Heat riser question

[mcditalia]

My Corvette never gets driven in the winter here in the east coast. Can i just take out the heat riser without making modifications (block off passages) in the intake manifold?

im also assuming that the heat riser moves back to the closed position ( outside lever in a horizontal position) and should move down ( vertical) when throttle is applied? When cold this lever will not snap back after being pushed down by hand.

 

[haganml]

The 3 inch tall valve in the passenger side exhaust is there to hold positive gas pressure in that side of the exhaust manifold to allow the heated exhaust gases to flow through the metal tube in that exhaust manifold to the choke mechanism. The heated exhaust gases were routed under the plenum in the intake manifold to help with fuel atomization with extreme winter temperatures.

As for testing that valve. Always check that valve with a hot and running engine. As you add throttle the valve should open as you have described. As soon as the engine returns to idle that valve should almost close and bob up and down slightly as the exhaust pushes past the butterfly plate.

If you want to remove that valve you should install an electrically heated choke (Holley part No. 45-224) to maintain the proper choke operation. The fuel injected engines did not use that heat "riser" valve and there is a spacer available that will eliminate that valve allowing you to use your existing exhaust system (and the long bolts in your stock manifold).

"Block off" plates in some intake manifold gaskets will stop the flow of exhaust gas under the intake, but you may find some cold run issues will happen.

So, install a electric choke, replace the valve with the fuel injection spacer part, and change out the intake manifold gaskets for some after-market "performance" gaskets that will block that passage. The electric choke should take care of the start-up and cold run in your scenario of always warm weather starts and driving.

You really do not have to block the passage under intake manifold, without that valve very little of the exhaust will flow from one side to the other.

Mark.

 

[mcditalia]

Already have an electric choke set up, so it seems the the only benefit would be to help the fuel atomization in cold weather which wouldn't effect me anyway.

I sprayed the outside pivot point for the valve with WD40 and now seems to be rotating more freely,swinging back to the closed position when cold, although i realize that i would have to take the valve completely out and lubricate it on the bench for best results.

 

[haganml]

Already have an electric choke set up, so it seems the the only benefit would be to help the fuel atomization in cold weather which wouldn't effect me anyway.

I sprayed the outside pivot point for the valve with WD40 and now seems to be rotating more freely,swinging back to the closed position when cold, although i realize that i would have to take the valve completely out and lubricate it on the bench for best results.

The exhaust system is subjected to a great deal of heat, WD40 is a great product with millions of uses. It will burn off of your exhaust system in short order. The best choice is a dry molybdenum disulphide product (enter Moly spray on Amazon.com). the vehicle drys off and leaves a coating of molybdenum on the metal. Great high temperature moving part lubrication product.

Mark.

 

[JohnZ]

GM dealers have a product made specifically for heat risers - it's called "GM Exhaust Heat Riser Valve Lubricant"; if one is stuck, it will usually loosen it and keep it operating properly.