My '80 MGB is now up and running with dual SU HS-4s. Thanks to everyone
who responded to my questions.
I managed to find a used, pre-1974 exhaust manifold, but there were some
problems with it. First, one of the studs which holds the head pipe on
was stripped and proved impossible to remove with any tools to which I had
access. I took it to a machine shop and had them remove all 5 (one was already
missing), so that I could start with new ones.
The second problem I had was the thickness of the flanges where the manifolds
attach to the cylinder head. The flanges on the exhaust manifold were about
1/8" thinner than those on the used intake manifold. Since the four middle
studs which hold the manifold to the head come out between the intake
and exhaust manifold flanges, the flanges need to be the same thickness.
I solved this problem by filing the intake manifold flanges down to
approximately the same thickness as those on the exhaust manifold. I am
keeping an eye on this setup to insure that the manifold gasket does not leak.
I had two choices for a head pipe from Victoria Brittish. The
pre 1968 (I may be wrong about the year) comes in two sections,
a "Y" section which bolts to the two exhaust manifold ports, and a
long straight pipe which connects the "Y" to the middle muffler.
The other option (post 1968?) is a single piece, including the "Y"
section.
I opted for the newer one and fitted it to my existing exhaust system. This
arrangement brings the exhaust system closer to the center of the car than the
original setup, and, as a result, the pipe passes about two inches to the right
of the notch provided for it in the cross member which sits just in front of
the middle muffler. This setup does not appear to be causing any problems
but it does prevent me from putting a second muffler clamp onto the
slip over section with which I am joining the new head pipe to my old
exhaust system. If I had it to do over again I believe that I would
use the setup with the separate "Y" section and purchase an appropriately
sized piece of exhaust pipe locally. I figure that would give me more
flexibility to get the parts lined up properly.
I had no problem tuning and synchronizing the carbs. With a Unisyn,
its very straight forward. Performance is noticably better although
I am still running the factory spec timing ( 10 degrees BTDC at 1500 rpm).
One final question. When I tried to set my timing, I discovered that my
distributor was stuck. Apparently, the timing on the electronic ignition
has been so stable that the POs never had to adjust it. Has anyone
ever run into/solved this problem. I loosened both the pinch bolt and
the two bolts which hold the pinch bolt assembly to the block. The
pinch bolt assembly was free to rotate, so I know that it was not holding
the distributor in place.
Peter Schauss email: peter.schauss@cubic.com
1980 MGB (dual SUs)
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