Dyno Dip at 5,300 rpm. Tuner is perplexed.
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The graph shows the HP and TQ dipping at 5300rpm. It lasts for 150 rpm where it picks up where the curve would be if there hadn't been a dip.
I asked if there was knock and pulling of advance and they said no.
What could be the cause of the dip. I don't want to lose power momentum.
Any suggestions as to what to look for or appropriate Questions to ask.
Steve
Car:
'02 LS1 TA
Heads Cam Headers, 85 mm MAF, Harland Sharp RR, Fast 90mm intake and TB
Right now it peaks at 425 RWHP; 393 RWTorque
I asked if there was knock and pulling of advance and they said no.
What could be the cause of the dip. I don't want to lose power momentum.
Any suggestions as to what to look for or appropriate Questions to ask.
Steve
Car:
'02 LS1 TA
Heads Cam Headers, 85 mm MAF, Harland Sharp RR, Fast 90mm intake and TB
Right now it peaks at 425 RWHP; 393 RWTorque
Last edited by steve-d; 11-09-2004 at 10:05 AM.
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You can get into resonances on the dyno that
just freak out the machine. If the line is jagged
rather than smooth this is likely. The dynos I
think have to a lot of "funny massaging" of the
load roller data to make things even look clean,
anyway. Though it would be interesting to see
the dyno curve lined up with wideband meter
and any logger data for spark etc. my first guess
is just the mechanical resonance or something like.
just freak out the machine. If the line is jagged
rather than smooth this is likely. The dynos I
think have to a lot of "funny massaging" of the
load roller data to make things even look clean,
anyway. Though it would be interesting to see
the dyno curve lined up with wideband meter
and any logger data for spark etc. my first guess
is just the mechanical resonance or something like.
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I looked at the pic, the AFR is not perturbed. I
still suspect it's the dyno getting jiggy and the
smoothed result is just off. Is this a repeatable
characteristic? Does the tuner give you any log
files to review for PCM abnormalities / complaints?
still suspect it's the dyno getting jiggy and the
smoothed result is just off. Is this a repeatable
characteristic? Does the tuner give you any log
files to review for PCM abnormalities / complaints?
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Yes, they are cro-mo comp cams push rods.
Steve
Steve
Originally Posted by WAHUSKER
Bent pushrods can cause this. But judging by your setup, you must have chromolys.
Last edited by steve-d; 11-09-2004 at 04:42 PM.
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Burst knock should only trigger on a large
delta CylAir and this is not where I'd expect
to see it (steady wide open, the only thing
that can change CylAir is a very sudden
change in volumetric efficiency).
Though timing logs sure would have value in
this case.
delta CylAir and this is not where I'd expect
to see it (steady wide open, the only thing
that can change CylAir is a very sudden
change in volumetric efficiency).
Though timing logs sure would have value in
this case.
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What kind of dyno? I used to have a dynojet with inductive pickup and it would do all kinds of things like that. Whats wierd on the dynojet is if the inductive pickup signal
hicups both the torque and hp curves are effected. I now have a mustang eddy current dyno and we use only optical pickup, which is very accurate and noise free
with no more problems like you mentioned. I am not putting down dynojet, but run the dyno in horsepower mode only, no pickup and if the problem goes away you in.
hicups both the torque and hp curves are effected. I now have a mustang eddy current dyno and we use only optical pickup, which is very accurate and noise free
with no more problems like you mentioned. I am not putting down dynojet, but run the dyno in horsepower mode only, no pickup and if the problem goes away you in.
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Mine has the same prob changed everything even got an msd 6a its the opti.... ill send you some dyno graphs after my 410.s installed my dyno sheet was 309 338 tq... this one was 298 328torque after 410s I compared and same dip results....oh yea i have all boltons, norr no heads or cam...
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I can't believe nobody has said it, but I'm betting its valve float. This is quite common in LS1s with weak/worn valvesprings, and always happens at 5300. I've had it happen twice with other LS1 combos I've had and it was always valve float.
You might do a search on "Dyno Dip", possibly in the internal engine forum.
You might do a search on "Dyno Dip", possibly in the internal engine forum.
#13
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Originally Posted by Nine Ball
I can't believe nobody has said it, but I'm betting its valve float. This is quite common in LS1s with weak/worn valvesprings, and always happens at 5300. I've had it happen twice with other LS1 combos I've had and it was always valve float.
You might do a search on "Dyno Dip", possibly in the internal engine forum.
You might do a search on "Dyno Dip", possibly in the internal engine forum.
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Originally Posted by Nine Ball
I can't believe nobody has said it, but I'm betting its valve float. This is quite common in LS1s with weak/worn valvesprings, and always happens at 5300. I've had it happen twice with other LS1 combos I've had and it was always valve float.
