Jump to content

Datsun 521 going from L16 to L20b

Recommended Posts



The old L16 is sad, smoky, leaky, slow and running on 3 cylinders.  Rather than pour more money into rebuilding this engine, I want to bump the power a little by dropping in an L20b.  Have a line on a good one for a good price.  I keep hearing that this is a super easy swap, but I can't believe it's a simple plug and play.  Will the L20b mount to the existing exhaust manifold?  Will I need to repurpose the L16 oil pan in order for crossmember clearance?  What else am I missing, or is my skepticism unnecessary?  Thanks!

Link to comment
  • Replies 1
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

There are few differences that can't be dealt with between the L16 and the L20B. It's just a matter of swapping L16 parts onto the L20B.



1/ Put the L16 oil pan and pick up tube on the L20B block.


2/ Use the 521 engine brackets and rubber mounts to the frame.


3a/ If the L20B is from a car it has a 200mm flywheel and clutch, same as the L16 and the transmission and release bearing/collar are a match.


3b/ If the L20B is from a truck it will have a 225mm flywheel and clutch and the L16 release bearing/collar do not match. If you know where the L20B is from go back and grab the release collar off the old transmission and put it on the L16's clutch arm. 


4/ If the L20B has the intake that is bolted to the exhaust manifold ('75-'77) you'll have to remove both and put the L16 intake and exhaust on.* If you have a '78-'80 L20B the intake and exhaust is separate and all you need swap is the L16 exhaust manifold. With the L16 exhaust manifold on it will bolt to your exhaust system. The L20B block is 3/4" taller so the head and exhaust pipe will sit that much higher. I put an L20B into my '72 521 back in the '70s and the 3/4" extra height was no problem when it came to closing the hood.



*The L16 and the later '78-'80 L20B uses a coolant flow from the head through both intake runners to warm them on cold days and cool them on exceptionally hot days. The '75-'77 L20B with the co-joined manifolds did not have this feature but when using the L16 intake all you need do is drill two 3/8" holes in the head to make this work.


5/ Use the L16 alternator. If the L20B is from a 620 truck it might work as they are a small diameter but car L20B alternators are really too large to fit easily.


6/ All L20Bs use a fuel return line and the 521 does not have the plumbing for this. Just cap it off or use the L16 fuel line to the carburetor. 


7/ L20Bs from the 620 or 720 trucks use a throttle cable to the carburetor and will connect up perfectly. Some cars use a linkage. Just pull the cable connection from the L16 carburetor and bolt to the L20B carburetor to convert it. 


8/ L20Bs have a stainless steel pipe from the exhaust manifold to the intake for the EGR. As you will be using the L16 exhaust that does not have this, just unbolt the pipe from the L20B intake and remove it. Best to pull the vacuum hose off the L20B EGR to deactivate it. 


9/ The '70-'71 521 had a manual choke, '72 had an electric choke. All L20Bs had electric choke so if yours is a '70-'71, join the electric choke to the idle cut solenoid wire to draw power from it.

  • Like 2
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.