eurospeed wrote:

torifile wrote:

English, please? I'm seriously lost about even what "detonation" IS much less why I should worry about it. I read the posts here that summarized the problem but I'm still not sure what the issue really is.

In short, detonation, AKA engine knock and pinging, is premature air/fuel ignition (usually not from the spark plug) that occurs before the piston starts to head in a downward stroke (the power stroke which moves your car).  Because the piston is still moving up or is close to TDC (top dead center) in the stroke, the premature ignition puts large stresses on the piston, wrist pin, piston rod, crank shaft, etc.  If it happens enough times with enough severity, you will punch a hole or crack the piston or damage other affected parts.

So how come we don't have hundreds of blown up Subaru engines on the floor of our shop? 

Not trying to be flippant - just seriously confused.

Detonation is a normal part of the life of just about any car. It happens from a variety of reasons: poor state of tune, poor fuel, bad environmental conditions, etc.

It is when the air/fuel mixture ignites at the incorrect time (not when the engine wants it to). It sounds like a ping, or bang, or bunch of marbles rattling around in the engine because it's basically an explosion with nowhere to go against a bunch of metal in a way it wasn't designed to handle.

In normally aspirated engines, it creates a force equal to the pressures it is under (compression ratio, positions of the internals when ignition occurs, etc.) and while not good, a few knocks (detonations) will not really harm anything. It happens, you try to prevent it from happening though.

In a turbo car, under full boost, you are at a very high state of compression....and the resulting detonations that can occur are typically that much more severe. Detonation can ruin your ability to maintain compression in the cylinder chamber, score the cylinder walls, crack pistons, etc. etc. Or it can do nothing....but it's more likely to damage something in a turbocharged (or super charged) engine.

I would say you don't have tons of blown up engines for several reasons: It doesn't happen to all subaru engines, alot of people who have subarus aren't WOT enough for it to incur serious damage....though this engine has only been out since 2002...., those who do drive it hard tend to know what to listen for or tend to go towards EM anyway...

So it does cut down a lot on the amount of actually destroyed engines out there.

That being said, how many engines are running low compression because of lots of detonation? I don't know....

Joe, you beat me to it sounds like you know more about it than i do but ill leave mine up anyway


What I wrote was merely a summary of what was written on the thread that is linked at the top of the page, since most people do not want to sift through 18 pages of redundant information.  I read almost all of it and probably all of the pertanant information.  I myself can testify that my car does indeed experience knock at times and i dont like it one bit, so It was in my best interest to read that thread.

Ok so what is Detonation?

Detonation is basically when the air and fuel mixture that enters the engine ignites before it is supposed to due to heat and pressure.  I dont know all of what exactly happens, but i know it is not good.  I think the cylinder can hit the valves, warping of the cylinder walls and head due to unven and rapid heat and other stuff, but dont quote me on that just know it is not good and over time will cause damage to the engine.  Detonation is often reffered to as a ping or a knock, depending on how severe it is.  On my last car, i heard it ping a few times and it sounded like pitchforks being hit real fast and it was pretty quiet.  I have heard it on the Aero and it sounded like a crackling, that would be considered a knock I believe.  The reason that you need more fuel in the cylinder when the pressure is increased is because it helps keep it cool until its time to spark it, i just know that a lean (more air / less fuel) mixture creates more heat and a higher potential for knocking and pinging.

Once again, if i am wrong about anything do not hesitate to correct me, I dont want to spread misinformation on this forum

Last edited by akaryrye (2005-06-29 00:31:13)

WRXVT wrote:

has anyone else on this thread experienced detonation - and if so was it with 93 oct?  The gentleman that said he had experienced detonation 3 times in the saab was on 91 oct. gas.  I'm just trying to see if this is actually happening to our saabs as well.

I want to add to this that as I recall, each time it happened, I had just filled up my tank.  I dont know if that has anything to do with it though.

FYI according to Trey Cobb, the 9-2x he looked at had a 2005 ECU

site:
http://www.wrxforum.com/cgi-bin/ultimat … 501#000000

^From what I've read, yes

well, i was thinking about it anyways... 

now, i better get an AP before my car blows up! 

Last edited by heathbar (2005-06-29 09:04:23)

WRXVT wrote:

FYI according to Trey Cobb, the 9-2x he looked at had a 2005 ECU

site:
http://www.wrxforum.com/cgi-bin/ultimat … 501#000000

"cobb tunes subarus, not saab's"
thats a quote from an apparent Cobb employee.

kinda scary if he really didnt know that the AP is being advertised for use on the 92x

of course a few lines down Trey clears things up..  but still......

athakur999 wrote:

I took that to mean that Cobb doesn't make any guarantees on the Saab.  Kind of a CYA.

I took it to mean that the employee who made that remark had not seen a 92x in their shop (and for all we know didn't even know what one was).  That quote was back in April, remember.  A hell of a lot has happened with the 92x in the last 60 + days.

eurospeed wrote:

owl wrote:

perhaps this detonation was the cause for the guy earlier on in this forum who posted about blowing his engine so early on...  this is the guy who was racing his car in the desert or something like that...

You mean spiff?  I'm fairly certain the engine failure was on a Linear and not an Aero.

wow, I'm surprised an enthusiast like spiff (at least from how he described his driving style) would have gotten a linear

Just listen to your car....is it detonating under continuous WOT ever?

If it's not...then you probably don't have to worry too much about this...

if it is...bitch and moan until they give you a STI engine....lol

Here's my story:

Two days after I bought mine 2 weeks ago I experienced a big bang. I was running on the 1st tank of gas the dealer provided. Only God knows it could have been 87 octane. I was shifting into second gear and I thought something happened to the tranny. It was an extremely loud bang. Prior to that I experienced a hesitation between 3d and 4th gear as the turbo was spooling up. I went and filled up with 91 octane immediately and the hesitation went away and didn't experience the big bang anymore..thank goodness. The bang really did sound like something blew up.

I will soon be getting the Cobb Accessport !!