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DETONATION, The Real Quest Killer


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#21 brianpaul98

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Posted 29 October 2005 - 01:00 PM

QUOTE
Just dont confuse cold clearnaces with hot clearances. The forged pistons may start out looser but since they expand faster once they are hot they should have a similar running clearance to grannies pistons.



Isn't this statement a bit contradictory? If the pistons start out looser and expand faster a tight piston to wall clearance like .002" will leave not much clearance.


What I'm talking about is machine shop engine honing clearances. I will need to find the paperwork on the piston to wall clearances where it shows NA engines all the way up to Blown / Supercharged and as you go more radical the P to W clearances increase. More power, more heat, faster expansion rates = more clearance. I found the ring gap paperwork from Wiseco but the piston paperwork is MIA somewhere.

All I'm going to say from experience is that if you put a brand new set of pistons in your engine with a stock P to W clearance of .0015" - .002" and you run the engine any other way than normal driving they will be scuffing the skirts and the cylinder walls after a few good hard runs.
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If its not broke, tear it apart and make it go faster!!!
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Brian Arnone
Lower Shores Performance
lower.shores.performance@gmail.com
New Jersey, USA





#22 Boosted_One

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Posted 29 October 2005 - 03:19 PM

QUOTE (brianpaul98)
Hey Mike,

Another thing I noticed about that piston was that there is black carbon down past the top ring. If the other pistons had the same thing the top compression ring wasn't sealing or lost its seal on those also. Now if it was just on this piston then its understandable and was probably due to the ring land failure. The carbon should never be down past the top ring or the compression rings have lost their seal and the engine will be losing a considerable amount of power.


Ya that was the only piston like that..

Those were total seal rings and I'd bet nothing much got past them. I had zero leakdown and 130+ a cylinder.

The motor held together fine, I mad 5 less RWHP than the previous run.

All the A/F readings were 12.5's then dipping down to the high 11's after 2700 or so.

I honestly had it tuned good and still can't see how I was detonating.

A piston like that would make some real audible sounds. And I would have let off that throttle fast.


Here is something else to consider... this headgasket blew on the same cylinders 2 years prior to the piston damage.

This was a rip in the stock air can hose that happened on the track.

Made 7 passes and the last pass I just leaned out...the thing was making 'marble in a can' sounds as loud as thunder then it felt like I lost 200 HP.

No longer than ONE SECOND after I heard it the gasket was blown.

It was a simple little rip and the unmetered air did just leaned it out. I was running a TDO6/5 hybrid with a 60 trim.

Good thing is the prior pass I ran a 13.6 so that was OK.

Shit  happens...



Felpro 8770 head gasket.
Mike K

#23 Boosted_One

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Posted 29 October 2005 - 03:24 PM

QUOTE (TurboRaider)
I would say it was detonation and the piston was hot and soft from the last dyno pull.  See the link to the article on why you would get localized heating at the edge or the piston.  Light / moderate detonation can cause localized damamage.  You are more vulnerable when you are alreaady making a lot of power and the piston temps are high.

When you have the motor loaded the pressure from combustion is pushing the top ring downward so there is no pulling load on the top of the top ring land.  The top of the piston is supported by the ring if it gets soft and starts to fail.

The mix enters under boost so you are not pulling a vacuum.  

Get some detonation soften the piston top up and once you back off the throttle and pull a vacuum the top ring starts to load against the top of its ring groove.  My guess would be that the pistons was already hot and soft and once it got pulled on it gave way.

How did it stay together during the run?  The top ring was supporting it, it was pinched down clamping the ring.

Thats my theory at least.  smile.gif

BTW I ran some informal tests on ceramic coatings on piston tops and did not measure any differance in heat transfer rate using a flame against the piston top between a coated and uncoated piston.  I'm not convinced.

Kevin C


Ceramic coating, what a damn waste of money. Never again. Screw that hoopla. I agree.

