3" Exhaust, Stock Tunnel Brace and Knock Sensors..... Lesson Learned.

[mlee]

WoW... good read...

I know someone right now who's pipes are bouncing off his tunnel brace...
I think I'll wait til AFTER our race next weekend to tell him...:emoticon7:

[GTAHVIT]

Originally Posted by mlee

WoW... good read...

I know someone right now who's pipes are bouncing off his tunnel brace...
I think I'll wait til AFTER our race next weekend to tell him...:emoticon7:

Knowing is half the battle.

[CamaroSpike23]

Originally Posted by GTAHVIT

Knowing is half the battle.

[RJT2SSRS]

I recently had Livernois Motorsports install the Corsa cat back exhaust for the
L99 Camaro. At first they said I had to leave the rear cross brace off,and i
must admit no exhaust noise on the way home. I already had installed an Elite brace to replace the stock one in anticipation of the new exhaust system.

Well a couple of days later I put the brace back on. Exhaust started hitting brace. Then I added about 1" of spacer's,exhaust still hit the brace. Took it back to Livernois to make sure the resonators had been rotated up before
the clamps had been tightened. The salesman (Darin)took the car back to the install shop and was told the Corsa exhaust was always going to hit unless the tunnel brace was left off,which Darin relayed to me.

Then I find this article on Camaro5(by the way thanks to everyone here) about
the timing retard from the knock sensors. Is there a specific amount of time after the exhaust makes contact with the chassis that the timing will go back to working normally/or does that depend on turn off/restart cycles?

[hoffmk2003]

I removed my tunnel brace for this exact reason.........

Ken

[GTAHVIT]

Originally Posted by RJT2SSRS

I recently had Livernois Motorsports install the Corsa cat back exhaust for the
L99 Camaro. At first they said I had to leave the rear cross brace off,and i
must admit no exhaust noise on the way home. I already had installed an Elite brace to replace the stock one in anticipation of the new exhaust system.

Well a couple of days later I put the brace back on. Exhaust started hitting brace. Then I added about 1" of spacer's,exhaust still hit the brace. Took it back to Livernois to make sure the resonators had been rotated up before
the clamps had been tightened. The salesman (Darin)took the car back to the install shop and was told the Corsa exhaust was always going to hit unless the tunnel brace was left off,which Darin relayed to me.

Then I find this article on Camaro5(by the way thanks to everyone here) about
the timing retard from the knock sensors. Is there a specific amount of time after the exhaust makes contact with the chassis that the timing will go back to working normally/or does that depend on turn off/restart cycles?

It retard is only while the knock sensor is active. the car doesn't go into "safe" mode until there are more factors, like detonation, misfires, etc.

so there is no need to reset.

Originally Posted by hoffmk2003

I removed my tunnel brace for this exact reason.........

Ken

According to GM that tunnel brace is there for Side impact survivability...

They highly recommend you leave it in.

I still have a small rattle but it is now back towards the mufflers. Must have happened when i pulled them to do the rear sway and cradle bushings. It's far enough from the knock sensor that it doesn't affect performance.

Need to find the time to chase it down.

[hoffmk2003]

Originally Posted by GTAHVIT

According to GM that tunnel brace is there for Side impact survivability...

They highly recommend you leave it in.

I still have a small rattle but it is now back towards the mufflers. Must have happened when i pulled them to do the rear sway and cradle bushings. It's far enough from the knock sensor that it doesn't affect performance.

Need to find the time to chase it down.

I strongly disagree.

The tunnel brace is there to provide lateral support to the tunnel which adds to the stiffness of the chassis. The camaro has a really high 1st mode of torsion like 23 hz if I remember correctly. Hence why this car is so "tight" as people put it, GM did a great job designing it so the chassis is not excited by road vibration inputs.

Removing this will have a negative impact in this regard.....however I don't believe much. I have not noticed anything different about the way my car feels or behaves, although I'm sure there is a difference.

Spacing the brace down is useless as well, you might as well take it off because when you do this you lose some of the bending support it provides. It still will provide shear and some torsion, but it gets some of it's strengthen by being right up against the bottom of the car.

The tunnel brace is not nearly as magical as everyone claims it is. You can get by just fine without it.

Ken

[GTAHVIT]

Originally Posted by hoffmk2003

I strongly disagree.

The tunnel brace is there to provide lateral support to the tunnel which adds to the stiffness of the chassis. The camaro has a really high 1st mode of torsion like 23 hz if I remember correctly. Hence why this car is so "tight" as people put it, GM did a great job designing it so the chassis is not excited by road vibration inputs.

Removing this will have a negative impact in this regard.....however I don't believe much. I have not noticed anything different about the way my car feels or behaves, although I'm sure there is a difference.

Spacing the brace down is useless as well, you might as well take it off because when you do this you lose some of the bending support it provides. It still will provide shear and some torsion, but it gets some of it's strengthen by being right up against the bottom of the car.

The tunnel brace is not nearly as magical as everyone claims it is. You can get by just fine without it.

Ken

Not gonna argue with you as I am not an engineer.

But I will say that my information comes from an engineer who is very close to the Camaro program. FWIW.

[bmorecam]

So how much total timing on wot are you suppose to be running and how much was it pulling?

