8psi sts knock/detonation/tune question
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8psi sts knock/detonation/tune question Hey guys, I've had my car dyno tuned at a respected f-body shop that knows their way around an sts car. But I've been seeing a couple degrees of knock at 7-8psi this spring. Brought the car back by the shop, and the made a few more pulls with it, and said to get absolutely all the knock out, they'd have to drop the timing down from 16 to 12. We ended up splitting the difference, and putting it at 14, and the last pull only picked up .1 degree for a split second. Thought I was good, but turns out, it looks like they didn't up the boost to take into account the street vs. dyno difference, so it was only making 6 psi on the dyno. On the street at 8psi it's picking up 3-4 degrees at times. A/F is right at 11.0 according to the wideband ... and the narrowband O2's are at around 915 and 920. I can feel the timing being pulled more and less when I get on it. It feels like abs brakes .... but during acceleration. I turned the meth kit back on (m15 nozzle), and it takes care of all but .1 degree or so of the knock, but the car still doesn't feel like it's pulling "cleanly" up top. just for information, it has tr6 plugs in it. Does anyone have any advice on what I can try next? I'm supposed to take it to the track this weekend, and can't seem to get the car running right. I'm running out of ideas to try. I'll probably try and talk to the tuner, but I don't even know what to ask him to try and whatnot, and I don't want to just burn the money blindly hunting for answers. So turbo/sts gurus, help me out if ya can. thanks.
Last edited by Karpellarpy; May 12, 2008 at 08:19 PM. Reason: spelling
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From: Columbia, South Carolina
I don't have an electronic copy 
, but will see if I can scan it tomorrow at work. graph looks smooth, (smoothing @ 5), and I have patriot dual valve springs and a set of hardened pushrods, so I don't think it's valve float. On the low boost (4 psi off the wastegate) it seems to clear up a good bit. I'm going to try gapping the plugs a little tighter to see if that helps.
, but will see if I can scan it tomorrow at work. graph looks smooth, (smoothing @ 5), and I have patriot dual valve springs and a set of hardened pushrods, so I don't think it's valve float. On the low boost (4 psi off the wastegate) it seems to clear up a good bit. I'm going to try gapping the plugs a little tighter to see if that helps. 
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From: Ft. Irwin, California (But Virginia is home)
I'm guessing that the shop didn't increase the burst knock parameters on the car. The stock values show "knock" if there is an increase in g/cyl volume of .20. A nice hot STS can jump as much as .50 g/cyl per 400RPM cell. The PCM without being told otherwise notes this increase in air volume as a knock event.....when in fact it's the turbo increasing airflow.
I had to fiddle with mine for a while to get it all sorted out. Would have never gotten it straight w/out the help of my friend Brian at Va Speed (cheap advertising for a sponsor
)
Anyhow, either increase the g/cyl values in the burst knock table or have your tuner do it. Should help solve your prob
I had to fiddle with mine for a while to get it all sorted out. Would have never gotten it straight w/out the help of my friend Brian at Va Speed (cheap advertising for a sponsor
)Anyhow, either increase the g/cyl values in the burst knock table or have your tuner do it. Should help solve your prob
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Thanks for the awesome information Schantin. I haven't purchased any tuning software yet as I haven't found a great way to learn these sorts of details. That's why I took the car to be professional tuned. I'll definitely bring this up with the shop. Only reason I know the car's recording knock is because I have a little scan gauge that lets me see sensor data out of the obd-II port.
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From: Castro Valley, CA
It sounds like the shop can't load the car enough to approximate street use... so they're ballparking the tune. You're running a MAF?
Would you be comfortable with a tune that disabled KR... as long as your wideband (and theirs) agree on a safe AFR while the car's on the dyno?
How much power was being made at 6 psi with timing at 14?
Would you be comfortable with a tune that disabled KR... as long as your wideband (and theirs) agree on a safe AFR while the car's on the dyno?
How much power was being made at 6 psi with timing at 14?
Would you be comfortable with a tune that disabled KR
How about taking a look at disabling KR and adding one of the J&S Safeguard intelligent knock controllers?
Jim
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your car feels like a dog cause you have no timeing at all, you need to get that timing back up, you clearly have enough mods to run 8psi but seems like something isnt right, tune can be hack or you might have a boost leak somewhere
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On The Tree
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No boost leaks anywhere (or exhaust leaks for that matter), I've tested for them. I'm starting to think it's the 93 gas I have in my area. I added an octane booster to my tank, and reduced knock retard quite a bit. Also, I threw in a new set of plugs, and gapped them pretty tight (.28-.30), and it seems to have cleared up some of the surging I was experiencing. I'm thinking I was getting a rich misfire at higher rpms. Disabling the knock sensors would be a bad move ... they are what is keeping the motor together by backing timing out to supress detonation. Just because the a/f is correct doesn't mean it wont detonate. I'd love to have timing put back in the car, but I can't, it'll just detonate that much more. I thought maybe it was due to the '98 knock sensors, but I've replaced them with the updated ones and the new harness. I'm starting to think I'm just boost/octane limited at this point ... which seems odd when I heard about everyone else pushing their setups to 12-15 psi. on pump gas.
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So I know that richening the fuel mixture help cool the combustion chamber, which helps with detonation, but at some point can it actually start going the other way, and cause/promote detonation? ... Could I have the car set too rich?
I agree with shantin, and the fact that its a 98. I dont think just changing knock sensors will negate the 1998 knock sensor sensitivity, as I think the pcm configuration is different.
1. check the temp drop with and with out meth.
2. besides wot timing, what is the rest like? Where is it knocking?
3. Does 100 octane cure the problem? I bet not, and I bet false, but do you know?
1. check the temp drop with and with out meth.
2. besides wot timing, what is the rest like? Where is it knocking?
3. Does 100 octane cure the problem? I bet not, and I bet false, but do you know?
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Any news with your knock situation? I have a Procharged 02 Vette that won't handle more than 13 degrees at 5 psi and down to 11.5 degrees at 8 psi. Basically it is behaving like a non intercooled Maggie. I am running good 94 Octane fuel and new plugs and still she knocks on the dyno. Have you checked your intake air temps?
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sorry, no updates. I wish I had updates, lol. My IAT's hang around 20 above ambient, then head down 20 below ambient or better at wot when the meth turns on.
I'm guessing that the shop didn't increase the burst knock parameters on the car. The stock values show "knock" if there is an increase in g/cyl volume of .20. A nice hot STS can jump as much as .50 g/cyl per 400RPM cell. The PCM without being told otherwise notes this increase in air volume as a knock event.....when in fact it's the turbo increasing airflow.
It works a little differently than that... The burst knock part is true, but it doesn't show up as KR. KR is solely a sensor based response. You can log for burst knock in addition to KR. If you don't, it just shows up in the cumulative total as a loss from the base table in addition to any IAT/ECT gains or losses against the base numbers.
I had the same problem awhile back.So I did a search on here and there was another member with a vette doing the samething.Come to find out It was his plugwires,so I ohmed mine and they were bad.The hotter they got the worse they would ohm.I bought some new wires and the knock went away.Hopefully It Is something stupid like this causeing your problem.
