Gurus...help. I can't figure out why I am seeing knock at certain rpms. The link to my datalog is below. I started out with the bottle coming on at 3,000rpm and then changed it to 3,500 rpm later in this scan. This is with 150 shot jets on a stock(tuned) LT4 with a hotcam. I had the car on a dyno yesterday and it made 498/547 with the A/F being pretty rich.

I have a FJO Progressive Controller bringing the nitrous on at 30% and ramping to 100% over .4 sec. With 100 shot jets I don't see any knock.

What's up with this...help please??

http://www.scandepot.net/viewscan.php?pk=5142


Thanks in advance for your advice!

Here's the dyno graph

forgive dumb question - but it is wet, right?

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Not a dumb question...I just forgot to include the info...it is a wet shot.

The knock you are seeing may be from harmonic block/header noise or un heat sheilded sensor with headers.
If the sensor is properly shielded and there are no problems with the engine mechanicaly try some teflon tape with a seperate ground wire providing the ground and see if this calms things down at those rpms. the knock sensor can be tuned in this way, you can check for proper function with a hammer and a timing light. Thats why I like to tune my knock sensor
Kudos for the dyno results! without a wideband to check for a lean condition first is pointless. innovate has them for "cheap" as well. Aloha

Good advice. That's what Josh and I were thinking, but it's good to hear somebody else say it. I can't figure out any other reason why I would see up to 10 degrees of knock and within 200 rpm it is completely gone even when the timing comes right back. I'm going to look for possible harmonics.

One other possibility that we considered is the progressive controller is pulsing the solenoids. I have it set to a .4 second ramp. I'm wondering if the pulsing solenoids are somehow being picked up as knock.

Any other ideas/suggestions out there?

My '89 is a totally different world but I have false knock whether N/A or on the spray. My dyno torque curve was ragged because of the computer pulling timing, putting back, pulling again, putting back, etc. Drops anywhere from 10 to 20 ft. lbs. each time, then comes back. Dyno operator says he is 100% sure it is false because we couldn't hear it at all and we were in a block garage. The air fuel ratio is 12.5 on spray, 13.2 N/A. We pulled the timing back 5 extra degrees and had the same results, only with much less power. Seems as tho no matter where the timing or afr is set it still has it. After the dyno I went home and disabled the spark retard system by snipping the brown wire going into the knock module. I put plugs on it so I can hook it back up if I want but I don't think I will. I wish I'd have known about that while still on the dyno. I'll likely go back to the dyno after I get my catback replaced. I know some will disagree but I think a 100K mi bottom end, roller rockers, headers, duals, many other mods, etc. causes false knock. I have a feeling you are plagued with false knock. You may have to find a way to disable your knock retard when spraying, and I am pretty sure yours is nothing like mine. I think your knock module is part of the computer.

If you don't mind me asking, what is your air fuel ratio N/A and what is it on the spray? I can't see it on your graph, for some reason it won't enlarge for me. Some are telling me 12.5 is too lean for spraying with stock pistons and rings, others are telling me I should run 13.2 both N/A and spraying. I thought 12.5 was good but I don't know.

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Mine is about 11 to 1, which is a little on the rich side, but better than lean. Here's a link to the dyno graph.

Dyno graph

I think it's false knock too, but it's strange that it only does it on the 150 shot. On the 100 shot, it doesn't knock at all.

Put some good gas in that thing and see if the knock goes away. If you get identical knock with 110 octane in the tank, then the knock pretty much has to be false.

I could see it good by the link, thanks. My air fuel ratio with the recommended nitrous and fuel jets was always too rich(Zex kit). We tried the 100 shot first and the afr was like 10.8 to 11.2. We put the fuel jet in for the 75 shot and it went to 12.5. Tried the 125 shot, same thing. Ended up with the 150 nitrous jet and the 125 fuel jet. Having the 1 step smaller fuel jet seemed to raise the air fuel ratio between 1 and 1.5, and it picked up about 25tq and 20hp at the rear wheels, again on a DYNOmite dyno.