L20 Aftermarket Intake Manifold Offenhauser,Edelbrock,Cannon

Down draft or single or dual side draft?

I imagine that a truck header is different from a car for clearing the torsion bars.

Luisgman 0

Posted November 29, 2018

Depends on what cylinder head port size you have AND what port size the Offy or Edelbrock intake manifold is!  The late W58 L20B cylinder head is the BIG PORT, so you really want the correct matching big port intake.  I was just sitting down to ask these questions, cuz I have two dual plane Offy intakes, but so far one is for the L16 small port head, the other is still bolted on an engine in a car!

Let us know what intake port size you have OR what cyl head CASTING # you have!

TJ

Denver CO

Luisgman 0

Posted November 29, 2018

I had one of the "Dual Plane" (split port) manifolds.

The damn web between the ports was stupid thick, and it flowed less than the stock manifold.

There is a nice Redline manifold on eBay right now (for the Weber DGV) for like $250.

Luisgman 0

Posted November 29, 2018

W58 cyl head casting is a BIG PORT, so you really do NOT want the earlier Offy for the L16 small port "210" casting.

I just had an old school 510 guy here today that used to modify back in the 80's & early 90's.  He said they dyno'd an L20B with different downdraft intake manifolds using a 32/36 Weber.  He said that the casting #W58 INTAKE manifold (cast on the top of the rear runner) flowed the best!  I sell every W58 L20B intake that I list!  You likely have a W58 INTAKE manifold on you 620.

I also have a BIG port Edelbrock manifold, but kinda want to hang on to it for an L20B 510 build........ 

So every time I pick up my L16 SMALL port Offy intake, I chuckle, cuz the "split" dual plane ports are TINY............really only suited for the small port L16 "210" cyl head!!

Luisgman 0

Posted November 29, 2018

Do you have the stock W58 intake on your truck?

Luisgman 0

Posted November 30, 2018

For a downdraft stick with the stock intake. Get a weber 32/36 that everyone raves about. >$300 and done.

I understand the theory of the Offy intake but even if the intake runner air speed is faster, it dumps into the stock intake port and slows down again. I agree with G Duax it can't possibly flow as much as the stock one. Like the 3 angle valve job. On the bench machine held just barely open it looks impressive but in the real world the valve spends very little time there.

Luisgman 0

Posted November 30, 2018

Not bad, but $250 ??  I could see under $175

And I had one of those also, damn runners are fairly small, then open up right before the head.

Don't think anyone ever made a true downdraft L4 manifold.

All that I've seen have little runners so any dummy can bolt them onto a stock engine, and feel good.

Someone sells just the head flanges on eBay that would be fun to play with.

A little thick wall aluminum tube, a little aluminum plate, and a little welding, and who knows what you could come up with. 

How about a tunnel ram :)

Luisgman 0

Posted November 30, 2018

I don't see a Canon downdraft intake manifold on eBay!  Links are a pain to post here............what does the eBay listing title say?  I'm curious!

I think you will do just great with a stock W58 intake & a new 32/36! 

TJ

Luisgman 0

Posted December 1, 2018

All I saw were dual sidedraft manifolds!  Will look again! ?

Still the best bang for the buck.

I did this on a U67 head, which other than the exhaust port shape, is the same head as the W58. I couldn't find a 2 into one down pipe so I made a KA24E from a 240sx fit.

Luisgman 0

Posted December 1, 2018