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Old 11-23-2001, 05:02 PM   #1
IBO
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Default Does N/A engine knock?

As topic, from what I know, only turbo engine will knock?
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Old 11-23-2001, 05:13 PM   #2
Longshot
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AFAIK Any engine can knock.. knock is caused by too much air not enough fuel... Turbo cars aren't that special

Korey
..its just a lot easier to get a turbo to knock/ping/detonate/throw a rod..
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Old 11-23-2001, 05:19 PM   #3
bsquare
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Detonation is not about forced induction, it is about too lean a mixture for the fuel you are using. If you use the same amount of fuel but with a higher octane rating you can eliminate knock. At some point, though, you just can't get enough fuel in, no matter what the octane rating, and you are done.

It is more common for (badly tuned) forced induction systems to do this because you are shoving a lot more air in. This leans out the mixture if you are not careful with your fueling, and then you get detonation.

Are you clear on what detonation even is?
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Old 11-23-2001, 05:31 PM   #4
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Quote:
Originally posted by bsquare
Are you clear on what detonation even is?
That fun noise you get when the 11 second DSM shows up at the dyno and has no engine management?

Korey
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Old 11-23-2001, 07:36 PM   #5
Richard L.
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Yes, an N/A engine can knock if it is out of tune or if it has sharp edges in the combustion chamber and/or piston domes. Sharp edges might glow hot and ignite the air/fuel mixture before the spark plugs have a chance to. This is pre-ignition and gives you that pinging sound. Pre-ignition and detonation can also be caused by other factors. Here is a link to a simple page that tries to explain detonation/pre-ignition:

http://www.hastingsinc.com/Service%2...reignition.htm

I know that my N/A 2.5RS will ping on 87 octane gas. I have to use 92 octane to avoid pinging.

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Old 11-24-2001, 03:25 AM   #6
LVSUBARU
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Knock can also happen from bad ignition timing, it's just not from a lean A/F. In any case it's BAD!
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Old 11-24-2001, 05:34 AM   #7
HndaTch627
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ALL engines knock...simple as that

Jeremy
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Old 11-24-2001, 12:14 PM   #8
fabulous12
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stupid question... knocking = ticking? cos mine does it like a champ.
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Old 11-24-2001, 12:52 PM   #9
Richard L.
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Knocking does not equal ticking. Knocking sounds more like many tiny marbles dropping in a tin can or pebbles hitting against the oil pan. Knocking is more likely to occur when the engine is under load, such as under acceleration or while climbing up a hill. Knocking rarely occurs while the car is idling unless you have a bent rod or a hammered rod bearing. In this case, it's a different kind of knock.

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Old 11-24-2001, 01:33 PM   #10
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Default knock=ping...

They're synonymous.

As for running 92 to avoid knock in your RS, you're just wasting your money. The EJ25 is designed to run on 87 octane gas. They're timing and fuel maps are designed with this in mind. Yes, running 92 will reduce knocking and pinging, but you won't be getting as much power as you would with 87 octage gas.

Anywayz, back to IBO's original question.

Yes, NA engines do knock - that's why they've got a knock sensor. Does my car knock and ping? Not on a regular basis, but I CAN make it knock if I'm lazy with the gas - i.e. I lug the engine when the car isn't moving and don't give it enough gas when in 1st. Does this happen very often, no.

LaterZ!
Darren!!
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Old 11-24-2001, 01:46 PM   #11
LVSUBARU
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If your motor has any kind of mods, I'd recomend 92!
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Old 11-24-2001, 02:18 PM   #12
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fabulous12 - sounds like you need to adjust your valves or maybe have an exhaust leak at the manifold

Yes, a N/A engine can "knock". A good question is, will you hear it b4 your ECU corrects for the condition?
[reaching for flame suite] I'd say NO! and if you wanna know why, go to your local college library and read some SAE papers on the subject.
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Old 11-24-2001, 03:11 PM   #13
Richard L.
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Quote:
Originally posted by p-car
Yes, a N/A engine can "knock". A good question is, will you hear it b4 your ECU corrects for the condition? I'd say NO!
If you will not be able to hear knock before the ECU corrects for the condition, then please explain to me why I am hearing pinging under load if I use 87 octane gas? I'm pretty sure my knock sensor is doing its job. I even tried a brand new knock sensor without any luck.

