Valve Float - High RPM breakup

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Apr 18, 2010 | 08:09 PM

boosted4life

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From: Laramie, Wyoming - 7220' elevation

Valve Float - High RPM breakup

I was just wondering if anyone had an example of what valve float sounds like on an ls1? I think I am getting valve float but not sure because it feels pretty bad and I thought valve float would be more minor.. seems kinda like a bad misfire but only at about 4500 rpms and up.

It is a 98 ss camaro with a 99 firehawk ls1 engine, vortech g-trim on 7psi. Mild cam.. I feel stupid because I didn't even remember to change the valve springs when I put my cam in my new motor..

Apr 18, 2010 | 08:16 PM

G Engines

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It may have too much fuel at the uper rpms ?

Apr 18, 2010 | 09:17 PM

MrDavid

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Doesn't sound any different on my car which currently is floating valves at 5800. Just feels sorta like hitting a wall, so to speak, in the powerband. Loses 80rwhp within the next 500rpms, but never sounds any different.

Apr 19, 2010 | 08:40 AM

Sluggish

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From: Fannett, Tx

I think I have a valve float issue also, but my sympton is boosting falling off fast above 6000. When the car is super fat it will cut out like your saying.

Apr 20, 2010 | 12:59 PM

boosted4life

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From: Laramie, Wyoming - 7220' elevation

Ok so maybe it fell out of the tune somehow? Because the car does have a tune for the larger injectors but the gm dealer reset my pcm when I was having problems with it.. I figured the tune was hard flashed..

Apr 20, 2010 | 01:08 PM

98Z28CobraKiller

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You could be dropping a cylinder or blowing out your spark.

Apr 20, 2010 | 02:58 PM

MrDavid

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You aren't making that much boost so its hard to believe that you're blowing out the spark. What heat range plugs are you using?

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Apr 21, 2010 | 05:14 PM

Black_98Z

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Might want to close up the gap on the plugs. I had TR6's gapped around .035 and it was blowing out the spark at 10-12 psi over 5k. Switched to NGK br7ef plugs. On heat range colder and gapped to .027. Fixed the spark blowout issue.

Apr 21, 2010 | 05:16 PM

#10

MrDavid

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From: Upstate, SC

Quote:

Originally Posted by boosted4life

tr6 plug with no change in the gap from what they come at.

I ran TR6's with stock gap when I was making 7lbs and had no issues with blowout.

Apr 21, 2010 | 07:28 PM

#11

boosted4life

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From: Laramie, Wyoming - 7220' elevation

Yea im running 7psi.. I just want to know what valve float sounds like because that is the most likely situation right now with boost + cam + stock springs.

Apr 22, 2010 | 06:35 AM

#12

MrDavid

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From: Upstate, SC

If you really think you're floating valves, put your car on a dyno with a wideband and watch the air fuel when you get into the upper RPM band. It will probably dip down into the 10's and you will see a drop in power when you hit that certain RPM and the drop will be pretty substantial.

Apr 22, 2010 | 10:07 AM

#13

boosted4life

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From: Laramie, Wyoming - 7220' elevation

Quote:

Originally Posted by MrDavid

Well it just feels like it cuts out at upper rpm's.. it is not smooth at all. It definately seems like a misfire or fuel problem.

Apr 22, 2010 | 09:31 PM

#14

MrDavid

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From: Upstate, SC

Then you NEED to have your car hooked up to a wideband to accurately address the issue instead of doing all the guess work.

Apr 23, 2010 | 01:02 PM

#15

boosted4life

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From: Laramie, Wyoming - 7220' elevation

Quote:

Originally Posted by MrDavid

Then you NEED to have your car hooked up to a wideband to accurately address the issue instead of doing all the guess work.

Ok ill do that.

Apr 23, 2010 | 01:30 PM

#16

RS_SS69

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What are the specs on the mild cam? If this was DanDans motor the springs have almost no miles on them, If the cam is small grab a set of yellow valve springs from a z06 or get some Duals. Are you hearing a rattling sound at higher rpms? If so thats detonation not valve float.

Apr 23, 2010 | 01:50 PM

#17

hellbents10

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Quote:

Originally Posted by boosted4life

There is the problem.

Apr 23, 2010 | 07:18 PM

#18

boosted4life

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From: Laramie, Wyoming - 7220' elevation

Quote:

Originally Posted by RS_SS69

Yep its dandan's motor.. but I don't know what springs he had put in it, im just assuming stock.. I have the springs out of my old motor I can use, I think they are the z06 springs. The cam is .520 lift.

Apr 24, 2010 | 11:06 PM

#19

MrDavid

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From: Upstate, SC

Cam lift won't be as important as cylinder pressure pushing the valves open when you get into the upper rpm band where you make the most boost. You need some springs that are rated at or above 130lbs of open seat pressure.

Apr 26, 2010 | 05:14 AM

#20

Bob@BruteSpeed

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Quote:

Originally Posted by boosted4life

I'd get the car retuned before you ruin the engine. You should never have a dealer touch the pcm after the car has been tuned. Bob

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