First Generation Firebird
Posted By: j.stary Transmission for Low RPM at high speeds - 01/14/22 07:41 AM
Hi there

I am a proud owner of a beautiful gold body - black vinyl roof 1967 Firebird with a 326 and a 2 Speed Automatic in it.

The thing is, that I am driving it 90 % of the time on the highway with 75mph.

I would like to put a different transmission in it so that the rpms drop significantly.

What transmission would you recommend?

Thank you very much for the advice.
Posted By: Bob S. Re: Transmission for Low RPM at high speeds - 01/14/22 12:04 PM
Another maybe simpler way is change the rear gears
Posted By: j.stary Re: Transmission for Low RPM at high speeds - 01/14/22 12:31 PM
Yes but this would also worsen the acceleration drastically. I need a transmission with some extra gears or even Overdrive.

The question is, which one fits into the car.
Posted By: barnbird Re: Transmission for Low RPM at high speeds - 01/14/22 04:42 PM
Hello, sounds like a beautiful example. Gold is one of those different then the norm colors on our first gens that I love. I understand what you are trying to accomplish given your driving conditions But as Bob said there are other factors that need to be considered even if you are moving forward with the Trans change. There are 2 main ways people tend to go when using preexisting transmissions. The first is a 700r4 and the second is the 2004r. Those are the two that you need to type in for your swap research. Just the basics: I believe you will need to do crossmember and driveshaft mods for both, most 700r4's need an engine to trans adapter, the 700r4 is designed to handle more torque then the 2004r but with your drivetrain I don't think that would come into play. Both use different gear ratios and that is where your rear diff ratio and engine torque curve come into play. Pick the wrong combo and you could find yourself with too numerically high of a first and second ratio or worse for you have too numerically low of a final drive ratio so that at highway speeds it's too far below its optimum torque curve. Most find that the 2004r fits their needs the best, but you need to do your research and decide for yourself. One last note either trans. can be built to handle high amounts of torque if you are thinking about future engine swaps.
Posted By: Bob S. Re: Transmission for Low RPM at high speeds - 01/14/22 06:40 PM
Another option is to go manual transmission. There is a new version of the Tremec 5 speed that fits better in the tunnel. That will provide tons of overdrive. There are different versions with different gear ratios. All the parts needed for the clutch, clutch pedals, and linkage are all readily available.
Posted By: Bartbird Re: Transmission for Low RPM at high speeds - 01/21/22 04:10 PM
Summit sells a few tranny's for BOP Buick Olds Pontiac bellhousings that bolt in, you can get quite a few, Butler has quite a few too, with the 350 you won't need a big dollar hi hp hi tq one either, the TH200 with over drive would be plenty. I would not switch to manual trans unless you really want a project. Link to Butler below

https://butlerperformance.com/c-123...-automatic-over-drive-transmissions.html
Posted By: Bob S. Re: Transmission for Low RPM at high speeds - 01/21/22 04:53 PM
Yeah but manual transmissions are much more fun
Posted By: bigchief Re: Transmission for Low RPM at high speeds - 01/21/22 05:42 PM
My boss builds transmissions.
The replacement parts for 2004r are getting next to impossible to find.
Would find a more modern transmission to use i f you want overdrive.
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