Thanks much for the input. Your great. I hadn't considered valve float, especially since the curve picks up past the dip and continues to 6400 rpm. I suppose it'd only take one or two valves to do that at a specific rpm to have an effect.
Harmonics, I suppose it could be a factor. How to check? Swap out balancers? Prior pulls months ago w/the same balancer didn't show any dip. Isn't it possible for them to "wear out" depending on the material in them?
Valve geometry? When I installed the Harlan Sharp RR and the hardened push rods, I made sure the roller tip was properly centered over the valve stem as the engine was rotated over by hand. I also used a push rod length checker. They appear to be the proper length. But I could check them (16!!) again if anyone feels there's the likelihood of a bent rod.
Thanks again. Much appreciated. If anyone needs to see the graph I could email it. I just can't post it.
Steve
I can't believe nobody has said it, but I'm betting its valve float. This is quite common in LS1s with weak/worn valvesprings, and always happens at 5300. I've had it happen twice with other LS1 combos I've had and it was always valve float.
Originally Posted by Another_User
Good call. I forgot about that one. Better yet, valvetrain geometry and/or harmonics.
Harmonics, I suppose it could be a factor. How to check? Swap out balancers? Prior pulls months ago w/the same balancer didn't show any dip. Isn't it possible for them to "wear out" depending on the material in them?
Valve geometry? When I installed the Harlan Sharp RR and the hardened push rods, I made sure the roller tip was properly centered over the valve stem as the engine was rotated over by hand. I also used a push rod length checker. They appear to be the proper length. But I could check them (16!!) again if anyone feels there's the likelihood of a bent rod.
Thanks again. Much appreciated. If anyone needs to see the graph I could email it. I just can't post it.
Steve
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It's called spring surge...I had it on my '00 FRC...At 5600 rpms, the hp would fall off 25 rwhp, for about 200 rpms, then it would be back just as fast as it went...before I figured out what it was, I had spent alot of money on different mods and Dyno tuning...
To solve the proplem, I bought a set of LS6 valve springs...Replaced them in the driveway and the hp dip was gone...There had to be one of the 16 valve springs that was acting up...And thus caused one cylinder to drop its power for just a fraction of a second...But long enough to be noticealbe under WOT on the road...
May want to try a different style or set of springs...
Peace...Gman
To solve the proplem, I bought a set of LS6 valve springs...Replaced them in the driveway and the hp dip was gone...There had to be one of the 16 valve springs that was acting up...And thus caused one cylinder to drop its power for just a fraction of a second...But long enough to be noticealbe under WOT on the road...
May want to try a different style or set of springs...
Peace...Gman
#17
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Originally Posted by Gman2002Z06
It's called spring surge...I had it on my '00 FRC...At 5600 rpms, the hp would fall off 25 rwhp, for about 200 rpms, then it would be back just as fast as it went...before I figured out what it was, I had spent alot of money on different mods and Dyno tuning...
To solve the proplem, I bought a set of LS6 valve springs...Replaced them in the driveway and the hp dip was gone...There had to be one of the 16 valve springs that was acting up...And thus caused one cylinder to drop its power for just a fraction of a second...But long enough to be noticealbe under WOT on the road...
May want to try a different style or set of springs...
Peace...Gman
To solve the proplem, I bought a set of LS6 valve springs...Replaced them in the driveway and the hp dip was gone...There had to be one of the 16 valve springs that was acting up...And thus caused one cylinder to drop its power for just a fraction of a second...But long enough to be noticealbe under WOT on the road...
May want to try a different style or set of springs...
Peace...Gman
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99% it is the valve springs. It is likely only one cylinder bugging out, but thats all it takes.
If you log your O2's, you will likely see lean dips on the bank that is floating.
Chris...
If you log your O2's, you will likely see lean dips on the bank that is floating.
Chris...
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Steve, I am the one who tuned your car. If I remember, you had an HS rocker C-clip break correct? I would look at the rockers first. I'm not a big fan of the HS rockers. Try and put the stockers back on. Takes 1 hour to do. Make sure the pre-load is correct. Then look at the valve springs. They are SLPs? SLP uses Manley singles which I've seen work just fine. If the rockers do not cure the problem, replace the springs with with Comp 918s or Crane Duals. I've seen float before, this is not float but rather a harmonic of the present valvetrain.
There were no air/fuel or timing anomolies that caused this. It is 100% valvetrain related.
Mike
There were no air/fuel or timing anomolies that caused this. It is 100% valvetrain related.
Mike
Last edited by mikey; 11-13-2004 at 10:13 AM.