I value your opinion as always Kevin. I can say there was detonation, or preignition evidence. That much is clear...but man it bugs me as to EXACTLY why. grrr  :evil:
Mike K

#24 brianpaul98

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Posted 29 October 2005 - 04:17 PM

The only other time I saw a head gasket like that was on a blower small block Chevy where he ran gasoline in an alcohol setup. Real dumba$$ because alcohol blower engines can run 11.5:1 compression before the boost of the blower but when you put the gasoline in there look out. On that small block engine it not only took out the copper head gasket but it blow torched through the head and block too. I would say that your engine problems resulted from more than just one cause and more than likey it was multiple things all put together that did it like too high of boost not enough octane fuel and most likely the ignition timing was way too high.

I'm going to ask a friend who has seen more carnage than I have too see what he thinks. It doesn't appear to be detonation though, just a leanout and I would say the head lifted to let the combustion gasses start going through then the blowtorch affect came into play.
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If its not broke, tear it apart and make it go faster!!!
----------------
Brian Arnone
Lower Shores Performance
lower.shores.performance@gmail.com
New Jersey, USA

#25 Boosted_One

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Posted 29 October 2005 - 04:58 PM

QUOTE (brianpaul98)
The only other time I saw a head gasket like that was on a blower small block Chevy where he ran gasoline in an alcohol setup. Real dumba$$ because alcohol blower engines can run 11.5:1 compression before the boost of the blower but when you put the gasoline in there look out. On that small block engine it not only took out the copper head gasket but it blow torched through the head and block too. I would say that your engine problems resulted from more than just one cause and more than likey it was multiple things all put together that did it like too high of boost not enough octane fuel and most likely the ignition timing was way too high.

I'm going to ask a friend who has seen more carnage than I have too see what he thinks. It doesn't appear to be detonation though, just a leanout and I would say the head lifted to let the combustion gasses start going through then the blowtorch affect came into play.



Max boost was 16 psi on that piston. Final timing 20* on an SDS4E. 30* total timing @3000 rpms.

The headgasket was running the stock timing curve on the stock TBI.

The headgasket I know as much was from the unmetered air. There was a huge tear in the air inlet boot, must have weakened from the long ride up to the track.

The headgasket and the piston are 2 totally different timeframes... the gasket I had in with that piston was the TEP metal shim.

I am very conservative on both timing and boost.
Mike K

#26 MikeMeyerhoff

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Posted 29 October 2005 - 09:14 PM

I'm also runing a sch284h cam with raised compression...  I noticed that my car seemed to idle better/smoother with higher base timing.   I understood that octane affected timing, but never really considered the cam specs could have a noticable affect.

I really need to do some tuning on my car!

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#27 Shelby

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Posted 30 October 2005 - 01:09 AM

a lot of guys don't  know or understand ,,this,,when you change the cam duration  and nothing else you will increase the amount of fuel in the intake charge,,why  cause the valve is open longer so more fuel/air has time to enter the chamber ,this makes the  combustion mixture richer then it was with no other changes being made
it's also the reason guys with programable ecus have to  change their fuel map after a cam swap,, this also works  back wards,, going  from say a 284 to a stock  cam will lean the  mix
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#28 Shelby

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Posted 30 October 2005 - 01:14 AM

QUOTE (Boosted_One)
QUOTE (brianpaul98)
The only other time I saw a head gasket like that was on a blower small block Chevy where he ran gasoline in an alcohol setup. Real dumba$$ because alcohol blower engines can run 11.5:1 compression before the boost of the blower but when you put the gasoline in there look out. On that small block engine it not only took out the copper head gasket but it blow torched through the head and block too. I would say that your engine problems resulted from more than just one cause and more than likey it was multiple things all put together that did it like too high of boost not enough octane fuel and most likely the ignition timing was way too high.

I'm going to ask a friend who has seen more carnage than I have too see what he thinks. It doesn't appear to be detonation though, just a leanout and I would say the head lifted to let the combustion gasses start going through then the blowtorch affect came into play.




