To get back to the OP original question:
The 340 (or 360) engine will almost bolt right in using all original brackets – except for a couple of areas:
- The left side engine mount, where it attaches to engine, is a different width. A person can compensate for this difference using longer bolts and some washers – but I haven’t really been fond of that method.
The other method is to find a 360 (or 340) Left side spool mount (from any A,B,C,F,M,J or R-body). These were still being made new (aftermarket) – but not sure about now.
- The newer 340’s and all 360’s use externally balanced harmonic balancers and torque converters.
If you use the correct balanced torque converter (for either A904/998/999 family or A727) then you will be fine. In my opinion, if a person needs to obtain a torque converter, it is better to get a balanced flexplate then use a 318 converter and just eliminate that hassle.
If you go with a small block stroker kit, then it will already have a neutral balance (318) so converter balance will not be an issue.
- If you are using the aluminum C171 A/C compressor, you will need a ’79 or newer intake manifold or an intake that has provision for compressor (if using A/C, that is). If your intake has a dual bolt pattern thermostat or thermostat is not in center-line of intake – then intake is good to go (if using the C171).
No A/C or using the iron RV2 compressor can use pretty much any intake.
- If replacing a 318 2-bbl with a 4-bbl, you also need to keep in mind that 4-bbls use a slightly longer throttle cable (about ½” longer).
Using a 2-bbl throttle cable is like playing Russian roulette with a round in each chamber. IT WILL CAUSE the car to have THROTTLE STUCK OPEN, if not WIDE OPEN the first time you open her up!
- The other thing is finding correct 4-bbl transmission kickdown linkage. Finding a complete and correct set is very expensive and hard to find. I recommend using an aftermarket kickdown cable setup. It’s easy and hard to mess up.
Almost everything else should bolt right in/up without problems.
Now getting back to what AJ/FormS is saying. A 340, a 360 or a 400 ci stroked small block will work great in an M-body if you have decent gears in the car.
An A998/A999 transmission has a much better low gear set than the A904 has. Your car should already have the A998 or A999 in it already.
The other is the 7¼” differential might not hold up to a powerful engine (IMO, anything larger than a 360 2-bbl) – so an upgrade to 8¼” (or larger) might be a good idea - or at least have parts under garage workbench when your 7¼” differential blows.
Any engine larger than 318 will need a much better differential gear set. 3.21 a good starting point. 3.55 or 3.71 preferred.
A person might be able to get away with a 2.93 gear set – but you
will not be happy with performance level.
A 2.71, 2.41 or 2.21 gearset
will be an utter or massive disappointment. Think of tying a 50-pound weight to a domestic cat’s tail. The cat will not be able to move from that location (literally).
Matter of fact, just changing a differential gear set (for a stock 318 2-bbl) to 3.21’s will wake up a 318 more than almost any other change you can make to the car.
In my opinion – I recommend changing differential gears
first, then look at what you want to change with the engine next.
BudW