Built motors and detonation
#164
Former Vendor
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Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 15,442
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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.
E85 is the reason I've been lazy about getting an EGT sensor into my manifold.
#165
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.
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.
#166
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.
#170
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.
#171
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.
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.
#174
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.
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.
#176
Former Vendor
iTrader: (31)
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 15,442
Total Cats: 2,103
"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.
#179
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.
(In lieu of a turbine shaft tachometer)
Last edited by JasonC SBB; 12-06-2011 at 11:39 AM.
#180
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.
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.