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Old 08-03-2010, 09:40 PM   #1
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Default OPG fluttering/detonation

After doing a search, I've found 9.3 billion threads all saying that the OPG will flutter about the width of the needle if you are experiencing detonation. I've noticed that my needle will do that around 7k rpm with my foot to the floor, so to experiment, I plugged in my stock ECU (which I'd assume would not cause detonation), and it still jumps around at 7k. Is it possible that just the vibrations from the already unsmooth BP or something other than detonation would cause this and that I'm not actually seeing detonation?


p.s. I hate how shitty the stock ECU is. Impossible to pass people around town.

Later, I'm gonna do a pull to redline, turn off the car and pull a plug and see what I find.
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Old 08-03-2010, 09:54 PM   #2
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You are highly unlikely to experience detonation at 7000rpm if you aren't experiencing it at 4500-5500rpm. Detonation resistance increases with RPM. I'd vote for not worrying about it, especially if it did it on the stock ECU.

The other test is to dump a few gallons of 100 octane in, or pull ~4 degrees from the areas where you think it's detonating, and see if it changes anything.
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Old 08-03-2010, 10:02 PM   #3
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Yup, pulled 3-4 degrees from the affected cells, and even added a bit of fuel and it still did it...
Good idea, gonna throw a couple gallons of 100 octane in and see what happens tonight.
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Old 08-03-2010, 10:03 PM   #4
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For the best (cheapest) effect, wait until you're low on gas to add the race gas.
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Old 08-03-2010, 10:21 PM   #5
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I'm in Sunnyvale and have two cans of Torco you're welcome to, but they've been sitting in a cabinet in my garage for about 2 years.
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Old 08-03-2010, 11:12 PM   #6
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Im almost on empty and I know where to get 100 octane 5 minutes from my house, I'm just gonna try that later on tonight.
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Old 08-04-2010, 02:36 AM   #7
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3 gallons of 100 octane/3 gallons of 91 in the tank and its still doing it. Think I'm just gonna try to ignore it. I don't think I'm detonating when the affected cells are at a ridiculous 29-31*
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Old 08-04-2010, 05:20 AM   #8
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Abe, you could always make some det cans to listen as well. Might be a nice investment since you'll be slappin a turbo on the car soon anyways.
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Old 08-04-2010, 08:51 AM   #9
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I've never been looking at the OPG right at redline, but I wouldn't worry about it. When mine fluttered due to det it was more than a needle width...it was noticeably schizo...and motor died shortly thereafter.

+1 on det cans, best purchase I made in the whole build...you only learn the det lesson once.
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Old 08-04-2010, 10:51 AM   #10
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Quote:
Originally Posted by thesnowboarder View Post
Abe, you could always make some det cans to listen as well. Might be a nice investment since you'll be slappin a turbo on the car soon anyways.
I have no idea where to even begin, but I've been thinking I def want to do that, even if its only for peace of mind.

gospeed, there was a few times where it didn't flutter as much as it just dropped to right above 30 but I had to shift/watch traffic so I'm not sure what it was doing.
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Old 08-04-2010, 10:54 AM   #11
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+1 on det can, makes street tuning that much easier. Still need a dyno to squeeze maximum power out of every cell, but you can at least find the knock threshold with a det can, which generally gets you close.
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Old 08-04-2010, 06:34 PM   #12
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My OPG used to act the same, jumpy all the time. Det cans are definately worth their weight in gold, you can make a set for like 10bux too.
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Old 08-04-2010, 06:41 PM   #13
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95 octane, reduced timing, no way it's detonating ONLY at redline. Don't worry about it.
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Old 08-04-2010, 07:23 PM   #14
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Quote:
Originally Posted by dc2696 View Post
Det cans are definately worth their weight in gold, you can make a set for like 10bux too.
More on this? I searched for a half hour and didn't find ****.
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Old 08-04-2010, 08:14 PM   #15
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Just throught i'd throw something into the mix here.

Just got back from a drive, opened the hood to check on several things. I noticed the CAS sticking out of the head by some fraction of an inch. I checked the bolt and sure enough, very loose. Hooked up megasquirt and the timing light, 5 degrees advanced. Looks like I forgot to tighten that bish down when I rebuilt the motor last time.

Lesson, check your base timing again and make sure its dead nuts 10*. Hell, start by making sure that you actually changed the 10 back to a -10 in megatune when you set the base timing last. I've forgotten that countless times.
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