Knock Retard After 1.9 Rocker Install

[L67PSI]

Hi all,

Looking for some advice after installing 1.9 Mace rockers on a VT L67. I did a data log Friday with standard 1.65 rockers and no knock retard, temp was about 33c. Then Saturday I installed the 1.9 Mace rockers, same tune & up temp was better at 29c. Then i had 5 degree knock retard and even more in another data log upto 11 degreed. See screenshots

log_standard_rockers.jpg

after mace rockers.jpg

I am running 98 RON mixed with a small amount of E85 to make 10% ethanol mix. Yes, I've checked the ethanol content so not guessing here. However I have no wideband installed currently. I did fatten up the PE multiplier (RPM) to add extra fuel.

Could this be a case of false knock? Due to more valve train noise?

How would you approach this? Pull timing first? Run again with supercharger belt off?

Thanks

[vlad01]

Yes, could very well be false knock. Did you upgrade the springs as well? if not I highly suggest you do or else the stock springs break pretty quick with 1.9 rockers as they tend to float and suffer harmonics with 1.9.

[immortality]

10:1 commanded AFR is bloody rich.

If it was a valve spring issue I would expect to see it happen at the top of the rev range in each gear at similar RPM but it only occurs in what I assume is 1st gear.

Looking at the commanded AFR, it goes richer at 7:22.5 which is exactly the same time it starts to pull timing. Lean it out .5 AFR and see what it does.

Might also pay to confirm commanded to actual AFR.

[vlad01]

Not necessarily, the rate of rpm change can effect noise output of the engine and other parts. I noticed this in my VR, kept getting false knock in first and sometimes on the gear change into 2nd. Even if I pulled the timing back from 27º all the way back to 9º it still happen. Knock ears confirmed it was just engine and gearbox noise, exhaust etc... there was no knock.

I always disable knock these days and tune in a few deg of safety margin using knock ears on the dyno.

[immortality]

It could be but I've been running 1.9 rockers with stock springs and I'm not getting knock at those RPM's.

The OP fitted the rockers and added more fuel to the tune so I'd take the extra fuel out first before looking at the springs as it's an easy test.

[Charlescrown]

I think if Kojab tunes in he'll tell you what he found with his car. I think the rockers were bottoming out on the studs.