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Old 11-24-2001, 03:25 PM   #14
HndaTch627
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wow you guys REALLY don't know how much subaru knock sensors suck...we hooked and an ocilloscope to one and drove around...barely read any knock at all...put the GM style one with the J&S in and you better believe that scope was jumping...they factory knock sensors suck...or at least the ones on the EJ25 do.

Jeremy
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Old 11-24-2001, 05:03 PM   #15
p-car
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HndaTch - how about helping us out and post info on the GM style sensor. I know there have been guys with 99 and older 2.5's that seem to think their knock sensors are too sensitive or send bogus signals.

Richard - Yes, I concede that you can put an engine into conditions where it will knock so bad that any fool will hear it and there's not a damned thing the ECU can do short of cutting the spark to all cylinders

I should have said that knock-sensors will detect detonation way b4 most of us will hear it under normal operating conditions. Normally, detonation occurs in 1 or 2 cylinders and the ECU retards the timing.
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Old 11-24-2001, 07:14 PM   #16
Richard L.
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HndaTch627, I think the only Subaru knock sensors that suck are the newer ones. Based on past readings, I was under the impression that MY99 knock sensors were too sensitive. This was why some people tried the "knock sensor mod". Perhaps Subaru tried to tame down the knock sensors and over did it with the newer ones.

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Old 11-25-2001, 04:34 AM   #17
HndaTch627
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I don't have any info on it as of yet...and i just got back from a party and i am wayyy tooo out of it to search for it. I will look for some info tommorrow, I've never heard anyone complain about 99's but i know as far as MY00-01 they do pretty much nothing.

jeremy.
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Old 11-25-2001, 08:01 PM   #18
Kevin Thomas
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Default Knocking on your engine's door

If the newer engine's knock sensor sucked, wouldn't you have lots and lots of engine failures? I mean engine knock is bad, really bad. If the stock knock sensor isn't doing it's job, that means the engines should be going bad.

The way I understand this is that the GM style knock sensor is just more sensitive than the stock sensor. That being said, since the stock 'knocking' isn't bad for the engine, the GM style one will only make your ECU retard the timing and cause you to lose horsepower. You will either have to deal with the lose of hp/torque or go with higher octane gas with the GM style sensor.

Don't interpret the last paragraph in the wrong way because I'm not saying that the stock 'knocking' is good for the engine. I'm just saying that if the engine was in fact knocking with the stock sensors, you should be seeing a lot of engine failures in stock trim. That haven't been the case.
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Old 11-26-2001, 12:25 AM   #19
LVSUBARU
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My J&S takes care of all my knocking needs!
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Old 11-26-2001, 10:25 AM   #20
Jademonkey
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I thought my engine was knocking all the time...even slightly when I was driving on flat roads, but even more so when I was going up hills. I took it to the dealership because I was using 91 octane and it was still pinging. After getting a lecture from the mechanic saying "ONLY USE 87 OCTANE!!" I switched back, and still get the knockinig, (what I think is knocking..sounds exactly like what Richard L described it as) But when I took it for a drive with him he told me that wasn't knocking/detonation/pinging. When I asked him what it was, he just mumbled something, and told me to refill with 87. Hmmmm...still makes the noise. Any suggestions?
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Old 11-26-2001, 10:38 PM   #21
LVSUBARU
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He told you to use 87 instead of 91!!! What a dumb a$$!! I'm sure the car runs fine on 87, but if you have done any mods I strongly recomend 91! I never use 87, always 91. If your motor was knocking all the time you would totally have a check engine light!
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