Gear drive Cam

[DeWynter]

If I wanted to run a gear drive cam, what is required? Will I have to program out the knock sensor or will I have to get a different one? I know that gear dive will make aditional valve train noise which may be interprited as knock. Are ther alternative knock sensors? Should I be changing something even for the roller rockers?

[Injuneer]

Earplugs.

Can't see how the KS could function with all that mechanical noise. Can't imagine there is one that can. One possibility would be a filter circuit of some sort on the wire to the PCM (sort of "build your own knock module"). When I did the solid roller cam, I asked about that approach, and the guys that built the engine said people have tried but have not been very successful.

[AJ52486]

I found a link to a schematic on Brent Franker's site for a knock sensor desensitization circuit. If you haven't been there before, you should check it out. The schematic can be found here. I'm not sure if it works, I just happened to find it.

[Injuneer]

"Desensitizing" means reducing its effectiveness...... like turning down the volume on a microphone. That's not a good way to solve knock sensor problems. The PCM can't "hear" the rattle of the gear drive, and it can't "hear" the death rattle of a detonating engine.

[AJ52486]

When you put it that way, this circuit doesn't sound like a good idea. I wonder if there is a way to use the same techniques for filtering audio to filter specific frequencies from the knock sensor?

From what I've read, a knock sensor generates an AC signal (just like an audio signal) that is interpreted by the PCM. If the knock sensor acts like a microphone, where a sound can be identified by its frequency, it may be possible to filter that frequency out. There is a filter called a band-stop filter that filters a small range of frequencies, but leaves higher and lower frequencies alone.

If someone had the equipment and the courage, they could connect their KS to an ocilliscope and compare the readings between the timing chain and the gear drive. If there is a distinct frequency that the gear drive introduces, this type of filter may work. The only problem with this is that the frequency is likely to depend on engine speed, and could cover a wide range of frequencies.

To get something like this to work, it would require lots of testing. I'm not even sure if the frequency can tell you where the "knock" came from. I'll have to do some more research to see if something like this is possible.

[Injuneer]

You already have that "device" in your PCM.... its a removable chip called a "knock module". Its a filter that is designed to selectively pass the sound signature of true knock. That is the genesis of the LT4 knock module. It was specifcally designed to filter the sound of the Crane 1.6 roller rockers that GM put in the LT4 engines. because that noise was getting through the standard module (filter), so they changed the filter.

As I mentioned, the shop that does my engine work and tuning (and is extremely computer savvy) is aware of efforts to build filters for the noise from solid roller camshafts. They just haven't seen one that is really effective. My solution is simple... no knock sensor at all. But the "tune" is backed up by more than 40 engine dyno and chassis dyno pulls, and NOTHING gets changed without more testing.

[DeWynter]

So even with the roller rockers I may get timing pulled? Can an LT4 KM go into a third gen? I really doubt it with out serious re-wireing. I wonder...

[Craig 94 TA GT]

So even with the roller rockers I may get timing pulled? Can an LT4 KM go into a third gen? I really doubt it with out serious re-wireing. I wonder...

I'm always fighting eliminating KR with just RRs and headers using the LT4 KM. I think it helps, but in terms of seeing my knock count, I don't know if it would be worth the trouble if it's hard to install into your car.