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Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
Hi first time posting and looking for some input on diagnosing a engine I just did a teardown on for a customer which looks to be detonation damage to me. Little bit of a back ground it's a 2.5l mazda engine out of a 2013 mazda 6 naturally aspirated and made 195bhp on a hub dyno(adjustments to the tune was also made while on the dyno) the weekend before a HPDE track event in which the number 3 piston had a chunk blown out of it. The compression ratio was a 11.1 forged piston but the engine builder didn't provide any documentation so I dont know what the actual compression ratio was and the car was running on 93 pump gas. I'm doing a full rebuild on it and possibly even tunning it myself cause the guy who orginally tunned it blamed it on foreign debris entering the cylinder causing the damage but to me it looks like all the pistons were running lean or too much timming advance causing the piston to melt and come apart causing the damage but I have been wrong before. Me and the customer aren't trying to blame anyone we just want to know what caused it and to prevent it from happening again. Thanks for any input I have alot more info to give just didn't want to overload with data so I will answer questions as needed and attach pictures to me it looks like all the pistons were starting to come apart around were the intake valve reliefs were cut into the pistons thanks again.
What ECU is being used to control the engine? What was the rev-limit? Is there any data logging showing engine temps, knock detected, etc?
It's a stock mazda ecu that was reflashed i want to say a 2.5 ecu from a mazda 6 and not the miata one that was orginally in the car ( the 2.5l engine is in a 2009 miata chassis) not sure on the rev limit but will try to find out what he had it set too. it also had a set of mild camshafts with molnar rods and arp bolts with a stock crankshaft. He doesn't have any data logging data from the track event when the engine went out but we are in the process of trying to get the datalog data from the guy who dyno and tuned it right before all that happened to see if that helps
It would be interesting to see the ignition timing vs. the stock timing, but with OE ECU's there are lots of compensations, so the main ignition tables doesn't always tell the whole story.
Another question, did this fail at the start of a session or after the car had been running a while (so it was likely very hot)?
Have their been any other changes to the MX5 Miata to support the 2.5L engine (additional oil cooler, larger radiator, hood vents, relocated engine by components to increase airflow through the radiator)?
Increased engine temps can lead to detonation (that probably wasn't seen on the dyno as most tuners keep an eye on coolant temp and don't operate above 100 degC), but the OE ECU has pretty good knock control (if it hasn't been disabled).
Just a reminder there is a good webinar on engine failures and what to look for:
The FOD claim doesn't really stand up to inspection - even with what appears to be a lot of debris pitting.
What I suspect is the pistons were running very close to their melting point with the sharp transitions initiating detonation and/or pre-ignition which resulted in the material loss. There are also some areas at the top (above the ring) where there is quite a lot of wear evident, and this could be due to being overheated and hence expansion taking up the clearance, or excessive clearance allowing piston slap/rock - what condition and wear patterns are evident on the skirts? The piston damage from what appears to be broken rings could also have been a symptom of overheating as that may have butted up closely gapped rings.
Thanks for the responses I will look at the engine failure webinar. The vehicle has a larger radiator installed but stock oil cooler and will talk to him about modifying the air flow for the radiators and venting the engine compartment and a aftermarket oil cooler due to the fact we live in a very hot climate and the car is doing 30 to 40 min track sessions at a time. I will also post pictures of the piston skirts for view and the block is at the machine shop but I did have some pictures of the cylinder walls as well I will try to find them to post. Not sure if the knock detection had been turned off or not. And I'm working on getting the software to reflash the stock ecu myself and see what the ignition and fuel tables are set at if I can. And I want to say he was on the end of his 2nd or 3rd session of the day when he was black flagged for excessive smoke so the car was already hot but I'll ask him again
Sorry, to clarify, I was referring to the pistons possibly being excessively heated, not the engine's coolant and oil.
Alright gotcha thanks I'll attach the pictures of the piston skirts as well I tried to get some pictures of the ring end gaps they look shiny to me like they were butting together on the top rings but hard to get my camera to focus on it