difference between knock and valve float noise?
10-27-2002, 12:02 AM
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difference between knock and valve float noise? are the noises produced be valve float ( or maybe the valves slightly hitting the piston) similar to noise made by knock/ detonation???
10-27-2002, 10:52 AM
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Re: difference between knock and valve float noise? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 1dirtyZ:
<strong>are the noises produced be valve float ( or maybe the valves slightly hitting the piston) similar to noise made by knock/ detonation???</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">If the valves are "slightly hitting the pistons" you'll soon find out when you have to tear down the engine.
Valve float or "valve toss" is almost always a high rpm problem.
If the valves are hitting the pistons, you'll probably hear it at any rpm.
Knock or detonation is load (and rpm) sensitive. You usually won't have it under partial throttle conditions unless you have an old SBC with vacuum advance distributor.
If you have a steady metallic noise it could be in the valve train.
Have you changed anything recently in the engine?
<strong>are the noises produced be valve float ( or maybe the valves slightly hitting the piston) similar to noise made by knock/ detonation???</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">If the valves are "slightly hitting the pistons" you'll soon find out when you have to tear down the engine.
Valve float or "valve toss" is almost always a high rpm problem.
If the valves are hitting the pistons, you'll probably hear it at any rpm.
Knock or detonation is load (and rpm) sensitive. You usually won't have it under partial throttle conditions unless you have an old SBC with vacuum advance distributor.
If you have a steady metallic noise it could be in the valve train.
Have you changed anything recently in the engine?
10-28-2002, 12:03 AM
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Re: difference between knock and valve float noise? i see , the reason i'm asking is recently i increased the boost on my car and at high rpm's i start hearing something like detonation, but nothing comes shows on the scan tool as knock.
the car was dyno tuned with no problems like detonation. so i was thinking maybe it was valve float at high rpm and that causes the valves to slightly touch the pistons ( forged with reccess).
could that be the case or should i pull more timing?
the car was dyno tuned with no problems like detonation. so i was thinking maybe it was valve float at high rpm and that causes the valves to slightly touch the pistons ( forged with reccess).
could that be the case or should i pull more timing?
10-28-2002, 07:42 AM
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Re: difference between knock and valve float noise? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 1dirtyZ:
<strong>i see , the reason i'm asking is recently i increased the boost on my car and at high rpm's i start hearing something like detonation, but nothing comes shows on the scan tool as knock.
the car was dyno tuned with no problems like detonation. so i was thinking maybe it was valve float at high rpm and that causes the valves to slightly touch the pistons ( forged with reccess).
could that be the case or should i pull more timing?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">How much valve-to-piston clearance do you have?
If it's not at least .080 on the intake and .100 on the exhaust (checked with the cam advanced/retarded where it now runs), you might have problems. If you are tossing the valves .080 I'd say there are big valve train problems.
How aggressive is the cam? duration? lift? rocker ratio? what springs? How high are you revving?
As you suggested, pull back some timing and see if the noise goes away.
My $.02
<strong>i see , the reason i'm asking is recently i increased the boost on my car and at high rpm's i start hearing something like detonation, but nothing comes shows on the scan tool as knock.
the car was dyno tuned with no problems like detonation. so i was thinking maybe it was valve float at high rpm and that causes the valves to slightly touch the pistons ( forged with reccess).
could that be the case or should i pull more timing?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">How much valve-to-piston clearance do you have?
If it's not at least .080 on the intake and .100 on the exhaust (checked with the cam advanced/retarded where it now runs), you might have problems. If you are tossing the valves .080 I'd say there are big valve train problems.
How aggressive is the cam? duration? lift? rocker ratio? what springs? How high are you revving?
As you suggested, pull back some timing and see if the noise goes away.
My $.02
10-28-2002, 10:34 AM
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Re: difference between knock and valve float noise? i pulled 2 deg out and the noise went , so i guess i have enough piston to valve clearance. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
now i have to deal with valvetrain noise after WOT... <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
now i have to deal with valvetrain noise after WOT... <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
