Power loss at 6250rpm for no obviously reason!!!

[rally1]

Hi there Guys, I have a 2003 VY Holden that I have fitted a 232 232deg .600 .600 cam, double valve springs, 80mm throttle body over the radiator intake, headers and mafless tune, the first problem was the new Capa OTRCAI was not up to the job at WOT the map was around 88-92, once I removed the filter it was back up to 100 so a better intake is on the cards.
My main problem is that when on the dyno ever time it reaches 6250rpm there is a massive loss in power that then picks back up just before the limiter at 6650rpm, at the same time as the power loss (spot on 6250rpm) the knock sensors pick up and set knock retard to around 1.5 deg this happens regardless of timing I have tried anywhere from 12 to 28 deg (locked timing) and there is absolutely no knock at all until exactly 6250rpm ever time which makes me think its false knock, I have also tried any where from 11.25 to 13.1 a/f ratio with no change in the dip in power and the knock still kicks in at 6250 ( the injector duty does not go over 88%). The VE map is dialled in burst knock of ect ect. I’m staring to think it may be mechanical such as valve train float that is then setting off the knock sensors, has any one seen this problem before as im really starting to pull my hair out.
Thanks in advance for any help on this matter.

[The Alchemist]

push rod deflection on the cards at that lift.
Could have told you about the OTRCAI they are ok to a point but pull a vacuum at higher HP numbers.

Mike

[SSbaby]

Have you tried flashing in an older (proven) tune to see if the results are the same?

[rally1]

Hi there Guys,
Yes I have tried a few different tunes with no change at all, I have also ordered new push rods knowing that they are the weak link in this set up but was unsure if that was the problem due to the fact that power comes back up just before redline, I really don’t know to much about push rod defection and how bad the effects can be but would assume that it would get worse with higher revs is this not the case?
This is the first time I have used the capa OTRCAI on a big cam engine and the filter they ship with it is not up to the job (a blue filter) I have never had a problem with OTRCAI that use K&N filters so will go back to them, with no filter the power went up buy 10rwkw at 2000rpm all the way through to 26rwkw at 6000rpm!! Thanks for taking the time to look over my question guys its much appreciated as I need all the help I can get on this one..

[SSbaby]

Maybe post a scan up?

[rally1]

I will try and do that soon, in saying that the saved files I have only have limited pids as I was trying to check as many as I could and I only saved a few, the customer is from out of town and will not be back till Saturday when I can save some decent logs. Thanks.

[rally1]

You will see I have a dead B2 O2 sensor, that fault only appeared half way through testing and I rest the fuel trims before every run to ensure it was not effecting the fuel mixture. This test was done yesterday being Sunday so I was not ably to get a new sensor.

[rally1]

Hi again, could I have weak spark as it starts to fail just as it is reaching peak cylinder pressure, Has anyone had a similar problem with spark on LS1 engines??

[joecar]

What wires are you using...?

[The Alchemist]

peak cylinder pressure would be be at peak torque around 4500 +/- 500rpm.
This is where spark issues would usually show up.
Unlikely to be your problem...

Mike


Hi again, could I have weak spark as it starts to fail just as it is reaching peak cylinder pressure, Has anyone had a similar problem with spark on LS1 engines??

[Delco]

We normally see that dip and recover when valve spring issues raise there head

[rally1]

It is running the factory leads and new GM AC plugs, are they an issue with bigger power GenIII we have around 270rwkw when it losses power.
I had wondered about the valve springs and contacted the supplier a few days ago for more info on them, they a double springs with an installed pressure of 135 @ 1.8 I think they may be Comp Cams sold under a different name. I could not check the installed height at assembly as the retainers would not fit in my height checker, at the time I “assumed” (the mother of all F%$# ups) it would be all right but im kicking myself now for not finding a way to check them, the suppler said it would not be springs due to the fact the power comes back up, have you seen this before Delco? If so we do have a set of Air flow research valve springs we could try.
I have included a few dyno runs the AFR is very rich but there is no difference in the point of the power drop from the earlier posts that have a smooth AFR of 12.9-13

[Delco]

It is running the factory leads and new GM AC plugs, are they an issue with bigger power GenIII we have around 270rwkw when it losses power.
I had wondered about the valve springs and contacted the supplier a few days ago for more info on them, they a double springs with an installed pressure of 135 @ 1.8 I think they may be Comp Cams sold under a different name. I could not check the installed height at assembly as the retainers would not fit in my height checker, at the time I “assumed” (the mother of all F%$# ups) it would be all right but im kicking myself now for not finding a way to check them, the suppler said it would not be springs due to the fact the power comes back up, have you seen this before Delco? If so we do have a set of Air flow research valve springs we could try.
I have included a few dyno runs the AFR is very rich but there is no difference in the point of the power drop from the earlier posts that have a smooth AFR of 12.9-13

Classic valve bounce graph , if it was exhaust or intake restrictions it wouldnt recover power.

seat pressure has nothing to do with it , it is a harmonic frequency thing

[rally1]

Thanks Delco I will fit the Air flow research valve springs and see what that does, Thanks again for your input its much appreciated. :)

[rally1]

Hi all, well we got the car back 2 day and checked the seat pressure at 1.8’ and it was only 110 instead of the specked 135, we had to fit .070 shims to get it up to the 135 but once back on the dyno the power dip was gone:) , we are going to fit new springs as we don’t like the idea of .070 shims as it is staring to get close to coil bind with the .600 lift cam. I have learned a big lesson from all of this and will always check my seat pressure from now on. Thanks to all that had input on this fault it was very much appreciated :cheers: