Engine Knock at mid-range RPM

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All of a sudden I am getting high knock counts around 3-4000 RPM that I haven't really had before.

Things I have changed recently are moving to IK24 plugs from 7 series NGK coppers, but I am not sure if this problem was before or after this.

I'm am between 10 and 20 counts. The car pulls a ton of timing and feels like a dog.

I've been doing some testing and I've found I can reproduce it anytime I want by holding the car with the brakes in 2nd at 3000 RPM and going full throttle.

Obviously you don't want to do this for long or you'll overheat the brakes, but it allows for an easy way to safely hold the car at high load at a specific RPM.

I can reproduce the knock everytime by holding it at 3K RPM. Boost is approx 16-17 PSI and I am running 365CC of 50% meth.

I've played with the AFRs and now have it running much richer at 3000 than the factory map. I'm running about 11.7:1 at 3K and the factory map calls for as high as 12.9:1 at high load in this rev range.

I've found it has reduced the knock counts, but I really shouldn't have to run this rich at this point.


Can anyone share what AFR they are targeting around 3-4K ? The rest of my tune above 4500 looks like 10.8 - 11.2 :1, but once the knock starts at the low revs it will not abate in the upper RPM ranges until the pull is aborted.


I'm considering moving to a 650cc meth nozzle, but I do not think I should have this heavy of knock counts with the 360cc nozzle.

I actually had very little knock this summer even down in Memphis when it was 100, so I am a little baffeled at this point.

One thing I am worried about is I may have some real mechanical engine problem that is causing the knock counts, but from what I understand about the knock sensor this type of noise is not the same frequency and shouldn't show up.


I have very good oil pressure, no smoking, and no lifter tick, but maybe under heavy load I am having some rod noise, but I sure can't hear it.


The other thing is maybe I have a single injector causing problems, but again I didn't see any plugs that looked leaner than the others when I had them out last week. I also do not seem to have a miss and the engine is getting the same MPG it always has. When the car isn't pulling timing it feels strong as hell.

[levani041491]

off topic but are you unning on cast crank ?

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Originally Posted by levani041491

off topic but are you unning on cast crank ?

yes, for the last 150K miles. Bearings and oil pump replaced at 138,000

[levani041491]

do you have anyproblems with it ?

[Forest Gump]

Originally Posted by levani041491

do you have anyproblems with it ?

uh, no. Your crank shaft is either in one piece or not. It either has journals out of round that have destroyed your bearings or it doesn't. It isn't like one day it could give you problems and the next it would be alright.

Some of the cast cranks had casting flaws and they would break, but the "good" cast cranks seem to take low power just fine. Since mine has been running for almost 20 years it really isn't the first thing on my list of worries.

[JayWilRTTT]

I would try putting the old plugs in and see if anything changes. Like you said you were running fine before on the same amount of meth. Also maybe check out your meth nozzle and sytem to make sure its working properly. Good luck

[lawdogg]

Do you have solid mounts?

Maybe put race gas in and see if it disappears?

[keithmac]

I run 11.5:1 in that are with no problems, normally 4000rpm region which gives the most problems (dip down to high 10`s their to stave off knock).

Bit of an odd problem how it`s come on in the colder weather?. 360cc 50% meth seems on the low side but as you say you`ve not had the problem before.

On thing is these engines are prone to knock if loaded up in low rpms, quite a few people have found this.

[Forest Gump]

Originally Posted by lawdogg

Do you have solid mounts?

Maybe put race gas in and see if it disappears?

I have poly front and rear mounts and stock sides.

I think I'm going to up the meth nozzle size and see if it gets squared away. I wanted to run the smallest one possible to make tuning easier, but I don't think this is enough.

I also have my doubts I'm really getting 93 octane at the place I go to. It is the only station I know of that sells 93, so I'm starting to think it is really 92 like everyone else has...

[Forest Gump]

Originally Posted by keithmac

I run 11.5:1 in that are with no problems, normally 4000rpm region which gives the most problems (dip down to high 10`s their to stave off knock).

Bit of an odd problem how it`s come on in the colder weather?. 360cc 50% meth seems on the low side but as you say you`ve not had the problem before.

On thing is these engines are prone to knock if loaded up in low rpms, quite a few people have found this.

thanks for the info. I didn't know it was common to run that much richer at low RPMs than the factory setup runs.

Overall the car is running great like this, but I'm going to switch to a 650cc nozzle to try to quell this knock.