BACK to High Performance 101 index page Next >>

Modifying a Doghouse Fan Shroud

By Ryan Ballou

A problem 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.

This leaves 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.

Unfortunately 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.

With those 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 and paint.

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 engine bay.
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
Click 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. Click 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. Click
6-With the duct removed, I did some drawing to determine what I thought would look best before I started any cutting.
Click 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. Click
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.
Click 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 primer.
Click 11-Always sand back to bare metal at least an inch or two from where you intend to weld, front and back if possible. Click
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
Click 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.
Click 20-Left rear after color sanding the primer. Click 16-A little time spent block sanding will clean this up. Click
17-Now we've got a nice clean edge with smooth lines.
Click 18-Left side ready for primer. Click
19-Right side ready for primer.
21-Right rear.
Click 22-Done priming and sanding, ready for some color. Click
23-Rear profile.
24-Front profile.
25-Here you can barely tell the shroud was modified at all, it almost looks like it was made like this.
Click 26-With the shroud back on the engine, you can see how much more room there will be when installing the dual carbs. Click 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.

BACK to High Performance 101 index page Next >>

About us | Contact | Events | History | Home | Images | Interactive | Links | Tech