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Detonation

Discussion in 'The Garage' started by mountainexplorer, Feb 27, 2005.

  1. mountainexplorer

    mountainexplorer 1/2 ton status

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    If you were running a SB400 motor with flattops and 64cc chamber heads on regular 87-octane fuel, think any damage could occur if driven with a light load for 70 miles?
     
  2. Fierospeeder

    Fierospeeder Banned

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    If you did have detonation. It would ruin an engine that quick. You will find out if it was detonation when you remove the head on the motor. It is possible something may have seized internally and caused damage to your motor.
     
  3. beater_k20

    beater_k20 Banned

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    if you run a big enough cam, you wont have problems with detonation as it will bleed off some compression. what is the displacement of the valve reliefs on the pistons? and what size cam are you running?
     
  4. mountainexplorer

    mountainexplorer 1/2 ton status

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    The cam is a Comp 292... .510 lift supposedly. The heads are 64cc chambered 041 casting heads. The pistons have 4 large valve reliefs. I'm not 100% sure on the exact displacement of them.

    This is the motor last July:
    http://community.webshots.com/photo/28668497/161802961FKJVFi

    http://community.webshots.com/photo/28668497/161803048hKPknU

    http://community.webshots.com/photo/28668497/161803252qoJxbl

    It has less than 2000 miles on it, and ran strong and didn't make a single noise until 5 seconds before it shut itself off. Something came loose on #8 and there is now a hole in the cylinder wall, based on seeing the coolant come out of the oil pan.
     
  5. ZooMad75

    ZooMad75 1/2 ton status Premium Member GMOTM Winner

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    64 cc heads and flat top pistons will give you a nice HIGH compression ratio. Even with the 4 valve reliefs, you are probably pushing 10.5 to 11:1 or slightly more. What octane rating of fuel were you running?

    Problem I see from what you wrote is that running Iron heads with that much compression it would be more prone to detonate even with the big cam. The iron heads are retaining a lot of heat and even though some pressure might be bled off with the cam the head still is keeping the heat in the combustion chamber. Add to that the possible use of 85-87 octane fuel and you have got the recipe for detonation.

    Just for an example, a buddy of mine built a punched out 400 (406) for his 88 1/2 ton. He ran Dart Iron eagle heads, big cam, flat top pistons and complete MSD ignition. It ran good, but to eliminate the detonation he had to run a mix of 93 octane premium and 102 octane racing fuel. Lucky the gas station around the corner had the good stuff for $3.50 a gallon! He could run straight premium 93 octane, but it usually started to ping lightly. So most of the time he had the mix of premium and race fuel just to keep it alive.

    If you had detonation happening, it could kill an engine in pretty quick fashion. It probably broke a piston and those loose parts put a hole in the cylinder/water jacket. Either way the block is probably toast.

    Bummer dude. :frown1:
     
  6. mountainexplorer

    mountainexplorer 1/2 ton status

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    I wasn't thinking when I went to leave to come back home yesterday and I just put regular 87 octane fuel in. Just one of those days where you have more things on your mind than you can keep up with. I do remember thinking, wait, I should have put Premium in like usual. But I was already done filling up.

    The sound I heard probably was a piston exploding. #8.

    Now I have to start all over with the one motor out of the 10 others that was done. Even though I had hardly any money into this motor, it still makes me real mad. I have another block lined up on trade, so I get to play Mr. Budget again and see if I can wheel and deal my way to getting another shortblock put together on parts trades. :crazy:
     
  7. ZooMad75

    ZooMad75 1/2 ton status Premium Member GMOTM Winner

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    87 octane is probably what did it over a 70 mile run. Knowing how loud my K5 is at highway speed (assuming yours is similar) I bet you never heard the pinging until it blew a hole in the piston.

    If you build the next one up similar, I'd throw a couple of bottles of 104 octane boost in the back, just in case you dump a whole tankfull of 87 octane in. 104 is not as good a premium, but it might keep the pinging at bay. Better yet, print up a lable for "premium fuel only" and sick it on the gas door as a reminder.
     
