I was getting some knock here and there in my lt1 and found out my intermediate magnaflow hitting on the crossbrace.I fixed that but still sometimes seem to get some knock like 3.5 maybe 4.5 when floor it and other times it seems dont' get any.I have been trying to tune it out but not sure its possible.I am running 91 premium that is best we get here right now.

Oh have no headers on car,just mild mods and have lt4 km already installed.
I would have thought it would get rid of this knock.Also would think 91 octane would be enough with stock timing.

Is some knock like 3 to 4 normal?? I am not sure what else to do or check.

 

The only time I ever saw any sort of knock retard with my "bolt on" setup was on lifting throttle shifts. Other than that, there should be no retard. A mod's list for your setup might help figure out why you have the problem. How many miles on the car? Any chance you have excessive carbon buildup in the combustion chambers? Coolant temps "normal"?

 

Ok here is full mod list..I have magnaflow catback,stock exh man and cats.
I have g2 air induction,holley filter,airfoil,tb bypass,160 stat,hypertech but just for gears tuning out.I have stock maf and maft but have maf disconnected right now.I have lt1 scanmaster for logging.I have autotap too if need it.I am not sure if the engine has carbon problems.It has 64,000 miles on the car .Not much service history.Could be original plugs ,wires and opti.I changed out water pump last year.It seem to run strong pulls to redline no apparent missing.Oh 3.42 gears.Fixed recent problem with pipe hitting crossbrace.That dropped out a lot of false knock.So is three or four degrees acceptable I would say that is when first floored and then it seems to drop down to 1 or 2 maybe.

So does that help..Oh yeah egr is unhooked.I have fans set to come on the 160 stat temp usually holds around 170 and weather here hot last couple days like 70 F to 80 but running 91 octane at 1900 feet above sea level.

 

I would still say that you should have "0" knock retard. One thing the EGR system can do is help reduce knock when lugging the engine at low rpm in the wrong gear. But that doesn's sound like what you are seeing. 91 octane should be more than adequate at 1,900-feet. Have you ever tried some 100 octane unleaded to see if that reduces knock retard?

 

We don't have 100 octane around here but can try some xylene or toluene ,use that in my turbo talons here and there same effect.Good idea that will tell me if its false knock.Can't have real knock on 100 or so.
Will try that and report back.
But still answer this ..is 4 degrees taking away much power or still ok?
What else can cause phantom knock..if not exhaust pipes..And why would it start higher when floored but then taper off usually..

 

FYI, 2 gal of 91 octane and one gal of toluene gets you about 98.6 octane.
If you already knew that, sorry... no offense intended.

 

Yeah I was just appoximating on the toluene.I have a can of xylene which I think is higher than toluene.
Today I ran the gas down ,had discount 91 premium and put in some fresh 92 gasohol.It seemed to have helped car was faster and only saw one instance of 4.5 knock but other times zero.! So would think its an octane problem.I know you cant go much from non wideband o2 but I was getting .878 or so on the 91 octane gas and now around .850 on the 92 on my scanmaster but think the gasohol runs at slighter different af for best power?
I can try going up a notch on my maft it was unpugged for this latest testing.
Did get best et and highest mph once with my tazzo vpc.Have been tazzoing all morning .The knock of course does hurt et and mph.I do think maybe got some big carbon happening in the car.It was likey granny driven for a long time before I got it.I have been doing my best to blow the carbon out thought like going 140 mph today for a bit!!

I will put some decarboner in the engine and might buy a water/alco system they really clean out the engine and let you run cheaper fuel.It appears our 91 discount gas is garbage.I aso had tank of gasohol 92 from last year in there and it must lose octane pretty bad in say four or five months.The fresh 92 seems to help and we are supposed to get 94 shortly.That will be nice but a bit pricey.

I don't think have any more knock from things hitting under the car that problem seems to be fixed with some washers on the x brace.

I still will likely try a gallon of xylene in a quarter tank or so and see what happens.I would expect zero knock of course.