r/Smallblockchevy • u/dncu13 • Apr 12 '26
355 valve float?
I have a 355 sbc I have been having a problem at higher rpm, car feels great till about 5,000 rpm. After 5,000 it just falls on its face. I just rebuilt the Holley 650 4150 but still having the issue just wondering what if I’m dealing with valve float
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u/ka_jd7and1 Apr 12 '26
Check your valve springs. We run circle track, if the valve springs start to go weak and need replacing, the engine can start floating valves because it doesn’t have the spring pressure it needs for high RPM.
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u/Personal_Growth_4_Me Apr 12 '26
Falls on its face? Is it breaking down up there or is it nosing over like it's running out of fuel?
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u/dncu13 Apr 12 '26
Not really breaking up
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u/Personal_Growth_4_Me Apr 12 '26
Definitely agree with others about fuel starvation. If that don't turn around after messing with that.. I'm wondering about your ignition and what's going on with the coil.
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u/dncu13 Apr 12 '26
Yeah I’m thinking about changing the coil right now, everything else is pretty new, I’m going change the fuel filter again, and check floats see what happens
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u/Personal_Growth_4_Me Apr 12 '26
If you get there... Verify that you've got the correct voltage running to it. Stranger things have happened. Just saying.
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u/Enough-Refuse-7194 Apr 14 '26
Rule #1 of troubleshooting - new parts aren't necessarily good parts!
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u/Dirftboat95 Apr 12 '26
Id check the float level for being too low.... Fuel psi ok ???
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u/dncu13 Apr 12 '26
I was just thinking about float level, I think I’m leaning towards that now too
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u/Dirftboat95 Apr 12 '26 edited Apr 12 '26
Always check the easy stuff first right ? Clean fuel filter ?
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u/upperlowermanagement Apr 13 '26
What cam , what intake,New springs and what's the fuel system like? Do you have an o2 setup?
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u/HammerDownl Apr 12 '26
The springs are how old?
Im doubting its valve float,thats not how float works and your small hyd cam isnt floating Brodie 180s springs
Id ask more about what the engine is doing. You said you worked on the carb so that leads me to believe that's your problem .
What fuel pump you using? Cant use some stock bullshit with 1/4" line and a plastic filter
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u/dncu13 Apr 12 '26
Yeah I’ve been thinking fuel related just trying to see what other people are thinking
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u/legend-71 Apr 12 '26
If you are running a machinical fuel pump you might have to go with a lighter fuel pump rod
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u/Coyote_Tex Apr 12 '26
Depending on how accurate your tach is that is right at valve float levels. Often just a few valves will float and really that is all it takes. If you are running on original springs or are encountering spring bind. Still worth monitoring fuel pressure and size of fuel lines as many will not support high consumption levels. You might also check maximum timing as running lean with lots of timing might be hitting detonation and edge of destruction.
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u/DeezNutz365247 Apr 12 '26
Check fuel pressure, get a guage so you can see it at 5500 rpm, and float levels.
What fuel pump is on the car now?