340 swap

Engine Swaps

  1. HectorVenezula

    HectorVenezula Active Member

    Messages:
    25
    Likes Received:
    0
    Joined:
    Aug 11, 2016
    Location:
    Fernley NV
    I'd like to swap my 318 for a 340 what kind of problems would I run into on the fifth avenue with the 904 transmission
     
  2. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    848
    Likes Received:
    186
    Joined:
    Apr 26, 2016
    Location:
    Southern Manitoba,Canada
    Not enough torque,lol

    The 340 has a high rpm cam in it and does not do well with FMJ rear gears.
    You can get past this with a cam change.Of course that will negate the effectiveness of the 2.02 valves, and if an early hi-Compression model, would probably put the engine into detonation by driving the cylinder pressure too high. And then there is the low-stall TC to deal with.
    Yes you could swap out your 2.21/2.45s, but you're still trying to launch over 2 tons of iron with the wrong combo.

    Ok if you build the 340 from scratch, you can over come all these issues. But then you might as well just grab a 360; it's practically a plug and play. And those 20 cubes are worth probably 20 ftlbs at stall-speed over the 340 and a total of over 40 more than the teener, also at stall-speed.

    Having said all that; I once put a 340 into a 65 Valiant with a complete 318 top end on it including the cam. That was a torque-monster. I got away with it for a few reasons;
    1) because it was 1974 and we still had decent gas back then, and
    2) and the Valiant was waaaaaaaaaaaaaay lighter and
    3) it had probably 3.23s in it
    4) I gave it a way to get rid of it's exhaust with fenderwell headers

    Oh wait, that's not what you asked,sorry
    You asked
    Ok then; I used a 904 from a 273, behind my 340 in that Valiant-wagon, and it lasted longer that the 7.25 rear gear,lol; about a year. Both were internally balanced applications, so I just screwed them together.
     
    Last edited: May 27, 2018
  3. HectorVenezula

    HectorVenezula Active Member

    Messages:
    25
    Likes Received:
    0
    Joined:
    Aug 11, 2016
    Location:
    Fernley NV
    Currently I have 2.75 or so in the rear and the 340 I found has the following description but I'm not sure how this would all stack up with the original transmission and my 8.25 rear end from an aspen
     
  4. HectorVenezula

    HectorVenezula Active Member

    Messages:
    25
    Likes Received:
    0
    Joined:
    Aug 11, 2016
    Location:
    Fernley NV
    Description for ad. It has been rebuilt with standard bore 10.5-1 compression pistons, Comp cam with .470 lift and 270 actual duration, double roller timing chain, windage tray, cast steel crankshaft that is drilled for 4 speed, 340/360 heads (3671587) that have been ported with hardened exhaust seats and 2.02 stainless intake valves, 1.60 exhaust valve, guides machined for higher lift cam, 3 angle valve job. Heads are good to .560 lift cam, have chrome molly retainers with 10 degree locks, magnum springs with damper. Block casting is 2780930-340 with a casting date of 5-31-72. The valve covers are cast aluminum that have been chromed. The block has brass soft plugs, HP oil pump. This 340 is for the guys or gals with a '72-'73 340 that was built with 8.5 pistons and always wanted the 10.5 engines of '68-'71 vintage. This engine still has the cast steel crank so you can use your external balanced convertor or flywheel with it
     
  5. HectorVenezula

    HectorVenezula Active Member

    Messages:
    25
    Likes Received:
    0
    Joined:
    Aug 11, 2016
    Location:
    Fernley NV
    I'm also unsure of the 360 because I don't know anything on external balancing and if the motor mounts would work. Plus I thought there was something about changing the oil pan.
     
  6. Aspen500

    Aspen500 Well-Known Member

    Messages:
    3,278
    Likes Received:
    944
    Joined:
    Feb 14, 2015
    Location:
    Rib Mountain (Wausau) WI
    The 360 requires a dedicated torque converter OR aftermarket flex plate with the weights on it for external balance, Otherwise, it's a drop in going 318 to 360. The pan only needs changed if the 360 is from a truck. They have a rear sump and cars are center sump.

