Nick Stacy

I have a very odd presentation of engine failure that occurred at my last drift event and would like to consult with the forum's elite folks. Relevant build specs are as follows -

Decked, 84mm bored BP4W ST 9:5:1 Pistons Manley Rods ACL Bearings
Freshly rebuilt and resurfaced BP4W head w/ ST springs ARP Studs
2871 Turbo @ 18 PSI
R8 Coils w/ BKR7E
93 Octane w/ Boostane
Fluidampr
Supermiata Re-route

This build was completed in April of this year and the car has ran 100+ laps with zero issues.

Did a few test pulls the night before traveling to the event after installing a new intercooler, moving WG reference point to intercooler end tank, and installing 3" stainless exhaust. First pull was great. Dead flat boost curve to redline, AFRs right on target. No knock. (i use det cans) Took det cans off. 2nd pull in a lower gear resulted in some spark blow out. Was running .034 on the R8s. Boost peaked @ 19 in the lower gear and spooled quick which is why I believe I blew out spark. (highest boost this spark config has seen) This was also the first few pulls since moving WG reference point. I saw my G4 Link Knock Light light up so I immediately got off throttle. 1.5 seconds max. The car made a pretty violent noise out of the exhaust. not quite a typical spark blow out noise. No ill effects I could identify. So I then did a 2nd gear pull and spark blew out slightly at high rpm, so I called it for the night. Bought new plugs, gapped to .030. Took it back out, no spark blow out, no issues. No identifiable issues on the logs.

Fast forward to next day, 7 hour tow to the event, FIRST lap out, I popped a freeze plug. removed power steering pump, reinstalled freeze plug with some RTV, bled cooling system, did some test pulls off track, no issues. So I got back on track, ran 6-8 laps without issues, then popped a 2nd freeze plug, and the car died after getting off throttle. I then cranked it to get off track, and there was a definite issue with the way it was cranking, still started right up, but was a fast, odd crank, like bad timing or bad compression. Never overheated at any point. did get fairly hot, 225-230 after two laps which is normal in 100 degree weather on a drift car. I also noticed bubbling coming from the dipstick hole after coming off track most likely indicating no longer pressurized scalding water in my oil pan. I run water and wetter.

Pulled motor the next day, leakdown revealed 30-50% cylinder leakage pouring out of all of the intake and exhaust valves. no visible cracks in the bores or head. no head warp. there is minor visible light leakage on all the valves. I expected to find leakage in the cooling system/crankcase. Can anyone help me make sense of this? I understand that if a detonation event occurred the night before during my test pull, it could have damaged both the valves/seats and a head gasket cooling passage without totally blowing the gasket. And that if the valve leakage was substantial enough it would not allow enough pressure in the chambers to pass through the cooling system to diagnose a faulty head gasket. Can an instance of spark blow out cause detonation? could the boostane have caused this? plugs are orange. Any other testing I can do besides a pressure test on the head and block? I am happy to get a new head gasket and valve job but not without a diagnosis first. What can I do to narrow this down? Tune and logs of the pre event test pulls attached. Thanks everyone. Going a bit crazy over here.

Mr Plow

Unfortunately far from elite, but I want to follow this for people's experience and advice.

It sounds like increased power from intercooler, boost reference change and 3 inch exhaust. Potentially has detonated on current map and damaged something or lifted head through torque, leading to water system pressurisation. Was there zero tell tale on your head gasket and surfaces?
9.5 CR pistons on a decked block/head = pretty significant overall CR to be running 19psi on pump fuel - octane booster or not - depending on timing (cant look at map or logs just now). The low RPM, high boost burp in testing was probably your highest cylinder pressure/torque incident and may have been the initial upset.

The leakdown test numbers are very poor if on suitably scaled leakdown tester for your engine. Not sure on the absolute link to your other issues and would look to double, triple check where the leaks are going, but too late for that if apart.

curly

iTrader: (25)

Those coolant temps are a little hot for me, but I realize it's difficult to build a coolant system that can withstand full throttle/boost for such long periods of time. In my experience, you're about 5-6 degrees advanced at the upper rpm, but mid range looks ok. If you're below 10 degrees (you're right at 10 now), you really should be looking at a different fuel.

Speaking of which, in the future, I'd highly suggest either a true race gas or E85, your engine will thank you. I did some minor tuning work on a Formula D car, and the **** those cars have to live through is insane. I also think anything below 11:1 afr is just throwing away gas, but that may be one of the things keeping your engine alive as long as it has, the extra fuel is just keeping cylinder temps down.

curly

iTrader: (25)

Looking at your logs, RPM should never go down under full throttle, your logs show that quite a few times, you may want to look into that.

Also, your injector duty taps out at 94.8, get some ID1050x injectors in there, you'll max out around mid 70's DC. If you're opposed to this, lean out your fueling to 11.2-11.4 (see my previous post, this might be a bad idea) or increase fuel pressure to 4 bar.

