I bought a 40 Ford convertible w/ 401 Buick & 400 turbo trans (64-66). I also have rebuild 200 r4 BOP pattern. The bolt patterns are not the same. I was told Buick didn't change till 67 for the "new BOP pattern". I would really like to put an overdrive trans in it, currently 2400 rpm at 71 mph. Buick people step forward & explain what I need to do please. A pattern for an adaptor would be great or tell me if someone makes one or prints of each would also be even better, I can make it. Both engine & transmissions are in cars now, so I can't see either to copy for a pattern.
Check out Centerville. Russ sells adapters to do what your looking to do. https://www.nailheadbuick.com/
The smaller Buick engines went to BOP earlier, I think 64, that’d be the 300 v8 and 225 v6. 2400 rpm isn’t bad at 70, ideally want about 2200. May be easier to just change the rear end gear depending on what it has for a rear. Torquey motors like a Nailhead can easily handle a highway gear.
Yes I bought the 40 from their estate. Fixing some things that needed attention. Lights, suspension bushings, battery, etc. I lowered the front a lot. Want to change to overdrive trans.... Can't get pics to work on here.
What rear end are you running as a 10 to 20% change may be easy with a change of gears. Although my son swapped a Turbo 400 out for a 200r4 in his Olds and IIRC we didn't have to change the gearbox cross member. Had to change the front uni on the tailshaft though.
I played around with an rpm calculator to try to guess your combination. A 2.56 rear gear, 26 inch tall tire and 1:1 top gear like your turbo 400 has, nets 2412 rpm at 71 mph. Changing rear tires to 28" tall brings rpms down at 71 to 2240. Not knowing any actual particulars about your setup, either taller tires or taller rear gears will get you nearer 2k rpms at 71. I'd do that in a heartbeat, rather than pull a turbo 400 for an overdrive....just my opinion.
IF that turbo has a switch-pitch converter I would definitely keep it! I kept mine with my 425 Buick Gran Sport engine and love it. It really jumps when you nail it!! Pun intended. Remember that anything is possible if you are not smart enough to realize it can't be done... Henry Ford said that I believe. Good luck..
Check out the Centerville Auto Repair website. There is a comprehensive tech article on how to put different GM automatics behind your 401. Some, such as the 200r4, require cutting off the bell and installing their special bell. Not a cheap option, but doable. Because the starter bolts to the block on a nailhead, a homemade adapter would create a challenge with both the flex plate and starter, or a special torque converter. Changing the rear end ratio would be my option, unless the need for a higher gear for take off is needed. I am using a 64 ST400 in my 40 Buick Coupe with a 2.91 gear and 28" tall tires. The 401 has plenty of torque to work.
Btw, I'm running 235/75 tires on rear on 16", yep, 16", rims. Fills the wheel well better, too, as well as lowering the required rpm for a set speed. Here is same tire on my pickup.
...the car has 235 78 15s....don't really need or care about quick performance since this isn't my performance car, just don't want a total dog though either. Was hoping this would be easy, doesn't look like it will be. I'll keep researching the problem & see what's going to work....
You didn't specify what year ST400 you have. 1964 was a one year valve body, and 1965-66 was switch pitch. The latter can be wired to raise the stall speed with a switch so running a taller gear would be no problem. Since the 401 is balanced externally, that has to be considered.
How do you tell what year you have & if it's a switch pitch? I was told the engine & trans was out of a 64-66 Riviera.
I agree with the comments on rear axle ratio.....go to a 2.70/3.00, and the comment on the high torque of the Nailhead.......no difficulty handling a high (numerically low) differential/bigger diameter tires, particularly with a switch-pitch TH400.......to get a lower RPM at 70 MPH....in a fairly light vehicle. But.....my Nailhead will run with ease all day at 70....on a 3.70 gear! Those engines are bullet-proof. They are such gas guzzlers it probably won't make much difference anyway.
Two ways- there will be a big tag riveted to the passenger side of the transmission case. If the number starts with 64 (such as 64 BN, it is a 64. 65 starts with 65 and so on. The second way is to look at the electrical connector at the back of the driver's side of the main case. A single blade on the switch will be a 64, and two blades will be a 65 or 66. Another way, if the engine and transmission came out of the same car, is to look at the engine codes stamped on he block. They are located on the passenger side just ahead of the valley pan. You can decipher the numbers to determine what year and car it was in. The engine production code will be stamped upside down on the driver's side, and will have two letters, such as KH. K is 1964, L is 1965, and M is 1966
...I looked at the engine #. Looks to be a K= '64, & trans has a single spade on wire. Thanks for the info.
You're welcome. The 64 ST400 is a one year only valve body, and while a 3 speed, has only drive and low shift selector. Centerville's website goes into great detail about that transmission. Nice thing is a standard TH400 converter fits it, and there are plenty choices for stall speed.
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