273 to 340 swap in 64 cuda auto advise needed
1.) There is no 1974 340. 1973 was the last model year for the 340.
Late '72 and '73 340 were externally balanced, '68 - early '72 were internally (neutral) balanced. Also, be aware that the late 340s had a unique external balance, different from both the LA 360 and the Magnum 5.9. We'll assume you have the late 340.
2.) Ideally, a custom torque convertor will be needed. The 340 came with a 727 and you have an early 904, which has a different input spline count and different "nose" diameter than later 904s. In a pinch, you can use your 273 convertor IF you use an adapter bushing in your crankshaft hub register (available from several sources, one of which is member @Charrlie_S , who makes and sells these, check for availability) and have the convertor rebalanced for your 340. As an alternative, you may be able to use the B&M flexplate 10235 instead of rebalancing the TC, but you may need to have it redrilled for the 904 TC, since it is for a 727 and not a 904. To my knowledge, nobody makes a 340 external balance flexplate for the 904.
3.) If you want manifolds, and have a Borgeson box, any of the A body 340 manifolds should fit. Early ones ('68-'71?) are slightly better flowing. This pic I stole from another thread- member @340duster340 appears to have done just that:
You could also *probably* get away with Magnum manifolds, which may need a bit of clearance work. Your results may vary.
On the passenger side, two bolts will line up (and I have seen cars running just those two bolts), but a triangular piece needs to be welded on and drilled for the third mounting lug. Sorry, can't come up with a pic of that at the moment, maybe someone else has one.
Also, you will need to use the kickdown linkage from your '64, and a 340 throttle cable bracket.
You will need a different radiator, as the newer 340 has it's inlet on the opposite side.
If you're keeping your AC, you may need to source later model brackets and pullies to mount it on the 340.
The late 340s used electronic ignition- you'll need a conversion kit to run it on your '64.
In order:
1.) There is no 1974 340. 1973 was the last model year for the 340.
Late '72 and '73 340 were externally balanced, '68 - early '72 were internally (neutral) balanced. Also, be aware that the late 340s had a unique external balance, different from both the LA 360 and the Magnum 5.9. We'll assume you have the late 340.
2.) Ideally, a custom torque convertor will be needed. The 340 came with a 727 and you have an early 904, which has a different input spline count and different "nose" diameter than later 904s. In a pinch, you can use your 273 convertor IF you use an adapter bushing in your crankshaft hub register (available from several sources, one of which is member @Charrlie_S , who makes and sells these, check for availability) and have the convertor rebalanced for your 340. As an alternative, you may be able to use the B&M flexplate 10235 instead of rebalancing the TC, but you may need to have it redrilled for the 904 TC, since it is for a 727 and not a 904. To my knowledge, nobody makes a 340 external balance flexplate for the 904.
3.) If you want manifolds, and have a Borgeson box, any of the A body 340 manifolds should fit. Early ones ('68-'71?) are slightly better flowing. This pic I stole from another thread- member @340duster340 appears to have done just that:
You could also *probably* get away with Magnum manifolds, which may need a bit of clearance work. Your results may vary.
Actually, both sides are different. The driver's side 273 mount can be used on the 340 by adding a ~5/8" spacer between the block boss and the mount bracket on the top rear mounting lug.
On the passenger side, two bolts will line up (and I have seen cars running just those two bolts), but a triangular piece needs to be welded on and drilled for the third mounting lug. Sorry, can't come up with a pic of that at the moment, maybe someone else has one.
Also, you will need to use the kickdown linkage from your '64, and a 340 throttle cable bracket.
You will need a different radiator, as the newer 340 has it's inlet on the opposite side.
If you're keeping your AC, you may need to source later model brackets and pullies to mount it on the 340.
The late 340s used electronic ignition- you'll need a conversion kit to run it on your '64.
