Folks,

I have a 2007 S2000 which I supercharged with Rotrex C38-92 using the Kraftwerks kit. I road tuned it myself with the guidance of a tuning expert that also has a supercharged S2000.

In 7/2020, I was doing a high RPM/low load datalog and accidentally overheated the car. Temp peaked at 260, it was over 250 for about a minute. Everything seemed to be ok, but in 9/2020, it began to pressurize the coolant. I replaced the HG and unfortunately got some incorrect advice that I should not have the head shaved, so it began pressurizing the coolant again in 3/2021. I did the job again and got it back together in 4/2021. The car immediately was burning a lot of oil, like a cloud behind me at every stop sign. I did a few datalogs and it was showing up lean, I added some fuel to the tune to bring the AFRs down. Within 20 miles, the car began to miss under even slight boost. It failed compression and leakdown tests, especially in #2 & #3. I took the head off and found a scored cylinder in #3. It took me ~14 months to source and install a replacement motor.

Yesterday I tore apart the old motor, and found all 4 pistons to have cracked top compression rings and varying degrees of knock damage. I don't understand where I screwed up.

Here is the last datalog I took in 9/2020 right before it began pressurizing the coolant. Fat-ish @ ~11.7 AFR, ended up at about 15 degrees of timing at the top.


I attempted a datalog in January, but on snow tires I broke traction like, 4500 RPM in 3rd. I attempted a datalog in 4ft and it began to break traction at nearly 100mph...fun stuff. Anyway, you can see that before the traction control started pulling throttle, it was actually pretty fat; no knock.



In 4/2021, after I finished replacing the HG a second time, the car was burning a ton of oil as I mentioned. Here is the first datalog I did that day. I pulled 2 degrees of timing from the tune just to be more conservative for this run.


As you can see, the car is way lean and it picked up one knock on the run, but to reiterate the motor was already smoking and it began to miss shortly thereafter. The only thing that changed with the car from 9/2020-4/2021 was the catalytic converter. When I was changing the HG the second time, I noticed the cat was disintegrating (Berk HFC) and replaced it with a resonated test pipe.

So, my thoughts on possible causes:

• The car was knocking all along and the knock sensor just couldn't see it for some reason.
• I got a bad tank of gas or put in 87 like an idiot.
• Failing fuel pump (it is still in there, Walbro 255, but now it is feeding a Radium surge tank with a AEM 340
• The O2 (replaced in 9/2019 with a Denso from Rockauto) was drifting and the car was lean all along.
• The overheat somehow caused this?
• ...????

Here are some pics of the worst of the pistons:



Last week, I iterated the tune on the new motor and ended up in the same realm as far as timing goes (~15.5 up top). I have run the car hard for maybe 10 pulls since then. As soon as I saw these pistons from the old motor, I pulled 4 degrees of timing from the tune on the new motor, did a compression test (all within 5 PSI, done cold) and a leak down test (all 3-5% leakage done cold/dry) and visually inspected all 4 cylinders for damage. The pistons look great with no signs of knock, thank God.




So, I am at a loss. Clearly I screwed something up, I just want to know what it was to avoid nuking the new motor, which was NOT inexpensive. I know these motors can be reliable under modest boost basically indefinitely, but not knowing how I killed the first one makes me want to pull the super and go back to being as fast as a Fiesta ST.

Does anyone have some insight or possible causes that I didn't come up with?

 

Here comes all the blame on Kraftwerks lol. Out of curiosity, when you did your HG, did you upgrade your head studs too, did you replace with oem studs or reuse old ones? I too am KW supercharged and was pressurizing my cooling system. Only under boost and it was lifting my head, but off boost, it was fine. compression, pressurizing cooling system test, combustion Leak detector, leak down no problems. I just recently replaced my HG and upgraded to ARP studs and it’s only been a couple days but it seems to solve my issue as of now.
maybe Low engine oil could of caused damage or Messing with the tune to correct the lean condition is what caused it?

 

I used a stock HG and new bolts both times. I was not lifting the head under boost, it was just straight-up leaking between #1 and #2, where it had warped slightly from the ovrheat.

And by all means, if someone can some how point to a supercharger making 15 PSI MAX as the cause while turbo guys do that all day, I am would love to hear it. The KW kit has a lot of issues, but the blower didn't fail, the stupid cog belt system didn't shred, and no bolts broke. I can't possibly imagine a reasonable argument blaming the supercharger beyond the blame due to any device making boost.

 

Additional thoughts on possible cause: as mentioned, I had been running a Berk HFC, but it failed and I noticed while doing the 2nd HG job. The material inside was turned sideways, so not a CLOG, but certainly a restriction. Could this have caused extra heat, leading to detonation?

 

1000C will not help !

 

Looks like you're tuned on Megasquirt? I was starting to think I was the only one!

Since it sounds like you're running basically the same tune as before, I have to think something else was going on with the last motor. The old vs new piston pics don't show any signs of being subjected to the same environment like you'd expect if it was a tune issue. Hopefully it was just a bad tank of gas and you can put it in the past and move on.

 

Low speed pre-ignition most likely.

 

I am using a KTuner on the stock ECU. The screenshots are from MegaLogViewer HD, highly recommended.

And yeah, I would love to move on...but having no idea what caused the failure is haunting me, which is why I created this post. I got this motor as a sweetheart deal from a friend, I just saw a similar package on eBay for like $13k. Now I am considering paying a tuner $1k to revise my tune because I have lost all confidence.

 

I would be surprised if that is the case, as the supercharger is only making 122 kPA @ 4k RPM and it increases linearly. Isn't that more of a problem on turbos?

 

It's mostly a tuning issue, seen many engines blown, NA and boosted because of LSPI. 7kpa is 1 psi so that's what 17psi? Or is that absolute? Aka 3 psi of boost? Where is the VTEC changeover and what does your throttle tip in look like at lower rpm? Any engine lugging?