I recently put heads, cam, longtubes, etc and had it tuned. Went back a week later to try some smaller wheels and it made like 40whp less and the tuner said it was spark knocking like crazy. He pulled four degrees out to stop the knock but still said it still had some. I had fueled up that morning, is it possible that I picked up some bad gas, the truck didn't seem like it was working badly but it does feel different without those extra 4 degrees of timing. I have read a lot about the false knock doing this, my timing was only at 19 before, so I believe its at 15 now, where can we safely go with this? I have always run cars without knock sensors, I think I am going to go without and see what's what, I've read that optimum should be 28-29 degrees so I'm sure I'm not even close to being at my potential. Truck is an 03 Yukon Denali XL, 6 liter, 799 heads, XR265 cam, longtubes, injectors, made 332 and 338 on the dynojet.

Any thoughts on where the timing should be, the weight of the truck would probably drag it back some but i was kind of disappointed with the numbers maybe its all in the knock retard.

 

15 degrees timing on a NA setup with just heads/ cam/ headers..
I ran quite a bit more than that on a 150 shot.

Sounds like either your knock sensors are acting up and he just saw that its picking up knock and decided to pull timing.

NO SES for knock sensors?
Ive desensitized my Knock sensors with the cam adding valvetrain noise, the noise is picked up by the knock sensors and giving a false alarm.. Possibly could be your problem.

 

That's what I was thinking, the additional valvetrain noise and the headers creating noise, could have also been the shitty fuel as that station is notorious for that in my area.....not much of a choice at the time. Pretty much our only good fuel around is the Shell V-power 91. Has anyone audibly heard a spark knock in a truck, I work for Acura and we have a big problem with people using lower grade fuel causing spark knocking, its very noticeable but I've never heard it from my truck on any fuel.

 

sounds like rocks in a tin can...

 

Could also be the headers tapping the frame?

Fill up with some race gas or add some e85 and see if the kr goes away. If it does, than it was real, if not then its false knock.

 

Do you have a stall converter in it? They can simulate a knock.

You might want to run a cleaner like seafoam through it just to make sure it is clean and not being caused by carbon.

What are all the changes that were made since it was set at 19 degrees?

There are guys running 30 degrees of timing on NA engines without problems. Your tuner should be able to tune for what works best for you.

 

Put brand new injectors in, so I would hope that they wouldn't be carboned up. I'm going to have a can of race fuel on hand this week when I go back to see if it helps. Truck still has the stock stall in it.

 

I meant seafoam to get rid of carbon in the combustion chamber.

 

Heads are fresh, just put them on also

 

if you can't hear it knock, id bet your sensors are shot.

id throw a bottle of heet in it and see what it does