I have a 2016 5.3 lt4 blower, cam , long tubes,e85…anyway my tuner didn’t say anything about upgrading from stock single 3” exhaust size. It’s straight through now kooks 1 7/8 LTs couple of straight through mufflers no cats. Reason I ask is before the cam I was 8.5 pounds of boost at 515hp, after the cam I am at 565hp seeing 10 lbs of boost on my gauge…wondering if I need more exhaust flow to get the boost down. I still have biggest pulley on and i don’t thinks it’s supposed to be putting out 10lbs. I guess I’m just wondering if others go to a larger diameter for similar setups. Thanks

 

8.5 at what rpm, 10 at what rpm? Maybe just higher rpm is where the extra psi came from. Dual 3" mufflers and no cats seems to me like it should flow enough.

 

I guess I’m not sure on rpms wasn’t paying attention. Also I didn’t have a gauge before the cam install. Boost info came from tuner. I should have clarified it’s two back to back straight through mufflers to quiet down the long tubes. So after long tubes I just have a single 3” pipe with mufflers all the way back to single side exit.

 

I'd think a single 3" pipe is a pretty good restriction at that power level.

 

https://www.exhaustvideos.com/faq/ho...pipe-diameter/

According to the chart here you do need more exhaust

I have a 3.5" system on my truck that has supported 500, and will
hopefully support 550 this next round. The chart on that link says I won't be able to do that either

 

I misread the first post, I was thinking that "a couple of straight through mufflers" meant dual exhaust.

 

same pulley as before?
old vs new cam specs?

these have a bearing on boost just as much as the exhaust size... for instance, if you're drawing a lot more through the intake valves without an equal increase in exhaust.

 

I went from a single 3" to a dual 3" and dropped 3 lbs of peak boost at 7k rpm. Your restricting it pretty good and making heat. I'd go true 3" duals and feed them thru 2 mufflers a piece or do what I did a go with 2 mufflers then fed them into a dual inlet and outlet x pipe muffler.

 

Have a 2014 sierra 6.2 with whipple and cam. I had headers into factory exhaust 4 inch pipe into qtp screamer. Then split dual out. I blew the muffler apart at 8lbs. Went to 3 in true exhaust. Runs so much cooler.

 

3 in duals would be the ultimate and probably not close to needed at your power level. A 4 single would also work perfectly. Pick whichever is easier for you. Iirc 03sierralt used 4in for years with his blown 370. Either or.