[Ross455]

I have hurt my engine 3 different times over the last 10 years or so. Each time the top ring lands were lifted on 3 to 5 Pistons. It was cylinders 5-8 each time, and each piston was lifted at the intake valve relief.
I have read lean was the cause and rich was the cause. I have a Fast AFR meter but was not logging when I hurt it this last time. Honestly I hadn't had an issue in so long I wasn't concerned. AFR is stable around 11 at WOT.
Blow thru carb. Annular boosters. 428 with home ported Edelbrocks and Victor.
Pump gas with 8.5 CR. MSD BTM pulling out 2 degrees per pound starting with 34-36 total. Around 10 lbs boost. No burned plugs.
I must admit to being foolish and laying on the rev limiter for about a full second doing a burn out on the street when this last episode occurred. Made a pass right after and finished off 3 Pistons. I really think it may have been hurt during burn out though.
Car runs 6.30s at around 110. 1969 Firebird at 3600 race weight.
Any thoughts would be appreciated. Other threads I have read it seems like the people with the answers don't want to give advice.

[70 bird]

What kind of pistons/rings, ring end gap??

[v869tr6]

The two different times I lifted ring lands was due to the front standard type power valve getting blown closed. Up to about 17 psi all was well, at 21 psi I had the trouble.

[Ross455]

Hellfire rings. I opened the top ring gap the last time it was apart. I don't remember exactly but I think I went to .028 to .030 to be sure the ends didn't butt. Bottom end has been together this time for about 8 yrs so I guess I shouldn't complain. It's a D1 Procharger with no intercooler.
I'm about to build a IA2 combination with a 4.35 bore and probably 4.35 stroke with an F1R and want to try to avoid this happening again. Always need to learn more.

[mgarblik]

If possible, could you post some pictures of the piston heads, eyebrows and lifted lands with a ring in the groove. As you have probably found out, there is allot going on in an engine when things go south. Also, you are correct, both excessively rich or lean can lift ring lands. That's why I would like to see the skirts. A band-aid most of us like to use is to retard the timing a little more when the lands lift. Continue retarding the timing until a 1 degree move slows the car down. Put back the 1 degree and you are close. Most people who tune this way find out they can retard the timing significantly from what they thought was right and the car will actually run faster. On pump gas which is not consistent tank to tank, you probably need 4-6 degrees less timing than you are running on boost. Use your wide band to get your A/F ratio where you want it, then back up the timing. Not sure how you arrived at your base tune-up but we found the general behavior of a Pontiac engine to be much more similar to a SBC than a BBC. A Big Chevy with it's chamber shape needs much more lead than a Pontiac. That cost us lots of pistons in the early days trying to tune our similar displacement Pontiac like a BBC. Don't be afraid to run really large ring end gaps, .007-.008" per 1" of bore is common with lots of boost. If you are having custom pistons made, try to soften all sharp edges and make the valve eyebrows as shallow as possible to avoid thin spots. Good luck with the next build.

[Ross455]

Thanks for the replies. I'm away from home but will post pictures sometime tomorrow. Learning by trial and error is expensive so I appreciate all advice.

[Ross455]

Future home of the new engine. 1962 Tempest. Built in NY but now happily residing in my garage in Alabama. Had a high compression 455. Will be street driven. A really nice build. Everything on the car is functional.
Hope to run mid 5s eighth mile. This is my reason for wanting to learn more.

[Ross455]

Picture of car

[Ross455]

I did have a pic on my phone of one of the pistons still in the block.

[Craig Hendrickson]

Originally Posted by Ross455

I did have a pic on my phone of one of the pistons still in the block.

Wow! That's an ouch. Let us know what you find.

[61-63]

That appears to me to be a kb371 step dish hyper piston. I am no expert at all but if that is so their website says, or said (not sure if they even make them anymore?) that you should have had more top ring gap than that on a boosted drag race motor.

Getting 8 years out of that engine ain't bad though it sounds like that was one heck of an engine.

[Elarson]

Originally Posted by Ross455

I did have a pic on my phone of one of the pistons still in the block.

Also consider that running a bit more piston-to-wall clearance might help. The failed area is a thin spot...where the dish cuts in close to the upper ring groove. If the piston top locally heats up (at the thin spot), bulges out and binds on the cylinder wall, it will peel the top ring land right off.

