Dialing in my 73 project Duster

[MoparChase]

Hi, all had my 73 Plymouth space Duster for about three years now. Would like to get it to the finish line in the next couple of years. The car came with a shear grip 7 1/4 rear end when I bought it. It was an original slant six but has a recently rebuilt 72, 340 it now.. have also rebuilt. The therm quad carburetor runs pretty good but without knowing the specifics on what was done to the motor I’m having a hard time getting it dialed in especially the timing.. has a stock electronic, ignition and distributor, but only seems to run optimally on a mixture of racing fuel and pump gas about 50-50 on stock high octane fuel. I’m getting some pinging and knocking. also hard to restart after it warms up timing is set about 15° above TDC. Was thinking it just might be too far advanced for this engine . Also, was looking into putting a larger rear end in the car before this one ends up broken or maybe build one for a spare in case this one does break. Anyone know of a cheaper solution than buying an expensive Moser or other aftermarket rear end and is the Ford 9 inch rear end a good option for this car and cheaper to build. I did not build this engine, but I believe it has a mild cam upgrade also has stock headers freshly rebuilt, 727 automatic trans and 391 rear end. It’s a fun car to drive but the high RPMs are no good for the highway. Any suggestions?

 

[missing linc]

A 7.25 rear end will not last long behind a 340. I grenaded several of them with a 318 4 bbl. You can put in a Ford 8.8 rear axle from an Explorer with a little bit of fab work, but they typically come with 3.73 or 4.10 gears, and a traction lok differential. Use the search engine feature here to find more information about the swap. An 8.75 a body rear end will not come cheap, and an 8.25 may not be stout enough, depending on your actual power output. A 9 inch Ford won't be real cheap either, but it will probably be less than an a body 8.75, and it will take all the abuse you can throw at it.

 

[Woody'sScamp]

A lot of 340 Dusters came with 3:23's from the factory. I have an 8 1/4 with 3:55's behind a pretty warmed up 318, so far so good. My engine builder told me my rear-end, built right, could handle 400- 425hp. I do believe my next upgrade may be a 8 3/4 rear. Also, I love the look of your Duster and the color!

 

[Syleng1]

8-1/4 is fine. Sure grip so both tires are splitting the action and you will go a long time. Reverse drive drops- no rear end holds up. Just be smart.
Syleng1

 

[rich_mc]

Nice ride... be sure to watch the for sale ads here on the forum for 8.75 rear ends too... I ended up buying a used one and redid the axle bearings and cleaned it up myself... I even regeared it myself, but after it being super noisy, ended up taking the center section to Moser and had them set it up properly. Super quiet now and what I should have done the first time... Ended up with a nice 8.75 set up at Moser but at a much lower cost than buying a whole rear from them.

 

[junkyardhero]

an 8.25 with a LSD of some type should hold up fine. keep in mind that most any 8.75 is going to be small bolt pattern unless it's been upgraded to big bolt, or it's a rear end that's been narrowed for our cars.

a 9" is a viable alternative and it's nice that you can have them built to spec.

the 8.8 is a popular swap for value as well as availability, and you get disc brakes too. just not a lot of gear choices and you'll need to do a little fab work to make it happen.