Can someone describe to me the symptoms of valve float? I understand that it is the inability of the springs to close the fast enough at high RPM, but how do I know when it is happening?
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
Found this:
Adding a turbo system, nitrous or anything that can increase the rpms of your engine over the stock "limits," the pushrods have a tendency to lose contact with the cam lobes (via the rocker arms) because the valve springs are not strong enough to overcome the momentum of the engine on the valve train components. This is commonly referred to as valve float, when the valves fail to completely close during the compression stroke, and/or can sometimes bounce off of the valve seat as it tries to follow the profile of the cam. An engine suffering from valve float has a characteristic sound; the engine will begin to cut out, making a rumbling noise. Valve float causes loss of power and usually leads to engine damage.
One way to combat valve float at high rpms is to add stronger springs, which will overcome the force of the valves being slammed shut as well as it bouncing off of the seat.
All that is interesting but I wonder about the 4,500 RPM number, isn't that lower than what a stock spring should handle? I wonder about your unknown cam, if it's an RV cam, wouldn't it be ground for low rpm and high torque. I wouldn't think you could go much beyond 4,500 with a RV engine. Don't know for sure, just a guess.
<span class='smallblacktext'>[ Edited Sun Nov 06 2005, 03:34AM ]</span>