Strange exhaust issue -'63 R1

[Hogtrough]

My '63 R1 Avanti has distinctly lower pressure from the driver side exhaust pipe - probably a third of the velocity of the passenger side. I checked Youtube and found various ways of checking for exhaust restrictions, including using a thermal imagining camera . Don't have one, but used my trusty laser thermometer instead. The results were rather dramatic: Driver side muffler 104 degrees, can easily hold my hand on it. Passenger side over 300 degrees, hot stove territory. This is a fully rebuilt engine that runs (in my opinion) very strong. What could cause this?

[mfg]

That’s odd!…. It’s usually the driver’s side that runs ‘hotter’ due to the heat riser valve, located in the exhaust system directly under the passenger side exhaust manifold, diverting exhaust through the intake manifold and into the driver’s side exhaust manifold.

This would remain true until the valve fully opens and then the exhaust temps basically equalize.

Did someone install the heat riser valve on the wrong side?

Short of that, there must be a restriction of some sort somewhere in the driver’s side of the exhaust system.

[Hogtrough]

I was. thinking the same thing and went out and looked, but very hard to tell from the top. Will jack it up tomorrow and find out.  I'm going to start measuring the temp at the manifold and see if somewhere down the line it suddenly changes

[Hogtrough]

Went ahead and checked. Temp at the manifold collector drops from over 300 degrees to 100 or so in front of the muffler. 

[mfg]

44 minutes ago, Hogtrough said:

I was. thinking the same thing and went out and looked, but very hard to tell from the top. Will jack it up tomorrow and find out.  I'm going to start measuring the temp at the manifold and see if somewhere down the line it suddenly changes

Good thought!

[Hogtrough]

Went ahead and did that. Exhaust manifold itself is around 275-300 degrees, exhaust pipe only a foot away or so is 110. DId they typical vacuum test for restricted exhaust and it showed no problem.