the devil within......
 

Just tore apart the might mouse and found another piston broken like the one I found in july. Don't know how long it has ran this way, but it has run a while like this.. before july I was running 89 octane and switched to 93 after piston problem. This second piston could have broke before that instance or not. Final timing was 32 degrees and a 9.9:1 comp ratio

Daddy has built motors for over 30 yrs and he has never seen this sorta disaster..

So far we think its pre igntion.

Building all new for spring.... and NO I am not telling what I am building :p :p :p :D :D just wondered what your opinoins were for what could have caused this.



Thanks

Travis

another

If it is detonation, the question is why did this happen with 9.9 compression, 93 octane and 32* timing?? The piston does not appear to have been run lean. :confused: When you tore up the piston the first time, did you go through the entire motor? From your post, it wasn't clear if you went through the whole motor the first time or just replaced the broken piston.

seized top ring. not enough end gap

Trav,
Interestingly enough , a friend and I just pulled down his 406SB to find exactly the same thing in #8. Reason was , had some blow by and comp. was down about 50 lbs in #8. All the pistons looked fine , not like a lean condition.
How was the back side of yours? This one was dark yellow to brown on the under side , indicating a whole lotta heat:mad: .
Engine was dynoed prior to installation and egt's were fine:confused: .
This also had a single plane intake and holley with 1" spacer , how about your's. As a matter of fact , the engine builder left this engine a little fat on the dyno just to be on the safe side because he knows how this guy tends to run his boat:rolleyes:
One other thing , engine only had maybe 50 hours:(

We think it was damaged when I was running 89 octane. I think this is the whole reason they were damaged. Cheap 89 octane. After the problem I changed to 93. When I repaired the piston in july Thats the only thing I fixed, pulled the head, oil pan and popped in the piston, was in a rush cause it was day before 4th july and we didn't have no reason to tear anything else apart.


Travis :)

Naa. I just checked my notes. That cylinder had a top ring gap of .021". Minimum in my mind was .016" if you go by ( .004" x 4.030") and the chevy hi per. book said minimum is .018". I was alittle bigger then both those gaps.



Travis :)

The back side of my pistons were all clean, no coloring at all. They had only been in the motor 98 hrs ( 3 months) They all looked brand new except for the crowns. I was running a 750 holley on the rich side with a dual plane edelbrock air gap intake, stock thunderbolt 4 ignition at around 5300 rpm.. and it spent most of the 98 hrs above 4500 rpm :D :D

Detonation!!! 9.9 to 1 compression with iron heads is gettin up there. Unless you are running a long cam and a fat A/F mixture my guess is even 93 octane is borderline. 32 degrees is fine if not a little low as far as ignition. What are your cranking cylinder pressures? Did you see any signs of small aluminum beads on the porcelins of your spark plugs when you were dialing in your motor? What are you running for spark plugs? On that motor MR43T plugs will burn real clean, but are really a little on the hot side which can lead to the big "D". My dad's 11:1 compression 355 was getting into light detonation on 110 octane fuel and we went to NGK R5673-8 spark plugs and haven't seen an aluminum bead on the porcelins since. If you still have the plugs take them to a good race shop and have them look at them umder some magnification to further analyze them. My guess is detonation.;)
It happens and thats racing!!!

OK, The light just went on:D . My buddy DID detonate a piston last year about an hour after we first took it out:( .
Like you Trav , he only changed ONE piston:rolleyes: ...I'll bet you this one was damaged but not visible:o . The bad one was #4 last time so we could see it (same bank) when we had the head off. Maybe it would be a good idea to change the rest of them just in case:cool:

Cranking pressures were between 180 -185 psi. There were no signs of aluminum material on the spark plugs, even when the first piston broke, there was still no aluminum on the spark plug The plug that I am using is the AC R43LTS to fit my vortech heads, the plug has a extended nose. With the extended nose the theory is the air/fuel mixture cools the plug because it is farther out in the chamber. Most of us think it was detonation, I guess I'll learn from my mistakes.. I can't really complain I have run the **** outta this motor, if only a few piston problems I can deal with that. The next setup is all around different.

Thanks for your help bro..

Travis

Yes I think it was damaged at the same time, but we didn't take that head off. I am changing to a whole new setup so new pistons are a must ;)


Travis

Wasn't the old theory on compression versus octane level 1:1.....and by that I mean, if you run 89 octane fuel, you cannot run higher than 8.9:1...or 93 octane....9.3:1:rolleyes: :rolleyes: :rolleyes:

This theory has been around a long time and only with aluminum heads were you supposed to be able to go over those formulas but only by a tiny bit....Especially with the stress that the marine environment puts on engine components:( :( :(

Travis, just something to ponder. My 13:1 compression 496 has a cranking compression from 180 to 185. I run 110 octane leaded racing fuel. MY dads 11.25 compression 355 cranks at 190 to 195 and he runs 110 octane racing fuel. His cam is a solid roller with 246/254 at .050 and .565" lift on a 112+4. My opinion is if you want to run pump gas cylinder pressures should be no more than 175, and 155 to 165 is a nice number. Run a longer cam that bleeds it down a little and twist it 6000 RPM. My dads Alpha SS has been hammered on for the past 7 years which includes many nitrous blasts at 6500+ RPM with no problems and 6000 RPM is nothing for a forged component 4 bolt small block. :D
Later!

What are you going to do with the 6 extra left over pistons??

Geeter-B. Thats a theory we have never heard, but its nice to know it now :D

Wette vette.... We new it was on the ragged edge of just being to much, I just needed it to get me throught the season and that it did :rolleyes: :D The new setup has aluminum heads and I think comp. ratio is gonna be around 9.5-9.7 this time. The only thing I am gonna use from this motor is crank, rods, roller rockers. Everything else is gonna be new again...



Hyperbaja.. Acutally I have 7 good ones.. But you don't want anything to do with these pistons LOL! They have had the life reamed outta them in onlya few months :D :D But they did the job :D


Talk to you guys ina few days Heading up north ..


Travis

travis,
was the failure in the same "hole" as the
one in july?
i'm on the DETONATION bandwagon too,
but curious if this the cyl. that failed before.:confused:
other 7 ok, if so, maybe a cooling issue pertaining to
that region?????
just curious.
jt

The piston in july was #1.. and get this the next broken one was in #2. Our buddie thought it was cooling issue, but it was never overheated and runs around 145--150 degrees. I was wondering if some how air was trapped or something.. :confused:


Travis