Full Custom Exhaust System HP boost?
 

Hey all. I'm bringing her into the shop in 4 weeks to get a full custom system installed. I'm having a high-flow cat slapped on, with 3" pipes - straight, no mufflers, split at rear axle - all the way through. It'll sound beautiful, but how much of a HP gain am I looking at? I know it lies in that high-flow cat...

A few weeks from now I'm also lookin at a ZZP downpipe and some nice headers.

All y'alls thoughts?

honestly exhaust won't give you much poswerit's more of a support mod.... and IMHO 3in all the way back no ffsfs on your v6 is not going to sound verry good but to one it's own. it's your car not mine

Gonna be loud, and youll lose back pressure, and some hp. So Ive heard.

Well I've heard some say there wouldn't be much gains, but I certainly felt it when I change over to the custom 3". A pretty big change, but I did have some supporting mods. The big change I feel is likely because I changed the downpipe. I don't completely understand your plan. Headers do not work with a ZZP downpipe. A powerlog will. Were you going to change over to a 3" exhaust and cat before changing the downpipe? That doesn't make sense. Is your car N/A or supercharged?

I have very low restrictive Magnaflow mufflers. It's still to loud and, like Budsjlm said, I do not like the sound. I do appreciate a decent performance gain.

Why not just a full downpipe up front- doesn't make sense to put on a HF cat, then replace it afterwards with a downpipe. Not to mention, the downpipe is the bulk of the restriction in the exhaust.

What is your engine and mods? I would bet a full 3" exhaust (they are doing it with a mandrel bender right?)- would probably be a bit too big if you're NA.

Depending on your engine and mods- I doubt it. If its a 3800- I really doubt it. It will be very loud, and very raspy.

Again, this depends on your engine and mods- but unless you've got a pretty heavily modded boosted engine, I wouldn't expect much of anything from the catback.

This of course depends if they use a mandrel bender- if they use a regular press bender, it won't flow nearly as well anyways- so it might end up more like 2.5" mandrel.

Travis, I kinda get what your saying and I was going to do something like it but I would recomend you have some mufflers on it so you have enough back pressure to create HP instead of losing some by not having enough BP.

Unless you have a S/C car, and even then, unless it's modded, a 3" is TOO big, On an N/A car, you will probably lose HP, but will definetly lose torque. IMHO it will sound like cr_p also. Needs to be balanced, and that's not balanced.

We need more info before we can help you. Like mentioned already above, 3" is far too large on a NA 3800. If you don't even have a 3800 of any kind (as in you have a 3400) then you will not gain any power and will surely lose power instead. Even a NA 3800 will lose hp and especially low end torque from that set up. My car has very little power at low rpms, but once it's opened up it makes up for the loss. Hope this helps and good luck with the build.

doing work from the cat back is going to be 0 gains unless you have good modifications and power from from before that cat already.

x2 on what everyone is saying. I would research that a little more before you jump into what would work on an older v8.

Even on V-8s, unless you have the HP to push, going to larger exhaust up front (like 2" headers) will trash your low end torque BAD. I'm told (by ZZP) that's the problem with the Pacesetter headers for the 3.8L . They are too large dia' tubes, and you'll lose torque UNLESS you got big HP, such as a modified S/C engine. Your engine needs a little back pressure to function right.