CRACK pistons????
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Joined: 07-23-09
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From: illinois
CRACK pistons????
hey, i have a 09 cobalt ss with hahn ic and intake and custom straight pipe. i got a hp tuneput on my car from this guy named corry. he does alot of turbo balt tunes around where i live and he had my tune on a conservitive tune which was 20 psi and spiked at 22. idk if it was me racing from 2nd gear 40 roll and it spinnin tires hittin the rev limiter that made the pistons crack or if it was the tune? or was it a combination of my shitty drivin and the tune?
thanks
thanks
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From: illinois
na just wasnt use to the tune and dropped it in second and when i went to race this kid and i floored it, it hit the rev limiter quick and i let off and peddled and shifted it early and floored it again then hit the rev limter again and just let off... it was just like seconds if that on the rev limiter...
na just wasnt use to the tune and dropped it in second and when i went to race this kid and i floored it, it hit the rev limiter quick and i let off and peddled and shifted it early and floored it again then hit the rev limter again and just let off... it was just like seconds if that on the rev limiter...
Over-revving can cause the pistons to rise faster than the valve springs pull the valves up. In an interference engine valves and pistons crash together if that happens.
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From: Somewhere in time
na just wasnt use to the tune and dropped it in second and when i went to race this kid and i floored it, it hit the rev limiter quick and i let off and peddled and shifted it early and floored it again then hit the rev limter again and just let off... it was just like seconds if that on the rev limiter...
Hitting your rev limiter won't cause your pistons to crack. I assume that your ringlands have cracked, if anything (or they mis-diagnosed). There's more to the tune than just keeping boost conservative. Timing makes a significant difference. No way to tell what's going on here without more information.
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From: Tejas
Your rev limiter is prolly already altered to 6700 or so with the tune? Not sure why piston would crack...usually ya see a bent valve. Maybe the valve hit it and caused the crack. Over reving will cause piston to come in contact with valve. If we have an *interference engine*, which I assume we do then:
Over-revving can cause the pistons to rise faster than the valve springs pull the valves up. In an interference engine valves and pistons crash together if that happens.
Over-revving can cause the pistons to rise faster than the valve springs pull the valves up. In an interference engine valves and pistons crash together if that happens.
I wonder if it was something to do with the limiter itself and knock. A tuned friend of mine messed up an NLS, tapped the limiter, and ended up cracking a piston at some point during that event (had the Subaru sound start immediately after). Upon taking apart the engine, there was no evidence of any valve-piston contact, and the piston was broken on the side.
There's a pic^. He had luckily already bought forged pistons so we put those in over that weekend. Anyway, due to that, my guess would be something not valve related.
He was also using colder plugs.
Overheating the rings cause them to expand more than the end gaps allow, forcing them to dig into the cyl walls and popping the ring lands off the piston. Anything that causes excessive piston/ring temps will pop a ring land.
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From: Kathmandu
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From: Woodbridge, VA
As it is though, people just stick stronger valve springs in the head and rev much higher than 6700.
I wonder if it was something to do with the limiter itself and knock. A tuned friend of mine messed up an NLS, tapped the limiter, and ended up cracking a piston at some point during that event (had the Subaru sound start immediately after). Upon taking apart the engine, there was no evidence of any valve-piston contact, and the piston was broken on the side.
There's a pic^. He had luckily already bought forged pistons so we put those in over that weekend. Anyway, due to that, my guess would be something not valve related.
He was also using colder plugs.
I wonder if it was something to do with the limiter itself and knock. A tuned friend of mine messed up an NLS, tapped the limiter, and ended up cracking a piston at some point during that event (had the Subaru sound start immediately after). Upon taking apart the engine, there was no evidence of any valve-piston contact, and the piston was broken on the side.
There's a pic^. He had luckily already bought forged pistons so we put those in over that weekend. Anyway, due to that, my guess would be something not valve related.
He was also using colder plugs.
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From: Tejas
Typically when a compression issue pops up on our engines, such as when a piston/ring is damaged, the engine will then run uneven, sounding similar to a Subaru's boxer engine like the ones found in the Impreza WRX or STI. I hear the Subaru's signature sound comes from the unique uneven design of its exhaust, but that's another topic. The bottom line is when our engine sounds like that, then you've probably got a compression issue on one or more cylinders.
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Joined: 06-23-09
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From: Woodbridge, VA
Typically when a compression issue pops up on our engines, such as when a piston/ring is damaged, the engine will then run uneven, sounding similar to a Subaru's boxer engine like the ones found in the Impreza WRX or STI. I hear the Subaru's signature sound comes from the unique uneven design of its exhaust, but that's another topic. The bottom line is when our engine sounds like that, then you've probably got a compression issue on one or more cylinders.