  8. beater_k20

    beater_k20 Banned

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    a 292 with a 10.5-11:1 engine is pushing race gas territory.
     
  9. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Damn, 11:1 in a motor known to run hot, with 87 octane and you never heard the pinging?

    I'd find that hard to believe.

    Are you sure the engine is damaged?
     
  10. mountainexplorer

    mountainexplorer 1/2 ton status

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    I don't quite think it was 11:1. Used the regular Fel-Pro thick head gaskets.

    I have heard this motor ping in the past, even on Premium, but when towing a heavy load or accelerating up a hill. Whats weird is the day I put 87 octane regular fuel in, I don't remember hearing it ping. Of course, I was being a slowpoke driver that day too and not pushing it very hard.

    Oh, and I know the engine is damaged cause theres a hole in the oil pan up by the starter, and both oil and coolant came out of the pan. I'll bet anything I'll find #8 piston shattered with a hole in #8 cylinder. I'll take pics when I pull it out and tear it down.
     
  11. thor

    thor 1/2 ton status

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    The 292 comp cam bleeds an aweful lot of cylinder pressure... You need atleast 10:1 to make this cam streetable. I don't think that's what did it. (my $.02)

    Detonation "usually" won't damage a cylinder itself, It will destroy pistons (usually a hole, or break the ring lands, but that won't cause collant in the oil) It will also pound the life out of bearings, but since it self shut down and has coolant in the pan there is some more trouble shooting to do to determine the cause.

    does it turn over and did it toss a rod?
    did it get hot and lose a head gasket?
     
  12. mountainexplorer

    mountainexplorer 1/2 ton status

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    Amazingly, this 400 always ran cool. I thought I'd have cooling issues with it being .040 over, but I have a nice 4-core radiator in it and its kept it from getting hot.

    Even stranger is the fact that the noise was sudden and abrupt... less than 5 seconds from when it started to when it shut off and blew a puff of smoke out the exhaust. I checked all the fluids, and external parts of the motor. It was not overheated at all, fluids were all up and good.

    When I tried to start it again, it acted seized cause the starter wouldnt turn it over. I reached down and turned it over by hand. Then hit the starter again and it cranked over freely and made NO noise, no clunking at all. But it spun over very fast like there was hardly any compression.

    Thats when I noticed the hole in the pan which wasnt there a few seconds before, and both oil and coolant leaked out. I can't figure out what could have broke loose and NOT be making any noise whatsoever when the motor cranks over. There wasn't even any loud thud when it shut down and blew the puff of smoke.
     
  13. thor

    thor 1/2 ton status

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    Detonation is hard on rods and bearings, but since you did not spin a bearing first, (or have a piston fail) I still don't think I would point to that as the cause of the rod letting go. When you do the autopsy, severe detonation would have left marks on the tops of your pistons like if you were peening it with a hammer.
     
  14. mountainexplorer

    mountainexplorer 1/2 ton status

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    I bought a Suburban for parts a few years ago, that had a blown motor. I pulled it apart and found a piston that was all pitted and eaten away up top... the rod was twisted and broke and the piston was sitting turned in the cylinder. It also wiped out that bearing (also #8) and #6 right next to it. The cam was also broke in 3 places. It had flattops and 58cc chamber 305 heads on it.
     
  15. 84_Chevy_K10

    84_Chevy_K10 Banned

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    Just so you know, for future reference, that makes it WORSE. Even though you have less compression with thicker head gaskets, increasing your quench distance like that makes for a more knock prone motor, not less.
     
  16. mountainexplorer

    mountainexplorer 1/2 ton status

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    What about it makes it worse?
     
  17. Robert79K5

    Robert79K5 1/2 ton status

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    I bought a 400 off a guy that was toast. Pretty much the same scenario as you.

    What happened is that it broke a connecting rod which in turn took out the cam .

    Fortunately it didnt damage the block at all so if this is what happened to you then you may get lucky and not have a ruined block.

