intake manifold

[npca-viking]

I have discovered a design flaw that might be affecting performance yet is very hard to detect. The intake manifold has a heat chamber in its centre area where hot gases from the exhaust manifold circulate to enhance the engines ability to get up and going when cold. Unfortunately, the casting created two very thin areas on either side of the centre spin of the mentioned chamber. To make matters worse, these thin areas are on the engine side of the manifold so hard to inspect and subject to some significant heat - so prone to eventually burn/corrode through. I have found this on both of my manifolds on the P40s I am rebuilding so I suspect it is likely a widespread problem. I nickel welded the two thin areas as cast iron is not happy with most other rods. This worked fine and I ran the beads down the full length of the spine.The holes do not affect vaccum as this area has a double wall and the holes are created on the outer one - allowing exhaust gas to escape and create an irritating noise when you thought your exhaust system was perfect. What is worse is that a leak of that size so intimate to the engine reduces the back pressure on the exhaust valves so that they hammer the seats harder than they should leading to overheating and the associated nasties that follow.