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Old 07-15-2003, 08:20 PM   #1
thebishman
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Default My experience with detonation (long)

I know that there's a dedicated thread for discussion of the dreaded pinging/knocking/detonation issue, but thought more people might see this if I placed it in a seperate thread. Moderator feel free to move it at will.

I picked up my STi last Saturday, and had to drive it 940 miles home, so I had plenty of time to 'experiment'.

Left the dealer with 11.1 miles showing and a full tank of gas. Of course I have no idea what brand/octane they filled the car with, but I was assured it was premium.

Anyway, when everything had had a chance to reach operating temp., I decided to see if my car pinged. It had approx. 50 miles on it at this time. In 4th gear at 3K rpm I rolled into the throttle, quickly reaching WOT. At 3.5-4K rpm there was a moderately severe detonation evident for about 1-2 seconds. This was easily heard above the roar of the Potenzas on a PA interstate, (think 747 at Vmax). After letting the car 'cool down' for a few miles, I did this a few more times all with the same result, i.e. 1-2 seconds of moderately severe detonation/pinging/knocking. At no time did I 'back-off' of the gas, I just let the car 'work through' the detonation. (If the pinging had lasted more than 2 seconds I would have backed off, but the detonation always ceased after that amount of time). So I thought what the hell, I've got a pinger, either Subaru will come up with a re-flash for the ECU or they'll buy me a new engine when I have a piston melt, (that's what a warranty is for after all).

At 208 miles showing, I topped off with British Petroleum's finest, (93 octane). After a few more miles, I tried the above again, i.e. WOT at 3-4K rpm in 4th gear. The detonation was still there but was slightly diminished, meaning it was not quite so loud and didn't seem to last as long. This was reproducible multiple times.

At 478 miles I filled up with Amocos, (BPs), finest, (93 octane). Once again after a few miles I tried the above, WOT at 3-4K rpm in 4th gear. Now the detonation was barely heard at all, and only seemed to last for perhaps less than 1/2 second. This once again was consistent all the way thru' this tank of fuel.

At 738 miles I topped up with BP's finest again, (93 octane). This time there was NO detonation/pinging/knocking AT ALL! I would slow enough to go to WOT at 3-4Krpm in 3rd and 4th gear; plus I would go to WOT at low rpms in 5th and 6th. Nothing I would do would bring on the dreaded 'pinging'. This was night time now of course with the ambient temp. down to mid. 70'sF, so I conducted a further experiment :....

Today I am at 967 miles, (I filled up at 955 miles), and I have Amoco 92 octane in the car, (the highest octane available here). It is 100F here and try as I might no matter what gear I choose, the car will NOT detonate when I go to WOT at any rpms.

So in my case, it seems that the ECU did in fact 'learn' to adapt and do what's necessary to prevent early detonation.
I don't know why mine should be any different from the rest of your cars that suffer from 'pinging' since after all the ECUs are in fact clones of each other. If I had a car that suffered from early detonation, I would fill up with good quality fuel; go take a long drive and try and force the ECU to adapt, i.e. do not back-out of the throttle at the first sign of detonation, but try and 'drive thru' it. Maybe the ECU has to see a certain amount, (i.e. degree of and duration), of 'detonation' before it even begins to try and adapt, but is what seems to have happened with my car.

As always, YMMV, and the above is just my opinion. But it is something to think about.
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Old 07-15-2003, 08:26 PM   #2
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interesting...
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Old 07-15-2003, 08:32 PM   #3
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Good to see some fresh air on this ping thing. Thanks for posting your findings

Truly,

Davis
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Old 07-16-2003, 03:39 AM   #4
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Good stuff.
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Old 07-16-2003, 06:00 AM   #5
ciper
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Personally I think this is a great thing! Subaru allows the ECU to be very agressive to start, and learn downwards to adapt to your fuel.

Meaning, a tank of race gas and a quick reset before your ECU before track/drag/autocross and you will end up taking more advantage of it.
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Old 07-16-2003, 10:11 AM   #6
KoneKiller
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Default For what it's worth

I am running "whatever gas station is closest when I need gas" brand of 93 in it.

The STi gets a mix of highway and city driving in hot, humid weather. And it gets autox time.

Only once have I thought I heard anything that sounds like pre-ignition, but I really think I may have been hearing the boost controller instead. I was WOT in 5th at about 80mph.

Whatever 'fix' Subaru supposedly has in the works.... I don't want it. Leave mine alone.
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Old 07-16-2003, 12:07 PM   #7
thebishman
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I'm with you Kone, I am not in the least worried at this point about the 'pre-ignition' situation since it has resolved in my car.
I am far more worried about a re-flash of the ECU detuning my car, and corrupting the wonderful torque characteristics of the STi.
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Old 07-16-2003, 12:34 PM   #8
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Mine was pinging like crazy after 10+ hours driving with a full car and bad gas. I tried to duplicate it but have yet to hear it again. Apparently, better gas helps and it IS learning...thank goodness. It'd suck to know there's nothing to do about it now.

RN
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Old 07-16-2003, 12:42 PM   #9
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So it seems like if you have higher octane available (93-94), some "tough love" is in order for the car because it can adapt. (And may be better for it to have a few high det. runs; then permanently adjust, rathar than always have small detonation for the life of the car). But I wonder if this should be tried for those of you only able to run 92 or lower. I wonder if the ECU can adjust enough to cope?
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Old 07-16-2003, 01:15 PM   #10
KoneKiller
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Quote:
Originally posted by Pre-diddy
But I wonder if this should be tried for those of you only able to run 92 or lower. I wonder if the ECU can adjust enough to cope?
I think that is the real issue! For those of us with good gas, it doesn't seem to be enough pinging to worry about.

