Hey Guys, I'm in the process of removing the thermactor bump on my 289 heads. Is it safe to do this with the heads on the engine( On a engine stand)? If so, what can i stuff in the exhaust ports to prevent shavings from entering?
Thanks!
If oyu're going to do this, do it with the engine upside-down and use a vacuum to remove any filings left afterwards. Also leave the rocker arms loose as to insure the valves are all closed while you remove the bumps. A pass with a retriever magnet in the ports wouldn't hurt either.
less than 5hp increase, if any, if your engine is all stock. I wouldn't even bother doing it.
But if you do, do as Hearne says, I would add that you should stuff a paper towel in the exhaust port, and make sure the vacuum is running while you are grinding.
I would not mess with it and if I did I would not remove it. I would blend it. Make it look like an aerodynamic bicycle helmet so there is less disturbance on the back side of the valve. The worst part of the port is between the valve seat and the the bump.