Rebuilding a 340

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irishfastback

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I am rebuilding the original 340 my 69 Dart came with.
Car has a 4 speed and 3.55 gears...also has the X heads...
Would like to run in the mid 12's...

Anyone have some good advice on a good set up.

thank you
 
Is the motor a matching numbers motor for the car?If so,a stock rebuild with some minor touches.If you can get a nother 340,then go all out and make it scream,Mrmopartech
 
It is the numbers matching motor...

What would you go with on the numbers matching motor???
 
if it were ME???...i would pull the original motor and build ANOTHER 340/360,THAT way you will always have the original motor. :thumblef:
 
IRISHFASTBACK I agree, freshen the original engine and store it away. Put together a stout 360. You will have more performance and will not cost any more to build. Good standard building practices and paying attention to detail. Pick up a mid 70's 360, it will have the crank rods and heads you will need. Square up the decks, .030 over, hyper pistons, shoot for 9.5-10.0 C.R., file to fit rings, resize the rods (ARP bolts), check out the short duration/hi lift hyd, cams Hughes and Comp offers. Shoot for .500 lift as installed, Mopar's old .484 gives .501 lift @ the valve (installed) with 1.6 rockers. Adjustable rockers with 1.6 ratio (cost same), Pressure check and mag the heads. Clean up mill cut , Good bowl port and gasket match, back cut the valves, Air Gap, 750 carb (I like vac sec's on the street). headers, and a good exhaust system (2.5"), your 3.55's are ok 3.91's would be better. 12's should be easy for this combo in an 'A' body. Good luck on your project. Terry.
 
That sounds like a good suggestion and good advice. I will go get a 360 block and start from there...Thank you for the great advice...
 
I'm in the same dillema also. have the #'s matching block and tranny, but don't know if I should rebuild or store and find something else to play with. The org. block needs some work and is already .030" over. Because of the rust in some of the cylinders, I think it will need another .030" over to clean up. Have thought I should have it hot tanked and shrink wrapped and set it in a corner somewhere. Then build something else. Decisions, decisions. Luckly, I am a long way away from having to make that decision.
 
could use original motor. the early 68 -70 340 has a better rod in it. 496 casting. these are stronger over the 645 casting. freshen block with a bore and hone with a deck plate, makes for round and straight bores= more power. install the mopar SST valves in the heads. some mild bowl blending will produce more air flow. I would use a cast or a forged piston. hypers require way too much ring gap. and are too brittle. the comp cams extreme energy cams are the way to go. very aggressive lobe shapes. can still use your original rocker arms. for a starter, use the extreme XE274H. intake manifold, stocker will produce good power or go to a edelbrock dual plane.
to run mid 12,s will require some suspension work. chassis is ET. I would go with the calvert bar/ spring system. it bolts on! you have a four speed trans. install a lighter flywheel. mopar sells a L/W steel wheel or use a aluminum flywheel. clutch type is important. the mcloed B&B/long pressure plate is a very good unit. George at Mcloed can fix you up with correct clutch. forgot, use a moly top ring set, get oil ring drag down to 16#. just food for thought. I work on a 72, 340 duster, stocker, it runs mid 11 secs.
 
I agree with the above post except;
hypers require way too much ring gap. and are too brittle. the comp cams extreme energy cams are the way to go
Click to expand...
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HyperU's need to be installed correctly or they'll fail. This is the major problem with building an engine with these. I've never had a problem with them.
While I like Comp Cams alot, shopping around for whats out there never hurt. If you want an aggressive ramp, other cam manufactuers offer more aggressive ramps than the extreme lione of cams.
Also note that Comp Cams themselfs have more aggressive cam lobes than there extreme line.

perfacar, Irishfastback, Dartfever welcome to the site.
 
I'd agree with the "store the numbers block". If you have plans to drag race the car, this is always the wisest move. As far as a replacement...There's no replacement for displacement. At least a 360. The longer the stroke, the stronger the engine will feel at a lower rpm. A 408 (360+.030 and 4" stroke crank) would be my best choice. You can run mid 12s with ease, with cruising gears, pump gas. Basically, anything with a hydraulic cam, a decently done set of heads (valve work, not necessarily porting), and decent gears/clutch/tires and you're there.
 
Hypers are fine, never had a problem with them. The 645 rods (340/360) are more than fine for a stout street/strip engine. Do the bowl work, no down side to that mod and cheap if you do it yourself... and you can.. an easy 40 h.p. (20 CFM) . Pick up a set of adjustable rockers..necessary no..but better to have them. Irish, your last decision should be the camshaft. Choose wisely. Terry.
 
I would agree that it's usually good to preserve a matching numbers engine when possible. My numbers matching 340 engine for my 73 Duster already has a rebuild on it at .030 over so I'll pack it away for now and be using a std. bore 340 that I got from a donor car years ago for my 414 stroker build. Good luck with your project.
 
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