A previous owner upgraded my '68 Mini Traveller with an engine from an early 70's Austin America or Austin 1300. The engine appears to have a standard A series cast manifold. A few months ago I installed a GEX155 twin box exhaust, which is an original style exhaust system for the Van/Estate. I used a two piece / two bolt clamp to attach the exhaust downpipe to the cast manifold, and held the pipe firmly in place with a jack while tightening the clamp.
The new system is MUCH quieter than the old glass pack muffler, and initially I did not detect any exhaust leaks. Recently I smelled fumes in the car. When I inspected the clamp there were carbon deposits along the threads of both bolts. I had someone cover the tailpipe with a wet rag and was able to feel an exhaust leak blowing around the sides of the manifold clamp.
When fitting the new exhaust, I was concerned that the bell on downpipe was too small for the cast manifold. Even with the leak, the downpipe held rock solid to the manifold. I used a mirror to get a bottom view of the pipe to manifold fit. The edge of the downpipe bell close to the firewall was covered by the clamp. However, there was an 1/8 inch gap between the downpipe bell and clamp on the side close to the engine.
I spent several hours trying to get a better fit, using two different clamp and bolt combinations, but always had an 1/8" gap on the engine side. The downpipe bell fits tightly on the manifold and is positioned correctly. There is no wiggle room. Using a digital caliper, I measured the outside diameter (OD) of the new exhaust bell, old exhaust bell, and widest portion of the manifold opening:
- New exhaust downpipe bell (OD) = 1.75"
- Old exhaust downpipe bell (OD) = 2"
- Manifold (widest OD) = 1.975"
The 0.25" inch difference between the new and old exhaust systems is huge. Was the new exhaust not flared out suffiently, or were there differences in the cast manifolds over the years the A series engine was produced? I have had several bad experiences with modern replacement parts not fitting correctly, and wouldn't be surprised if this is another manufacturing defect.
It would be helpful if others could post cast manfold and traditional style downpipe bell measurements for comparison. I could also use some advice on how to fix this problem. I see several alternatives:
- Find a used cast manifold that has a 1.75 opening and fits the new exhaust (assuming this exists)
- Cut the downpipe off the old exhaust and weld or clamp it to the new exhaust system
- Replace the cast manifold with an LCB header like: http://www.7ent.com/...s-c-aeg364.html
- Get an RC Conversion downpipe which fits a cast manifold: http://www.7ent.com/...npipe-ldp1.html
In the last three cases welding and fitting will be required, since the GEX155 twin box exhaust has a smaller pipe diameter.
I want a solution that results in the quietest possible exhaust system. With an Estate, more performance is not my goal (unlike most people who have questions about stage 1 kits, etc).
Thanks,
David Schwartz
Framingham, MA
