floating valves?

[shadowjeep]

i have heard people say they have heard of someone floating the valves when the rpms were so high. can someone explain this to me, just what is this and what happens inside the heads and combustion chambers when this happens?:confused:

[Elliott]

At high rpms if you don't have enough seat pressure from good springs, real good springs, the valves float at open and don't fully close. If your valve train isn't designed for high rpms (or what is considered high rpms for American short stroke motors) you can suffer alot more then just valve float, ie busted parts which you are gonna hope don't drop into your cylinder or slap a piston. I had triple Isky valve springs on my lil TR4 that would allow me to run well past 8grand, and wrap the tach without valve float.

[8379qtj10]

That TR motor will scream then!!!!
Valve float losses a ton compression and blows intake gaskets on turbo cars I have tunned on. Oh can't forget that slapping the piston thing that Elliott talked about.

[Elliott]

Yep, solid lifters are sweet!

[Lazarus]

like elliot said, my analogy would be like a ball in a swimming pool, if you push the ball down fast enough you can push it down again without it hitting the surface, then try that with like a basket ball, the latger ball would be like having stronger valve springs, it is much harder to keep the ball down just like it is much harder to float the valves with stronger springs....

[byson1]

The rpm "redline" that most manfacturers state for their motors is the point the engine starts to float the valves. The rpms are so high that the valves don't have time to fully close before they are being pushed open again.

[shadowjeep]

in other words, when the valves start to float you loose compression and run the possiblity of blowing gaskets and the risk of detonating your engine.

[Elliott]

Just loss of power really, your compression will go out the exhaust. Your timing will not be effected.

[shadowjeep]

i think i understand now, its more like a rev limiter than anything. once you max out the rpms you just loose power. provided you engine can take the abuse at those rpms anyway.:D

[rockjeep44]

I found out 2 weekends ago that my 360 floats the valves just over 6500rpm. You can actually hear it in this video...

http://www.rebelrockrunners.org/andrew/valve_float.wmv

And here, I hit 6400rpm without valve float
http://rebelrockrunners.org/gallery/d/17830-1/andrew.wmv

My next motor will still be an AMC but will be more capable of the high RPM action. I am still extremely happy with the abuse this one has taken. It is only mildly built and is still running great. Even after those antics.

[Desert Beast]

valve float? pshshshh

what about "lifter launch"? :thumbsup:

http://www.southbaycustoms.com/fullsizejeeps/lifterfd.JPG

6500 rpm up olds hill @ glaimis.
ill give it to the amc motors though, this still ran w/ 1 psi of oil for the rest of the day. didnt idle that great but it got me back.

[rockjeep44]

****, how long did you hold the 6500rpm? Mine is still running fine with good oil pressure.

[shadowjeep]

wow desert beast, i havent seen anything like lifter launch.

[shadowjeep]

I found out 2 weekends ago that my 360 floats the valves just over 6500rpm. You can actually hear it in this video...

http://www.rebelrockrunners.org/andrew/valve_float.wmv

And here, I hit 6400rpm without valve float
http://rebelrockrunners.org/gallery/d/17830-1/andrew.wmv

My next motor will still be an AMC but will be more capable of the high RPM action. I am still extremely happy with the abuse this one has taken. It is only mildly built and is still running great. Even after those antics.

cool vids, at least now i know what it sounds like.

[Desert Beast]

****, how long did you hold the 6500rpm? Mine is still running fine with good oil pressure.
haha, not long after that happened. :drivin:

olds is a pretty big and steep hill, so i wasnt going that fast, mainly just spinning all 4 creeping up the hill.

it was rocker arm failure that caused the lifters to be able to leave thier bores. just make sure you check you rockers.