Max boost was 16 psi on that piston. Final timing 20* on an SDS4E. 30* total timing @3000 rpms.

The headgasket was running the stock timing curve on the stock TBI.

The headgasket I know as much was from the unmetered air. There was a huge tear in the air inlet boot, must have weakened from the long ride up to the track.

The headgasket and the piston are 2 totally different timeframes... the gasket I had in with that piston was the TEP metal shim.

I am very conservative on both timing and boost.


you know Mike i have  beat my stock  engine much harder then you did your engine  and so far i have had not a single problem after i went to the arp studs , and  durring that time a saw almost 30 lbs boost   more times then  i want'd to hehe , and run 18 lbs every  day
now i will say  a ONE time   boost spike  kill'd  new head with the stock  bolts , crack 'd the head and  blew the head gasket ,but it still ran for another  300 miles  untill i had the time to swap the head out
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#29 brianpaul98

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Posted 30 October 2005 - 01:46 AM

You just need to get one of these and be done with it.



No more ripped boots to worry about.
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If its not broke, tear it apart and make it go faster!!!
----------------
Brian Arnone
Lower Shores Performance
lower.shores.performance@gmail.com
New Jersey, USA

#30 Boosted_One

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Posted 30 October 2005 - 06:44 AM

Brian - this is where I am at -







That ripped boot was on my TBI setup 4 years ago..Karman Vortex MAS...I'm now on a MAP sensor and SDS... I'm much past that... wink.gif
Mike K

#31 Boosted_One

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Posted 30 October 2005 - 06:52 AM

QUOTE (Shelby)
you know Mike i have  beat my stock  engine much harder then you did your engine  and so far i have had not a single problem after i went to the arp studs , and  durring that time a saw almost 30 lbs boost   more times then  i want'd to hehe , and run 18 lbs every  day
now i will say  a ONE time   boost spike  kill'd  new head with the stock  bolts , crack 'd the head and  blew the head gasket ,but it still ran for another  300 miles  untill i had the time to swap the head out


I got studs too...that's mandatory.

Truthfully I don't think my combinations were all that great either on that last setup.

All I know is I changed everything I thought was an issue and this new motor is night and day difference.

I went for reducing backpressure, did mods to the block and other things like an agressive head port, header, larger hot side A/R.

I've never had a setup that pulled decent past 7K and this one does now. smile.gif

Live and learn... when I was modding the last setup in '98 there wasn't a nice platform to go by like we do now....
Mike K

#32 TurboRaider

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Posted 30 October 2005 - 11:13 AM

QUOTE (brianpaul98)
QUOTE
Just dont confuse cold clearnaces with hot clearances. The forged pistons may start out looser but since they expand faster once they are hot they should have a similar running clearance to grannies pistons.



Isn't this statement a bit contradictory? If the pistons start out looser and expand faster a tight piston to wall clearance like .002" will leave not much clearance.


What I'm talking about is machine shop engine honing clearances. I will need to find the paperwork on the piston to wall clearances where it shows NA engines all the way up to Blown / Supercharged and as you go more radical the P to W clearances increase. More power, more heat, faster expansion rates = more clearance. I found the ring gap paperwork from Wiseco but the piston paperwork is MIA somewhere.

All I'm going to say from experience is that if you put a brand new set of pistons in your engine with a stock P to W clearance of .0015" - .002" and you run the engine any other way than normal driving they will be scuffing the skirts and the cylinder walls after a few good hard runs.


What I was commenting on is that your inital clearance depends on a number of factors.  On a cast, higher silicon alloy piston the initial clearance is smaller because the pistons expand a lot less.  That is not saying that if you run them harder they dont need a bit of extra clearance, but not to the order that a forged piston made of a low silicon alloy.

When hot both pistons will have / should have a similar running clearance that are a lot tighter than many would beleive.  

Kevin




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