Eric

[Tom Vaught]

Originally Posted by Ross455

Pump gas with 8.5 CR. MSD BTM pulling out 2 degrees per pound starting with 34-36 total. Around 10 lbs boost. No burned plugs.
Other threads I have read it seems like the people with the answers don't want to give advice.

Most of your specs look good except for this one.

You start at 34-36 degrees of timing and then at 10 pounds of boost you have 14-16 degrees of timing. (with 2 degree increments).

Personally I think that with a 8.50-8.75 to 1 compression ratio you should be at 21-22 degrees at max boost with good gas and be removing 1/2 degrees per pound of boost.
So 5 degrees to 21-22 is 26 to 27 degrees of timing total.

The burn rate does not change greatly with the extra boost, just the charge density goes up and the extra fuel/air burns for a longer time as the piston goes down the bore. The initial firing point should not change much under boost. The PUSH is longer, the initial ignition point still has the same approximate sweet spot.

As an extra comment, Charlie66 has run a 4 cylinder with different levels of boost over the years and has run the same locked distributor at 27 degrees for the entire time. He takes the car on 100 miles trips.

Tom V.

[Tom Vaught]

I thought of one other thing, say your MSD BTM has a glitch and does not pull out the timing properly, see it happen with even Pro teams stuff.

Now you have 10 psi of boost with 36 degrees of timing and you kill a piston immediately. Better to be at the max safe point on timing (near 27 degrees)
based on a bunch of Boost testing with different engines, without retard and
then pull less timing under normal conditions.

Also I do not think that the Power Valve would be "blowing closed" at 10 psi boost
but you never know. Who built the Boost carb for you?

Tom V.

[Ross455]

It's a JE 2618 piston. Tom you may be on to something with the box. Earlier that same day I made a 1st gear hit and it seemed to rev higher than normal. I checked the recall and it went to 7300. My chip is at 7000 and it had never failed to limit the engine to that exact spot. I assumed maybe a bad pill or something. Box is over 10 yrs old. May be time for a new one.
I built the carb. Basic Hanger 18 mods. PV in front blocked off rear. I guess that's the most frustrating part is it ran so well for so long and then goes that bad so quick.
I still wonder about being on the rev limiter as long as I was (it did check at 7000 by the way). Could that have loaded it up with fuel and caused this.

[69FIREBIRD76MM]

Can you post pictures of your car? Like to see what it looks like. Thanks

[Tom Vaught]

I just had another thought, do you only run race gas or are you buying the typical "Ethanol mix" gas pump gas in your area?

The Ethanol will attack the Power Valve diaphragm material and cause the PV valve not to work properly. Check that deal too. Especially if it has been in the carb a while.
Tom V.

[Ross455]

It was 93 octane pump gas. Around here every premium pump it seems says may contain up to 10% ethanol.
I will disassemble the carb and update with what I find. May have even been a piece of trash in a main jet. The damage was toward one corner of the engine. The 4 and 8 piston looked like the picture. 6 just starting to lift but not burned, and 7 with a small crack in that area and obviously was very hot at that spot.

[Tom Vaught]

Whole Boost calibration is based on that PV opening up with the larger PVCR orifice flow numbers. What size PVCRs did you have in your carb and what size was it, (even though it was home built)?

Tom V.

[Sun Tuned]

I'm not wanting to crash into this thread, but would like to add this along with what Tom V said.

A local marine place here in town had been having problems with carbs for awhile on customers boats or so it seemed. The guy in back of the shop was really good friends with my dad who also had an automotive repair shop. Dad was always good friends with "Woody" at counce marine.

Well ol man counce buys Woody a alcohol hygrometer to play with...
Woody buys a gallon of gas each day on the way into work. The boat place will only use "their" fuel when servicing customers outboards. Woody starts using this new toy, and records his results on a spiral notebook....

One Exxon station Woody stopped at sells him a gallon of gas that contained 32% alcohol content gasoline. No wonder customers had been complaining about fuel mileage of their boats. The rest of the results on his spiral notebook were fairly consistent at 8-14%. But several were all over the map between 5-20%.

Now for a guy trying to tune around all this...

Be careful and be consistent as possible.