I keep thinking I have a handle on my knock retard when at WOT, and then I end up having to fill up with a new tank of gas, and things seem to change. I want to blame it on the gas, but I'm just not sure. Last time I had knock retard, I added 3 gallons of 105 octane to my less-than-half-tank of gas. The KR didn't go away until I had driven about 35 miles! I was doing plenty of WOT runs along the way, too.

I've got a switchable 5lbs/7lbs of boost STS turbo. It's pretty awesome, making the car 2 seconds quicker in the quarter mile, but I wanted to get back my off-the-line responsiveness, so I had them change the system to give me more tuning lattitude. I've been trying to tune only at 5 lbs of boost because 7 actually has a boost-activated methanol spray assist which helps cool the intake charge. Plus, I was trying to simplify what I'm looking at.

I'm using the MAF tables to adjust how much air the computer thinks its getting so it'll add fuel only when it needs it (at higher boost levels). Between 4000 and 5000 RPM, I can get as much as 10 degrees of KR, but the car still feels strong. I've increased the grams of air the computer sees at this RPM by 9% and still get the same KR. Is there a way to consistently tune this out? Is dropping to a 160 degree thermostat an effective way to kill this? I've already tried the LT4 knock sensor and it gives the SAME readings as the LT1. Am I going to have to use octane boost all the time?

Right now, I've got my O2's consistently above .95 volts at any RPM at WOT. They're even pushing 1 volt when I'm getting big KR, so I know the car is plenty rich (at least with the combination of MAF adjustments and KR).

Any great ideas anyone?

 

if you're getting knock with regular gas but it seems to go away when you add octane booster I would think that your knock sensor is accurate

From what I've read changing the knock sensor to an LT4 does not make a difference in knock reading. People have changed to an LT4 knock module which is a small chip that sits in the pcm and that seems to work.

 

It took a bottle of octane boost and 3 gallons of 104, and driving a lot of miles before knock retard mysteriously went away. Next tank of gas, it was still gone (for the whole tank). So I went to the same place to fill up the third time, and the knock retard is back. So, if it's real knock retard, what's the easiest way to get rid of it? Cooler thermostat? higher lift rockers? (to reduce boost stacking, perhaps)? Do I have to lower the engine's compression? (that's not an easy option!)

 

My own personal experience has been that when you are trying to run pump gas and have to lower the ignition timing lower than 28 or 29 degrees to control detonation you get to a point of diminishing returns, this means you might be able to make the detonation go away with 24 degrees of timing but you cant make any more power with 24 degrees of timimg.
Secondly, if you have to run a fuel air mixture lower than 12 to 1 to control detonation it does not work as good. when using pump gas, I prefer to see a fuel air mixture of 12.6 to 12.9 for max power under boost and 14.7 to 14.9 in no boost, light load, just cruising down the road.
It’s my opinion the average ideal turbo street motor would run a fuel air mixture of 12.9 to 1 and ignition timing of 30 degrees under full boost using 92 octaine unleaded pump gas. I would try to make this happen by altering the static compression, amount of boost and inlet air temp (by using a charge air cooler).
About the knock retard, it’s a band-aid fix to control a problem. It’s not for making power it’s to stop the motor from hurting it’s self. When it’s doing it’s job it is reducing the power out put of the motor.
Do you have an inlet air temp gage you can monitor? If so what is your inlet air temp under boost?
I didn’t see mention of a charge air cooler in your post. Are you running one?
What does .95 volts translate into in terms of the actual fuel air ratio?
What is 10 degrees of knock retard in total ignition timing degrees?
Wastegate

 

12.9:1 A/F would make more power (usually) but that seems awful lean and too risky to me. Low 12's is much safer in my opinion. These Lightning guys tune for 11.5 to 11.7:1 A/F and they're knocking on the 9 second door.

You are definitely correct on the timing issue. If you have to give it all up just to run "X" amount of boost on a certain fuel, you'll likely make more power adding the timing back in and pulling back the boost, plus response, etc. is much improved.

 

Sounds to me like your running the edge of knock with your high compression (stock?) motor. Slight changes in gas quality put you into a situation where your getting knock retard. The only way your going to get rid of it is reduce your timing in the 90-100KPA range using tunercat or LT1 Edit, which it seems you have one or the other.

Boost + No methanol + no intercooler + high compression = a great recipe for Detonation. Maybe you should get the methanol to turn on while using the 5psi setting. The high octane rating of the methanol might allow you to run more timing than without it and recoup some of that lost power from backing the timing off. I know if it was my car that alky would be spraying everytime I hit boost, especially on the stock motor. I'd be doing everything I could to help it live longer!

Bill

 

Yes, the motor is stock. So, yes, I'm probably asking for trouble...

No, don't have an intercooler -- the turbo is in back, so the longer intake run cools the charge a little. I don't have a guage, but when STS monitored it, I think they said it was 70-80 hotter than ambient at the Throttle-body. At 7 lbs, Rick said the temps were dropping back to nearly ambient. Maybe I should cruise around at 7 lbs all the time, especially after smoknz's comments! I haven't done any logging on this tank of gas at 7 lbs. I'll try tomorrow.

I used the LM-1 portable wide band sensor for a while, but it was showing that I was 10.0/1 at 2000 RPM and 11.9/1 (sometimes 12.0) at 5500 RPM. At 7 lbs of boost, the top reading dropped to 11.7/1. My problem with it was I naturally tried to lean out the low RPM range, but ended up just introducing KR and not changing AFRs much at all.

Based on the time I spent both freescanning and wide band testing, I would say .99-1.00 at the bottom is right around 10.0/1 AFR. .93 volts at 5500 would be the 11.9 to 1, I guess. I've since riched up the top to be at least .95, and sometimes more like .97.

I'm using tunercat and Excel to mess with the MAF tables. The 2 together make it pretty easy to try new things.

 

wastegate, I forgot to answer your question about KR. I was dropping to 24 degrees of advance at 5000 RPM (the 10 degrees of KR). Interesting on that last logged run that KR dropped a little as I approached 5500, letting me get to 29 degrees of timing.

 

Your changing your MAF tables to adjust WOT A/F? I would try the % enrichmwent at WOT vs RPM table and leave the MAF alone! Whats the highest MAF reading you see during a run at 7 psi? does it ever get close to maxing out?

Bill

 

Because of turbo lag, it seemed like a more accurate way to apply fuel only when needed (when the boost comes on) rather than just as the revs build. Plus, I could use the combination of RPMs and air flow, and look at the KR on the adjacent cell. If I was getting a lot of KR, I'd say there was a little more air. Of course with this last tank, it seems like nothing will eliminate the KR!

I think 471 used to be the max number, which at 7 lbs I was hitting at around 5200 RPM. I've upped that number to 511. This is a 8.5% increase. Most the cells in that fourth table have been increased by 9%, which definitely bumped up my O2 voltages at the top 4000-5500 RPM range.

 

I think that a properly configured setup doesn't need a knock sensor. In your case, it sounds like you have "real" knock and need to solve the problem by using better gas, lowering your CR, decreasing the boost, retarding the timing, making it richer, adding water/alcohol injection, or some combination of the above. My KS has been turned off for four years and I have not had any detonation related problems. So it can be done.

Rich Krause

 

Well at 471 or so your maxed out! anything above 5200 RPM and your MAF isn't adding anymore fuel, there is where the PE tables become VERY important!