For those that do not know the Dynomax VT muffler is a straight through with a spring loaded flap pushed open by the exhaust gas. This allows you to have a drone free cruise, but when you stand on the throttle, the flap gets pushed open, and the muffler flows and sounds like any other straight through.
The spring used in the muffler has 2 tensions available, one for small capacity engines and one for large. After doing a lot of reading up, I found that on a 4G63 the valve is open at highway speeds if the VT with the light spring is used, causing drone. I have fitted a VT with the heavier spring and it works great. It's nice and quite in the cruise (you can still hear the engine, think mild sports system) and the valve is fully open at large throttle openings by around 10psi.
But there is a problem. My cammed, 7.8 compression, 2 liter will not hold the valve off the stop at idle, it pulses it. This means the valve rattles terribly at idle. I have a solution that is only temporary at the moment. I have fired a screw up into the muffler, just behind the valve to hold it off the stop and dampen it with a bit of rubber over the screw tip. Unfortunately the rubber only lasts about 100km before it melts and you have a terrible rattle at idle again.
Does anyone have any suggestions for something that will dampen the rattle, and survive in the muffler in direct contact with the hot metal?
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