67 twin turbo dart
The motor that was in the car and I took out when I sold it to you had the same problem. The rings didn’t seal correctly on the Dyno. I tried a lot of things like you did and none of it worked. I didn’t have to change any of my gaskets though put a GZ vacuum pump on it. Problem fixed.
Same motor that is now single blow through CSU e85 custom built Carb. Four bowls and four Needle & seats. The vacuum pump is under the driver side blow off valve.