^^ That is very interesting. I hope this will solve OP's problems.

 

This was my thought as well after reading the O.P. I had similar issues with my VIII back in the day.... I was able to spot it by looking at the piston tops when changing plugs one day... three were black as night, the 4th just had a light tarnish to it. Replaced the injectors and the knock problems cleared right up.

Symptoms were random knock all over the place under wot, varied from run to run. Would not take the same timing as other VIII's and required richer over all afr. After replacing the injectors and then retune I was able to pickup about 30hp or so across the board.

I would think though that you guys were able to get a look at the pistons when you scoped it so this may not be the issue, or it may only show up under wot at high duty cycle so the hot plug test might be the way to go.

Edit... Just saw you guys already swapped the injectors. And to SiC's point about the exhaust, deffinetly check that, or for that matter just drop the catback off the car for a quick dyno pull and see if there is any improvement. I've seen plenty of cars not reach their power potential due to catbacks that neck down.

 

Thanks for the input guys...I'll check out the exhaust, that will be a bummer if that is the issue because I love this exhaust.

Sic...where would I look to see if it has the stamp?

 

It'll be a metal plate about 1inch by 2 inches or so on the muffler and center pipe but I saw pics of your exhaust and it may not have it for the US export model. Can you look into your tail pipe and see how large the inner diameter of the muffler is? Is it narrow like 2 inches? Or is it a straight 80mm?

 

Here's some pics of my old exhaust with the restrictor inside and the JASMA plate.

 

^The Greddy exhaust starts off with a 2.5" pipe for about an inch or so, so it would mate up with stock cat. Could this little sliver of taper bottle neck the whole system?

 

If you're running the stock cat it shouldn't cause much of a restriction there. But if you're running a 3 inch straight pipe then reducing to a 2.5 inch piping afterwards will cause some restriction in the exhaust flow.

If it has the 2.5 inch taper for the stock cat, I'm really thinking this IS the JASMA exhaust with the 2 inch restrictors in the mid pipe resonator & muffler.

 

Wow, my exhaust doesn't look like that at all...it looks like someone stuck a roll of paper towel in there!

 

It looks like someone stuck a paper towel roll in your exhaust?

 

Did you check yours out? I also have the Greddy and my exhaust does not have the JASMA plate. The muffler seems to have a straight 3" hole, but I do have the taper for the stock cat.

I noticed my car (w/ blouch dom2.) does not like to hold boost above 6500rpm's even with a forge wg acuator (25 psi tapering to 20psi). I'm wondering if the bottle neck exhaust is the cause of this.

 

Even with a restricted exhaust, the boost should hold more than that. You may have another problem. I was hold 27-26psi on the actuator that came with my Dom2.0. I actually backed off the actuator since it was holding too much boost, not giving my any room for adjustments. Currently, I have it set to 25-24 psi and I'm controlling it with an HKS EVC.

 

So I finally had a chance to inspect the exhaust. The muffler definitely isn't tapered down like your old one...but I do have the neck down piece right after the cat.

I can't see into the resonator...but I have a feeling that it is not restricted. I'm hoping to get some time at the shop soon to test out a few theories. Still considering the coil pack thing and the MAF...but I'm sure we'll take off the exhaust as another test.

 

Good luck in your trouble shooting. I just started experiencing some random knock on a FP Red w/ 1000cc injectors. We are pulling 2* out of it up top to see what happens. My knock is not audible, but you CAN feel it on the street on an ultra hot muggy day.

What amount of Knock Retard are you seeing? I'm only seeing random 0.35's and some 0.7's.

- Louis

 

I'll have to check in with Bryan to get the actual knock counts/timing retard. I'm finally going to have some free time to actually work on the car this weekend...so hopefully I'll have some better news.

 

10-12 counts at some points with 23psi or so

up to 6-8 at 20psi