Manifolding Notes for B18/20 Motors.  
R. Kwas Nov2017


Factory Manifolds
Non-Factory Configuration using Factory Manifolds
Non-Factory Manifolds


Stepped Spacer / Manifold Washer


Volvo went through a number of Intake and Exhaust Manifold evolutions in the many years that the B18/20 were produced and installed into cars, not to mention boats.  Each has it's reason for existing, and I've tried to collect pictures and descriptions of the various styles here to give an overview, plus touch on advantages and disadvantages.  Approximate years of use and markets given refer to what is known to the author, based on what was delivered from the factory, which was market dependent.  Non-factory Manifolds were also developed by second source suppliers to allow fitting single down-draft or side-draft carbs, and non-factory combinations of factory Manifolds are not uncommon.  What one may find on a engine now, after such a long time, may certainly have been changed from what the factory delivered...


Factory Manifolds: 

One-piece cast, for a single down-draft carb (typically the Zenith VN36, for European delivery vehicles), with a 4-1 Manifold for Exhaust. 


Intake Manifold for single side-draft SU or ZS(gag!) .  This would have been paired with a separate, cast, 4-1 Exhaust Manifold shown below. 

Picture by Volvoniac M. Neuner, used with permission and thanks. 


Double sidedraft carb aluminum cast intake Manifold (as was typical for US delivery vehicles '66 and earlier).  It would have also been paired with the separate, cast, 4-1 Exhaust Manifold shown below. 

Note fastener holes of the throttle linkage bracket in-line with balancing tube.


The 4-1 cast Exhaust Manifold: 

This shop has Nickel plated the Exhaust Manifold casting. 


One-piece cast Iron Dual Intake, with 4-2-1 Exhaust Manifold (approximate years of use: '67-'68). 

On what looks like a late B18 (Cast-in Alt pivot).  Note angled throttle linkage bracket at Orange and bolting flange for Intake is equal in thickness to Exhaust area, so a simple (thick) washer with a fastening loop for one end of the Throttle Return Springs is used, hence the Loops at Blues
Picture source:

Manifold Washer with throttle spring Loop.  It is extra thick because it needs to bridge a gap between the two Manifolds. 
When making non-factory combinations of Manifolds (particularly when installing a Header), a step between Intake and Exhaust Manifolds may occur.  This requires special attention to assure Manifolds are and stay securely fastened!  See also below. 


Dual Throttle Manifold (used '68-):  This is the one to stay away from!

Massively heavy, many more places for false air to enter, puddling of fuel in the center Pre-Heating (and Heatsoak) Chamber, inconsistent idle, miserably poor starting after heat-soak...if I thought about it, I could probably think of a few more reasons not to use it because of that ridiculous Intake...however, it is paired ( a one-piece casting!) with a very good 4-2-1 cast Exhaust.  The best thing one can do is to simply cut the Exhaust off for use, and to just recycle that miserable Intake part (or to use it as an anchor for small watercraft) ...but save those SUs, and while the SUs are off the Manifold, check those Throttle Overrun Valves


Non-Factory Configuration using Factory Manifolds:

Intake:  Early aluminum casting suitable for dual SU or Zenith/Stromberg carburetors.  A vacuum port used for PCV and/or Brake Assist Unit may be located in the center of the balancing tube, pointing up, OR longitudinally at the front, in-line with the balancing tube, facing forward. 

This is probably everybody's (the author's too!) favorite setup!  Early Aluminum Intake combined with later cast Iron 4-2-1 Exhaust from an injected setup.  This  combination, is the cleanest, best performing setup, with best longevity. 

Separate Alu intake, and Iron 4-2-1 Exhaust. 
Cool intake, and highest performance factory Exhaust. Here, mounted to an E Cylinder Head. 
(Note horizontal throttle linkage bracket at Orange.)

Combining that Exhaust Manifold with a stock Headpipe from an 1800E, which has a 2" outlet, and from there back, a custom Exhaust System is a good performance setup, with good longevity.


Non-Factory Manifolds:

Intake Manifold for Single Down-draft Weber (DGEV)...a favorite of those who think they can bolt-on a tune-up! 

This Manifold is plumbed to the Cooling System for preheating the mixture.  


You can even install a Holley four barrel carb onto your B18/20.  Picture from an ebay offering. 


Dual Weber (Solex) Side-draft Manifolds: 

Manifolding for dual side-draft (DCOE) Webers places the Intakes of the Carbs quite close to the inner fender, leaving little room for Air Filters.  Below, installer only has installed shorty stacks. 

Support (not visible below) in addition to the Manifold, for the overhanging mass of side-draft carbs, is highly recommended!


Dual Weber DCOEs with stubby stacks, because there is little room for proper Air Filters. 

Selecting Air Filters which include little tilt-up runners to locate the filters up and away from the inner fender, is an option.   

 Dual Weber DCOEs with Air Filters.   


Intakes for Weber DCOEs by TWM are two separate castings. 

A one-piece casting with a connecting brace, in the Mangoletsi version (bottom view!) 

Stiffening spines are cast into this version (Manuf.?), where they are also separate.  These are the ones supplied by Volvo with the Competition Service (Solex) kits, and are the only style the author would install without additional support for the overhanging mass of the carbs.  

I expect these very long (SPR) manifolds for Weber DCOEs, would put the intakes of the carbs into the Wheelwell of a streetcar,
to say nothing of where that would put Air Filters......I'd like to see Carbs mounted on them and a measurement...! 
I expect this arrangement is only suitable for race cars with purpose-built engine compartments.


Since this is the highest performance setup, DCOE Weber carbs are typically paired with a tubular Header on the Exhaust.  Clearance to Generator/Alternator can be close, but there is room.  Below, examples of two difference setups with a header:

Delco Alternator on SW-EM bracket clears Header just fine. 

Some of Phil Singher's fine work! 




Discussion on the subject:


Other Details:

Stepped Spacer / Manifold Washer:

Exhaust on this injected motor has been changed to a Header, resulting in a large step from Intake Man. to Exhaust Man.  The thickness difference is very apparent in this view.  A stepped spacer/manifold washer has been manufactured and installed to accommodate the difference, and allow the nut to bear on a surface perpendicular to the fastener axis...the best, and a sharp solution!   


From the How-to-Impress-the-Wife (or maybe not) - Dept ! 

Baking on a coating in the oven. 


From the I-Wish-I Had-it-Dept...for the man who loves ME!

We don't need no stinking Webers!


Some pictures were "harvested" from the Internut and credited to the source where possible.  Otherwise, these notes are Copyright © 2017.  Ronald Kwas.  The terms Volvo, SU, ZS, and Weber are used for reference only.  I have no affiliation with any of these companies other than to try to keep their products working for me, help other enthusiasts do the same, and also present my highly opinionated results of the use of their products here.  The information presented comes from my own experience and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at, at the readers discretion.  As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles! 

You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the SwEm site as the source.  If you donít, youíre just a lazy, scum sucking plagiarist, and the Boston Globe wants you!  As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the odd metaphor and probably wise-a** comment. 


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