Chasing False Knock

[RubyRedBoost]

I have been picking up false knock while logging with Greg from Lund racing. As you can see in the pic my SW headers were tagging the A/C line bracket bolt on the passenger side. By cutting the head off the bolt it lowered the count from 2.4 down to 1.3 but Im still getting counts and losing timing. I get the knock counts at 3-4k rpms only. WOT pulls are flawless. Do you guys have any other ideas as to how to remedy this? I have also installed a oil separator and switched fuels with no change. Exhaust is tight from headers to tip. We are stumped at this point.

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[sloppymax]

Is the 1.3 the amount of positive knock you are seeing at 3-4k rpms now that you cut the head? It only occurs at partial throttle? What oil separator did you install?

 

[ero 5.0]

I had the same issue with my SW headers, and had to file that same bolt down a little bit. They also were vibrating up against my steeda front K-brace, so I had to tweak that a bit too.

 

[RubyRedBoost]

Yes exactly. After cutting the bolt head it dropped significantly. I installed the newer JLT with the steal mesh. Ive caught a teaspoon in a day and a half so it's definitely working. I haven't completed ruled out octane being an issue. I will be pulling plugs after work to check gap.

 

[RubyRedBoost]

I had to sawzall most of the bracket off. The header was still making contact with the nut/bracket.

 

[Demon Coyote]

I'm experiencing false knock too but I haven't look at my passenger side header to see if it's making contact with the A/C line bracket bolt. Mine just randomly spikes up and goes back to normal and it seems to happen in between shifts. Most likely NVH between shifts might be causing my issue. I will take a look at my passenger side header and see what's going on. I have SW as well.

 

[dubster99]

I've been wondering if mine are contacting there too. How did you get in there to cut it off? I don't want to take that header off again.

 

[RubyRedBoost]

I used a hacksaw first but had to finish it up with a sawzall. We first cut off the head of the bolt. Then today put it up on ramps before re logging and saw it was contacting the nut and part of the retainer for the bracket. I was extremely careful with the sawzall and cut enough away. This stopped all knock in the 3-4k range immediately. Then I started logging knock again. 1-2k range with is from the diff locking on turns and scrubbing the tires. I believe it is a torque management issue now. I will definitely keep everyone updated. Now I can tell you if you aren't running a catch can, get one. Mine was installed Friday and as of now has picked up almost a tablespoon. Its a needed mod.

 

[dubster99]

I've got one as well. I just haven't had time to get under there and see if it's actually contacting that bracket/nut/bolt. I wonder if I could get in there with a dremel...

 

[RubyRedBoost]

You can see it from the top. This is a frequent issue with these headers. You're probably having contact.

 

[Jeff's FRC]

Is it possible to take a pic of exactly what you cut off that AC bracket? I'll be installing SP longtubes in the spring and would like to take care of that bracket while the header is out. You're not the first person to have this issue...

 

[RubyRedBoost]

Here ya go. As you can see I diagonally cut the nut in half and followed through the end of the bracket creating about another .25" of clearance. Nut is still holding tight. I ziptied the line just incase but its still solid.

 

[Jeff's FRC]

Awesome thanks!

 

[gtmiller1001]

On my last turbo car I was trying to eliminate octane issues or anything other than vibration from causing knock and just ran the tank all the way down (tuned and was using 93 pump gas) and bought a 5 gallon jug of Shell URT (104 octane I think).

I believe that's the best way to do it....go way beyond whatever the tune is written for octane wise and see if it still produces the same knock values.

If you think you've completely fixed your header contact issue I'd try this and see what happens.

 

[RubyRedBoost]

Lund just got back to me. False knock is fixed after everything I did. I only pick up a little now when turning slow. Its from the Torsion locking and the tires scrubbing. We were able to recreate it. Car is running solid now and adding timing again. If I were to do the header install over again I'd just delete that whole bracket. It was a pain to get in there after the fact.

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