About Jesse Moser Expertise I specialize in the Plymouth Duster from 1970 to 1973, allthough 1974 through 1976 Dusters are nearly identical. 340s, Twisters, Feather Dusters (the cars!), whatever "A" body Duster you have, I can probably give you some info.
Experience I own a 1973 Duster with the Twister options package. I've been searching for information on this specific car since 1995 and have acquired much general and specific knowledge in the process.
Organizations belong to: Mopar Mailing List
Question I have a 1972 Plymouth Duster with a 225 slant-six. It is the original engine and it was rebuilt. Im thinking about dropping 360 ci V-8. The slant-six isn't powerful enough for me. Would it be a good idea to go with the bigger engine or should i just keep the original?
Answer Jason, sorry I didn't reply sooner, but I've been spending all my free time making improvements to the Dakota that I just bought. On to your question...
What you do with your car is your own descision. All I can do is tell you what you CAN do and what's involved. So that's what I'll do.
If you drive this particular car daily, I would reccomend that you stick with the 225. There are a lot of ways to simply improve the performance of any slant six. The most popular for any engine would be carburetion and exhaust. Mopar, in the 70s produced what was called a Super Six. A 2 barrel carburetor and aluminum intake manifold made it special. In 1976, the Feather Duster was produced. Its main purpose was fuel economy. The 225 engine was specially tuned and had a high flow exhaust manifold. These two pieces together would be ideal. The Super Six setup is relatively easy to find, but there were only a few thousand Feather Dusters made, so Headers or simply a larger exhaust pipe would be more reasonable. After these, you might look at the gear ratio in your rear differential. Most likely you will find, by a tag bolted to the cover, that you have a 2.76 ratio. This is great for economy, but also makes for a pretty boring ride. Especially with a 6 cylinder. A 3.23 or 3.55 ratio would bring noticable improvements without any engine modifications.
The disadvantage of swapping in a V8 into a slant 6 car is the fact that you can't just change engines. The transmission will also have to be changed. It probably wouldn't be a bad idea to swap the rear end too, which means shortening the driveshaft. Then there are things like motor mounts, the cooling system, suspension and brakes. If you end up with a 360, 340 or even some 318s, you will get a heavy duty (automatic) transmission. Now, even if you don't swap rear ends, you have to shorten the driveshaft. Of course, just by putting in a V8, especially the 360 you had in mind, you get an instant improvement in performance in simple stock form, and parts are more readily availabe if you do decide to modify the engine.
If you're on a small budget, all of the details of a V8 swap will get expensive and then you've likely got added gas consumption to deal with. My 318 gets about 18 MPG with 80-90% highway driving, an automatic and a 2.76 rear end. And I usually drive pretty conservatively. Depending on your personality, there might be indirect costs involved. I myself probably would have a hard time staying off the gas if my own Duster had more power, leading to more tickets and more tires.
The decision is completely yours, but I hope I have given you an idea of what you could do either way, and made it a little bit easier for you to decide.
