My engine needs a rebuild. Its not gone to crap yet, but its on its way. Number 8 cylinder has been giving me trouble for a while and just threw a check engine light for a misfire. Conveniently when I went to Oreillys to have the code read it missed its *** off. There's oil leakin into the cylinder, so itll have to be rebuilt, not right away but soon. We're plannin on this summer.

My dad and I were talkin the other day throwin around ideas and he brought up throwin in a 340 and using the manifold off my 318 with the injectors, sensors etc. I was wondering if by some chance that the manifold for my 318 would bolt up to the heads of a 340. I've looked around and a couple sources say that the older 318, 340, and 360 parts would in some cases interchange, but I'm not sure about the Magnum 318.

The main reasons I would want to reuse my manifold is obviously for the fuel injection, plus I'd be able to use my stock computer, (right?). I think I won't be able to pass inspection without the OBD and all that still intact.

Anyone have any ideas on this subject?

 

just a little bump

 

A 340 would be an awesome engine swap. Thats a good idea if it would work! I even thought about a 440 once but mines running to good to swap in a new engine. (knock on wood).

 

***thinking out loud***the magnum heads are diff so the intake would be diff.. plus trying to keep the obd you have a few sensors on the block crank sensors and the ones back under the intake if i remenber right

why wouldn't the 340 pass e-check??

if the motor ran clean and you have a cat i wouldn't see why it would fail, unless you e-check diff than the way ohio was.

sorry it took so long, i couldn't stop looking at your truck

 

the only way to run an LA 340 with your FI setup woul be to use a set of magum heads, but it sounds like its your heads that are failing on your 318. Also the magnum engines use a roller cam so you would have to get a retrofit cam or run a flat tappet cam.
I think your best bet would be to rebuild the 5.2, or a 5.9... but im not sure about the ECM compatibility.

 

Isnt the 340 a 360 with a 318 crank?

 

Nope.

 

Then what is it?

 

The main difference between an "LA" 318 and 340 is bore. 318s spec out at 3.910 bore X 3.310 stroke. A 340 has 4.040 bore. Steel cranks are interchangable, both are internally ballanced. 340's depending on year, used different cam profiles, forged connecting rods, and the 340 T/A/AAR motor used different heads and valve gear. 72 and 73 340s went to a cast crank and like thier 360 cousins were externally balanced. They are the "smogger" 340's and most guys get the block and toss the rest.
360's use a cast crank, have a different stroke, and are externally balanced. All have the smaller 1.80 intake valve heads. 360's made thier performance introduction in 1974. Thier reputation has improved a bunch since then, but in thier day they were low compression smogger motors that got poor mileage. Sound familiar?
Motor mounts are way different and you would need to swap into magnum drilled heads for the intake. 340 heads, especially the earlier ones use 2.02 intake valves. In 71 or 72 then went down to a 1.80 intake. 318's use smaller valves and small port heads to match.
A 340 is a great motor (and I should know ) but I believe you wouldn't notice a huge power increase in a truck. You'd be better off stroking out a 5.9 to 408 or 426 and untilizing the ease of bolting up your current tranny and PCM hookups. I think hughes makes a kit that will stroke a 318 magnum out to 390 cubes.
If you have access to an early high nickel 340 I would sell it to someone who can use it to restore an older musclecar. The money you get should easily start you on your way.

 

not to mention it would depend on what you were using your truck for. 340's are known to be high winding motors. I would think you would want a motor with the peak numbers low in the rpm range in a heavy truck.