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Using L16 or L20B Hitachi on a L18? Feasible?

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I have a 74 620 L18 manual transmission and have the following issues:

  • the carb is missing and
  • the manifold EGR passage tubing fitting (to exhaust manifold) has been welded up and
  • the EGR valve is removed and a block-off plate is bolted on.


Finding a L18 anything is really difficult since it is only for 1 year.


What about a complete L20B manifold/carb?


NOTE:  I saw a pic of a 1977 manifold and it looks like it has air pump injection plumbing - was this a California only variant???


What should I do?


Thanks in advance,




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You do not want the L20B manifolds.  You'd have to change the tailpipe and other things to make it work, and those air injection tubes were on all L20Bs, at least all 1975+ ones.  Heck, some L16s had them.  The 75-77 L20B manifolds are bolted together, and the 78-79 have different exhaust port designs.


The L16 and L20B carbs are the same bolt pattern as the L18 carb (L18 and L20B, plus 1973 L16s are the same major model, DCH-340) just differences in jetting and accessories to the carbs for emissions purposes.  I've run an L20B carb on an L16 so it'd be fine on a L18 too.  Of course, you could get a Weber kit from Redline (32/36 DGEV and adapter) and avoid some of the hassle of picking up an Indonesian "rebuild" carb (or a worn out junkyard one) since the Hitachis are all 35 years old or more at this point. 


Are you having to have this smogged, which is why you want to change manifolds?  Otherwise an L16 intake would be "cleanest" as it didn't have the EGR stuff at all. 

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Thanks for the reply.


If you've run a L20B carb on the L16, sounds like there is no problem going down in engine size.  I guess maybe the only advantage of the L18 is that it is the "middle" engine and a L16 or L20B carb is only a "one step" change. 


Here in PA when a car is 25 years old, there is only a visual inspection.  A Datsun from 1974 would be very unfamiliar to any inspection stations, however, I wonder if they have a Check List of things to look for such as EGR, air pump, etc?  I guess I could go to my inspection guy and ask him about the EGR etc. if he needs to see it.


Its king of sad.  If there is one year you avoid if you want a 620, is the 1974 L18. 


I would like to find the proper 1974 parts for this 620 if I could.  I really hate seeing something cobbled up even if it is an old daily driver.


As far as identifying Hitachi's, I think thee was an ink stamp so that makes it very difficult.  Does that sound right?

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I suppose if I ran into a complete Weber setup for next to nothing, I'd put it on, but I really like to see 100% original when I look at an old car - even if it is a rat.


Thinking more about the welded EGR passage...  It looks like they broke the boss since half of it is completely missing.  So maybe they decided to simply weld it up.


I could remove the passage, properly weld repair the boss, drill a new hole, and tap it.  Of course for US cars, it would be a NPT, but I have no idea what Datsuns use are far as pipe, tubing, and flare fittings.  It appears there is a fitting that goes in the passage - then the tube nut threads onto that fitting.  Of course would have to get the fitting AND the tube - but I do have the tubing that is still connected to the exhaust.  It was cut and the other half (that went to the passage) was tossed.




Just called the inspection garage and they said since its more than 25 years old, they don't look at anything - there is no emission testing.  So I could block off the EGR and forget about it.  Obviously the most expeditious solution.

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If you already have a Hitachi carb, that runs good on another 4 cylinder L engine, it should run OK on a street driven Datsun.  Ideally, it should be tuned or jetted to the engine, but reality is a L-20-B carb on a L-16, will just act like it would on the L-20-B but the L-16 would have to be revved higher to demand enough air to open the secondary.


If you put an L-20 carb on the L-18, the carb calibration probably will be more off from the EGR being deleted, than from losing 182 CC's of displacement.



L-16, 1595 cc

L-18, 1770 cc

L-20-B, 1952 cc

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Actually, for a given size carb w/secondaries, it should take higher revs on a smaller engine to open the secondaries.  If the engine was small enough, the secondaries would not and should not open.


But the EGR is a good point.


Are fuel and bleed jets and emulsion tubes available for the DCH 340?

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Why the EGR Passage boss was busted off and welded:


I think I have the answer to this: 


The bottom "side" of the boss was broken off.  I suspect someone had a wrench on the fitting and was pushing down to remove it - but it was galled and they used excessive force which simply blew off the side of the boss.


If I'm going to not run the EGR, if I want it clean, I should make an "EGR Passage Block-Off Plate."


Then there is the possibility of using an L16 manifold?

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I think the L16 pre 1974 are the most desirable since they have no EGR.  


Also I would conclude that an L16 Hitachi DCH 340 carb would be best for the L18 if the EGR is to be eliminated.


So another Question:


Can the L16 intake manifold be used on the L18 (and L20B)?

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