[ssmike]

I recently installed Dynatech lt's with catted mids and I've noticed anywhere from 2-7 degrees of knock retard at 3200 and 5400 rpm's at 1/4 - 1/2 throttle. I'm using a SCT X3 handheld to datalog and I can duplicate it very consistently. I'm thinking it's some kind of resonance but I don't hear any rattles or bumping of the exhaust on the tunnel brace. Is this knock retard normal? I have a JRE tune but I've had 4 revisions (different cai's) and its still doing it! Ted said it may be a false knock but I can't locate the source. Any ideas?

[f5journal]

I'm just getting into this subject...but I think I have the same...something causing retard on a M6. I have an odd noise in my engine starting at 2500 that the dealer says is normal for the LS3..we will see

[f5journal]

I have a update on my car, and think it belongs more appropriately here than on the fuse pull thread

BACKGROUND

Here's the basic story. Car started a fluttering slight exhaust leak/lifter sound (or maybe injectors flapping) at 1000 miles or so (right after a fill up at a Mom and Pops station in TN). This is on the right side of engine.

A few weeks later I installed my GM GFX kit. We are talking Oct-Nov 2010.

Throughout the past year the car seems sluggish, I pull fuses and it runs fiine for a few hours. But in general, I have been laying it off to hot 100 F temps here in SC.

For months now, I have been thinking the knock sensors are being set off by the flutter sound I mention

Also, from day one there has been a slight rattle at the rear of the car on the right side due to a GFX bezel and the exhaust tip

So, I remember this thread and say, "surely the slight rattle at the back is not making it all the way forward to the KR's"

THE UPDATE

Well, I did a temporary quick fix of the exhaust rattle with some rubber material pounded in there.

First test drive...runs better and guess what. Only slight flutter sound in the engine. Like the problem went from 2-3 lifters, injectors or whatever to only 1 (one)

Did a fuse pull, and guess what, no flutter and it runs way better like it does when I normally pull the fuses.

That was Saturday. It's still running right this morning.

Now something may change, but I believe the sound was from overworking injectors or something similar to be discovered.

If you do the math on this. The car will run on the high octane table for a while with the KR's pulling timing. Then it will go to the low octane table and run worse BUT STILL PULL TIMING because the false knock is still there.

In the morning it will run on the sensors alone in the short term mode until it warms up and then revert to the LTFT table and retarded timing from KR

This is exactly what it feels like is happening. And now it's time to go to work on it.

Thanks GTAH and PQ

[GTAHVIT]

Sorry I missed these posts, I know they are a few months old.. My bad.

Originally Posted by bmorecam

So how much total timing on wot are you suppose to be running and how much was it pulling?

IIRC it was pulling almost 14 degress at WOT.

Originally Posted by ssmike

I recently installed Dynatech lt's with catted mids and I've noticed anywhere from 2-7 degrees of knock retard at 3200 and 5400 rpm's at 1/4 - 1/2 throttle. I'm using a SCT X3 handheld to datalog and I can duplicate it very consistently. I'm thinking it's some kind of resonance but I don't hear any rattles or bumping of the exhaust on the tunnel brace. Is this knock retard normal? I have a JRE tune but I've had 4 revisions (different cai's) and its still doing it! Ted said it may be a false knock but I can't locate the source. Any ideas?

You can change the sensitivty on the knock sensors but I would be VERY careful going down that road... I will say that I am still pulling a couple degrees of timeing at WOT even now. But, I'm ok with it as I've purposefully kept a safe tune to avoid any detonation.

Originally Posted by f5journal

I have a update on my car, and think it belongs more appropriately here than on the fuse pull thread

BACKGROUND

Here's the basic story. Car started a fluttering slight exhaust leak/lifter sound (or maybe injectors flapping) at 1000 miles or so (right after a fill up at a Mom and Pops station in TN). This is on the right side of engine.

A few weeks later I installed my GM GFX kit. We are talking Oct-Nov 2010.

Throughout the past year the car seems sluggish, I pull fuses and it runs fiine for a few hours. But in general, I have been laying it off to hot 100 F temps here in SC.

For months now, I have been thinking the knock sensors are being set off by the flutter sound I mention

Also, from day one there has been a slight rattle at the rear of the car on the right side due to a GFX bezel and the exhaust tip

So, I remember this thread and say, "surely the slight rattle at the back is not making it all the way forward to the KR's"

THE UPDATE

Well, I did a temporary quick fix of the exhaust rattle with some rubber material pounded in there.

First test drive...runs better and guess what. Only slight flutter sound in the engine. Like the problem went from 2-3 lifters, injectors or whatever to only 1 (one)

Did a fuse pull, and guess what, no flutter and it runs way better like it does when I normally pull the fuses.

That was Saturday. It's still running right this morning.

Now something may change, but I believe the sound was from overworking injectors or something similar to be discovered.

If you do the math on this. The car will run on the high octane table for a while with the KR's pulling timing. Then it will go to the low octane table and run worse BUT STILL PULL TIMING because the false knock is still there.

In the morning it will run on the sensors alone in the short term mode until it warms up and then revert to the LTFT table and retarded timing from KR

This is exactly what it feels like is happening. And now it's time to go to work on it.

Thanks GTAH and PQ

Man! I hope this works out for you!

When mine was at its worst I could hear that flutter Loud and clear.... It's like the car would pull like a train for a quick second then bog down and fight it....

Hope that helps. Keep us posted.

[f5journal]

So...you know the flutter sound??? Does my description sound correct? And what do you think it actually is?

Darryl