[DeTomaso] Turkey Trays

Larry Weston lplugw at hotmail.com
Wed Mar 28 08:55:18 EDT 2007


As I rememeber the exhaust crossover in an intake manifold was one piece of 
a two part system to heat the incoming air charge for better low speed 
drivability. The other piece was the "Heat Riser",
which was a flapper valve in the outlet end of a cast iron exhaust manifold, 
controlled by a bimetallic spring.

When the exhaust manifold was cold the flapper would be in the closed 
position, forcing exhaust gases up through the intake manifold crossover 
passage and out the opposite side exhaust manifold.
The flow of the hot gases would warm the intake until the engine warmed up 
and the bimetallic element opened the flapper and the exhaust flowed out 
through the exhaust pipe. Flow through the intake manifold would essentially 
cease because there is no more pressure differential pushing it through the 
restrictive crossover passage.

With no heat riser valve I would say what liitle exhaust gas that travels 
through the crossover passage is probably cooled by the incoming air and 
evaporating gasoline and never retains enough heat to burn/bake oil on the 
bottomside of the manifold.

I'm in the middle of changing my intake. Considering the comment that metal 
turkey tray gaskets can actually dent an aluminum manifold, I'm prone to 
going to the composite gaskets with no tray.

Any comments?

Thanks,

Larry

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