I'll be trying to attempt to install the True Dual Exhaust on my 80 vette soon. I bought it thru Mid-America. My question is to someone who installed this same system on the same year Vette. Do the pipes that hook directly to the stock manifold need ANY type of dount gaskets or do they hook ( bolt up too ) directly to the three studs the come off the manifolds. The reason that I ask is that currently on my stock exhaust there is a spacer of some sort on one side and a dount gasket on the other. Are these same pieces needed for the True Dual Exhaust setup.

Thanks Tom

I would call Mid-America's tech line and ask them. This is their system, they should be able to advise. This is what their customer service is for. Let us know how they respond.

That should be a little flapper valve I think on the drivers side that lets the engine heat up before it opens. Careful on removing the bolts...soak them with penetrating oil over nite. I had one break the ear off the exhaust manifold trying to get it off. I went with heddman headers for 1/2 of the price of a new manifold. Cut and reworked the crossmember and ran duals. Now if they need replaced I won't have to get anything special just straight back.

The flapper is the heat riser valve. In very early cars it was controlled by a thermostatic spring. Later it was vacuum controlled by a vacuum pot on the side of the engine. The vacuum was controlled by engine manifold switched on and off through a thermo vacuum switch mounted on the intake manifold, or the thermostat housing. The flap shut when the engine was cold, and opened when it warmed up.

When it became vacuum controlled it was then called an EFE valve. Early Fuel Evaporation valve.

When cold it restricted exhaust flow on one side of the engine. This forced hot exhaust up into the intake manifold, across the manifold, and out the other side into the exhaust manifold and out the pipes. The hot flow was used to heat the intake manifold and intake air. That caused the fuel to evaporate sooner. This improved cold driveability and helped the engine warm up faster, with fewer emissions. The same passage through the intake is what feeds the EGR valve.

When the engine warmed, and the flap opened, there was equal pressure at both exhaust manifolds, and the flow across the intake stopped, and stopped heating. If the flap stuck open, cold driveability suffered. Cold emissions went up. When stuck shut the restriction would cause some hard acelleration power loss, and could overheat the intake air and fuel. This could make the car run poorly and cause fuel boiling in the carb. This could lead to vapor lock.

If you need the heat riser valve depends on what exhaust system you use. Most of the time it will stay in place.

Ken Styer