I probably didnt phrase that the best....as you have seen yourself detonation can produce a variety of side effects...all pending on the root cause.

My position on your conditions is that it is not detonation. Detonation will not crack a block without significant other evidence/conditions occurring.

Number 4 chatter is a given when things are less than optimal....and that is evident in the photo....my questions where what else are you seeing in conjunction with that?

I will post more pictures later of piston tops,combustion chambers.
What else would you like to see?

Anything abnormal.....
at the track right now on my phone and about to get real busy....will look tomorrow am at what you have

#4 Chamber

piston

Are you running it with fuel from your 2 stroke weed whacker?

Is that a COMPLETELY filled block?
You can see that the distribution is all wrong

That speckling look your pics are showing are sure signs of detonation. Also looks like your burning allot of oil witch promotes detonation. The One chamber pic doesn't look nearly as bad as the pistons, but seems to show some slight speckling as well.

P-Body,no block is filled to the top of the core plugs.
Trendz,no 2-stroke !
Sport, oily look is probably from the winterizing. Engine was only run maybe 5 minutes since put in storage last fall. I put Stabil in each carb. thru the vent and fog the engine.
When started all that stuff is still in there.
Never smoked,used oil. Plugs were fine last time checked.
Who knows what the piston tops would look like after a run

Perhaps the intake ports were sucking oil and causing the detonation and black piston top issue?

Did the plug have a dark side on the porcelain?

Did you post a picture of the intake ports or can you?

Thanks for sharing I am learning lots of good stuff from this thread!

That motor is NOT sealed up at all and number 4 is oiling pretty bad..........or at least a good bit worse than the others. Pistons don't look like that because you ran some stabil through it. It's not sealed very well. And is it me, or are the valves seriously sunk in that chamber. Are they all like that?

Clearly you have some issues going on in the photos above. I’m not a fan of filling these blocks as they are venerable to begin with and then you compound the problem with growth and shrink cycles from the thermal dynamics. That will focus the stress in the areas that can move and gray iron is weak to begin with.

IMO…..I would do another build using a stock block as I don’t believe your power level is anywhere near a problem. Don’t fill it, use ARP studs on the mains, and have them in place with all the machining processes, specifically when line boring, cylinder finishing and decking (if done). Use aluminum caps if you think they help….but FWIW….I never have used them and for the same reason as I don’t fill (thermal growth dynamics). The #4 hole may look worse because it detonates the least….IDK…..the carbon on #6 looks like some of it may have been “blasted” out…..lol

You deal is pumping a lot of oil…..maybe detonation has contributed to the rings not sealing and is some of the culprit there, pull the pistons and closely inspect the ring faces and piston lands, that should disclose more. Now that we know your block has been filled and you didn’t disclose any bad news with the other main caps/mating surfaces…..I further do not believe it was detonation that cracked the block. Start fresh, make things right and it should live…. BTW…..who did the valve job? , maybe you should take your stuff elsewhere?….lol….it can defiantly make more grunt than it did….lots of low hangin’ fruit on that tree….lol

Did I understand you are using a stock six pack intake? If so, ditch it and find the wieand or build one similar, as mentioned, it’s not the hot set up for even distribution at upper RPM….another potential source of detonation.

Ok, thanks for all the free info.

The carbon is soft ,comes off with fingernail.

Heads are "as shipped" from Muscle-Motors 1999. Guides are good but those spring pockets hold alot of oil. Maybe the seals can`t keep up?
I not so sold on the rings/pistons not doing their job.
It makes good power for a "junk" motor....
6bbl intake that isn`t any good
.590 MP cam that is obsolete
Stage^6 heads that were never any good
.030 3.75 440 runs into the 9`s @ 3,050lbs.

I will look for the source of the oil,and start FRESH,no block filler, and see what I get........

I use hardblock and won't run a stock block without it. Hardblock is magnetic because it's designed to heat and expand and contract like cast iron.
Oil causes Detonation, nuff said.
You have more oil then I like. I would check everything that controls it.
Sounds like the heads might need seals and oil drans if u can.

Your intake might need a surface cut if it's letting oil in around the heat crossover. I try to block all that crap.

Not trying to be a smart azz here.......but whether you are "sold" on it or not, that motor is NOT sealing. It pumps a lot of oil and that doesn't come from the seals. That is by the rings. The bores are either too big, not straight, not round, the rings just never seated.......or all of the above. If it was sucking oil in the ports, it would smoke. By the rings, not so much.

The pistons that are "somewhat" clean near the top, that is just a function of the quench and where it makes enough heat to burn the oil off. Number 4 is cold. That cylinder makes no power.

The motor could have ten or 1000 passes. Carbon is black, but it's dry. Oil is wet and shiny..........that's what I see.

Opinions are like..........well you know........and everybody has one, but I am a firm believer in both alum caps and hard block in cast iron motors. Obviously ALL the machine work has to be done AFTER the pour. Factory cylinder walls can be thin. The hard-block is to KEEP THE BORES ROUND. They don't stay round, it will NEVER seal

And those heads are in SERIOUS need of some new valve and a decent valve job. Can't be any margin there and they are WAY deep

All good points Monte, I don`t claim to be an "expert",but I ain`t a novice either.
I will pull some pistons soon and post what I find.
I`ll wager a dirty sock that #4 has damaged ring lands again.
I had too much clutch in the early days and loaded the motor too hard.
Ran it the same way for many years.
Never had an issue till I tried a 2-step,,then a 4-spd.
Live and learn

Do you have a mid plate attached to frame and elephant ears on front? Or does engine hang from trans mount to the ears? Full cage? What type trans, clutch, rear tires? Just trying to get a feel of the shock loads to stand the car up like that. Does it do it every time? Good looking car by the way, one of my favorites.

Thank you...been my baby for 34 years.

No midplate
Basically "3" point mount 2 at the front 1 rear.
Everything but the halo-bar. Everthing is tied together.
Jerico DR4,4.88 Dana,14x32 MT stiffwall.
Without the wheeliebars it would go vertical.
Thats what 50/50 weight distribution will do with a torqy motor.
The 4 speed is not going back in and is for sale....

You might want to consider changing engine shops.

Piston/rings #4

Rings are free and side clearance OK.
Thought I would find damage.