Is it a good idea to swap my 225 slant 6 for a 340? I have a 71 Duster and its just about as clean as they come around here. The only problem is that my slant 6 is in need of a rebuild and is only getting about 10mpg at the moment. Everyone is telling me that instead of rebuilding it, I should drop a 340 in it. Is this a very good idea? Or would it be easier to buy a car that already has a 318 and just work from there? I understand that in my car youd have to change the tranny, rear end, motor mounts and driveshaft. But would you also have to change the brakes, suspension and add power steering to it?

Your 225 Cu. in. slant is only getting ten mpg and you are thinking that adding a 340 would be better than rebuilding the slant?

I will let that soak in for a minute



Ok, the heart of the question. What is your goal, improve upon the mpg you are currently getting? Add more hp so your mileage may stay the same but your enjoyment level goes up? Spend some money making the car into what your friends want you to have?

I am probably starting to sound like someone else on the board right now but I just am having trouble following your line of thought on going to a 340 vs getting the slant six rebuilt.

To answer part of your question if you put a v-8 in there for street use and you intend to drive the thing a little fast it may be worthwhile to improve the brakes. Power Steering wouldnt be a necessity you could probably get away with a different ratio manual steering box. Suspension upgrades would depend on the intended final use, street car vs race car.

Help others who may reply by explaining a little better why you are interested in this swap and then we can provide the discussion necessary to note this is a slant six board and there are numerous other boards with information to help you with the swap.

Brian

Bohmer you do sound like you are channeling one of our most knowledgable members. The 225 duster in a good state of tune should net you 20-25 mpg. You'll never get a 340 near that without a pretty serious overdrive.

I feared that was happening when I made the original post.

ESP give us an idea of what your goals are for the car. Yes, it is possible to put a 340 or 360 or 318 in your duster and moparts.com and forabodiesonly.com both will provide you with lots of information and support from people who have done these swaps.

Depending on your goals some here will provide substantial information regarding ways to acheive those goals with a slant. Unless you have a v-8 car handy, it may be cheaper to achieve your goals with the slant 6.

if money is an issue (it must be as fuel economy is at stake) then just buy a reman longblock from your local parts place, swap it all in, and hope for the best. but of course you had better hope your carb and ignition and just about everything else in the drivetrain is in good shape.
just how tired is your engine? is it burning oil and smoking badly? is your trans in good shape (not slipping?) if the entire drivetrain is crap and you're worried about economy you could probably find another car for less than what it would cost to rebuild everything and do it right.
maybe the car just needs some service work. when was the last time the valves were set or the carb adjusted? are the plugs and wires ok? fuel and air filters? bands adjusted? a little tlc goes a long way, i bet you could find a few mpg if you looked.

-james

_________________

Hey, just a thought. My Duster was getting 10 mi. per gallon. BAAAD. Then I began to pay more attn. to things. Turns out my speedometer was not correct. Nor was the odometer. This will have the apperence of poor mileage. With my foot as heavy as it is, I am really getting about 15 in my kind of driving. Not too bad for me.

_________________
ifyoubegintothinkyou'relosingcontrol...it'salreadygone

Depending on the engine condition, state of tune, etc., decent mileage is possible out of a large V8. One year I drove my 440-powered 69 Charger from VA to the Nats in OH, drag raced it, back and forth from Brice Rd, and drove it home. The average for trip, racing, etc was 19 MPG. My buddy drove my 318 71 Challenger, no racing, and it did 18 for the trip.

Hell yeah its a good idea!!, two days ago I buyed a 360 Duster and swaped 2BBL carb to 4BBL and is a road killer!!, currently I´m looking at north of my country for a 340 to swap my 225 for the V8.

But is true, a 318, 340 and 360 V8 will never match fuel economy of Slant 6, but the V8 will give you a lot of fun for those extra horses.

_________________
Mopar Muscle is well defend by Slant Six!

Valiant Duster 1971

No
Do yourself a favor and use the Slant to learn engine rebuilding on.
If everyone told you it's fun to pound nails in your skull would you consider doing that?
Yes, sell me the Slant Duster and move on.


You would have to upgrade everything except for adding power steering.


Now when can I pick up the car?

_________________
Official Cookie and Mater Tormentor.

Ok my slant 6 is extremely slow. Were talkin slower than almost any 4 cylinder out there. Quite possibly even slower than most 3cyl Metros. Its got 98000 original miles on it. When I mash the gas getting on the freeway or going through a yellow light, the car smokes. Nothin real bad but its still quite noticable in my rearview mirror. It also shoots out a ton of black crap out of the tailpipe upon start up. Ive got quite the spot and line going down my driveway of this stuff. It looks to me like it needs a valve job. Not sure if im right but its my best guess. Ive done a complete tuneup of the car a few times and have replaced almost all of the engine components (carb, water pump, fuel pump, filters, alternator etc etc). Basically I feel like I do a good job of keeping up on it. I just dont feel like the problem is one of those $40 jobs. It sounds a lot more like it needs a rebuild, or valve job at least. Thing is that im not good enough to do this myself, but I do have a few friends who could probably help.

