Knock at Trubo Transition only
 

Ever since my rebuild, I've had a mysterious spike in my knock readings. Most of the time when driving around I will see low knock readings (30 or below). But occasionally I see a a nice high 130 or so. I've narrowed it down to the transition point (4500 rpms).

If I am already in twin mode (go over 4500 rpms, then down to 3800 and then excelerate past 4500 WOT) then I will not see the spike, ever.

But when I transition - I can regularly see the spike. I have some mods - basic stage 3, but with the '99 turbos and a new y-pipe that came with the new engine.

I know that the only way to really know what is going on is to get my ass to a dyno w/ a wideband - but until then, has anyone else seen this? Any wild speculation?

I suppose it could be some noise - but it also seems like with all that's going on in the transition, maybe there is some low level knock. I sertainly don't hear anything that sounds like knock in the cabin. Everything seems quite smooth.

any thoughts?

There are numerous actions happening at transition. PC gate opening, then turbo control gate opening, charge control valve opening, charge relief valve closing, and sudden boost change(spike or dip) that affects power. The WG migh also be flapping.

Any of these can make noise. Boost spiking can also make power beyond the safe limit if your maps are not set properly.

I get the same thing. I also have a J&s and it shows activity at trans too.

Mine did this just before I sucked down an apex seal. It will not know for long. Send you ECu back to XS engineering. They will rough it in for your mods and mail it back. Eliminated the knock on my rebuilt motor and turbos.

Why would I send the ECU back to the tuner (SR, not XS, btw), especially when I have had it dyno tuned after purchase at KDR?

My equivalent to that action would be to take it to KDR for more tuning, or a local shop with a dyno and wideband.

But I have a trace of where the "knock" is happening. What would be the risk of backing off the ignition at those cells by a couple of degrees? Part II of this question, is would I do that to both leading and trailing, or just leading? (or just trailing, but that doesn't make as much sense).

More Data
 

Today I adjusted the leating ingition back 2 degrees (across the board) in the test page of the commander. And the knock at transition went down, by about half. I set it back to normal, and high knock readings came back.

Set took 4 degrees of leading, and knock became a blip - about 40 instead of 140.

So I don't think it's turbos transition noises. I think it is a problem in the maps :( The frustrating part is that I can cross the same map points (rpm and load) while in twin mode wihtout a single blip - knock readings of 20. So I'm a little weary of degrading the timing too much.

I don't think these cells have been modified by either KDR or SR.

So I think I should take off 4 degrees in the cells I believe are most affected. My two questions are - how wide should a spread out the changes (degrade to 1 dgree off in 4 cell radius, 2 cell radius, 6 cell radius??) and what should I do about the trailing ignition?

thanks in advance for any advice.

Yet More Data
 

My ignition maps do appear to be altered. And are already pretty retarded compared to stock maps.

see attachted text file for the segment of my leading timing.

I'm a little afraid of taking off even more. Some areas are already -6 degrees from stock.

Any thoughts?

My Mods - basic stage 3:
PFC - obviously
'99 Efini turbos and y-pipe
PFS Intake and IC
High Flow pre- and main-cat.
Catback.
nothing else that should affect fuel, etc.

it is probably the spike you are getting, computer can't act fast enough to compensate for a spike. retarding timing will not always reduce knock but generally will alwayts reduce knock reading on PFC

Re: More Data
 

be careful, make sur eyou adjust leading and trailing to gether, preferably trailing first. negative splits are believed to cause harm if had at the wrong places.

Can't you just add more fuel at the switchover point?