Thread: Exhaust gasket zzp downpipe leak

I have tried 3 different exhaust flange gaskets all new felpro metal design with a new 3" zzp catted down pipe. I still have a leak heard only under throttle. The last time I added some copper rtv on the crush part of both sides. Flanges look good no cracks. Seems like the gasket is just to small diameter to catch 3" flange.

Any body have any experience with this and have any advice?

I pulled it off again and used a mahle gasket, a bit different style. This time I checked the flanges for straightness. The pipe flange was warped so I set it on some wood and beat the ear back down until it was straight with no daylight on a straight edge. It still leaks but only at higher pressures. Gonna try some thin wire with same style gasket and some copper rtv and thin ss safety wire if it is warped again. Only torquing to 26 ft lbf according to gm manual. I still feel like there is very little surface width of the crush part of the gasket to seal it due to the 3" pipe size.

Hey I realize this thread is pretty old, but this is a problem I’ve been living with for years.

Ever since I first put my zzp downpipe on uears ago it’s been ticking. I’ve tried different gaskets, I’ve tried rtv, I’ve taken it down and reseated it a few times. Always ticking, never gets any better.

I can hear it when it’s at high idle on a cold start, and under medium or higher throttle. The last time I took it down I could see the thin little carbon trail.

Zzp just always tells me it’s impossible, their pipes have no known defects, and I must be installing it wrong or using incorrect gaskets.

I never heard anyone talk about warped flanges from welding before so that really interests me... you just used a straight edge to look for light, and actually found it was warped like that? Then hammered it back to shape? Almost 6 months later now, has it stayed fixed?

I’ll have time to take the pipe again since I try to keep it garaged when there’s salt on the roads.

zzp doesn't tell the truth all the time. I know a guy who bought a downpipe from them and the mating surface wasn't completely flat so it wouldn't seal.

are you sure you aren't getting lifter tick?

Yeah, that’s kinda what I was implying, that they’re just blowing me off. I’ve asked them a few times and they don’t even wanna talk about it. Just “nope they don’t leak, it’s you, okay bye” lol.

But as for the lifter tick, I was thinking that too, so when I did my LIM gaskets last year I replaced all 12 lifters with new ls7 lifters from intense, and the tick is unchanged.. plus I can see carbon tracks on the flange when I take the pipe down.

I never attempted to check the flange for straightness, though. The idea never really occurred to me until now, so I’ll put that on the to-do list.

with LS7 lifters I guarantee some of it is lifter tick

Mine still leaks but its better than it has ever been. I am not happy about it at all just have too many other things going on to mess with it anymore. Last time I used thin wire rtv and new gasket. The wire seemed to make a difference.

Maybe its the flex section itself that's leaking. The flex on the SLP headers were known for having a ticking sound under throttle. I've heard the same for some of the ZZP flexpipes as well. The fix was to put some header wrap around it. Been living with mine wrapped up for well over 10 years lol. A good way to find exactly where your leak is coming from is to do the seafoam test.