Exhaust Manifold Temperatures

[andyp]

I've just been talking to somebody that does various finishes on cast exhaust manifolds and he is going to have a bash at mixing up something that will look original but not crack and fall off after 5 mins.

He asked me if I knew what sort of temperatures we were talking about. I didn't. Has anybody taken a reading after giving the engine a good thrashing?

Andy

[Moeregaard]

I've seen E-Type manifolds--both cast iron and tubular--glow cherry red on long, nighttime runs. Since steel starts to visibly glow at roughly 900F/467C, I would estimate that the exhaust-gas temps are in this region, possibly higher at elevated power settings.

[Heuer]

Andy

The reason the manifold finish cracks is not to do with the high temperature but with the rapid cooling when water hits them. This either happens when you find a deep puddle and it is thrown up or, more typically, from rainwater on the bonnet which rushes forwards and into the louvers when you brake. All it takes is a few drops on the hot manifold and cracking starts which quickly accelerates and the finish is lost. The original Jaguar porcelain finish was the most long lasting and many have tried to find something better but none have worked as far as I can see - you will get about 1,000 miles before the finish drops off.

But to answer your question - at high speed on a hot day the manifolds will reach about 600c.

[andyp]

Thanks chaps. I'll pass that along with the news that we'll be doing quench testing from cherry red before I try them out.

His first thoughts were a metal oxide-ceramic composite. I've no idea whether that is a good or bad idea but I'll let him have an old manifold to play with and some photos of the factory finish and see what he can can up with.

At present I favour a rusty cast iron finish as something that lasts 1000 could be gone in a busy week.

Andy

[Moeregaard]

I looked into re-porcelaining the manifolds when I restored my '65, but was put off by the cost and questionable durability. I finally sandblasted them clean and applied grey VHT from a rattle can for a nice result that held up well. I've seen manifolds aluminized, but the silver finish looks a little too "tarty" for an E-type's engine compartment.