Combustion Chamber Pitting

[zack_280]

I have the head off of my motor due to a series of unfortunate events.

 

Motor Details:

The engine had <1000 miles on it per the PO and that is probably accurate. The engine was built by Sunbelt about 7 or 8 years ago and the PO never really got the tune sorted out. There was noticeable pinging when I test drove it but it didn't seem to have any compression issues and ran pretty well when it wasn't being pushed too hard. It is an F54/P90 with a Garrett GT35R turbo and some other shiny stuff. I am in the process of installing an MSII ECU. As I said before I removed the head due to a series of unfortunate events and saw this.

 

Here is another pic. This one with no flash.

 

 

 

When I first took the head off the pistons were coated in a nasty gunk and so was the combustion chamber. I thought I could see signs of pitting, but was just hoping that it was only sludge. It wasn't. Here is a pic of one of the wiped chambers and one that hasn't been touched.

 

 

 

 

 

I haven't cleaed up the other chambers yet, but they all appear to have similar pitting. Given that I plan to run 12-18PSI of boost and will be driving this car on race track what is the appropriate course of action for the head?

 

 

 

Thanks for the help.

 

 

 

Zack

Edited May 6, 2011 by zack_280

[z-ya]

Detonation will cause that kind of pitting. Noticeable pinging (or any pinging for that matter) is bad for any engine, especially a forced induction one. I am assuming that one of the unfortunate events was the head gasket blowing...

 

You will need to smooth all this pitting otherwise the hear will be even more prone to detonation. I would also have the head pressure tested. And, make sure that there is no pitting in the area where the head gasket sealing rings sit.

 

What is a "PO"....

[zack_280]

I think the series of unfortunate events started with me purchasing this car, but a blown head gasket wasn't one of the events.

 

 

I assume by 'smooth all this pitting' that means having it welded and reshaped...If that is the case, what would be a ballpark figure for the expected damage to my wallet? Just looking for an idea of what this should cost.

[cygnusx1]

It seems like plenty of expensive port work has been done to it, so you need to compare the price of porting a new head to match, with having the one bad chamber welded and re-cut. If it's just one chamber, it might not be too expensive. However, the cheapest is to let it be, give it a GOOD tune, and then have the dyno/tuner dial it down a few notches for safety margin. Also check that injector, if that's the only lean chamber?

[zack_280]

It's not the only lean chamber. They all had similar pitting. I think it was due to the JWT reflashed ecu, terrible wiring from the PO, and the wrong injectors used with the JWT reflashed ECU. Ironcally the injectors used were 750CC instead of the 420CC injectors that JWT recommends.

[rsicard]

It's not the only lean chamber. They all had similar pitting. I think it was due to the JWT reflashed ecu, terrible wiring from the PO, and the wrong injectors used with the JWT reflashed ECU. Ironcally the injectors used were 750CC instead of the 420CC injectors that JWT recommends.

 

Zack_280:

 

It is obvious that detonation is the cause of the pitting wherein some of the material has melted away. It was not said what type ECU was reflashed. Need to determine what the compression ratio is of the present setup. More importantly the MSII ECU needs to have adjustable timing map and VE map that are somewhat easy to change. What will be the method by which the MSII attains crankshaft timing? What is the present setup of the EFI and Spark timing by the reflashed ECU? Ignition timing on a boosted engine is VERY important over the whole RPM and dynamic load range. As the engine is lugged down with dynamic load the spark timing needs to be automatically adjusted appropriately otherwise detonation is CERTAIN. The crank timing method needs to very accurate and the ECU needs to be reprogrammed based on appropriate feedback data. Also photograph the tops of the pistons for reference purposes.

 

One sure fire method to arrest damage to the head and pistons is to have them coated with ceramic coating. I have done this in my shop and the results are very good. I presently am outfitting a Small Block Chev V8 to a 240Z with Electromotive TEC3 Ignition and EFI and it is VERY precise ignition and fuel injection system. The preliminary stages of EFI setup are already done. Have experience in previous EFI modifications.

[Tony D]

Yep, detonation damage from inaudible and what most people think is 'harmless' detonation long-term.

 

Remember people say to check your plugs for signs of silver (aluminum) after some detonation---now you know where it comes from! Either the head, or the piston crown.

 

Ceramic Coating may be the least expensive alternative to salvage the head, but the damage between the seats won't be helped by ceramic... Lost material there means the chance of a lost seat eventually.

[zack_280]

Zack_280:

 

It is obvious that detonation is the cause of the pitting wherein some of the material has melted away. It was not said what type ECU was reflashed. Need to determine what the compression ratio is of the present setup. More importantly the MSII ECU needs to have adjustable timing map and VE map that are somewhat easy to change. What will be the method by which the MSII attains crankshaft timing? What is the present setup of the EFI and Spark timing by the reflashed ECU? Ignition timing on a boosted engine is VERY important over the whole RPM and dynamic load range. As the engine is lugged down with dynamic load the spark timing needs to be automatically adjusted appropriately otherwise detonation is CERTAIN. The crank timing method needs to very accurate and the ECU needs to be reprogrammed based on appropriate feedback data. Also photograph the tops of the pistons for reference purposes.

 

One sure fire method to arrest damage to the head and pistons is to have them coated with ceramic coating. I have done this in my shop and the results are very good. I presently am outfitting a Small Block Chev V8 to a 240Z with Electromotive TEC3 Ignition and EFI and it is VERY precise ignition and fuel injection system. The preliminary stages of EFI setup are already done. Have experience in previous EFI modifications.

 

 

The ECU was from a 300ZX. There is more detail at the JWT website, but it was reflashed for their '450' HP kit. The maps cannot be modified. The fuel injectors per the JWT site are supposed to be 420CC, but the motor had 750CC injectors. The PO had gotten around the disparity through use of an APEXi 'piggyback' ECU. I do not know the compression ratio. Crankshaft timing will be from a 36-1 EDIS wheel. I have a coil per plug setup driven directly through the MSII. No photos of the tops of the pistons, but there is nothing really to see. They are all pretty smooth except for the barely noticable fly-cut for the intake valve. I did a compression test prior to buying the car and came up with 125PSI on all 6 cylinders.

 

Looking at the block there is a noticable horizontal 'scar' on the #1 cylinder wall and a vertical score on #6 that is harder to see, but pretty easy to feel.

[zack_280]

Thanks for the good news Tony.