Cracked #4 Piston on 393W - Opinions Please

[ryan287]

Anybody know why this happens? I noticed the water jacket right next to the cylinder was fairly occluded with a loose piece of sealant...thinking it may have caused a local overheating issue on the cylinder wall.

Engine has maybe 20k mi on it and has always ran perfectly - no overheating issues or anything. Happened under full throttle in 3rd at about 4000RPM.

All the pushrods are fine, piston connecting rod still fine, and valves seem fine. There's no sign of the missing piston chunk - it seems to have been chewed up and spit out the exhaust.

Thanks for your input

 

[NicksTrix]

what kind of pistons are those? have you had any detonation? what compression and grade of fuel are you running?

 

[Ourobos]

^ Exactly. Looks like cast / hypereutectic pistons.. Doesn't take much detonation to break them at the ring lands.

 

[airbur]

Is that the ring gap on the right side where the chunk is missing? If it was gapped incorrectly there are a multitude of issues that can occur.

 

[ryan287]

what kind of pistons are those? have you had any detonation? what compression and grade of fuel are you running?

Unfortunately, since my last move, I'm missing about 1/2 of my "Bronco file" so I don't have specific engine info other than the cam profile: Flat tappet hydraulic lift .520, Duration @.05" = .222, Lobes = .112.

This was probably around 9:1 or 9:5 compression, with Edelbrock Proflo and RPM heads (1.6 rockers). I never ran into detonation, and had it running on the rich side according to the stoiciometric reading on the control module.

I'm looking at a lot of options now that this thing has to come out....maybe a 408? Maybe a crate? It's tough to get my head around all the options, but I'm assuming I'm going to have to rebuild the engine and heads.

 

[ryan287]

stamped on top of piston: HI32CP 040
096-04-11-8

Anybody know what this is?

Thanks,

 

[needabronco]

From the number on the piston they are .040 over, you shouldn't bore your block any more than that. If the bore is scored your shopping for a new block unfortunately. If your lucky the bore will be OK and you can get away with a new piston and a set of rings, but I'd double and triple check the rest of the bores and replace the rest of the rings.

 

[bmc69]

stamped on top of piston: HI32CP 040
096-04-11-8

Anybody know what this is?

Thanks,

Very common/popular Speed Pro (Federal Mogul) piston for the 393 stroker. Easy to get a replacement.

The thing I would be most worried about is a cracked cylinder wall, caused by the piston mashing that broken chunk against the head. If the block checks out OK and there is no wall scoring, I would put a new piston in 'er and roll on.

 

[Ourobos]

Without rebalance on the rotating assembly??

 

[bmc69]

Without rebalance on the rotating assembly??

Matching the weight of replacement piston to one of the originals should be done...hopefully the replacement piston is not lighter. Weight variation between identical pistons of same mfr are typically quite low. It also depends on how the engine was balanced too; not all balance shops/techs remove any weight from the pistons and only take it from the rods. Piston weight match should be checked regardless.

 

[70_Steve]

stamped on top of piston: HI32CP 040
096-04-11-8

Anybody know what this is?

Thanks,

Speed-Pro Hypereutectic Pistons H132CP40
http://www.summitracing.com/parts/slp-h132cp40/overview/make/ford

 

[WheelHorse]

What's the spark plug look like?

What's your total timing at 4000 under WOT on your map?

What octane are you running in her?

Who tuned your Proflow?

Does it still have the 29lb injectors in it?

When you had it stabbed to the floor, were you watching the AFR gauge to see if it had maintain a low 12 ratio?

Have you ever ran it on a dyno to see if the duty cycle was maxed out on the injectors?

Just thinking out loud here.

 

[ryan287]

What's the spark plug look like?

What's your total timing at 4000 under WOT on your map?

What octane are you running in her?

Who tuned your Proflow?

Does it still have the 29lb injectors in it?

When you had it stabbed to the floor, were you watching the AFR gauge to see if it had maintain a low 12 ratio?

Have you ever ran it on a dyno to see if the duty cycle was maxed out on the injectors?

Just thinking out loud here.

Timing is 4 degrees at 3500 & 3 degrees at 4500 @ WOT.

I only run 91.

Some guy at Superior Automotive Engineering in O.C. They built high end muscle cars. He did it on a dyno.

Still has the original 29lb injectors.

I didn't watch the AFR this time, but I have watched it in the past and it was closer to 15.

I wish I had been more involved in the dyno, at the time I was more interested in getting rid of flat spots. It was years ago.

Thanks for all your help everybody - very much appreciated.

 

[73azbronco]

My take without a real close look is ring gap to tight, incorrect, ring grew, expanded, caused top of piston to chunk, that and the gap is right under the failure.

 

[Ourobos]

29# injectors? Never heard of those.. Did you mean 19#? If so, you possibly ran it lean, regardless of what your meter says.

 

[00gyrhed]

detonation.

What is the volume of the combustion chamber? From the picture I am going to guess no larger that 58cc

that piston has a 15 cc dish, even with w 26 cc dish and 61 CC heads my 393 still had a 10:1 compression ration and I run 93 octane pump gas. (partly due to my high lift short duration cam) A 15 cc dish would need just the right cam to run on pump gas.

If you follow the link above and run the compression ration calculator you come up with 11.5 - 12 to one compression ratio. Not sure any pump gas would actually carry that ratio wit a reasonably street able camshaft.

I am no expert but when I was building my 393 this was a major concern with all the vendors I talked to.

 

[Ourobos]

I run 11:1 on my 418 with 93 octane and 10 degrees base timing FYI.

 

[WheelHorse]

29# injectors? Never heard of those.. Did you mean 19#? If so, you possibly ran it lean, regardless of what your meter says.

It's an Edelbrock thing as far as the 29# go, supposed to support 450hp.

 

[WheelHorse]

Timing is 4 degrees at 3500 & 3 degrees at 4500 @ WOT.

I only run 91.

Some guy at Superior Automotive Engineering in O.C. They built high end muscle cars. He did it on a dyno.

Still has the original 29lb injectors.

I didn't watch the AFR this time, but I have watched it in the past and it was closer to 15.

I wish I had been more involved in the dyno, at the time I was more interested in getting rid of flat spots. It was years ago.

Thanks for all your help everybody - very much appreciated.

Under WOT you should have been at the 12.8-12.5 afr. Do you have the dyno sheet from when you had her dyno'd? Mine shows the afr line on the bottom of it.

Unless your fuel pressure was cranked up, I'd still question the 29# injectors supporting a 393.

Your timing # is missing something. Most SBF's like 32-36 total timing under WOT. Some like a little more, some a little less and only the dyno can prove what it truly likes.

Plus, if something as silly as your tank vent becomes plugged or the extended hose momentarily collapses, she pulls a vacuum and you run lean, there goes a piston. It's why I always ran a AFR gauge and kept a good peripheral on it while WOT.

I even run an AFR gauge on my stock 2bbl.

 

[WheelHorse]

I run 11:1 on my 418 with 93 octane and 10 degrees base timing FYI.

What's your total timing under WOT? Base plus total centrifugal at say 4000G.