Blue Angel

I was reading the latest copy of GMHTP and their article with the C6 header install said something that piqued my interest... they are getting knock retard after installing American Racing headers.

Since they tune the car in that article, you'd think that they'd be able to fix it if it was simply a problem with actual knock caused by an increase in exhaust flow, but they didn't mention being able to tune their way out of it. They also mention that this is a common problem with C5 and C6 cars with aftermarket exhaust systems.

I have LG Pro Longtubes with cats on my '02Z and I'm getting knock retard after a hard run through the gears. The car currently has the stock tune.

At high RPM (over 4000) I have a hard metallic "buzzing" sound coming from underhood somewhere, especially on decelleration.

My personal "theory" is that the primary tubes on the header are vibrating together causing this noise, and the knock sensor is picking this up and dropping timing because of it. The knock retard goes away after a short rest of driving normally.

Anyone have similar experience? The article in GMHTP got me thinking about it, maybe there's an inherant vibration problem with adding long tube headers to the C5/6?

Corvette Don

BUBBAS 01Z06

ECS just did my Cam, 90/90, Tex clutch and ARH's....Doug @ ECS sent me an email:

"I did have an issue with knock retard, I had to lower timing fairly heavy to eliminate it. If you would like to run some octain boost I can raise it some and pick up the power some, but then you would have to run it regularly"

So perhaps its the norm with the ARH headers.....get a tune and that should eliminate it !

Blue Angel

Thanks for the info guys!

Anyone else with input on this?

Billdog350

Some tuners claim that the LS1 knock sensors are overly aggressive and they reduce the sensivity of it, which some tuning programs offer as an option. I found myself pulling crazy timing with my tune due to knock but when slowhawk tuned it, he was able to add back in tons of timing without knock. The issue was that my tune was very choppy and the MAF and VE tables weren't smooth...causing rich and lean spikes which caused knock. Expert tuning by Don smoothed out the MAF and VE performance and eliminated knock. I'm not saying ANYTHING about other tuners, just the fact that Slowhawk was able to eliminate knock at about 7 degrees higher across my entire tune vs what I had done myself.

Ikester

Ive read that headers may lean out the mixture, regardless of the brand. so a tune is often done after the install. Thats what I would do if I did headers on a stock car.

If you think about it, the stock tune was made for the stock components. after you start upgrading parts, you have altered the setup from factory.

nwdanner

When I first put LGM Pro LTs on my car my stock PCM would detect knock as well. It was so bad that my max RWHP on the dyno was a disasspointing 330rwhp (from 324rwhp without headers). A professional tuner was able to fix the issue in my car and put my car just over the 350rwhp range.

Also, I seem to remember someone at LGM saying this was a common issue with the factory 2002 PCM tune (or something like that).