426 Hemi Swap

[DoubleAwesome13]

I want to put a '68 426 Hemi in my 74 Roadrunner. I know that the K frame will have to be swapped out but what else is needed? Do I need a K frame from 68 or will any year fit it? Any advice is appreciated.

 

[66 Sat]

Are you buying the engine or have you already got it? The reason I ask is a 68 hemi motor is going to be pretty expensive to buy if it's running and in good shape. If not, it's an expensive rebuild compared to the other more standard motors e.g 440, 383 etc. To then put it in a 74 Roadrunner, you'll never get your money back. I don't know your circumstances but the dollars are always worth considering.

 

[JB400]

68 k member won't bolt up. You'll have to have a 74 style big block k member with conversion mounts for the Hemi to bolt up. You'll also have to upgrade the rest of the drivetrain, suspension, and even the fuel lines to accommodate it.

 

[tonysrt]

I put a 472 hemi in a 71 Cuda. Prior to hemi had a 440 in car. With the Hemi the starter cable had to be replaced and the throttle bracket. I did put a hemi K frame in the car and thought that was all I needed. I did this about 15 years ago when Mopar initially came out with the crate motors. Nothing like getting pushed back into the seat by Hemi power.

 

[FitzyB5]

I just put a 66 hemi in a 67 Coronet that started with a 318 then had a 440.Used tinman motor mounts. After a little grinding and manipulation it fit like a glove without hemi k frame.

 

[DoubleAwesome13]

Are you buying the engine or have you already got it? The reason I ask is a 68 hemi motor is going to be pretty expensive to buy if it's running and in good shape. If not, it's an expensive rebuild compared to the other more standard motors e.g 440, 383 etc. To then put it in a 74 Roadrunner, you'll never get your money back. I don't know your circumstances but the dollars are always worth considering.

I have found the engine and I am trying to see what I'm looking at for parts. It is a long term build and money isn't an issue. Its just a block and I plan on building it slowly. Just wondering what parts ill need aside from just an engine rebuild (K member, Transmission, Torsion Bars are what I know so far). As of right now its just a dream but im weighing my options between the 426 and a 440 stroked.

 

[wyrmrider]

See if that 68 Hemi block is worth its weight in gold to someone with a 68 Hemi car that needs it
the Hemi conversion heads on a 440 block I have had good luck with and great people to work with
less costly to build than a real hemi unless you can swap meet the parts
also wedge 440 heads have really improved but some are too big for the street giving the Boss 302 syndrome so bvvc of big numbers and watch the low lift numbers and velocity
price what modern valve gear costs for a real hemi (if you go beyond stock OEM hemi valve lifts)

 

[Stylin']

If you decide not to build the Hemi my '68 needs one, what's the casting date on yours?

 

[73HEMI_RR_GTX]

I want to put a '68 426 Hemi in my 74 Roadrunner. I know that the K frame will have to be swapped out but what else is needed? Do I need a K frame from 68 or will any year fit it? Any advice is appreciated.

I can tell you this will be a fun project. I agree with 66 Sat, you will never re-coop your investment with the cost of parts today. But I can give you some pointers since I have done this swap.

1) 426 Hemi

2) Big Block 727 transmission with Hemi flex-plate

3) Hemi offset Power Brake Booster or convert to manual Brakes or move Hemi engine 1.5 inches forward to clear stock Brake Booster

4) 73-74 Big Block K-Frame or if you decide to move motor forward to use stock brake booster than you can use a 73-74 Small Block K-Frame because you will have to notch the K-Frame and relocate the motor mount brackets forward on the K-Frame.

5) Driveshaft will need to be modified (lengthened or shortened) depending on engine location.

6) Hemi Engine mounts Left mount has to be fabricated. Right mount can use stock 73-74 Big Block spool mount. But you will have to drill the tabs that are cast into the block to accept the spool mount.

7) Shift linkage and kick down linkage will have to be modified.

8) 26 inch Radiator

9) Engine accessory pulleys and brackets will have to be matched up.

This is just what I can think of now. I’m sure there will be more got ga’s and if anyone else can chime in

 

[scot]

A 68 K Frame will not fit in your car as others have said. I did a search at Schumacher and Tinman and did not see Gen II Hemi conversion mounts for your year car. Maybe you could use an Elephant Ear mounting setup.

 

[mattsmopars]

Please check the block to see if it has a partial vin stamp on it for all of us who are looking for there original engines. You mention it being a 68 and that could mean used in a 68 car if so that vin is stamped on the rear of the block flange that would mate up to the bell housing, close to the oil pressure switch location. If its a later block but still cast in 68 but used in later build car 69-up location is on passenger side oil pan rail. If you could check that would be awesome.
Matt

 

[73HEMI_RR_GTX]

Please check the block to see if it has a partial vin stamp on it for all of us who are looking for there original engines. You mention it being a 68 and that could mean used in a 68 car if so that vin is stamped on the rear of the block flange that would mate up to the bell housing, close to the oil pressure switch location. If its a later block but still cast in 68 but used in later build car 69-up location is on passenger side oil pan rail. If you could check that would be awesome.
Matt

My 68 Hemi is an replacement block. There is no numbers stamped on it. Casting date on the block is 11-9-68