Been trying the stub stacks almost an entire season. I did add bowl vent tubes. My theory was that the air flow wentover the stock vent holes dropping bowl pressure. For sure they have a better shape than just cutting off the choke horn. It helped in the early part of the run. 660 mph gained close to 1mph.
Doug
My machinist uses those on his 2.5 liter hydroplane engines that run 500 Holley 2 barrels. He plays with the profile on the flow bench to max it out.
It makes a statistically significant difference on the dyno.
Kevin