The main two problems are gas mileage and power (car starts up and runs forever). I would be ok with getting 10mpg if I had a V8 in it. There would be nothing to complain about......but having the gas mileage of a V8 big block and the speed of a Geo Metro doesnt sit right with me. Thing is that ive had this car for about 5 years and it was my first car. I really cant see myself driving anything other than my Duster. So I want it to be my daily driver. I dont necessarily need it to be a speed demon, but power is always nice. Im just confused on the best route to go with it. Paying to have it rebuilt costs a ton. It seems to me like if im gonna throw that kind of money at it, I might as well make it faster and worth more while im at it. Im just wondering what you guys think is the easier/more efficient route? Im not dead set for or against either. Im ok with getting close to 20mpg and not having much power, and im also ok with getting 13mpg and having decent power. Just wondering what other, more knowledgeable guys think about it.

this is where you are going wrong...you need to sell it to ME then you will be on the right track id build the slant if i was you, i'm so jellious i dont have a slant car anymore

_________________
Cuda Progress
The dart as it sits now

If you were in my area, I'd tell you to bring it over and see what's up...
$1200 for a long block...(average for a rebuild on your core in my area)


A 'bean counter' would do it this way:
Duster=payed for and free
7.25" rear 2.76's(?)=installed 8.75 rear $500-1200 8.25" rear $300-800 (and change to LBP rims, and change driveline in both upgrades)
Brake upgrade 10" drums(SBP from your 9" SBP):$200 (assume you like your life and buy new hardware but buy the front end assembly to install)
Brake upgrade 1973-1976 Discs LBP (you bought the 8.25" right?) $300
Tranny for 340 (A-727 SB junkyard dippy cop car 'cheapy') $250
Torsion Bar upgrade (swap early 70's slant six bars for 1973-1976 890/891 bars out of junkyard) $20-50 (may get package deal if you pull them with the LBP disc brake setup)
Schumacher motor mounts:$150+SHI(not the current price...was the price a few years back when I thought about a 318 swap...LOL)
New exhaust $300-500 (you do it and have a welder...someone does it for you...you want and 'X' pipe right?)



Slant six:

Remanf long block from some company $1200 (you turn in a core and reinstall all your equipment if in good order).

You have it rebuilt: $2000 at worst
Head = $300-400
Rebuild kit = $300
Machining and assembly = $600-1000(ask who does good work in your town at a fair price)
Add more if you decide on more cam,etc...than what's in the 'rebuild kit'

You get a 340:

You get lucky and some mopar guy has a 1973 cast crank 340 to give you for a 'steal' because he's needing the $$$ for the down payment on a 1969 Charger 500 in some old lady's barn...$1200 (last price I saw paid for one that might have run when pulled 5 years ago)

You get luckier:
Wildcat Auto Wrecking has a machined and bored 340 already to go for you with the kit, a 10-10 crank, and a set of J-heads that need 'freshening up'....$2500 (they sometimes also have a 340 'core' laying around for you to work on for $1000...)

You decide that the 340 is not a great idea and decide a 360 might've been a better choice:

Junkyard 360 $350 (plug and play, smokes as much as you current slant has more power, gets the same mileage...will need torque convertor for the cop car A-727 as the 360 is externally balanced...$200+)

Remanf 360 $1400 (check you local auto parts store/etc...add a few hundred $$$ for core charge...still need torque convertor, but it's plug and play)


Anything runs faster as soon as you throw money at it....

-D.Idiot

There used to be a real nice 1974 Dart Sport 360 in town (like #2 condition) for a whole $8,300....(yellow, black stripes, black interior, automatic)...

Or,,,,,change the timing chain, valve seals, plugs, wires, cap, rotor and set the valves. ....get 23.7 mpg and laugh at your experts.

Most cars in this situation die,,,because the owner wont just address the issues in a sensible manner. If you want better mileage why not figure why the engine you have that is known for economy isn t delivering?

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Ok my slant 6 is extremely slow. Were talkin slower than almost any 4 cylinder out there. Quite possibly even slower than most 3cyl Metros. Its got 98000 original miles on it.

********************************
Something is wrong here. Even in stock trim a slant six should be able to keep up with traffic.
********************************

When I mash the gas getting on the freeway or going through a yellow light, the car smokes. Nothin real bad but its still quite noticable in my rearview mirror.

