i have a fresh 355. i always ran 94 oct. fuel. one day on my way home from the store it started to run rough. the next day i drove it i let it warm up and the put it to WOT. it started to ping. i cheched my timing with the vac. adv. disconnected @ 950 rpm. it was at 30* adv. i backed it down to 18* adv. it still pinged. i figured it was bad gas. i drained the tank and ran 110 (turbo blue) the pinging dramaticaly reduced but it was still there. my comp is like 10:1 so i know its not too high.

i thought that i could have a lot of carbon buildup on the pistons and comb. chamber. i pulled the heads. NO carbon. the left side bank head gasket was burned (blackish looking) between cyl. #'s 4 and 6. the right side bank gasket was burned completely through like a 3/8 gap between 3 and 5 cyls.

my question is: were the blown gaskets caused by the detonation or pre ignition or was the det. ar pre ignition caused by the blown gaskets.

either way i have to replace the gaskets so any help would be greatly appreciated. thanks

 

anyone?

 

too lean?? lean conditions will cause pre-detonation.. its one of my main concerns running 11.1:1 on 92 octane..

yes, the blown head gaskets were from the pinging.. you should NOT be pinging anywhere near 10:1, especially on 94 octane..

 

im just confused cuz the pinging just happened all of the sudden. it couldnt just jump out of tune.....id hope not. i also richened it up and it still pinged.........
?

 

Check the quench distance and run the DCR numbers again.

 

its non computer controlled.

 

Quench distance= actual distance from piston crown to cylinder head. Deck height + compressed headgasket thickness.
DCR= Dynamic Compression Ratio, the compression based on the intake valve closing well after bottom dead center on it's way up. Available HERE.
Since the gasket problem occured in the middle of both heads, I would check both heads for flatness, make pultiple passes with the torque wrench following the torque sequence when the headbolts are tightened and verify the actual coolant temp when it is back together. Any of these could have caused the problem in addition to detonation.

For reference:
Detonation (pinging): Sounds like a herd of pingpong ***** bouncing under the hood. Everyone has heard this on an engine that is lugged up a hill. Hard on head gaskets. If it is sustained for long enough, preignition occurs.
Preignition: Has a loud knocking sound; ignition of the fuel charge when the piston is still early in the compression stroke. Everyone has heard this when an engine is idled way too high and the key is turned off. Clock-clock-clock. Destroys pistons, rings, valves and rods.

 

thanks. i fixed it today. i replaced both head gaskets and now there is no ping. timing is at 20* @ 1000 rpm vac adv. off