Dodge 340 swap

[Gordon Maney]

If it were me and I had a 340 laying around (A real 340, not a bored and de-stroked 360) I would not trade it straight across for a 360, even in the same condition. 360's are a whole ton more common than the limited production 340's ever were, hence not nearly as valuable or sought after. 340's are a better overall block for someone looking to build a high performance road racing rig (what the motor was designed for in the first place) and are pretty sought after. If I had the choice between the 2 I would take the running 340 and put it in the truck. Drive it, but post it up for sale. Proof of running makes it worth more to the average buyer. When you get the right buyer to give you what its worth ($1500+/-), sell it to them, build a 360 and pocket the change. The 360 will fit exactly the same as the 340 so all you are talking about is a couple hours worth of work pulling one and putting the other in its place. You can even get stroker cranks for the 360 to push it up to 408 for all the cubes you could ever want and need. Google searching Dakota 408 will bring up quite a bit of forums discussing the topic, and how potent that combo can be in a truck.

Just a bit more information that I think would be valueable to you for your decision process. Use it however you like, I am not trying to force you one way or another. Just trying to educate you on what you have and what you are looking into.

That's really interesting.

[MoparFreak69]

That's really interesting.

I would love to make my 360 in my donor frame for my '59 into a 408 stroker. That would just make the ride that much more of a blast.

[Gordon Maney]

I suspect the answer is no, but will the 408 stroker crank fit in a poly 318?

[MoparFreak69]

A little excerpt I found in a search;

Differences Between Poly "A" engines and LA engines


Heads are very different:

Intake and exhaust arrangement for the Polys is I-E-I-E-I-E-I-E, where the LA/Magnum arrangement is E-I-I-E-E-I-I-E.
Poly valve arrangement is canted with intake and exhaust valves angled opposite each other, while LA valve arrangement is wedge style with all valves aligned in a row at the same angle.
Poly heads have the intake valves on one side of the rocker shaft and the exhaust valves on the other side, while LA engines have all of the valves on the same side of the rocker shaft.
Poly and LA Rocker arms are different.
Poly heads are much heavier than LA heads.
Valve covers are different:
Poly valve covers have two bolts in the middle of the cover. LA covers have five smaller bolts around the outside edge of the cover.
Poly valve covers are also scalloped at the lower edge, while the lower edge of LA valve covers is straight.
Pushrod angle is different. Poly 318 blocks had the original 59 degree lifter angle to work with the Poly heads, so the pushrods are much closer to being in line with the lifters than in LA and Magnum engines. Because Chrysler carried over the basic Poly block design with different head designs for the LA and Magnum families, the pushrod angle is much worse.
Poly blocks are different (although they will accept LA heads):
Poly blocks have deeper reliefs on the intake side of the deck to clear the straighter pushrod angle required by the Poly heads.
Poly blocks are a bit heavier due to their non thinwall castings.
Poly blocks can sometimes take up to a .130 overbore - much more than LA blocks.
There is a possibility that one bolt hole in the bellhousing area may be a little different on earlier versions.
Poly and LA camshafts are different due to the different valve arrangement
Poly lifters were solid. Except for early LA 273 engines, all LA lifters were hydraulic.
Poly "A" Pistons are different due to the different cam timing, so the valve reliefs are in the wrong places for LA engines.
Intake manifolds are different
Exhaust manifolds are different

Similarities Between Poly "A" engines and LA engines


Poly "A" blocks can be used with newer LA and Magnum heads.
Transmission bellhousing bolt pattern is the same.
Crankshafts interchange with 273/318 and internally balanced 340 LA engines.
Oil pump and distributor drive shafts are the same.
Oil pans from 273/318/340 LA engines will fit
Dampers from 273/318 and internally balanced 340 LA engines will fit.
Distributors from all LA engines will fit.
Poly timing chain and sprockets are the same as LA engines.
Poly block deck height, bore spacing and 59 degree lifter angle are the same as LA blocks


Basically what I am seeing is that as long as you use 360 flywheel/flex plate & torque converter/harmonic balancer you should be able to put the 408 (known as a 4" crank) stroker crankshaft into the poly block.
The 360 is externally balanced, where the 273/318/340 cranks are all internally balanced. The 360 is the only one that takes specific balancing parts because there isnt room to swing the necessary balancing weights internally.

[Gordon Maney]

Hmmmm.....

[MoparFreak69]

Confirmed, the 318 with the 4" crank becomes a 390 with stock bore.

I second and third the hmmm..... My Wrangler has an LA/Magnum 318 in it, with a Magnum 5.2 awaiting some work and installation (so I can have the roller cam/lifters).......

Might have to stroke it before it goes in.

[Gordon Maney]

I am getting some information from another source indicating the 360 stroker crank won't fit in the poly engine. He is exploring some alternatives. I am waiting to learn his views, then one of us will post what he learns.

The intrigue builds.....

[MoparFreak69]

I am getting some information from another source indicating the 360 stroker crank won't fit in the poly engine. He is exploring some alternatives. I am waiting to learn his views, then one of us will post what he learns.

The intrigue builds.....

Actually, he is correct, to a certain point. I was misled slightly with my information about a '360' stroker crank fitting in. I am sure it will still fit in, others just havent considered the extra parts necessary to make it externally balanced. They do make a 4" stroker crank for the 318/340 engine which will drop right in. Same stroke, just internally balanced. That stroker crank is good for the A 318 as well as the LA 273/318/340 apparently with only minor notching sometimes necessary.

http://www.moparmusclemagazine.com/h...wer/index.html