********************************
What color? Blue? Black? White? Blue = worn valve stem seals, worn valve guide, worn cylinder rings and bores. Most likely it is the stem seals. Do a good compressions check to test. If the motor has been really abused you may already need a ring job, but 98,000 miles on a slant six that has even been marginally maintained should be about 50,000 miles from needing a ring job.
********************************

It also shoots out a ton of black crap out of the tailpipe upon start up. Ive got quite the spot and line going down my driveway of this stuff. It looks to me like it needs a valve job. Not sure if im right but its my best guess.

********************************
You might need a valve job, but it sounds to mee like your carburetor needs adjustment or a rebuild. Black crap on startup is typically unburned fuel making its way through the exhaust line.
********************************

Ive done a complete tuneup of the car a few times and have replaced almost all of the engine components (carb, water pump, fuel pump, filters, alternator etc etc). Basically I feel like I do a good job of keeping up on it. I just dont feel like the problem is one of those $40 jobs. It sounds a lot more like it needs a rebuild, or valve job at least. Thing is that im not good enough to do this myself, but I do have a few friends who could probably help.

********************************
Did you go through the new carb and adjust it before you installed it? I have never had a factory remanufactured carb come out of the box with the right settings. They are usually way off. What kind of carb do you have?

I am a self taught mechanic and I will tell you that you would be surprised at what you can do for less than $40 with a slant six.

********************************
The main two problems are gas mileage and power (car starts up and runs forever). I would be ok with getting 10mpg if I had a V8 in it. There would be nothing to complain about......but having the gas mileage of a V8 big block and the speed of a Geo Metro doesnt sit right with me. Thing is that ive had this car for about 5 years and it was my first car. I really cant see myself driving anything other than my Duster. So I want it to be my daily driver. I dont necessarily need it to be a speed demon, but power is always nice. Im just confused on the best route to go with it. Paying to have it rebuilt costs a ton. It seems to me like if im gonna throw that kind of money at it, I might as well make it faster and worth more while im at it. Im just wondering what you guys think is the easier/more efficient route? Im not dead set for or against either. Im ok with getting close to 20mpg and not having much power, and im also ok with getting 13mpg and having decent power. Just wondering what other, more knowledgeable guys think about it.
******************************

Okay, I say keep your slant six and spend less money getting it to run right and upgrading it than you would swapping to a v-8. I have done the slant six to v-8 swap (319) and it is alot of work and money to do right (unless you do like I did and have a complete slant six car and a complete v-8 car parked next to each other) and not really worth doing in my opinion. Not many cars are cooler than a slant six Duster.

First off, as I noted above, it sounds like at least your carburetor is not functioning correctly. Get a factory service manual or even the instructions from a quality carb rebuild kit and rebuild the carb making sure to set everything to factopry specs. Pay attention to your choke since it sounds like it isn't working right.

Secondly, what emissions systems does your car have? Depending on where you live, your car is most likely emissiosn exempt, and even if it isn't, a well tuned slant six will pass any sniffer test anyway (but maybe not a visial test). Slant six emissions systems, especially in the early 70s, were not very well integrated into the overall operation of the engine. They usually damage performance while only marginally decreasing emissions (with the exception of the ir pump and catalytic concerter systems-I recommend keeping those).

I recommend you do two things right now: (1) disconnect and plug the hose going to the EGR valve. If you have visual emissions inspections fill the tip of the hose with gasket maker and shove it onto the EGR valve. Let it dry overnight before you run the engine. (2) bypass the O.S.A.C. valve. Follow the hose from the carb to the little black box on the firewall or side of the air cleaner. Disconnect the hose that runs from the box to the distributor vacuum advance pod at the box and plug it into the vacuum port on the carb where the other hose that runs form the carb to the box plugs in. (While you are at it, make sure that the distributor vacuum advance pod is not ruptured. Suck on the hose-you should feel some resistance and eventually not be able to suck. If not your diaphragm is ruptured).

Those two changes should make a big difference by themselves. Follow those by a good valve adjustment and advancing your timing to about ten degree before top dead center. Reset your curb idle speed afterwords.

Try it, you'll like it. Then you can move onto more advanced things like kickjdown adjustment, distributor recirving, bigger exhaust pipe(s), bigger cabr/cam/valves etc... All at a much lower cost than swapping in a 340.

Don't forget that your Duster also is geared for economy. A new rear gearset or rear axle with 3.23+ rear gear will make a big difference in performance.

Try all these things before you make up your mind about abandoning the slant six.

In the hands of a good mechanic, your Slant can be adjusted to run well or you would know the exact cause why it is having trouble. (bad carb, stuck distributor, burned valve, worn cylinder(s) etc.)

My bet is that the valve lash needs adjusting and the distributor advance system is not working as needed.
I have worked on many so-called "worn-out" Slants over the years and had them running great in a few hours and under $40.00 in parts.

As also noted, check your rear end gear ratio, a high geared Slant (2.76) will have sluggish acceleration, especially if it is out of tune. A high geared, out of tune V8... acts the same.
DD