The Stovebolt Site Forums The Shop Area Engine Shop 1951 chev w/261

I just bought a beautiful 1951 5 window Chev that has a stock 4 speed, orginial rear end (inclosed driveline) and a 261. I want to keep the 261 but change over to an automatic (maybe a 700R4 if possible)change the gear ratio in the rear end so I can cruise the freeway. What parts do I need?
If I can't use a automatic maybe a good tranny with overdrive. HELP. Also need a Rochestor BP carb for a rebuild.

Lloyd from Washington

Engine adaptor is available for an AT. The rear end needs to be changed to an open driveline. Since the rear must be changed it would make more sense and be more economical to get an appropriate ratio and use a less expensive tranny like a TH350 and get the same results. You'll need an oil cooler and lines, shift linkage, crossmember, mounts, etc. A T5 manual 5 speed can also be used.

You truck would be a 3100 series as you've described it and the standard engine was a 216, not a 261 unless it has been changed. If so then your OK with the transmission change. That is a pretty good engine.

The automatic tranny conversion on your truck might also involve altering your floorpan. There has been a considerable amount of threads on the adaptor used to mount an automatic on these old straight sixes.

The need for an adaptor is that the engine is mounted using the bellhousing which bolts to the 3 or four speed and can easily be mounted to a five speed. To put in an automatic you need a flex plate instead of flywheel. Also, since all automatics include the bellhousing and none will bolt to the rear of the six cylinder engine, you need an adaptor plate that somehow incorporates engine mounts. Then you have to deal with the shifter issues and of course the overdrive, kickdown and speedometer issues as well as open driveline (axel and driveshaft).

One option might be to use an old powerglide transmission like the ones that came behind these same sixes in the cars of the era.

The more popular option (and the one I took) was the use of a T-5 from an S-10. The five speed top loader manual transmission bolts right to the original bellhousing and the shifter comes up about six inches behind where the original one did. You would still have to get a new rear axel and drive shaft, but that is less work than bellhousing/engine mounts/tranny mount/drive shaft/axel.

There are lots of threads on this site on the topic. Try using the 'search' button at the top of the page.

Tom Langdon of the Stovebolt Engine Co. has one and I have read that Buffalo also makes one.

I really like the 261 in my '48. If you had a 3/4T, switching to the 4:10 rear-end from an approx. '68-'72 would improve road speed and is an easy swap. Don't forgot to look at those brakes if you intend to go freeway speed. A dual reservoir master cylinder and a new front end with disc brakes would be very good.

Any relation to Prouty Insurance which used to be in Poulsbo? Former NKHS grad here.