S2ki Team,

I am currently working on the break in period of my S2K after an engine rebuild. The original cause for rebuid was detonation on two cylinders, disintegrating one spark plug and galling on one cylinder wall.

It's back together with 0.25mm Oversize OEM pistons, new bearings, new conn rod pins, and a cleaned up cylinder head. Naturally, I'm looking to avoid having the same catastrophe again. I suspect the original cause of failure was due to a misfill of the aftercooler on my part after a change to the 3.6in psi pulley. (I'm assuming) I recall not having filled again after cycling the pump. When I inspected the engine, the aftercooler water level was at the bottom of the heat exchanger in the resevoir.

From when I originally got the car, I had gradually increased the ignition timing from 16 deg BTDC at 9k to 20 deg. In doing so knock volts had increased from 1.0 volts to 3.3 at maximum. I stopped my advancement there as I wasn't looking to be on the edge but knew the tune was too conservative before. At each minor adjustment, I made fuel adjustments to keep the AFR around 12.0. There was a torque gain easiy detectable by the inaccurate butt dyno.

I drove around this way for a few months without problems. However, when I was applying WOT, it was always on country roads and for short periods of time. The first time I was able to enjoy a road course last year, I had the failure. It only took about 3-4 min of beating on it before the spark plugs resigned.

I have a couple questions for you guys:

1. Do the ignition values seem unreasonable? I'll post a map. I may have a profesional tune done this year.

2. It sounds to me like the IAT's were too high. I wasn't logging at the time, of course, so I can't be sure of what it was during the detonation. Anyone know what are some usual IAT's? My logs during the 40 degree weather show typical IAT's around 95deg when driving it in a spirited fasion. I'm going to put in some moderate trims for IAT's to stay on the conservative side. There were none before. Doh!

 

That sounds like alot of timing . I can tell you this, my timing maps are MUCH more conservative than yours . I am running a stock ap1 with a vortech supercharger boosting 12 psi . I have beaten the crap out of it at times and no problems . Also it should be noted that i paid for a professional tuner to do the tuning for me . I run an aem ems by the way . 95 degrees F is nothing , start worrying when you see 150 + .

 

Yep. That's a bit too aggressive on the timing. The best thing to do on the timing map is take the AEM base file, interpolate then timing out into boost. When you are done, for every 1 psi of boost, reduce timing by one degree.

That should be plenty safe. Head to the dyno and tune for max best torque at that point (or get a G meter).

20 degrees is too much timing at peak, man. Good luck.

 

 

max timing should be around 15 with an 11.5:1 afr.

 

That's not really true...

 

July,

I compared your timing map to mine because we're running similar setups.

I don't believe your peak boost timing is your problem. I think you detonated at high rpm/mid boost levels. You are 4 degrees more advanced than I am in that range. I think you need to start over. This map advances really fast and then drops off rather quickly as load goes up.

I would back off timing in the 119 to 138 kpa range...it substantially more advanced than mine which has proven rather safe.

 

well if he's having detonation issues with a 9psi pulley, i would say drop the timing down or afr down. one or the other. especially if he's "self tuning" and not a professional its best to give yourself some lee-way instead of blowing things up which he is on his way to doing with the current setup.

was hoping a massive response like this wasnt necessary, but for some i guess it is.

 

Alright, I'll move forward with this and move the ignition back 4 degrees from 100 to 140kpa and 2 degrees from 140-160kpa. Then I'll retune for AFR. I actually ran this way for a long time with no problem. I'm actually going to try out the 3.2" pulley and meth injection this season but I'll be hitting up a professional for that tune unless I can figure out what AFR's I should target and get free dyno access again.

 

In my experience with the Comptech SC, as long as your afr is good (11-12) at 9psi and your A/C is functioning properly you shouldn't have any detonation issues with the stock N/A timing map (27degrees peak?) Not enough to destroy a motor! I run meth injection for good measure these days, but I'm still running the stock ECU/Injectors making 9psi on my f22 at 9k 360whp. With the meth injection it actually looks like I could use some more timing in the mid range. i think your issue was with your A/C as you mentioned when at the track and your AIT killed you.

I know of some local guys that have killed their motors on the track at the base 6psi with no A/C incorporated in the system. High AIT will cause major detonation for sure, huge variable.