black_knight

iTrader: (1)

Right after 5400 RPMS!

Car has stock heads and cam; mods in sig.

black_knight

iTrader: (1)

Compare this to my friend's graph: he has similar mods and his is nice and smooooth.

NLang

iTrader: (12)

I'd check out those springs of yours-looks like valve-float to me...Good luck bud.

black_knight

iTrader: (1)

Yeah, I was thinking "valve float," but they're stock springs and a stock cam. Granted, there's about 70,000 mi on 'em. Is it likely to be valve float?

Parks02WS6

I don't know what else it could be. I thinking the same thing but they shouldn't be floatin till up around 6,000 but you never know...

NLang

iTrader: (12)

That's all going to depend on how tired the springs are. The average LS-1 enthusiast really uses their LS-1 pwr...It's definitely not uncommon to wear out the factory springs with a factory cam-been there, done that...

niphilli

Do you have access to any diagnostic software? Looks to me like your CPU is pulling a bunch of timing? Could be float I guess but most of the float cases I have seen just level out on power (no drastic 25RWHP drop)?

black_knight

iTrader: (1)

Someone told me it might be sone K&N oil on my MAF... does it look like that to any of you?

XTrooper

If the PCM were pulling timing due to KR it would also richen his A/F mixture to overcome the perceived lean condition and his A/F ratio is constant during the pull.

Whatever the problem is, it's almost certainly mechanical in nature. I'd start with the valve springs.

P Mack

iTrader: (6)

It doesn't look like a MAF problem because your air/fuel is good.

pkincy

iTrader: (1)

Very, very common on stock om mildly modded LS1s. I was never completely able to figure out the root cause but was able to tune it out with LS1Edit. Generally happens around 5500 rpm.

Perry

pkincy

iTrader: (1)

[QUOTE=XTrooper]If the PCM were pulling timing due to KR it would also richen his A/F mixture to overcome the perceived lean condition and his A/F ratio is constant during the pull.

Since when does the Knock Retard circuit add fuel?

Perry

Kalijah98z

When i got my car tuned, it made the same "hickup" around 6200rpm and it was due to a loose connection on the plug wire. That maybe the case, but timing also sounds more feasable, b/c of how much the curve dove down.

NLang

iTrader: (12)

First guess, I say it's week springs causing valve float, or maybe even a bent p-rod. My second would have to be with niphilli-a kr issue. Or possibly float or a p-rod banging and causing kr. That'd do it for sure.

niphilli

[QUOTE=Perry Kincy]
I have never heard of this either, want to elaborate on this trooper?

Gman2002Z06

It's not valve float...If it was vlave float, the power after the anomaly would not come back up...i.e. your power would drop totally off after 5400rpms...

What it is is this...SPRING SURGE...It a harmonic (vibration) problem that alot of the stock springs are afflicted by...

In effect what is happening is this...The spring starts to vibrate in an uncontrolled manner at a specific frequency...Usually around 5400~5600 rpms...The spring looses it ability to control the valve totally, thus, you loose power in that cylinder...This vibration only lasts for a fraction of a second and then the frequency of the motor changes and the spring once again works as usual...

I had this exact same thing on my '00 FRC...5400~5600 would drop 20 rwhp, hen it would come back to full power instantly...I tried everything under the sun to correct the problem...

Finally swapped the valve springs out for a set of LS6 springs...And the dip was gone forever...

Peace...Gman

black_knight

iTrader: (1)

I think I will be doing a cam swap and maybe getting the heads ported. If it is a valve issue then that would get it.

Maybe soon I will check the spring pressures. What should they be?

Gman2002Z06

Spring pressure has nothing to do with the problem of spring surge...The springs will check 100% fine...Problem occurs due to the vibration of the engine and a particular, individual spring starting to vibrate at its natural frequency...All springs, brackets, etc. have a natural frequency that they will vibrate at...Designers try to design around this by adding ribs, supports, anything to change an items natural frequency so that it does not occur at the vibrational frequency's that the engine produces...Unfortunately, they cannot control it totally...Dual springs work great at reducing this effect, because each spring is designed to have its natural frequency at a different value, i.e. one spring may have its N.F. at 500hz, while the second spring may be at 700hz, so the springs shouldn't vibrate at the same period in the rev range...

Do at least a spring change and you will see the dip vanish...

Peace...Gman

black_knight

iTrader: (1)

Thanks, Gman!