    I guess the number 8 piston would be the most vulnerable since its in the back of the line for coolant flow right?

    good luck mang :crazy:
     
  18. ZooMad75

    ZooMad75 1/2 ton status Premium Member GMOTM Winner

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    How is using a thicker gasket vs a head with higher volume (say 72cc) increasing your quench distance? either way, the volume of the combustion chamber is more. I'll admit using a thicker head gasket is not the ultimate solution to increase the combustion chamber size. Some times you have to run them. With his high lift cam and flat top pistons it would seem to me that the thicker gaskets might have been needed for that extra security to keep the valve faces from smacking the pistons at max lift. That being said, we are only talking about very small difference in thickness between a "thick" gasket and a "thinner" gasket. Yes the head gets spaced further away from the piston, but only by an amount of like .020" or less. Thats not even taking into account the actual thickness when the head is torqued to spec.

    Running steel shims for gaskets to limit the "quench distance" would most likely put dents in the pistons from the valves smacking them at max lift. (keep in mind it the cam's lift is multiplied by the rocker ratio making the movement of the valve that much closer to the piston)

    Bottom line is, with that high of a compression ratio with Iron heads it would make it more prone to detonation on 87 octane regardless of the thickness of the head gaskets. Had he been running aluminum heads, he could have got away with the cheap stuff because the aluminum retain less heat than an Iron head would have. 93 octane premium is pushing the limit with 10.5/11:1 compression ratio on a carburated engine without the fancy knock control that a fuel injected engine would have. The electronic controls start pulling timing back with the slightest amount of knock detected by the knock sensors. The knock is not audible yet when the system starts working. Without the electroinic controls I would back the total timing off a couple of degrees to help limit the pre-ignition. You would loose a slight amount of power at the extreme top end of the power curve, but it would be less prone to detonation.

    I'm sure that the piston in the #8 hole on allens rig has the characteristic marks of detonation. Since the pan was not damaged when he first stopped, but then damage shortly after trying to restart it I would think that piston got hung up in the cylinder by broken chunk of aluminum (or the ring lands broke causing the rings and chunks to stick the piston to the cylinder). When trying to force it over with the starter, the stuck piston caused the rod to bend and break causing the resulting hole in the water jacket and pan.

    We won't know for sure until Allen does the autopsy. We want carnage pics by the way!!
     
  19. smalltruckbigcid

    smalltruckbigcid 1/2 ton status

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    Quench is defined as the distance between the top of the piston and flat part of the head... the part away from the valves. Quench is not the area above the valve heads, that is chamber size and is sized in cc's. You can get away with 11-1 and iron heads but you need to polish every sharp edge in the chamber and run good gas and tune accordingly. It would help even more to have the chambers ceramic coated to aid in heat rejection (it helps to pass more heat out the exhaust) but that isn't cheap.
    George
     
  20. ZooMad75

    ZooMad75 1/2 ton status Premium Member GMOTM Winner

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    Sure quench is what you say it is, but still a thicker gasket also increases the combustion chamber volume. The combustion chamber includes not only the chamber in the head, but the volume of the gasket, any valve reliefs or dish in the face of the piston and the volume down to the top of the first compression ring between the piston and the cylinder. you can't get an absolutly accurate compression ratio measurement without taking all of that into consideration. Yes you can get close with just the boresize/stroke and combustion chamber volume, but it's not totally acurrate. Plus if the piston is set below the deck at TDC you have to account for that too.

    What I'm getting to here is that blaming the detonation on the thickness of the head gasket is missing the mark. There is more at work contributating to the detonation with the iron heads, 87 octane and timing. I'm doubting the aspect that the .020" or less difference in compressed thickness of the head gasket was the ultimate cause to his problem. If anything the slight decrease in quench area is offset by the slight increase in combustion chamber volume as far as detonation is concerned on a backyard built engine. Ultimately it was the high compression, Iron heads and crappy 87 octane fuel that did him in.

    I don't think your wrong as far as decreased quench contributating to knock sensitivity, just that it's not the only reason for the failure in this case.
     

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