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Merry Christmas!! L20 offy intake?


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So I got a long time wanted offy intake for my newly acquired '77 620 with the L20. I have a question about it working on the head I have. The head I have is the U67. The manifold I got is 6144 DP and the back side of the manifold is flat and ported with 4 threaded holes. What goes there?! I'm trying to make my engine compartment as less cluttered as possible, so all the egr and smog related crap is going away. I thought the back of the intake would just be rounded. Did I get the wrong intake? Thanks and Merry Christmas!!

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It's actually an L20B. The L20 was a six cylinder engine.





The '75-'77 L20Bs all had the intake bolted to the exhaust manifold. It used hot exhaust directed up onto the under side of the intake to warm it and help vaporize the fuel droplets. Four bolts hold them together with a metal plate to seal and keep separate sandwiched between. 




Looking downward from the carburetor you can see the corrugated spacer plate between the manifolds.


Do you have this exhaust manifold? If not make a metal plate with 4 holes for the bolts to seal this hole on the bottom.





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Thank you so much! I understand now. It's a non issue for me then, cause I'm going with a long tube header. However what is the flat portion on the back of the intake for? Does offy  have one that's rounded? I thought I saw that before.


I don't know how to post pictures, hopefully that works 

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Oh... that!!! It's for bolting the EGR manifold onto. You should even if not using the EGR because then you can keep the PCV valve functional. That is important. You could thread that middle hole so the PCV will screw on and fill the other two with JB weld.






What does the under side of the intake look like????


If for a pre '73/'74 intake there would not be that flat spot on the side because there was no EGR then.

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I was and have before just let pvc vent to atmosphere, with a little K&N stye filter. But either way I'll have to see what looks best, egr manifold or some sort of block off plate.


Here's a picture of the truck I used have and the way I did the pcv.




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 Before the introduction of the PCV valve in '62, oil changes were done at 3,000 mile intervals and you were very lucky to have an engine last over 100,000 miles. With PCV, oil changes are extended to over 6,000 miles and engines were cleaner inside and are easily capable of twice the mileage. Make every effort to get and keep your PCV functional. It's easy enough, benign in operation, has no effect on mileage, performance or running. The valve cover hose goes to the air filter so the fumes don't escape into the cab or drip oil all over. Everything is there on the air filter housing, don't mess with it for the sake of a tiny blue filter.

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Does your Offy intake port diameter match the large ports of your U67 head?  I believe Offy made an earlier small port & a later large port.  The later large port will have a flat mounting point with air ports, on the outside facing the left inner fender.  This was for the factory EGR block to bolt to, so Offy could sell it as an approved emission intake manifold.  Offy would NOT have made a later big port intake for the L20B, without that mounting point (I think that is what you meant by asking for a cleaner "rounded" intake??).  That said, you can either fab up a "blanking plate" to block  off those holes/ports, but there is no real way to make it "pretty"!  Another option would be to cut/grind off that ugly EGR mounting point & weld up all the holes, then polish paint or powdercoat to make it look better, but that would require somebody with aluminum welding skills.  If you pursue that, my suggestion would be to bolt the intake up to an old cylinder head, to avoid any heat damage from the welding!  FYI the original 68-73 510 "210" casting heads are kinda boat anchors, so would be the cheapest to buy as a mock up head.  I suppose a good welder could carefully weld up the holes while bolted/mocked up to your existing head, if that is all you have, but he would need to be EXTREMELY careful with residual gasoline etc in that vicinity!! 😳  Hope that helps!

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Above is the '78 -'80 L20B intake with the EGR manifold removed.


Below is the same manifold with the EGR casting ground away and shaped. The left EGR port was JB welded up and the center hole threaded for the vacuum fitting and the right side EGR port threaded for placement of the PCV valve. It now looks like the much earlier '68-'73 L16/L18 intake but has the larger runner diameters and the coolant flow from the head to the by-pass hose.




The '75-'77 intake is basically the same but bolts to the exhaust manifold below it and has no provision for the coolant flow through the runners to the by pass hose.

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