detonation question/LT4 knock module
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Joined: Sep 2000
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From: Tampa,FL
detonation question/LT4 knock module
Here's the question. I have a bit of confusion here. I want to run a 100 shot in my internally STOCK LT4 and feel that's not an issue with plugs/race fuel etc. I will not be pulling timing - just 50/50 fuel mix. But here's where I get confused. People talk about using the MSD box to pull timing when using 100+ shots. Since the LT4 detects knock and/or detonation, why can you not safely rely on that to signal the ECU to pull sufficient timing? With that said, if it DOES do that..can it only pull a certain amount of degrees and no more? And on a further note, once timing is pulled via the ECU, when will it return the timing to it's normal state? Next key turn, 50 miles, immediately? Looking for good solid info please...thx 
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Joined: Jul 1999
Posts: 3,946
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From: Marianna FL
My understanding is that when the ECU pulls timing, it pulls a lot of timing--not 'just enough' to prevent detonation. It would be better to adjust the timing down a little via the MSD than have the computer pull the timing.
Melting Slicks
Joined: Dec 2000
Posts: 2,719
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From: Fremont Oh
The stock ECM pulls a max of about 12 - 15 degrees at WOT. When knock occurs and is detected as soon as the knock disipates the timing is returned almost immediately.
Since the pistons are cast aluminum it is more of a preventive nature to pull some timing before the knock occurs...
In other words if knock is detected rapidly, it will pull a ton of timing out of the curve. If you an understand how much it is pulling before hand, you can potentially keep it from detecting knock by simply pulling a few degrees to start with and it will either not pull any timing or less.
So in a sense yes the ECM may pull the timing required but also with the shot of NOS the dynamic copression creeps up rapidly and really you are better off with a CDI ignition of some sort to light off the fuel, as well as perhaps a step or two colder plug and a reduced gap. This can also help the knock.
Are you running a logging program to see how much and where the knock is occuring? My guess would be on the onset of hitting the button.
Hope this helps,
MO
Since the pistons are cast aluminum it is more of a preventive nature to pull some timing before the knock occurs...
In other words if knock is detected rapidly, it will pull a ton of timing out of the curve. If you an understand how much it is pulling before hand, you can potentially keep it from detecting knock by simply pulling a few degrees to start with and it will either not pull any timing or less.
So in a sense yes the ECM may pull the timing required but also with the shot of NOS the dynamic copression creeps up rapidly and really you are better off with a CDI ignition of some sort to light off the fuel, as well as perhaps a step or two colder plug and a reduced gap. This can also help the knock.
Are you running a logging program to see how much and where the knock is occuring? My guess would be on the onset of hitting the button.
Hope this helps,
MO
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Joined: Sep 2000
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From: Tampa,FL
Thanks Mo and others for input. I do have the autotap software so I will log that a bit here soon. It's ashame the ECU pulls max timing and not 'just enough' accordingly. I also assume the LT4 program..although different...operates in the same respect. I wish I had some tech data from GM to review. I'd be all over that!! 
Melting Slicks
Joined: Jun 1999
Posts: 2,872
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From: Wilmington NC
Originally Posted by ~db~
It's ashame the ECU pulls max timing and not 'just enough' accordingly. I also assume the LT4 program..although different...operates in the same respect. I wish I had some tech data from GM to review. I'd be all over that!!
with a 50/50 mix race fuel on a 100 shot I doubt you will run inot any issues whatsoever as long as your fuel jetting is correct and your AFR is nice and fat. you may want to add an msd 6a box for a better spark under more severe cylinder pressures. nitrous and high compression tend to blow spark out so a colder range plug and a tighter gap is also a good idea to prevent this from happening!
have fun with it... should be a hoot!
Chris
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Joined: Apr 2004
Posts: 4,532
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From: Lahaina Hi
Follow the rules of nitrous,you should be ok.
1 1/2 degrees for every 50 shot.
B8EFS NGK plugs .35 gap and I use the MSD6AL box and the plug in that you have to order with the box so you don't have to butcher your wiring.
