Jump to content

1978 620 Long Bed

Recommended Posts

About a month ago I picked up a 78 Long Bed from some kid who bought it as a work truck, took it apart, shattered his clavicle, lost his job, and then sold it to me non-running. I scored it for $600.


I've been doing research since then, trying to find out just what I got myself into. :rollseyes:


First things first, I'd like to get the engine solid before anything else. Now I don't know too much about engines (I used to pride myself cause I was the only one of my friends who could change their own oil :lol:), so I was hoping all you datsun geniuses could give me a hand.


The stock engine is an L20b with a W58. I've picked up a closed chambered W53 along the way. I'm considering 3 possible builds:


1) Stock L20b with W53 (8.662 compression ratio)

2) Stock L20b with W53 and L18 pistons (9.609)

3) 1mm overbored L20b with W53 and late L28 flatop pistons (10.498)


(I used the Ozdat Engine Design Utility to get those figures, assuming a 1.5mm Nismo gasket. Hope I used it right.)


My first question is "How much compression?" This is going to be a daily driver, so no 100 octane race fuel.:rollseyes:


My second question is about head work. Some more research that I've done has said you can convert any of the closed chambered heads to the SSS head simply by opening up the intake port to 1.50". Is this something I want to do? I've also read something about valves from a P90. What does that mean/entail?


Doing even more research (I said I've had this truck for a month and haven't touched it right? :rolleyes:), the Shadbolt/Colt 449 cam sounded interesting (for, again, a daily driver). Anyone have any experience with this cam?


The last point I'd like to mention is I live in the great state of California, home of the SmogNazis. Any idea as to how any of this work could effect my chances at passing the emissions test?


And the obligatory picture. Thanks in advance for your help.


Link to comment
  • Replies 4
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Since you are in the Peoples Republik of Kalifornia,i have to agree.Webbers won't pass smog visual.Putting a header on it will not help at all.ANd don't remove any PC stuff.Speaking of which i'm parting out a 79 KC California model.


You can rebuild the motor but don't go higher than 10 to 1 CR.And that is the ragged edge for a driver.

Link to comment

They won't be tearing it down but it does have to have all smog in working order. This is no big deal just pull the air pump belt off and plug the vacuum line to the EGR once it passes and good to go until next years test.


If the W-53 head is a standard p-nut volume


1) Stock L20b with W53 will be.............................................. 8.90 to 1

2) Stock L20b with W53 and L18 pistons................................. 9.91 to 1

3) 1mm over-bored L20b with W53 and late L28 flat top pistons.. 10.87 to 1


Actually a hair less as I was using the standard 1.2mm crushed Nissan gasket.


I wouldn't run over 9 to 1 but it depends how good your reg. or premium gas is.


The intake runners can be opened up but this will slow down port velocity at lower speeds (where you do most of your driving) and may only help breathing at extreme RPMs. The intake valves on the W-53 are 65mm and the exhaust are 38mm which are the biggest used on the L20B heads. I don't know what the P-90 L28 valve size is but a lot of machine work and expense for a small gain in breathing.

Edited by datzenmike
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.