After 10,000 miles, 4 of 6 Pistons were like this. And why would this be Detonation caused (if so). Looking to go Forged. Any Help Anyone?
Robert
So tell me what the Hell Happened here.
- Thread starter supraguy31
- Start date
After 10,000 miles, 4 of 6 Pistons were like this. And why would this be Detonation caused (if so). Looking to go Forged. Any Help Anyone?
Robert
Boost Level was around 18psi, Fuel Mods are MKIV Fuel Pump, MAF-T, AEM FPR, Wideband, SAFC, with a 57 Trim CT. I really didnt Expect this since I was doing a simple Rod Knock Fix. Decided to change the rings and Waaalaaaa.....
Im hoping that this is just piston failure of just a bad set. I can get most of my money back if so. He is Pretty reluctant at this point because he has never seen a set of Pistons to that. All of them are broken in the same area. 1 of them broke on other the top and Middle ring lance.
Im hoping that this is just piston failure of just a bad set. I can get most of my money back if so. He is Pretty reluctant at this point because he has never seen a set of Pistons to that. All of them are broken in the same area. 1 of them broke on other the top and Middle ring lance.
18 psi on pump gas? Do you know what your AFR's were at full boost? You know where i'm going with this...right?
jdub said:
Full Boost AFR were between 11.2 to 11.5
Detonation maybe is where you are going? I cant get anything any Better here in El Paso. 91 Octane is the Highest that they sell
hmm, i dunn 18psi on a 57trim is not extreme to me. i've run 19psi on my 67mm on pump gas and have hit 490rwhp.
i know we don't have different setups, however that looks to be something other than detanation.
what was the condition of the head gasket?
i know we don't have different setups, however that looks to be something other than detanation.
what was the condition of the head gasket?
supraguy31 said:
I would bet on detonation...that's all we have here in AZ (91 Octane). At boost over 14 psi or so, your asking for it on 91 Octane...especially if you're running a stock thickness MHG and you had both your head & block decked, raising the cylinder compression. Your AFR's look ok though..I was also thinking you might be running lean.
Looks just like my piston from my origional motor, broken 2 ringland's. detonated ( i believe) and spun a bearing, though i do recal a time when the motor hiccuped, that may have been after the bearing spun then the ring got caught higher up in the bore. restarted and kept driving (noisily).
Jdub, You hit it on the Money. My Builder and his Ultimate Wisdom Had the Head and Block Decked and then Decided to reuse the Toyota Stock thickness headgasket. I found this out about 2 months after that, I jusr recently bought a 2mm MHG to replace it since I was doing a Rod Knock Fix. Now Im glad that I did check the Pistons and Decided to put new rings in.
Do you think that since he reused the same factory HG again and with the head and block being Decked that this is what caused this. Low boost was set on 1 bar and High boost was set to 1.25 bar. Yes, I do use this car at the 1/4 mile Drag strip once in a while so there has been times that I used the 1.25 bar setting.
Robert
Do you think that since he reused the same factory HG again and with the head and block being Decked that this is what caused this. Low boost was set on 1 bar and High boost was set to 1.25 bar. Yes, I do use this car at the 1/4 mile Drag strip once in a while so there has been times that I used the 1.25 bar setting.
Robert
supraguy31 said:
Well man...it darn sure didn't help. Higher compression + high boost + pump gas = BANG.
Edit: The increase in compression does depend on how much material was removed from the head/block, but it adds up fast. 10 thousands from each is about .5mm.
Since you're gonna be taking this motor apart and the surfaces were decked, have the RA checked on the head and block...having them lapped down to <30 will allow the MHG to seal well. And, if it's a new MHG, don't use any spray sealer on it...new MHG's have a coating from the factory to effect the initial seal. A spray sealer can turn the factory coating into goo.
Last edited:
Were the rings properly gapped? Hmm?? WERE THEY?!
I broke 2 pistons in my turbo Camaro when I went SLIGHTLY lean, overheated the rings, which over-expanded and broke the 2nd ring land.
I broke 2 pistons in my turbo Camaro when I went SLIGHTLY lean, overheated the rings, which over-expanded and broke the 2nd ring land.
Doward said:
LOL...sounds like a Dirty Harry movie. "Do ya feel lucky Punk...well, DO YA"
:biglaugh:
When I ran down the dragstrip and missed 3rd gear bad, my car started to putt immediatly afterward. A tear down revealed I had broken ring lands just like yours in number one cylinder. Maybe an instant of detonation did me in. How about you? Did you miss a gear and over-rev? I'll post pics soon. I'm not at home.
EDIT: http://www.supramania.com/forums/showthread.php?t=19332
Those are my pics. Same as yours.
EDIT: http://www.supramania.com/forums/showthread.php?t=19332
Those are my pics. Same as yours.
Last edited:
We got alot of suggestions here, and no IJ comments...
Something is definately wrong..
lol
I think Doward may be on it, or it went lean (low fuel pressure?) and detonated. I hate guessing though... so I won't
Something is definately wrong..
lolI think Doward may be on it, or it went lean (low fuel pressure?) and detonated. I hate guessing though... so I won't