P.Dow, I'm not a professional mechanic but in my opinion the heat riser is a useful device because it helps an engine to warm up quickly. The sticking heat riser is a problem that I have also had on two of my vehicles, a '71 Dodge van that I bought new and a '36 Chevy pickup that I restored in the early 1970s. I still have both of these vehicles.
Well over 25 years ago I made a modification that has permenantly cured the problem. I drilled the heat riser shaft holes in the exhaust manifolds oversize and made and pressed in stainless steel bushings and I made stainless steel shafts for the heat riser valve. Now, there is nothing to rust and no sticking.
With regard to dual exhaust, when I built a dual exhaust for the van, which at the time had a bone stock 318 V8, fuel economy immediately increased by about 1 1/2 MPG. The dual exhaust incorporated an H-pipe, that reduces noise and according to performance experts also increases power. Not having a dynomometer, I can't comment on the effect of the dual exhaust on power.
If you want any details of the stainless steel parts I made please feel free to email me at
[email protected]. I hope this helps!
