[dcfirebottle]

I've had my 69 for thirty years plus. Still pretty much stock except for the engine (400) has all the goodies. I'm running a Currie nine inch in it and the suspention and a few other areas of upgraded parts but that's pretty much it. (kept the original rear as well, in case I ever sell it). Also, It's been restored a couple times and done well each time. It's a convertible and I built it pretty much as a touring car. (Have a 68 firebird for my street rod needs).
All that being said, my question is, I'm tired of having just three speeds. The car is currently geared at around three to one. It has the T350 in it now with only about fifty K on the rebuild. One option is to tidy that up and add a (I believe they're called) supplemental planetary gearbox to the mix. I watched Lou & Jared on Carfix add one to a Mopar hotrod.
The other option is a 200R I bought for another project, that I never used. Came out of a El camino. I have everything but it will need a rebuild and maybe some upgrades as well. Think both will cost around the same. Just would like some input from all you firebird experts. All comments are welcomed and appreciated.

[Richie Hoffman]

i have put 200r4in many early f bodies
i put gear vendor overdrive in A bodies had to cut floor haven’t put in f body yet

[Formulajones]

You'll never regret doing an overdrive in one of these classics. It's hands down the most requested and most complimented drivetrain modification I see. Every single person wonders why they didn't do it sooner.

If it were mine, and I already had a 200r laying there, that's the direction I would go.

[92GTA]

I've been planning for the past 3 years to go from my TH400 to a 4L80E. 3 weeks ago I decided to swap in a Tremec T56 Magnum as for a 1st gen, it requires zero modification to the tunnel. I'm buying my complete kit from SST on the 15th. I'm really stoked.

At first, I was going to build a car that was a compromise between the drag strip and the road course, but then decided I would be much happier going all-in on handling instead of compromising some to do straight line. So, since no trans-brake, I'm super happy to be going with a 6-spd manual.

[dcfirebottle]

Appreciate the responses guys. I have a manual in my 68 so I kind of want to keep the 69 an auto. Plus my wife is more willing to drive it when It's time for someone else to take over on the longer hauls. I'm leaning toward the 200r as well. It's and easy swap compared to the 700. Can't take as much horsepower either but you can build them to be relatively tough. At least tough enough for this application. Thanks again.

[Formulajones]

The strength wouldn't concern me, as there has been many in the GN's going in the 8's and 9's for decades back as far as I can remember Lonnie at Extreme Automatics building them for all the GN guys.

With one built properly I wouldn't flinch at a 200 behind any decent running Pontiac.

[FrankieT/A]

I have mixed emotions between the 700 and the 200...the nice thing about the 200 is they have both bolt patterns for bolt up. But they get expensive with all the upgrades they need to make them live. A stock 700 with the TV cable will not need hardly any upgrades but you have to use an adapter plate. An electric trans(like a 4L60E) requires a, what I call, expensive control module, usually about $700 for that alone. JMHO

[1funride]

I have been contemplating the same myself, but for me the decision was made when I took my car to the chassis dyno, the TH400 is a huge power loss and then add in another power loss with a gear vendor and there just isnt enough power left over........ I would go with a more efficient standalone overdrive transmission.

[Formulajones]

Just for the record, the gear vendor is documented only losing 1 hp per 400 hp. It uses a highly efficient cone clutch system that has virtually no parasitic losses.

It's nothing you'll notice on any street car, or race car for that matter and is one of the most popular overdrive setups used in very high HP applications and cars running 7's at well over 200 mph. Most commonly seen in events like drag week.

[1funride]

Can you share the documentation/testing on the gear vendor loss of only 1hp/400? That would be remarkable.

[1funride]

Any more on your overdrive decision? I am contemplating putting one in my 68 Firebird this winter.

[Stripes]

Our 69 fb had a th400 transmission. Swapped in a 700R4. You cant even see the adapter plate. With our 3.55 rear gear, it makes the car have equivalent of 4.20 gears in first and 2.48 gears in OD. No tunnel mods required. Swapped crossmember, shortened driveshaft. Had a turnkey swap for $1200. Same cooler lines. At 55pmh it upshifts to 4th, Set to only lock up the convertor in 4th. Corvete servo allows full power up ships to OD. HUGE improvement.

[Cliff R]

Here is the part required to make the trans upshift into 4th/OD at heavy/full throttle and allow high speed cruising in OD w/o trying to downshift into 3rd with spirited driving.

https://transmissioncenter.net/shop/...t-sleeve-k015/

The servo is actually the component that applies the band.

200's are more popular simply because of the ease of install not requiring an adapter. Some also claim a better gear spread between 1st and 2nd but for the most part that is just regurgitated/outdated info folks throw up on this topic when it comes up. I've set up PLENTY of older cars with 700/R4's and 4L60's and never once has the 1-2 upshift ever even been noticed as the slightest issue with any of the end users.

Same thing with using a non-LU converter. Someone typically jumps in with some nonsense about overheating the transmission if a non-LU converter is used. That might be true if you use some "loose" poorly coupled converter or generic unit, but not even the slightest issue with a well chosen custom built unit. I prefer non-LU for retrofitting vs setting them up to LU once the trans has reached 4th gear by ground the LU solenoid on a normally "open" 4th gear pressure switch even if you are running the supply voltage thru a vacuum switch on ported vacuum. With a good converter you'll be fine for "normal" driving without LU, and most of these heavy vehicles enjoy a little torque multiplication at lower vehicles speeds in 4th/OD as they will climb a steep grade or increase vehicle speeds in traffic w/o lugging the engine or having to use enough throttle to make the downshift to 3rd, for example.......Cliff