Have been thinking about swapping a 360 magnum into our 65 b body . It currently has a mostly stock 70 340. The 340 is getting a bit tired . The only reason I was thinking 360 is so I could rebuild and have an engine ready to put in . Was considering aluminum heads and a Holley fi system. An engine has recently come available . It’s a 2000 360 magnum with EQ heads a cam and dual plane manifold. It’s fairly cheap at $600. Although the heads are ci maybe this is a good base for a build ? Looking for 375-400 hp . Is that realistic with either engine with a stock lower end ?



Thoughts ?

I would save money and just rebuild 340 .there. is a few differences in the swap that will add up$

Sounds good. That motor will slip right in. The Magnum motors still have the LA mounting ears cast into the block and I believe the ear spacing on them is the same as 340/360 LA motors. Only thing you need to worry about is balance and that can be solved with a B&M flex plate. I don't know if the EQ heads have the same issue with high lift cams as the factory Magnum heads. Factory heads needed the spring seats machined to allow for cams with more than .520" valve lift.

And make sure it has a center sump oil pan.

It's really a straightforward swap.

Magnum has a roller cam, which is good since so many are having trouble with flat tappet lifters these days.

Magnum has no mechanical fuel pump provision, which is a negative for those wanting a mechanical fuel pump.

I think the engine mounts are different between 340 and 360 blocks on the driver's side, but that is not a big deal.

Personally I would skip the EFI and spend that money on a 4" crankshaft instead. Even a mild 4" crank engine with good heads and a modest camshaft would provide a lot more bottom and mid range power for street driving.

https://youtu.be/nbY7UGuZAfA?si=P9a1juyaBYOszh8F

Only early blocks have la mounts.. You will need oil pan and torque converter for balancing issue. You will have about a grand in all parts .two thirds to a 416 stroker kit for your 340

All the early ,1968 to 1971, 340 motors were internally balance, all of the 360 were externally balanced. so that needs to be addressed, taken care of as mentioned about getting a correct externally balanced torque converter for your 360 motor

I've pulled 2000 model year Magnums with the ears on them. Are you sure about that? And there is no need to replace the TQ if it stills stalls in the desired range for the application. Balancing is solved with just the correct flex plate. Take a look at that 5.9L. Check for the ears, a center sump oil pan and a timing cover with provisions for a mechanical pump (look inside for the pump eccentric). If it checks all those boxes and you plan on taking your time with the 340 do it. You can always sell it later on too.

Early magnums had mech. Pump provision later didn't. Flexplate costs more then conv. So going as far as pulling motor I would want new conv. It's a wear item.also deck height issues 360 is an inch taller so check exhaust for clarence.if starting from scratch I would go magnum but since he already has a motor that is capable of 400 hp i would go with what you got

Damn. My '91 360 had no fuel pump provision, I had to add a camshaft with the snout and the eccentric. Different deck heights? NOT. Mains are larger. Magnum heads and exhaust manifolds are worth the swap alone. Note the 360 Magnum external balance is NOT the same as the older 360's.

He is buying aluminum heads

Icing on the cake.

If it was me, I'd be figuring out which engine should get a 4.00" crank, internal balance if need be, and the aluminum heads.
If the 340 is a match for someone who wants the original block, you could offset some of your costs.
Building the 360 would lessen down-time, plus you'd have only 1 swap.
360 pan differs from 340 at the rear; may be an added expense if you go that way.
But either way, a 408-416 with alum heads makes for a nice street engine.

These guys love spending other people's money.

If either motor is going to get rebuilt before the car gets used, and you add aluminum heads and the efi, any advantage the 340 may have had is pretty much gone. Then if you add the 4" crank kit, any engine balance issue should be the same for both motors.

Then the choice between the two motors becomes pretty much just a matter of costs of the same build between the 2 motors, (which are going to end up pretty close to the same HP. The 360 purchase has to be included in that price comparison). Then consider the bragging rights that come along with the 340 (which is mostly just a donor block at this point, and most younger guys won't understand what makes the 340 special), and which motor build best fits the time frame for driving the car. With both motors built with pretty much the same parts, the differences between the two is going to be pretty small.

Assuming the car runs and moves as it is, building the 360 while still driving the car may be worth whatever the cost difference may be. If you rebuild the 340, the car is down until all the parts show up and the 340 can be assembled, which could have a pretty questionable time frame these days. With rebuilding the 340, the car may well sit out some or all of next summer's driving enjoyment. At the same time, if you build the 360, and if it doesn't get done before next summer, you can still drive the car next summer. That would be a big part of my consideration.

^^^ That was my point, though you've elaborated on it better.
What I don't know, of course, is the OP's budget, how "tired" the 340 is, how he uses the car, etc.
So, I'm just spit-balling, with an eye on down-time and bottom line.

Depending on where the OP lives a call to the local machine shops should be in order. Here they are all loaded up with work and are 9-10 months out, or simply not accepting any new work at all as they have no more room to store people's engines inside. If you have a running car and the local engine shops are loaded with work it would be best to keep the running engine in it and build a new engine on the side.

If he's going to run the 340 accessories he will need the 340 style timing cover and there is your mechanical fuel pump provisions, lol. Just make sure the cam has the ling snout or you get the adapter. This is really a non-issue especially since he's talking about going EFI.

Taller deck height? Try again, same deck height. He will need a pass car style oil pan.

Yeah deckheight facts got intertwined with big block

Thanks for all the helpful responses.
The reason for the post was because a 360 mag was available close to me for 600 . It has eq heads and all the magnum front accessories . I have since spoken to the builder and the heads are just stock replacements small valves , so other than having all of the front accessories Idont see it as a Great deal .

I don’t have a set budget in mind but it’s always my nature to keep it tight and I think a stroker kit puts me in a place financially that I feel is two much .

The car is a frequent weekend cruiser that my wife and kids also use a lot , and it makes the occasional trip to the track .

I say the 340 is tired as it probably has 75k on it . I rebuilt it 25 years ago. Starting to blow by , rear main leaks oil pressure down a bit .

I do know of a low mileage 360 short block for for 300 , and I do have a 340 bare block . Just thought the late model 360 made more sense than dealing with a 40 plus year old block.

The balance thing might be an issue. This car has gm 4L60e. I’m guessing it has a gm pattern with an adapter flex plate that goes from the mopar crank to the gm converter.
Gary