And I would bet that many of the pingers have modded their cars in some way... especially those intake systems that pull hot air from under the hood. Blitz for example... dumb dumb dumb
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Old 07-16-2003, 01:26 PM   #11
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My dealer filled w/93 - I ran it down to the 1/2 tank mark and topped off w/94. I've got 290 miles, have hit 4k, and heard nothing that sounded out of the ordinary. (thanking God as I type). Thing pulls like a mother....
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Old 07-16-2003, 02:14 PM   #12
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Quote:
Originally posted by KoneKiller


I think that is the real issue! For those of us with good gas, it doesn't seem to be enough pinging to worry about.

And I would bet that many of the pingers have modded their cars in some way... especially those intake systems that pull hot air from under the hood. Blitz for example... dumb dumb dumb
please get edjumacated before calling people dumb....thanks.

http://www.clubwrx.net/forums/showth...threadid=29319

quick summary- intake temp (at the cone) does NOT matter as much in a FORCED INDUCTION car because of the design of the system. the intake temp is going to be heated up anyways AT THE TURBO, and then re-cooled at the intercooler. a smarter solution to getting colder air into the combustion chamber is to get a larger or more efficient intercooler.
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Old 07-16-2003, 03:01 PM   #13
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I have 671 miles on my car and I have never had any ping problems.

I am one of the dumb, dumb, dumb ones. I have a Perrin short ram with TurboXS RFL-TI and it runs like a bat out of hell. As a rule, OEM intakes are very restrictive and that has always been bad to me.
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Old 07-16-2003, 07:18 PM   #14
KoneKiller
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Quote:
Originally posted by happasaiyan

quick summary- intake temp (at the cone) does NOT matter as much in a FORCED INDUCTION car because of the design of the system. the intake temp is going to be heated up anyways AT THE TURBO, and then re-cooled at the intercooler. a smarter solution to getting colder air into the combustion chamber is to get a larger or more efficient intercooler.
I'm sorry, but you cannot remove the rules of thermodynamics with an intercooler.

If your intake temperature is higher at the air inlet to the system, your charge temperature will be higher. The degree of which is determined by the efficiency of the intercooler. We all know that air to air intercoolers are very inefficient at low vehicle speeds and are completely incapable of dropping the temperature below ambient temperature at any speed.


The formula for the temperature drop of any radiator is:

(ambient temp X efficiency X -1) - Tpost turbo = Tout

The rule of thumb for most quality intercoolers is an 0.8 (80%) thermodynamic efficiency at speed. So a 220 degree charge temp out of the turbo will be dropped to 148 degrees or so with a 90 degree ambient supply.

If you increase the intake temperature significantly (say 40 degrees) and the intercooler remains the same, the intake charge temperature WILL be higher than with the stock intake system. How much, I don't know. With a theoretical 80% efficient I/C, a 260 degree post turbo temperature would be dropped to 188 degrees by the I/C. Hey... wow... that's 40 degrees higher!

And remember this assumes a highly efficient intercooler setup which the WRX is NOT in low speed operation.

Some sources suggest that every 10 degrees F of charge temperature costs you 1% in HP.

So what you really have here is a superheated intake supply (coming right off the turbo heat shield for the Blitz) being heated further by compression and the native heat of an exhaust driven turbocharger being partially cooled by an air to air intercooler. Unless someone can show me data suggesting that the intercooler is efficient enough to return the charge temperature to ambient, my point stands.

Someone needs to spend the money on a couple of thermocouples and a data logger comparing the ram air gizmo with the stock intake plumbing. Maybe I'll get around to it.

The other issue with these 'ram air' setups is what is going on in the engine compartment at speed. I expect the air is hot from radiator, intercooler, turbo and exhaust, but what is the underhood pressure? Is it higher or lower than ambient? My guess would be that it might be lower, although that big scoop may change that. In general, underhood pressures in sporty cars are lower than ambient, that IS the purpose of the front air dam.

This is one of the reasons that Subaru picks the air up off the slot in the hood, right above the bumper as it's a high pressure area. Wouldn't it be ironic if the 'ram air' devices gave you 10bhp on the static dyno but cost you 20 at speed. Has anyone really tested this??

In some ways I don't really care to as long as I keep winning at the track, I don't need to be tweaking. But I have to admit, I want to learn whether the theory is right or wrong in application. There are so many many factors at work here and intuition nor theory is enough.
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Old 07-16-2003, 08:57 PM   #15
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AVOturbo's Ross Wilson, who is a very good tuner (and AVO is one of the major, if not the major, aftermarket maker of turbo's and intercoolers, so is very in tune with the entire process) is, and was, the first to admit that putting a ram air filter on my car would increase air temperatures. That's the reason they also make air boxes (and are working on one for my series of car). And he also said that when sitting in traffic with that setup, ping/det chances increase, especially if I use full throttle in those situations (his words on that - "don't use full throttle you idiot").

In his opinion, and I trust it fully, the standard air box setup is better if you are not going to build an airbox around the ram-air that connects to the old airflow system. A ram-air will flow more air, and that is necessary when going with better flowing intercoolers and turbo's, but don't expect stock levels of safety in traffic conditions. Use of a intercooler waterspray is recommended.

Cheers,

Paul Hansen
www.apexjapan.com
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