Pd1

iTrader: (38)

I think I know why my car doesn't like any midrange timing -- my somewhat restrictive muffler. I'm currently running a 3" O2 (WORKS), with the WORKS 3" DP, test pipe, WORKS 3" IP, mated up to a StealthWORKS muffler, which is a modified stock muffler. The flange on the stock muffler only has a 2.5" or so opening, so there's a significant flow disruption occurring. During WOT runs, the restriction is there....but when I let off of the throttle, that backpressure sends a shockwave all the way to the engine. By running very little mid-load timing, I'm able to avoid knock. I'll attach of log of what happens when I run a reasonable mid-load timing map.

What do you think of this theory? It makes sense to me, and I know the car didn't do this when I was running my 3" TBE.

RazorLab

iTrader: (8)

I've seen the same thing tuning 100% stock evo 9's. I believe your theory is correct.

but man you are running some low timing! Although 27psi peak

C6C6CH3vo

iTrader: (9)

Finding the cause of this will be a game of forensics.

Whoop_ass

iTrader: (7)

I also have this happening.
also mid throttle, get into boost and then let off.

Pd1

iTrader: (38)

My problem was instantly cured with a 3" muffler. It was the stock muffler inlet flange and modified stock muffler (StealthWORKS) that was causing the problem. I'm back to running healthy midrange timing again.

mrfred

iTrader: (50)

That's interesting to know. All the more reason to get a good high flow exhaust.

roger smith

iTrader: (4)

John you have a stock job? I guess you don't really need to change much if you have a FQXXX.

I don't remember my car ever doing this. I have a turbo-back and a Tomei BOV so I'm on a different boat I guess.

But I'll try to keep an eye out.

jcsbanks

Stock BOV. "job"?

roger smith

iTrader: (4)

sorry. I meant "your whole car is stock?"
I assumed yours was modified a lot since you're one of the ECU experts.

jcsbanks

3" exhaust, Walbro, airbox mod, AVC-R, modified OEM fuel pressure regulator, sometimes meth in tank.
Hard intercooler/turbo inlet pipes as FQ spec.

C6C6CH3vo

iTrader: (9)

Stock blow off "job"? Evo's don't come with blow off valves (or pressure relief) they use diverter (or bypass) valves. So if a BOV is used then it isn't stock, right?

jcsbanks

We (UK) would refer to the standard unit as a recirculating dump valve or a recirculating blow off valve (as opposed to vent to atmosphere). Whatever your preferred terminology, I have the standard arrangement which we're all familiar with

fid

iTrader: (18)

It is funny I found this thread because I have been having a similar problem recently, but in the opposite effect. When cruising, lean into the throttle alittle and back out half way and it goes real rich (10:1) then jumps alittle lean (15.8:1) and then it settles back to 14.7:1, no knock. Mostly only happens in higher gears too. But I can make it happen on command. I have PTE 780cc injectors and so far I have tried: rescaling injectors, raising/lowering latencies, went back to stockairbox with nothing helping. Also sometimes the car freaks out and goes real lean when coming to a rolling stop with the clutch in but eventually settles back to stoich. Please keep the thread updated if you guys come across any more info .