Modifying a Doghouse Fan Shroud
By Ryan Ballou
that always seems to arise when running dual carbs on a VW engine
is that of clearance. Another issue is that of what to do with the
heater outlets on your fan shroud when you're not utilizing a heater
box type exhaust system. The easy fix for this problem is to go out
a buy an aftermarket 36hp style doghouse shroud. The problem is that
with few exceptions, they simply don't cool as well as a stock shroud.
Then there's the shroud that was used by the VW Thing that did not
come with heater outlets. However even if you do find one in good
shape, it won't be cheap.
The fix I
chose to go with was modifying my own shroud in a way similar to the
Thing shroud. This mod is time consuming, and does require access
to and some skill with a MIG welder. The first order of business is
to cut off the blower outlets. They are held on with only three spot
welds and will pull out of the shroud once those welds are removed.
With the outlets gone, it's a good idea to mark up the shroud with
a felt pen prior to any cutting. I chose to eliminate the humps on
the sides of the shroud since their sole function is to provide air
to the outlets.
you with a partial cavity on either side of the shroud where air will
still not flow. I took a chance by modifying the internal vanes and
cut the lower half of each of these vanes out, thereby allowing air
in the outermost channel of the shroud to be directed to the heads.
Before and after CHT readings showed a slight improvement in cooling
so taking this chance paid off.
the new shape of the shroud puts the outside edges passing through
part of the cavity left when the blower ducts were removed. A small
piece of 22-gauge sheet metal was cut to fit and welded in place to
fill the gaps. Keep in mind that welding sheet metal this thin can
be tricky with even a good MIG welder, go slow and only lay down half
inch beads at a time so you don't put too much heat in the shroud.
sections filled in you can now cut your new side pieces to close the
shroud back up. Remember that when welding thin sheet metal, your
best chance at avoiding blowing through is to cut your patch panels
to a perfect fit. Once the new sides are in place, use a disc sander
to finish the welds and smooth everything out. You'll likely have
some warping to deal with too. I pulled my shroud straight again by
drilling a few of spot-welds holding the internal vanes in place.
Then I bolted a piece of angle iron to the face of the shroud using
existing mounting points for the Alt and coil brackets. With the shroud
held straight by the angle iron, I re-welded vanes where I drill the
spot welds, essentially using them for structural support. Finally
a little Bondo here and there and the shroud was ready for primer
Over all this
wasn't a performance minded project, though it certainly does make
working with the engine easier. The carbs are easier to R&R, plugs
and wires are easier to reach, and it really does make the engine
just look a whole lot cleaner.
1-Here is our before
picture, and an old one at that. It's tough to see the clearance
issues here, but in general this just isn't a very clean looking
2-Here you can see exactly how close the carbs are to the humps
on the shroud. A quick pass with some feeler gauges shows a gap
of less than .010". Depending on which intake manifolds are
used, this gap will vary.
3-What you didn't see in the previous two pictures was how much
I had to hammer the shroud to get that .010" of clearance.
So much in fact that I split the seams of the shroud
4-I chose to cut this tab off rather than drilling the spot-weld.
This section will be removed anyway so finish isn't important.
5-This weld was easier to drill since cutting the whole section
out would have taken longer, there is also a spot weld on the
inside tab. I cut this one and then ground down the tab to leave
a finished surface when done.
6-With the duct removed, I did some drawing to determine what
I thought would look best before I started any cutting.
7-Now it's just a matter of cut along the 'dotted' line. Go slow
and do your best to make both sides match. You might even want
to make a template on paper and fold it over to check symmetry.
8-With the sides removed you can see the outer most air direction
vane and how it will create a stale air pocket if left alone.
9-I decided the best course of action was to cut the vane about
half way up. That way the air coming through that section of the
shroud would be directed towards the heads.
10-I figured that with the shroud opened up, this would be a good
opportunity to spray the insides with a rust treating and preventative
11-Always sand back to bare metal at least an inch or two from
where you intend to weld, front and back if possible.
12-The new side piece is just a strip of 22-gauge sheet metal
that I cut to fit and the stitch welded into place.
13-Profile view after fitting the new sides.
14-With all the welds sanded down the shroud is starting to take
on a finished look
15-Inevitably there will be some distortions from cutting and
welding, the quick and easy fix is good old-fashioned Bondo. Make
sure you do a good job at surface prep if you want this to last.
20-Left rear after color sanding the primer.
16-A little time spent block sanding will clean this up.
17-Now we've got a nice clean edge with smooth lines.
18-Left side ready for primer.
19-Right side ready for primer.
22-Done priming and sanding, ready for some color.
25-Here you can barely tell the shroud was modified at all, it
almost looks like it was made like this.
26-With the shroud back on the engine, you can see how much more
room there will be when installing the dual carbs.
27-Finally with everything reinstalled, you can see exactly how
much more room there is. There's a good solid inch of clearance
at to the carbs and with the blower ducts gone, the shroud looks
100% cleaner. No more ugly caps to look at.
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