1949 upgrade to 454 tranny advise needed.

I could use some advise on my project, that is, upgrading a 1949 Buick Super with a Chevy 454 BB. I have already found some very useful threads here, and I am appreciative to all who have contributed.

First, I need to disclose that my knowledge of engines and transmissions is extremely basic. Up until a few weeks ago, I had no idea what a cam is. But, I am doing a lot of research, reading textbooks, searching online and asking my mechanic and others for guidance.

I intend to use the car as a daily driver. Around town, and probably some trips up the California coast, wine county, etc. Probably some serious freeway miles. I also tend to be a pit of a lead-foot, and like to drive pretty hard around town. Never to be raced, and I have no concerns about top-speed. I have three kids that I want to come home to.

As of now, we mounted a 454 BB that we obtained from a donor 1973 Chevy Cheyenne. I cannot access the stamp on the engine block, so I do not have exact details, but the stock hp rating by my research hovers around 275. With an upgraded cam, etc., I plan on getting at least 350 hp, and hopefully more.

The donor car came with a TH400 transmission. My initial plans were to put in a 700r4. However, my mechanic advised me to keep the 400. After my research, I came to the realization that while the 700r4 could handle 350hp, it would need to be made after 1987, and still be “built right” to handle any abuse I may throw at it, especially if I go higher performance. The 400, on the other hand, is reportedly “bullet-proof.”

I should mention that my mechanic converted the original rear-end from a closed to open drivetrain. He promised me that original Buick rear-end can handle the new power. Any thoughts on that?

The differential on this rear end is, per my investigation, 4.45:1. That seems to me like a really low gear. My shop manual lists a 4.10:1 ratio as an “option.” I honestly don’t think I’ll never know unless I open it up.

So, with my current package of the BB and the 400, with a 4.10 or 4.45, my understanding is that I should be able to move within the neighborhood fairly aggressively (and probably burn through a lot of fuel).

However, I would like to be able to take this car on the freeway at comfortable speeds, without having the engine run too fast, and without too much noise. I few years back, I had a 1970 280 Benz with 3 speeds, and I hated the high RPMs. So, I think to meet this need, I should get an overdrive. The way I understand it, one option is that I can add an Overgears. Another option is to change out the tranny entirely. I am now leaning against a 7004R, but perhaps a 4L80e. Cost savings is helpful, though not critical.

Any and all advice would be appreciated.


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Oops. I meant Gearvendors (not Overgears)

Even with overdrive, a 4.45 gear is a lot for highway driving. Since your not looking for a peaky high HP engine, build the BB to take advantage of the gobs of torque it will produce in the lower RPM range. Maybe something along the Edelbrock performer line with a max RPM of 5500. Change axles to get around a 3.5 ratio. Ford 9'' has a 3.50 while Chevy has a 3.42 ratio . Fuel economy will be much improved with the lower RPM and still should get decent mileage.

As for trannys, I would use some type of overdrive. The 4l80e is electronic and requires an aftermarket controller. Early 700R4 s can be built to handle the power easily. It will spin the tires long before it tears up the trans. Put on slicks and you are on your own. Never priced a GV overdrive, but if the TH400 is good it could be an option.

Thanks cal1320

I have become concerned about my rear end and have done some research. I found a local guy who specializes in Buicks and have learned that any third member from a '40 to '55 Buick will trade out nicely. He just so happened to have a '52 complete rear end with a 3.53 that he is willing to trade for my old beat up, but complete, engine. My stuff is probably worth more in trade, but it is easier for me this way to unload it instead of trying to sell it.

The GV is not cheap. $2,600 new. However, the cost difference between a strongly built 700r4, a 4l80e (with computer) or the 400 with a GV is not imperative to me in the big picture. So, I think I will likely stick with the workhorse 400.