God forbid you from hearing this, though.
The least pleasant sound. And if you do hear it, or anything else that even remotely resembles it, let off that throttle right away.

Another thing, I really dislike is the barely audible detonation that I encountered a few times in the summer, or with bad gas recently. It is so quiet, that you can barely hear it, but if you do, it sound somewhat like a hard drive on your computer when hard at work. This thin quiet rattle. When I was getting this, it was usually in the 4K area at a very light throttle, just barely above cruising.
More throttle, and it goes away, as boost builds up and more fuel kicks in, but just in that range... Pulling back on the timing a degree or two fixed it for me.

 

Interesting. I've never heard that before. I'll have to pay attention for that when the temps go crazy again.

Never. I just took it apart and cleaned it off a little.

 

This is the reason I was asking about the sound so intently. I get something very similar to this. Low RPM, higher gears, low throttle. Barely audible metallic ringing. Goes away at higher throttle or RPM. I was hoping it was something normal, like the sound of injectors opening (it is really quiet).. But could it be detonation?

Ideas anyone?

 

High RPM, low throttle rattle/ring is the AUX port sleeves rattling in the housings.

 

Will have to look into that.. Was there a thread around here somewhere?

 

How come it goes away with changing the ignition curve? Or maybe changing the curve changes the vibration pattens and that makes the rattle go away?

 

Lots of good info---thanks---to fess up i had the "sound" while accelerating when i reached a little over 8K in 2nd gear. temps cool less than 200 on both oil and water. Intake cool to touch. It cleared when i let off(immediately)---no cel etc.
So I am doing the usual--looking at plugs, coils etc. My fuel pump is approx 1 1/2 yrs old, maybe 20K on it. I wouldnt think that would be the problem but thanks to MM's insight, I guess i had better check it out. Appreciate that.
I dont want that to happen again.
No problems ever at the lower rpm ranges.
Seems like a lot of people have experienced detonation?
oscd

 

I've heard what's almost like a sizzling sound...imagine frying apex seals in axle grease over an acetylene fire...

I consider the 2 gallons of race fuel I add to every tank as insurance against the apex seals cracking and popping whilst frying.

 

The OE calibration has an incredible amount of ignition timing. Gobs more than the rotaries before it.
It is totally incompatible with FI.
I don't know what Pettit's flash is doing for sure, but I doubt they removed any significant timing.
I pull more than 20° at the torque peak and that barely does the trick for west-coast 91 octane and a bunch of boost.

The description of someone stepping on a coke can is pretty accurate.

 

when i just begun working on the matrix map (a year ago or more) i remember mapping out a basic setup, and taking it for a ride, and the first time I went into boost, at around 5 psi it made a single and a very sharp metallic "ding" which was loud and profound enough for anyone to hear. It scared the life out of me then. Luckily I was spared to tell you the story And I know better now not to make it too lean from the get go.

 

I always build my "theoretical" maps to produce 9.8:1 and then work my way up.
Surprisingly, I actually made just as much power at 10.8: as 11.1:1, so I'm sticking with safe.
Sure, there is more power at 11.9:1, but at 12 PSI, there is also a LOT of detonation potential at 10:1 compression and desert heat.

 

How are you pulling more than 20° of timing with the Ultimate? I thought it was limited in its ability to pull timing...

Great info guys!!!

 

I can pull up to 40°.

 

I really dont know the particulars of the flash. there are people running it with many thousands of miles logged. I asked if it was a the conservative side and was assured that it was a conservative tune---not on the edge. And i am only getting --what --8lbs? at the most ?
The plugs looked good afterward -- no lean look to them, but much more could be going on with my car. Step by step approach.
oscd

 

Well one thing I have found is a VERY dirty crank sensor. It had at least 25% of the sensor covered with oil/grit and possible metal---it was sticking to the magnet. I must have spilled some oil down that way when i filled the S.C?. The shavings i think are from the install work i did. I will scout that a little further.
So while I am at it I am doing the little ATF trick. Wouldnt hurt.
I am thinking for security sake i may need to get the water meth kit--especially for the track.
oscd

 

I think you guys are refering to the marbles in a can sounds.

1) This has been traced to vibration and harmonic vibration that is causing that noise under your engine.

OR

2) air inside the cooling system. Noise sounds like it's comming from center of dash or glove box. If you had a lot of air in the system it would gurgle.

3) ports opening up. By the time you read the RPM on the dash it has changed from the actual RPM that has caused that condition. Search for ports.

If it's not 1, 2 or 3 then......... ? ? ?

 

It's not the marbles sound, at least not the one one from the youtube vid. Marbles is typically described as a high RPM issue. This is low RPM, high gear, low throttle input...

 

Is it like a slight metallic vibration that almost sounds like the vibration clips on your brake pads are dragging on the rotors? Like: "Shing shing shing shing", only constant?

 

oh so we are all getting this?
I thought it was my tune bing to aggressive, and bad gas, and hot temps... Well temps are not hot now.
I actually shut off the music yesterday, and this morning and tried to reproduce it, and yes, I could reproduce it easily. To be sure it is not tune based, while driving in this mode,I started pulling back on the ignition, and even after pulling back 10 degrees, it changed nothing. the sound was still there. So I know now, that it is not from the tune.

 

I got a sound like this when I installed my midpipe. Its pretty constant reguardless of throttle or gas or rpm, sounds like marbles popping coming from the center column.

At this point I've passed it off as being normal engine noise

 

Yep, I get the same "aux port rattling" noise when I give a little throttle when I am in too high of a gear at a low rpm.

 

cool, nice to hear

 

The midpipe can touch the cross brace and get a vibration type sound--check that.
oscd

 

also check the heat shield for being loose.. had to have mine tack welded.. it would make the sound at 2750 and 3800 rpm..l

the clue was that it would do it on deceleration...


beers

 

BOOOO for detonation!!!