that I have experience with them I can see how they are a big leap forward and have tremendous potential. The 10L80 and 10L90 have the capacity to handle a good big block, and are built with the bell housing pattern to mate to a big block. You will need to work out the torque converter and flexplate, as well as electronics. But there is a better choice.
In my opinion, the perfect spread of ratios is in the 8 speed automatics. The GM 8L90 would be ideal, except the proprietary electronics in them makes a swap very difficult if not impossible. Then there is the ZF 8HP family. All of the GM and Ford transmissions are based on the ZF design. The best of these is, in my opinion, the 8HP. The trans is built in a number of sizes and configurations. They have huge and growing aftermarket support. There are a number of different controllers and adapters on the market. And the trans cores are much less expensive than the GM units. I think the 8HP in your big block Chevelle would be the best thing you can do if you keep the car an automatic. The one change I might make is going to a 3.08 or 3.36 gear, from the 4.11. But, maybe you will like it with the 4.11.
Manual transmissions are a whole other conversation.
HowdyDooder@reddit
Does the Gear Vendors require getting a new driveshaft? The 4L80 or maybe a built 4L60 seems like the way to go to me as those options seem like the most straightforward of what you laid out, but I’m not super-experienced with this stuff and may be overlooking something.
Chev_hell@reddit (OP)
Almost every option would require a new driveshaft. The gear vendors unit bolts on to the back of the trans where the tail cone was and adds more length to it.
Lucreth2@reddit
I feel like gear vendors is the buy once cry once solution here. It's the least actual work and is pretty much guaranteed to give you what you want without cutting the car apart.
Mavrosian@reddit
I have a gear vendors unit in my '66 Falcon, and it's fantastic. My manual 3 speed toploader has 6 forward gears, with the last being overdrive. Push-button switch in the shifter, easy and fast shifting.
girthypeter@reddit
4l80 with manual valve body. A gear venders is probably the right move because you can keep your car niceeith same functionality but just add a push button
Lrrr-RulerOfOmicron@reddit
I had a friend with a Chevelle. It had a few drive trains. Originally had a 350/350 then to change to a 454/400. Later the 400 was replaced with a 700r4. After a few years it got a 6.0 ls with 4l80. It stayed that way for 20 years. I think the ls and 4l80 were much more refined to drive with plenty of HP when called upon.
I think it depends on how you want the car to feel. If you like the way it is now build a 4 speed auto. I am only experienced with 700r4s. When built they perform well.
If you want to be more refined and have the right gear every time you want to accelerate hard a 6l80 is the way to go in my opinion. My truck is heavy and the 6r80 helps the coyote find the right gear since it is not a torque monster.
Maybe go test drive a newer Camaro and see how you like gearing.
Pyroblock@reddit
8hp70
Chev_hell@reddit (OP)
I've seen 1-2 guys doing it. I know adapters exist for the 454. I don't know what electronics exist for shifting it. I wouldn't be able to use my old school console shifter for that
Pyroblock@reddit
you'd use a turbolamik controller for it and you can wire up an old school shifter with it if you use this https://www.haltech.com/product/ht-011227-th400-standard-case-transmission-selector-position-kit/ it's what I'm doing because I had a 700r4 shifter, and I converted the mechanical linkage into an electronic one, it's a lot more work for sure, but for the size of a 4l80 you shouldn't need to cut up your car and you get 8 gears, it's a really awesome transmission that can already communicate directly with your holley
Chev_hell@reddit (OP)
My holley doesn't do any tcu control, it's the early Terminator version but I'll check out the link you provided, thanks!
Pyroblock@reddit
the turbolamik communicates to the holley over can, the turbolamik is the tcu, not the holley
Powerful-Lobster-631@reddit
Check local tranny shops. I might go overdrive. Usually do one upgrade/ winter project per year. Gives me time to save up
rudbri93@reddit
I looked into a tkx for my '72 cutlass and yea, pricey. I went with a 2004r, its a direct swap for the th350. The tv cable isnt too hard to set up. Sadly i have to warranty mine so i dont have many miles on it but they can be built for power and have lockup converters.
RhubarbIcy9655@reddit
2004r can be built for the power, but when a 4l80 is available they are no longer a viable option. I had a 2004r built by extreme automatics when my cutlass was still olds powered. Even with a really well thought out lockup system, the drivability was not great. That was the issue that convinced me to go LS back in 2012. A 4l80 will handle the power without blinking and can be adjusted electronically, making it easier to tailor to a given combination.
PowerfulSuction@reddit
Gear Vendors is the move
Big-Energy-3363@reddit
Take a hard look at GearBendors
Chev_hell@reddit (OP)
I've talked to them and even visited the facility. They are stout units, I be had friends that had them behind TH400's and it was a cool combo