    Your 8.25 would probably be fine with the 340. More than likely the tires would break loose before the differential. A stock 904 is kind of iffy. All depends on how you drive the car. At any rate, if you keep the 904 as is, install an aux. cooler. As mentioned, with the stock converter and rear gears, you may be a bit "soft" off the line until the engine gets into it's power band. As long as it's not a '73 340 *which are external balanced), the 340 is also a drop in.
     
    Jonnyuma likes this.
  7. Oldiron440

    Oldiron440 Well-Known Member

    Messages:
    1,209
    Likes Received:
    226
    Joined:
    Apr 25, 2017
    Location:
    Iowa
    You can run any thing in any thing but to run that 340 your going to need a loose converter and gears in the 3.73 range.
    You just can't expect to run stock components.
     
    Last edited: May 27, 2018
    AJ/FormS likes this.
  8. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    848
    Likes Received:
    186
    Joined:
    Apr 26, 2016
    Location:
    Southern Manitoba,Canada
    I highly recommend to pass on the 340.
    And here's why:
    That 270/.470 lift cam in a true 10.5 compression, stock bore (which IMO, is NOT a rebuilt engine in the first place), will make an undriveable engine in your FMJ...... because the cylinder pressure is waaaaay too high for pump gas and iron heads. The Wallace says 170psi@138VP@1000ft elevation


    unless you are at 3000ft elevation or greater.
    And if you are, the bottom end will still be as soft as a 5.2Magnum at sealevel.

    What you really want is a 9.8 LA360 with a 262 cam and an ICA of 57*. That will really move the old Fifth out! This is fall-together-engine; with the flat-top pistons .012 down in the hole,small eyebrows, an .028 gasket, and 72cc regular iron small-valve open-chamber heads. That's; 2.5+5+6.5+72=86cc and in a 4.04 bored 360 that makes 9.75 Scr ; easy-peasy. Slam it together and start smoking the tires. The Wallace says 159psi@143VP. Lookitthat, less pressure and more VP; that's the way to do it.
    Well hang on;
    Yur gonna need some supportwurx; Carb,intake,air filter system,distributor,coil, wires, dual exhaust, HO manifolds or shorties at least, a shift kit and aux cooler for the trans, and a posi for the back, plus tires of course,lol.
    And she may not like the A/C or the factory cooling system.
    In this combo, the 360 might be OK with the 2.73x2.74=7.48 starter gear........ for awhile, lol. But you might as well start saving for at least 3.23s.
     
    Last edited: May 27, 2018
  9. HectorVenezula

    HectorVenezula Active Member

    Messages:
    25
    Likes Received:
    0
    Joined:
    Aug 11, 2016
    Location:
    Fernley NV
    Do you guys have some transmission advice. I've done some mild improvements to the 318 it's up to 425 lift and still at a 9:1 compression but it feels like something is still holding it back could it be the transmission
     
  10. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    848
    Likes Received:
    186
    Joined:
    Apr 26, 2016
    Location:
    Southern Manitoba,Canada
    You have 9/1 teener ?
    What kind of car is this?
    What are the trans ratios? A 904 is 2.45-1.45-1.00
    The very similar A999 is 2.74-1.54-1.00 and a loc-up TC
    What is your stall rpm?
    I doubt it's your trans.
    Cam specs?
    Check your cylinder pressure.
    What elevation are you at? 4100ft?
    I didn't think there ever was a 9/1 teener in an FMJ; I thought they were all barely if at all 8/1 ers.
    You can't put much of a cam into an 8/1 teener before the bottom end goes soft, and then it feels as you say.
    The Oem cam is a 240/248/112 and in at 108 this makes about 116 psi in an 8/1 engine, @4100 ft.
    A 252/112 cam drops that to 110
    It's a little better at 9/1 ; namely;138psi and 131
    So do a compression test
     
    Last edited: May 27, 2018
  11. HectorVenezula

    HectorVenezula Active Member

    Messages:
    25
    Likes Received:
    0
    Joined:
    Aug 11, 2016
    Location:
    Fernley NV
    The 85 and newer 318s have the 302 heads giving them the 9:1 and you hit the elevation right on the hea
     
  12. BudW

    BudW Moderator Staff Member

    Messages:
    3,276
    Likes Received:
    888
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    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.
    Flexplate.jpg
    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
     
    AJ/FormS likes this.
  13. HectorVenezula

    HectorVenezula Active Member

    Messages:
    25
    Likes Received:
    0
    Joined:
    Aug 11, 2016
    Location:
    Fernley NV
    My understanding is that going from 200ish gears to 300ish gears required different shimming inside is this correct?
     