You will need to remove the limiter GM has on your engine.
The MSD 6AL box has a limiter chip,better way to go.
You will need to up grade the fuel pump to a warlboro 20000169 after a while.
106 no lead gas is the ticket but expensive compaired to c-16 or c-14 race gas.
When running nitrous you can't miss a gear.
Anything can be done you will just feel better if something goes wrong and the motor blows, you feel you should have paid attention to the rules.
I check my nitrous hookups without the bottle hooked up.
Just floor it without the nitrous and turn the switch on and see if,the car falls on its face.If it does then the fuel system is working properly.
1 1/2 degrees for every 50 shot.
B8EFS NGK plugs .35 gap and I use the MSD6AL box and the plug in that you have to order with the box so you don't have to butcher your wiring.
You will need to remove the limiter GM has on your engine.
The MSD 6AL box has a limiter chip,better way to go.
You will need to up grade the fuel pump to a warlboro 20000169 after a while.
106 no lead gas is the ticket but expensive compaired to c-16 or c-14 race gas.
When running nitrous you can't miss a gear.
Anything can be done you will just feel better if something goes wrong and the motor blows, you feel you should have paid attention to the rules.
I check my nitrous hookups without the bottle hooked up.
Just floor it without the nitrous and turn the switch on and see if,the car falls on its face.If it does then the fuel system is working properly.
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Thread Starter
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Joined: Sep 2000
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From: Tampa,FL
Originally Posted by lcvette
there is a reason for this... once knock occurs it requires pulling a much greater amount of timing to stop it then if you had not had knock occur on just a degree or two lower base setting.. make sense? knock changes the temps in the combustion chamber so much so fast that the becomes much more prone to detonation and therefore even a few degrees pulled would not halt detonation. and timing is returned very slowly not instantaneously if you watch your logs carefully.. it adds it back a little at a time for safety reasons.
with a 50/50 mix race fuel on a 100 shot I doubt you will run inot any issues whatsoever as long as your fuel jetting is correct and your AFR is nice and fat. you may want to add an msd 6a box for a better spark under more severe cylinder pressures. nitrous and high compression tend to blow spark out so a colder range plug and a tighter gap is also a good idea to prevent this from happening!
have fun with it... should be a hoot!
Chris
with a 50/50 mix race fuel on a 100 shot I doubt you will run inot any issues whatsoever as long as your fuel jetting is correct and your AFR is nice and fat. you may want to add an msd 6a box for a better spark under more severe cylinder pressures. nitrous and high compression tend to blow spark out so a colder range plug and a tighter gap is also a good idea to prevent this from happening!
have fun with it... should be a hoot!
Chris
As far as removing the limiter goes?? why in the heck would I want to do that? Sure you don't want it to bounce when spraying but I also don't want a POP as it spins a bearing. If I get a MSD box I can regulated it that way, but hopefully won't have to.
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
The factory limiter squeezes the fuel not a good thing with nitrous.
In short leans the motor by lowering the voltage to the intank fuel pump.
I run a Aeromotive a 1000 in tank pump,never had a problem.
The pump is the size of half a loaf of bread and just fits in the tank.
But of course I am the only one on the island that pumps Nitrous .
$7.50 a pound.
You can get away with a presure regulator and 106 oct or better fuel and the car should be fine .I would shift about 300 to 500 rpm's less than you normaly do .
I would not shoot off the line, It cost me a motor mount and a left front shock with a 100 shot.
In short leans the motor by lowering the voltage to the intank fuel pump.
I run a Aeromotive a 1000 in tank pump,never had a problem.
The pump is the size of half a loaf of bread and just fits in the tank.
But of course I am the only one on the island that pumps Nitrous .
$7.50 a pound.
You can get away with a presure regulator and 106 oct or better fuel and the car should be fine .I would shift about 300 to 500 rpm's less than you normaly do .
I would not shoot off the line, It cost me a motor mount and a left front shock with a 100 shot.
