Sunday, 11 January 2009

Manifold Problem

The original Shorrock installation used the 948 twin carb cast exhaust manifold. This is okay, but the engine would sure breathe a lot better on a branch manifold.

About 10 years ago I managed to get hold of an original but rusty mild steel branch manifold for the MkII Spitfire. Unfortunately this fouled on branches number 2 and 3.

A few years back I bought a John Kipping stainless steel branch manifold suitable for the 948/1147 setup. This looks like there will be just enough clearance of branches 2 and 3...

I need a spare 1147 head to check for sure.

The real problem is the pressure relief valve incorporated into the Shorrock manifold. There's no way that's going to clear branch number 4...

Once the valve is removed, it fits no problem...

But the Shorrock unit needs the protection of the pressure relief should the engine backfire out through the inlet manifold. So the problem is how to incorporate the valve into the manifold.

Two options spring to mind...

Cap the end of the manifold, drill and tap a hole on top of the manifold to accept the valve in it's a new location.

Lewis Jones did something like that on his 1300/1500 Spitfire utilising the Herald 13/60 inlet manifold...

The casting of the Herald 13/60 manifold has a flat section at this location suitable for a vacuum gauge pickup. There is no such flat section on the Shorrock manifold.

The second option would be to attempt a remote location using suitable plumbing.

As noted by others, discharged fuel/air mix over a hot exhaust manifold doesn't sound very clever, so I'm thinking relocating away from the exhaust is a good idea. Just not sure how.

I'm thinking of a banjo bolt arrangement, anyone know of any such specialists or have any other suggestions?

Here's a few more photos showing the manifolds together.

UPDATE : Following a suggestion by Dave Powell, I made contact with Derek at Flexolite (01684 541 941 /

Fortunately Derek had a Shorrock to hand and was able to tell me the 1" UNF thread (20 TPI) is a complete bastard size, and so I'd need to get the plug made especially, as well as obviously needing a tap of the same size to cut the new thread. Nothing insurmountable then but he left me plenty to think about...

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