If anybody remembers, I thought I lost like 6 lb boost with my bigger engine. I don't know why that scan config. was reading the MAP so wrong, but the config I'm using now shows that I only lost about 2 psi, it has about 9-10 psi actually. That leads my to believe that I have surpassed the flow capabilities of the stock muffler, although it is still pulling above 5000 rpm. I don't know how well, because of the KR. That leads me to my question: Everybody knows that you will gain power while losing boost with a less restrictive exhaust. What everybody (me) doesn't know is, if I open up my exhaust, will the reduction in boost lessen the engines tendency to knock (if it is indeed knocking due to boost level)? Or, will the KR still be there because the engine will be flowing more air?

 

I would think a 408 with 8-10psi would need more than the stock muffler.

 

Well yeah, but that's not what I'm asking.

 

If the boost drops then the tendency to knock would decrease as well because your cyl. pressures will be lower. Ultimately you want to make the engine as efficient as possible, for example: Going back a couple years, pre intercooler 8-9lb boost then after intercooler 6-7lb however it still ran better with less boost. When I put on my LT's and ORX with dual 3" exhaust my boost droped another 1.5lb but it pulled stronger still with less boost. Then I ditched the MAF and ran 4" to the blower and gained about .5lb


I guess my point is that by opening up the exhaust you may loose some boost but also may gain some power at the same time. Less boost= more timing before hitting KR. I just realized my rant most likely was a waste of yours and my time but maybe it will answer something... If I seen right in one of your previous posts you CR is 10.3? How much timing are you seeing at WO when the KR hits? What is your exhaust setup?

 

I would think so based on logic, but i am no tuner and things are not always logical.

 

KR shows up at 14 sometimes, 15 others, the highest I've seen is 16°. It is asking for 17°.
Long tubes into stock 6.0 exhaust.

 

I would have to say 17 is a bit high for your CR. Also technically a larger bore engine will see a little less timing then a smaller bore on the same setup. Again JMO. I would open the exhaust up some, do you have Cats?

 

Stock (.030 over) bore. Yep to cats.

 

You need to tap a 1/8'' hole in the exhaughst pipe before the cats, and after the cats before the muffler, and see. I use a cheep oil gauge, and copper line. That way you can see if it's the cat's or mufflers restricting you.

 

That will work, although I am not sure what would be considered a acceptable amount of back pressure... Anyone know?