TouringBubble

iTrader: (2)

Alrighty ... more random, unexplained knock. Don't you guys just love it?

The car is a '05 GSR. Cams, full exhaust, etc. The usual. EDM ROM for Tephra 5.1 with the USDM knock filters copied over (issue existed w/ EDM knock maps as well).

When cruising under partial throttle between 3500 and 4000 RPM it will spike HUGE knock ... sometimes 20 - 30 counts. Nothing audible. This also occurs randomly during pulls, but only if the pull is started below 3000 RPM ... got WOT at 3000+ the pull is clean.

Advancing or retarding timing seems to have no effect on the knock. Fuel is in check ... 11.2:1 on the installed Zeitronics WBO2.

Downpipe was hitting the front crossmember. We removed the bar and it seemed to make the knock less consistent, but did not rid it completely. The heat shield is noisy on the test pipe as well, but we weren't able to address that issue yet. That could still be the issue.

I'm afraid that it may be the clutch (ACT) or another element in the transmission as nearly every other culprit I can think of has been addressed. The only other time I've seen an issue this bad it was caused by MIVEC settings and was across the majority of the low range and very consistent. The fact that is disappears if you hit the throttle later is just baffling and makes me think it is resonance related. The cams are at 0º with stock gears.

Anyway, any help would be appreciated. I'd like to exhaust all possibilities before recommending a new clutch.

biggie5252

iTrader: (47)

Sounds very similar to the issue I'm having although mine doesn't spike that high, that I'm aware of/logged, and does it closer to 3000rpm. It doesn't do it if I give it a decent amount of gas or wot. It's the worst in 6th gear during light/partial throttle acceleration where I maintain a relatively constant boost.

I'm pretty sure I don't have any rattles. At least I don't hear any when I shake, beat the exhaust and IC piping. I've been running the same tune for quite awhile and this just started happening in the last couple few months. I also have an ACT clutch. Which one, I don't know. It was in the car when I bought it.

C6C6CH3vo

iTrader: (9)

Maybe at wot the noise drowns out whatever normal mild knock there is (which probably always exists from NOx) along with a blast of compressed intercooled charge.

MR Turco

iTrader: (16)

I would take care of the heat shield, like you mentioned, and go from there. I don't see why the clutch would make noise at a certain RPM and not others. I would think if it were the clutch it would make noise from off to on throttle at any RPM.

JohnBradley

iTrader: (30)

Which ACT? Sprung or unsprung? Aftermarket flywheel?

TouringBubble

iTrader: (2)

That's kind of the reverse of what is happening ... early throttle (100% @ 2500) shows the knock but later throttle (100% @ 3000) does not.

Aaron, I'll try to get that info. From riding in the car I'd think sprung. Not sure on the flywheel.

Another though is motor mounts. High throttle at low RPM stresses the mounts longer than a later throttle application. Torque also rises/peaks sooner. The catch is that is knocks under part throttle too and in the same RPM area.

C6C6CH3vo

iTrader: (9)

What cams are in the car?
Does anyone know if this same problem (80 -120% knock at part to moderate throttle < 3000rpm) has been witnessed with stock cams?

Depending on the cam profile, your basically shortening both expansion and compression strokes and it seems this would be more counterproductive at part load/low rpm.

I have exact same problem, GSC 272I/264E cams installed 55,000 miles ago.
Problem is intermittent and independant of the following:
intake/coolant temp
octane
three different single plate clutches (including stock)
timing/afr
mild changes of tranny oil (unconfirmed)
EGR (once closed recirc and no change)

Happens mostly in lower gears, between 200 - 800hz, and depends on certain throttle input. Typical knock is 3 - 10 counts

biggie5252

iTrader: (47)

I have Cosworth M2s. Your issue seem a little bit more inline with mine. Mine is also intermittent, but easy to reproduce. I don't know about octane changes as I generally use the same 3 stations (all shell). It definitely doesn't really respond to timing/afr either. I might try toying with Mivec and see if that helps.

TouringBubble

iTrader: (2)

Clutch info: ACT MB7-HDSS.

Stock Flywheel.

The owner confirmed that the knock issue didn't seem present before the cam install (he installed Tephra patch with the knock light on) so the clutch is pretty much taken out of the equation.

Cams are Revolver 262s I think. Stock gears. I'm starting to think we just need to roll back the cam timing about 2º on the intake side ...

dan l

iTrader: (3)

Were the HLA's bleed before the install of the new cam? What brand/weight of oil and what kind of filter is he using.

TouringBubble

iTrader: (2)

Lifters were bled. I believe he's using AMSOIL 10W-30 ... unsure of the filter.

dan l

iTrader: (3)

Do you have a stethoscope or even a vacuum line pushed over an intake manifold stud to listen to the motor? I've gotten rid of similar knock with an OEM filter and heavy oil, like 15w/50 mobil or Rotella T. I'd just be cruising on the highway and bam 43 counts of knock that would last 5 seconds or so. Completely random. I would say listen for lifter tick.

Ph3n1x

iTrader: (12)

Max is 36 counts^

Darwinn

iTrader: (6)

Is it possible to have 36 counts of knock with lifter tick ?


TouringBubble
Your car with balance shafts?

dan l

iTrader: (3)

On a 1g DSM its 43. My evo isn't old enough to have these problems. However back in 2001 I spend a number of years trying to figure out "knock", what it meant, determining what was fake, and how to eliminate phantom knock. My car only had 88K back then, about the mileage many evo 8's are getting into........