  14. Oldiron440

    Oldiron440 Well-Known Member

    Messages:
    1,209
    Likes Received:
    226
    Joined:
    Apr 25, 2017
    Location:
    Iowa
    I thought the 340 and the 318 used the same mounts and the 360 is a different mount and oil pan.
     
  15. HectorVenezula

    HectorVenezula Active Member

    Messages:
    25
    Likes Received:
    0
    Joined:
    Aug 11, 2016
    Location:
    Fernley NV
    That's what I heard too which is why I looked at those instead of the 360
     
  16. Gator

    Gator Well-Known Member

    Messages:
    258
    Likes Received:
    21
    Joined:
    Aug 12, 2015
    Location:
    south jersey
    340 and 360 use same mounts.i agree with bud w try a gear change youll notice a huge difference.
     
    BudW and AJ/FormS like this.
  17. Duke5A

    Duke5A Well-Known Member

    Messages:
    186
    Likes Received:
    61
    Joined:
    Apr 6, 2018
    Location:
    Michigan
    • 273, 318 & 340 use the same oil pan. 360 is unique.
    • all small blocks use the same passenger side mount
    • 273 & 318 use the same driver's mount, 340 & 360 share one to themselves

    The difference between the driver's mounts is spacing between the ears on the block. It's no big deal to shim it with a longer bolt and washers if you didn't feel like purchasing the correct mounts.

    You never did specify what your goals for the car are or your budget. I'm going to assume cruiser/daily driver. I agree with what's been posted already. A 340 could work with the right cam, but if it is a true 10.5:1 motor then you're going to be flirting with detonation with a milder cam. Stay away from this motor unless you're making a drag car.

    Find a junkyard 360 Magnum motor in decent shape. Pop it apart for inspection and re-gasket it. Center sump oil pan, 4bbl intake, LA timing cover (use your old one), an eccentric to run a mechanical fuel pump and a balanced flex plate. Easy 300 HP even reusing the factory cam and it'll bolt right in.
     
    BudW likes this.
  18. AJ/FormS

    AJ/FormS Well-Known Member

    Messages:
    848
    Likes Received:
    186
    Joined:
    Apr 26, 2016
    Location:
    Southern Manitoba,Canada
    Yes and no... you would need the appropriate spider case
     
  19. BudW

    BudW Moderator Staff Member

    Messages:
    3,276
    Likes Received:
    888
    Joined:
    Mar 4, 2012
    Location:
    Oklahoma City
    This is spot on.

    Car
    (center sump) small block oil pans are all the same - except between 273/318/340 vs. 360's.
    Pickup oil pans are rear sump and motor home are front sump - so neither will fit a car. They also have 273/318/340 vs. 360 versions.

    When (if) looking for engine mounts - you want to look for spool mounts.
    spool SB mount.jpg
    Older (non-spool) car mounts and trucks/motor homes do not use spool mounts.
    thSTZ9UMMU.jpg
    Old mount.jpg
    Older car type mounts (both halves) - which will not fit any FMJ car. Truck mounts are also different.


    In regards to differentials - there are some differentials that either need spacers (depending on which differential you are working with) or the correct carrier (for spacing difference).
    My experience is most drivers will want to install an limited slip carrier at same time as a ring/pinion gearset change - so any spacing problem is solved at same time.
    BudW

    Edit: this is what it looks like when installing a Left 318 mount onto a 340 or 360.
    318 mount on 340.jpg
     
  20. 5th avenue Rob

    5th avenue Rob Well-Known Member

    Messages:
    49
    Likes Received:
    23
    Joined:
    Jun 15, 2018
    Location:
    Arizona
    Used a magnum 5.9 with a 999 trans in my 65 plymouth. It ran very strong. I used a cheap cross winds air gap intake and a 600 edelbrock carb. Stock 3.23 gears.

    004.JPG

    237.JPG