Cylinder head pitting

[Jrguzman]

So I'm in the process of changing my head gasket in my ka24det and I've noticed there is a good amount of pitting on all the combustion chambers located on the cylinder head. Only on the intake side. Anyone know the cause or delt with this. I'm running a t25 at 7 psi this is the second head gasket in a year. It's blown in the same spot twice. Any insight would be appreciated

[gaz_moose]

sounds like DET, what are the edges of the pistons like?

blown HG in the same spot is probably a warped head, did you get it skimmed??

[S14DB]

Does the pitting look like dimples or corrosion?

[Jrguzman]

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[S14DB]

You running E85?

[Jrguzman]

Originally Posted by gaz_moose

sounds like DET, what are the edges of the pistons like?

blown HG in the same spot is probably a warped head, did you get it skimmed??

Pistons and cylinder walls look great. It's strange because it's only pitted on the intake side of the cylinder head and it's looks like it outlines where the fire ring was on the head gasket

[Jrguzman]

Originally Posted by S14DB

You running E85?

No just pump gas 91, it's a ka24det t25 sti injectors aeromotive fpr and walbro fuel pump. With cp 9:0:1 pistons and eagle rods

[S14DB]

Tune? Injectors matched?

[Jrguzman]

Originally Posted by S14DB

Tune? Injectors matched?

Yes it's a Nistune ECU tuned by rs enthalpy

[ANDY black s13]

seen same/similar damage before and each time it was too much ignition advance in the base map
with limited info on ECU and how it was set up,that's all I have
edit: see ecu info,check the timing advance

[Jrguzman]

Originally Posted by ANDY black s13

seen same/similar damage before and each time it was too much ignition advance in the base map
with limited info on ECU and how it was set up,that's all I have
edit: see ecu info,check the timing advance

Yeah I set the timing on the distributor almost all the way retarded. I believe the ecu is tuned for 15 degrees. But I was trying to run really conservative since this is my daily. I noticed that the piston were very wet on top with fuel and figured that would be ok

I remember trying to set the timing with a timing gun and couldn't get the timing to go down any less than 20 degrees on the crank pully. But when I pulled up the info on ecutalk it said the car was idling at 10 degrees. So I'm not sure what's going on there.

Also any idea why the damage is limited to the intake side of the cylinder head in the combustion chamber?

[S14DB]

The burn is not even in the cylinders.

[S14DB]

To elaborate. It could be timing, fuel mixture or a leak in the cylinder, oil blow by.

[Jrguzman]

[QUOTE=S14DB;6259396]To elaborate. It could be timing, fuel mixture or a leak in the cylinder,

Okay thank you, its all four cylinders though and the tops of the pistons were wet with fuel. Is it possible to detonate with a rich mixture and timing at 9*? The machine shop I took my head to found some of the valve guides to be worn and not seating properly.

[ANDY black s13]

Originally Posted by Jrguzman

Yeah I set the timing on the distributor almost all the way retarded. I believe the ecu is tuned for 15 degrees. But I was trying to run really conservative since this is my daily. I noticed that the piston were very wet on top with fuel and figured that would be ok

I remember trying to set the timing with a timing gun and couldn't get the timing to go down any less than 20 degrees on the crank pully. But when I pulled up the info on ecutalk it said the car was idling at 10 degrees. So I'm not sure what's going on there.

Also any idea why the damage is limited to the intake side of the cylinder head in the combustion chamber?

not 100% on why its inlet side as a few theories are floating around but none
really confirmed, a similar thing happens with rb's more so the 26's with the squish pad outer edge suffering det damage at 650/700whp and the cure is radius the sharp edge of the pad or some remove most/all of the pad if aiming for over 700,jun mines etc do variations of it
,exhaust side on the rb26 is a much smaller pad with valve radius cut outs
but same as your KA it's only inlet side showing the det pits,


possible crank pulley groove and wood ruft key are worn (if it has come loose in the past especially) and it's not bang on 0 degrees at tdc and/or wear to distributor drive gear not giving you true timing numbers,
look into that ecutalk as well as he seems 10 degrees off like a signal delay ?

[S14DB]

Originally Posted by Jrguzman

Okay thank you, its all four cylinders though and the tops of the pistons were wet with fuel. Is it possible to detonate with a rich mixture and timing at 9*? The machine shop I took my head to found some of the valve guides to be worn and not seating properly.

It's that the burn is uneven not that the mixture is off. Note how the intake side is clean and the exhaust side is carbon fouled.
The valves not seating properly will give you a leak and introduce turbulence that will effect the burn and mixture distribution.