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Triumph TR6 - Hot Manifolds

John's thread on idle speed reminded me of another little "test" I finished up about 3 weeks ago. It kinda tied into the oil viscosity testing, too.

My '73 has the Goodparts triple ZS manifolds. Even with the coolant line blocked off, they still get hot on a warm day. What to do... There isn't really room between the manifolds for some sort of heat shield, and wrapping the exhaust isn't a good idea, so I hear. So I wrapped the inlet manifolds thinking that would keep out engine compartment heat and cool 'em down. Did a nice job, too. Took a drive, then checked under the insulation to see how cool the manifolds were.

They were HOT - too hot to keep fingers on for more than a second or so. Actually seemed hotter than without the wraps. So it's fair to say that almost all of the heat to the inlet manifolds gets there by conduction from the head, and the wraps were trapping the heat. Exhaust wraps and heat shields don't do anything to prevent that.

Since a duct brings cool air to that part of the bay I removed the wraps so the manifolds would at least get some convective cooling. And that's where it stays....unless I decide to put some cooling fins on those things.

Brent B


I wrapped my headers in an expensive heat wrap and notice a very significant reduction in undhood temperatures.

The problem with wrapping is it reduces the life of the headers - or so they say.

But the underhood and manifold temps are cooler for sure.

John Parfitt
73 5 speed.
John Parfitt

Yeah - wrapping carbon steel headers is not a good idea. The heat is definately one issue, but so is moisture. Hear tell they'll crumble after 3 seasons. No probelm with stainless, though.

What I saw may be strictly due to the Goodparts aluminum intake manifolds. Thermal conduction is THE mechanism that makes them "hot". In fact, after the engine is shut down for about an hour the inlet manifolds are quite a bit hotter than the exhaust manifold!

Brent B

Hi Brent & John

That was one of my concerns with electric fans rather than the engine driven with the TR setup.

The constant mechanical does have an air flow over those parts. Plus provides reasonably cool air to the original air intake port.

Always wondered why the intake right above the exhaust. But I think reasonably warm gas and cold air makes the most volatile power mix? If you have cold air coming in?

From my experience Brent the aluminum will sink the heat out of the cast head. On a chevy small block we use a carbon spacer to the carb to reduce heat sink effect from aluminum intakes.

As for wrapping original cast headers. They pretty much stay head temp or less. After market thin wall steel headers will increase bay temp. so ceramic or another type of coating/wrap would be a benefit. Any coated header must be coated original inside and out otherwise 3 years is about the limit steady running. The inner coating does the work outer coating is cosmetic. Moisture and acids from exhaust rot from inside mostly


Bill Brayford

Does anyone think the manifold cooling pipe also serves to prevent the manifold from getting too hot?

Rick O.
Rick Orthen

I too think the coolant pipe thru the intake not only cools the mani but more importantly stabilizes the temp with a range similar to the thermostat. This would I suspect improve engine stability and fuel economy.
B.R. Horne

This thread was discussed between 16/05/2004 and 18/05/2004

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