I know the longer I spend drinking around a campfire, the greater the chances that something explodes. Must be a related system.

 

Correlation indeed, except I must be made of higher octane. I usually just catch on fire... :(

 

WOW,
Great thread. It also brings up more questions.
Are very many people using EGT's? Pre-turbo or post turbo?
Are there any EGT comparisons between an E-85 tune and a 93 octane tune. Or 93 and WI.
Anybody's build using coatings on their piston's to control heat/detonation?
-JB

 

Not a lot of EGT data, sadly. E85 runs SIGNIFICANTLY lower EGTs vs. pump gas. Presumably water injection will drop EGTs as well, although not nearly as much as ethanol will.

E85 is the reason I've been lazy about getting an EGT sensor into my manifold.

 

After looking at the failures of the supertech pistons I suspect (like many) there is a flaw in the design. That thin lip on the piston around the exhaust valve relief is a hot spot resulting in pre-ignition/detonation.

Look at the OEM design and the attached piston from CP. Both grind out that area.

Also notice how thick the upper ring land is on the CP piston.

After following all of CP's success on Porsche air cooled motors I plan to use em for my built Miata motor.

 

CP makes great pistons... but what Supertech failures are you speaking of? There are many many people running them on here and the only failure I remember was due to supertech sending 11:1 pistons instead of low comp pistons. I for one have been running supertechs now for about 6 months, 2 track day, 1 hillclimb, 5 autoX's and 10,000kms of street driving @230whp without issues. Savington runs them in his race motor and he makes more power than most of us here.

 

During my research I found several examples. Even Savington has had a piston fail in the same area I refer to. While there are lots of successful builds using them there are also more than a few that failed in that valve pocket area. It's far from an ideal design.

 

Post the examples. I know of two, mine (caused by a failed ic coupler and inadequate intercooling) and zx-tex (wrong pistons put into motor). Not exactly damning evidence against them.

 

How does a failed IC coupler blow up a motor? I don't understand this.

 

I will dig up the 3rd one I found and post the link later.

In ideal conditions there is not going to be a problem with the supertech pistons. It's when things start to go wrong that the weak point of the piston fails. They have all been in that same area.

One of the things you do during a high end build is polish out the sharp edges in the combustion chamber to avoid hot spots as a source of detonation. I strongly believe this was overlooked by supertech in the area of the intake pocket near the edge of the ring land. Eliminating that sharp thin edge will decrease the hot spot and help the piston survive less than desirable conditions.

My comments and opinions are not meant to discredit anyone's products. I am only trying to help advance the forged miata builds with the knowledge I have obtained from my nearly 30 years of playing with engines on various other marques.

 

I know they weren't, but the way you posted before you were making it sound like there were all the failures. I'm sure if you look around you could find failures with CP, JE etc. pistons as well. Two failures on here, both because of extenuating circumstances. Tons of us running these pistons on here without problems.

We'll see how they do tommorow with some dyno tuning. Going from 14 PSI to 17ish PSI on the Rotrex with a new intake manifold. I'm sure they will be just fine as they have been.

Oh, and did I mention my piston/wall clearance is .0025. Zero blowby, no oil consumption, leak down test 7-8% across the board as of two days ago. And I race the car like many others here. So far so good.

 

O.K.,
I suppose now would be a good time to ask a couple more questions.

Has anybody used thermal coating on the top of their pistons and/or in the combustion chamber?

Has anybody used Total Seal Piston Rings in their builds?

 

Me and the guys around here have been going on about the durability of these said thermal coatings. We figured, since we have E85 it wouldn't be worth screwing with it. But, If I ever have to go somewhere with only gas, It would be nice to know.

 

I actually took that CP piston photo, local customer had them custom made. I do not remember the application. I would love to run CP in my future 1.6L built block but they currently don't have availability for the 1.6L. Might be the guinea pig?

 

almost a shame to cover that with a cylinder head...

 

Coupler straight off the turbo is weakened by the heat from the EWG, it ruptures but in a spiderweb fashion so you can't see the cracks. Poor boost response but still making ~14psi so we ran it all day, vs. wasting time tracking down a "boost control" issue and not getting any chassis tuning time. Finally was poking at couplers after the 5th session and ended up sticking my finger straight through the hole. God knows how high the IATs were with the turbo singing away at absolute full strength with a shitty eBay radiator stuffed in the mouth at an angle to help keep the CLTs low. I'll never know for sure, but I think that the super, super high IATs combined with the environment (Calspeed, ~40+sec of WOT in 5th and 6th) caused some damage. Turning the power up to 320+whp the next day didn't help, either. Fixed the leak, turned up the boost the next morning, got a little greedy with the timing, and ended up punching a hole through one of the pistons. Again, 22-23psi pulls in 5th and 6th on a crappy little intercooler with internals that had probably already been harmed was a recipe for disaster.

"less than optimal conditions" is probably an understatement.
standard supertech:


#3 from my first blown longblock:




So yeah, the Supertech slugs will fail at the edge of the valve relief there - after you put them through enough abuse to dent/crack the center of the piston a quarter inch straight down.

Replaced the pistons with another set of Supertechs, and significantly increased the intercooling ability, and I haven't had any further failures of that nature.

Not trying to badmouth CP, I like the thick ring lands, small wrist pins and short little skirts as much as the next gearhead, but just because they may be better doesn't mean the Supertechs are bad by any stretch of the word. I'm sure the CPs would have shown signs of abuse after what I put the first set of Supertechs through.

 

I would love to know what CHT's were during the meltdown. I agree no piston would survive that kind of torture. Were you running E85 at the time?

 

CP piston. still establishing causes, low octane fuel used, timing challenges while starting up, rich mixture. mostly operator error in not reading up. a bit expensive learning, but I was building a car not just an engine. Now I have to decide what to put in.

 

A turbine inlet pressure gauge would have shown an indication of this issue...
(In lieu of a turbine shaft tachometer)

 

Sorry to bring an old thread back from the dead, but I just picked up a new turbo project with a nasty rod knock. I opened up the bottom end and noticed one of these is not like the other.





I bought the car as a project expecting to see a stock bottom end. What I found is fully built motor that failed. These are Wiseco K556M84 (84mm) pistons with huge rods. This motor also had ARP head studs. It looks like the bore size was just a bit big and the previous owner was getting on it before the engine got fully warm which caused piston slap.

Anyone else got any ideas of what could have caused this?

Here is a shot of the top of the number 4 piston.