30th Oct 2013, 00:07

It's true that the Chevrolet V8s are much quicker off the line than the Oldsmobile 307s. However, the 307 is the most durable and reliable engine I've come across.

13th Sep 2014, 05:32

I personally prefer the 5.0L versions of the Brougham much more. The 5.7L versions had their suspensions jacked up and were really geared for towing. They ride kind of high and a little harsher, as it uses the police-duty suspension package borrowed from the Caprice, being that the regular suspension would probably give out under heavy towing conditions. The 5.0L versions continue to use the traditional soft suspension that was more for the average Cadillac buyer. Sure the 5.7L is faster, but that's it.

13th Sep 2014, 13:18

Regarding the 305 vs 307 debate, while I've never owned a Brougham, I've had many Delta 88s with the 307 and many Caprices with the 305. However, my Delta 88s were all 1981-1984 era cars, so they had a different sort of 307 than the one in '85 and later cars (including the Broughams). The early 80s 307 was quite reasonably powerful - anyway adequate - due to different heads or something. I wonder does anyone know if it is easy to swap out older 307s or even 305s for weaker 307 found in late 80s Broughams? I would assume there are still a lot of those engines available at quite a cheap price.

14th Sep 2014, 15:18

Based on my experience with the 307, it has everything to do with the way it's been maintained. The 85 and later 307s used swirl port heads, and when they are running right, they are a pleasure to drive. Nice smooth throttle response, fairly decent pick up, and a nice hum sound - never a growl. The problem I've seen with them is carbon build up in the intake manifold, failed intake manifold gaskets, improper procedure when setting the ignition timing, and failed EGR valves that were misdiagnosed. Everyone will assume the carburetor is going bad, but it's usually those other things that throw the mixture off, causing sluggishness. It's usually never the carb itself.

14th Sep 2014, 16:25

I own a 1985 Buick LeSabre with the updated, underpowered 307. And let me tell you it's hard to notice on paper, but compared to the older version, the 1985 and newer 307 is nothing short of a useless boat anchor. It is reliable and durable, but struggles nearly as hard as some of Buicks old carburated V6 engines to maintain a decent speed on the highway, or on hills in our modern world.

With as slow as my Buick is, I can't even fathom this motor in a car like the Brougham that weighs almost half a ton more. I bought my 1985 because it was a Collector's Edition, but unfortunately the engine is anything but collectible.

Regarding engine swaps, you would want to check if the bell housing from the 305 fits the transmission you are hooking it to. If it doesn't, usually you just need an adapter kit that matches the bolts up.

Also, if you are hooking anything bigger than a 305 to a transmission from the 1980s, you will want to have your transmission rebuilt. The 200-r4 transmission put in 1980s GM cars is not built to handle torque from any V8 larger than 5.0 liters (some did come hooked to the 350 diesel, but that was a boat anchor as well). Go to a performance shop that is familiar with Buick Grand National, Chevy Monte Carlo SS, Camaros, Firebirds, etc. While the 200-r4 is junk from the factory, you can install aftermarket shift kits and valve bodies for them to handle well over 500 pounds of torque; more than most stock V8s put out even today. They may be able to sell you a transmission cheaper than rebuilding your own. Just do some research. Do not go to your local transmission shop that is run by an old, dumb farmer. They know nothing about modifying transmissions; only changing fluids or doing complete replacements.

If it were me I would simply try to find a complete engine and transmission from a early 1990s Brougham or a 1992-1996 Buick Roadmaster. They are getting harder to find, but they are out there. You would need the computer from the newer engine to work in your older car.

That, or if you really like the Brougham, just try to find a good clean 1991-1992 with the Chevy 350. They are pretty spendy today though, and seem to be more prone to rust than a lot of GMs from that time period.

FYI almost all GM V6 and V8 small blocks and big blocks are interchangeable with the frames on all GM full and mid size RWD cars from the late 1960's onward. Sometimes the mounts and frames need to be slightly modified, but in the end they can all be easily made to fit. If you don't want to worry about matching all the electronic BS and pollution control stuff, find a Chevy 327 motor, or a good Oldsmobile 350 V8 or Chevy 350, and go from there.

15th Sep 2014, 21:14

The best engine swap for an Olds 307 is the Olds 403. No matter what the car is, it's a simple and direct swap. The only thing different is the down pipe bolt pattern on the exhaust.

19th Oct 2016, 18:52

The 350 only has 10 or 15 more hp than the 305. Most people say they couldn't tell the difference without driving them back to back, other than accelerating at very high speeds already.

20th Oct 2016, 18:18

The 350 is a really great engine. People commonly swap or put that engine in vs a 305. Plus it can easily be upgraded for further HP boost. Can't go wrong with the mass and weight of a full size luxury car. Better passing etc. Just like a 307 from the past. Put a 350 in.

21st Oct 2016, 01:24

90-92 Cadillac Brougham Engine Power Output:

90: 5.0 4bbl: hp 140@3200: torque 255lbs/ft@2000

90: 5.7 TBI: hp 175@4200: torque 280lbs/ft@2400

91-92: 5.0 TBI: hp 170@4400: torque 255lbs/ft@2400

91-92: 5.7 TBI: hp 180@4200: torque 280lbs/ft@2400

The Chevrolet 5.0 and 5.7 engines used in 91-92 accelerate almost the same as I speak from experience. The commenter is 100% correct about the acceleration characteristics. The 5.7's greater torque curve is noticeable at highway speeds.

21st Oct 2016, 15:36

Bottom line, you could spend the same money on a replacement 350, and get more power, the same mileage and durability, size and weight. Why put in a 305? Go with a 350, one of best engines ever produced. You can do far more to it and swap out some of your 305 parts over to it. I feel the resale will improve as well.