Nick Stacy

@curly Thank you so much for the input. I think the rpm dropping under full throttle is the spark blow out I was experiencing. Maintaining a perfectly ideal coolant temp on drift cars is very difficult because of the reduced air front due to the cars physical angle and overall lower physical speed whilst still being pushed to its limits. The runs are very short so it doesn't see high temps for very long and it only creeps up at the very end of the run. Also, fully planned on going e85 and new injectors next season OR lowering boost. TBH, i will probably lower boost and just be happy. This sport can be very unforgiving and I am a middle class gent. Fun is the most important part here for me personally. Can't have fun when you are broken, so increasing the margin for error is probably the smart choice. The thought with the rich afr under full load is indeed to keep cylinder temps down. I don't mind wasting a bit of fuel for added protection, but I do see your point. I also have a fully adjustable AEM regulator. I upped ignition advance in the higher rpm because from what I've understood the BP can handle the added timing up top, and I never heard a single trace of knock up there. ever. But not opposed to lowering it for added head room/security.

@Mr Plow I also suspected head lift to some degree. I feel like that would've been mitigated by the ARP studs but who knows. The head gasket looked fine on teardown. But that doesn't necessarily mean anything. Nothing obvious. The leakdown was done on the engine stand and the leakdown was indeed pissing air out of every single valve. So if the valve faces/seats were damaged enough, it wouldn't allow me to diagnose a bad head gasket via leakdown. Unless the gasket leakage was worse than the valves. Which it wasn't. No air coming out of the cooling system components. Maybe could do a hydrocarbons test. I definitely agree with you though, I believe the initial upset happened during testing.

Thanks guys

Mr Plow

The smoking gun is currently missing from this debrief. I'd get your head and block pressure tested if possible and may find the issue given no obvious HG fault. Potentially a crack opening up with high heat condition caused by your initial testing burp. Long shot but I'd knock it off the list if I was going to effort and cost of rebuild.

I'd also aim for insanely good/low RA figures on the deck and head surfaces of any rebuild to again help the MLS HG. Potentially try an Athena gasket as more tolerant of surface finish and potentially more tolerant of intermittent head lift. Don't quote me on it - only personal thoughts.

Nick Stacy

agreed. Head is getting pressure tested before the valves/seats get refreshed. Would be smart to pressure test the block as it needs new freeze plugs anyways. Under closer inspection, the head did reveal a very small amount of detonation on the head mating surface itself on the intake side only on all 4 cylinders. Should be able to resurface and be fine but there was indeed detonation at some point. This must have been cylinder pressure Induced det and not spark advance induced det. Sounds like I found the max boost for a 9:5:1 ratio built motor on a 2871…LOL

Nick Stacy

Update to this thread if anybody has anymore insight.

The head gasket did indeed blow in between 2 and 3 and there are heat marks around cylinder firing ring 1 leading straight to a coolant jacket. So this is how the cooling system was getting pressurized under boost/full load.

My head shop guy got back to me, the exhaust valve guides fried and all the valve seats across the board came out of round. All of the valves are perfectly sound. Very weird. You would think the valves would have went first.

Clearly the motor saw an excess of heat and/or cylinder pressure. It is possible that the valve wear happened slowly over the course of the season or everything happened all at the same time/event. Anybody have any ideas as to how something like this happens? Valve seat and guide wear could potentially be my rev limit setup. The car saw a lot of limiter this past season. Progressive spark retard and spark and fuel cut. Maybe EGTs going up due to the spark retard + leaning out due to fuel cut but I see no lean events in the logs on limiter. Maybe just too much boost with the 2871 on pump gas at 9:5:1

themonkeyman

While the pistons are quoted as 9.5:1, while the motor is apart Id encourage you to CC your chambers and measure deck height to actually calculate the true compression ratio. I suspect you’re probably at 10:1 or better. But yes more injector, less fuel, and ethanol will all help it live longer at current boost levels. Ethanol is more resistant to knock but it also runs way cooler, which is a huge reason the drift guys love it.

LeoNA

I believe the ST pistons are spec'ed based on .010" of material removed the deck surfaces. I have also read posts of people claiming the compressions is a bit lower then specified. The limiting factor is hard to define because boost will vary with the volumetric efficiency of the engine. Output might be the best way to determine the ceiling for this application. There is a finite amount of power that can be achieved on a particular fuel. The limits can only be raised so much by increasing the AFR and reducing the timing. This is the combustion cooling strategy. When one goes too far the EGT's will become too high, and the combustion temps will be erratic. Erratic meaning, unstable or appearing to be stable with a specific use. A good example would be a tune that was ok on a relatively flat track with shorter straights in cooler ambient temps and then has catastrophic failure on another track that has the counter. The benefit of a higher static comp is better low end, out of boost TQ, but at the cost of higher rpm output. E85 would be a good solution. Lowering the compression and boost a bit might also yield a larger margin for error. FWIW and I'm only guessing, it appears you substantially under built for the output.