m05fastbackGT

I'm debating installing an old mac catted prochamber in which I recently gutted out the cats.. My reason for gutting them, is I don't want to risk causing possible damages by running ceramic cored cats with FI..

I'm not really looking for any substantial power gains, but rather looking to reduce cabin drone from my Borla Stingers.. Anyhow I've read quite a few posts from previous threads claiming that running an O/R prochamber works really well for reducing the amount of resonance drone..

Currently I'm running the stock catted mid pipe with the Borla S type (stingers) but the resonance drone is horrible between 1500-2000 RPM in both 3rd and 4th gears around town at 25-50 MPH..

So my questions are this.. Will the sound of running a gutted catted prochamber produce any resonance drone from the larger opening inside the shell of the gutted cats or will the sound be similar to running an O/R prochamber that doesn't include cats ?

In the meantime, any type of feedback and support will be really appreciated..




-Rocky..

07 Boss

I would think that you may encounter more issue with gutted cats as opposed to a straight pipe. But I am no engineer.

IMO as couple of small resonators mounted mid pipe and staggered might be your best bet for removing any drone. I used a couple of these.

Bert

Personally, I would avoid messing with the cats if at all possible, to stay clear of any problems with the law. Some other way to reduce the drone sounds better to me.

m05fastbackGT

After doing some further research, I went ahead and ordered a pair of Vibrant 18" resonators, part # 1793 from Summit Racing.. As for the gutted cats are concerned, I'll be having a shop cut off the gutted shell casings altogether and have 10" sections of 2.5" diameter stainless steel pipe welded in their place..

This will convert my Mac catted prochamber into an off road prochamber.. My only concern is will the S-types lose a significant amount of volume outside of the cabin with the resonators and o/r prochamber paired together, or would I have much better results by just pairing the resonators and S-types with an off road H/X mid pipe section instead

Bert, the only ways to reduce or eliminate drone is by either swapping to a quieter sounding muffler with the stock catted mid-pipe in place or add resonators..

Since I like the sound of the Borla S-types, except for when they drone, I intend on sticking with them.. Therefore my only other option is to add resonators along with the mac catted prochamber in which I'll be having a shop convert over to off/road by cutting off the gutted shell casings and having 10" stainless steel 2.5" diameter pipe welded in their place..

I also recently found out that as long as I don't put over 5000 miles per year on my car, we have an emissions exemption law here in PA.. So I shouldn't have to worry about running into any issues with the law being that I won't have to go through all the hassle of being required to pass emissions inspection anyhow

07 Boss

I can't speak for with the Prochamber, but when I put my mid mounted those Cherry Bombs they did not reduce volume. They changed the tone a bit, mellowed it out, not as raw sounding, but no significant change in volume. I have them paired with Outlaws so they were pretty obnoxious. The Cherry Bombs just toned it down a bit.

The Prochamber is just a tuned resonator. I'm not sure how it will interact with another set of resonators. Maybe the Vibrants you are going to put on may change the frequency or something. Exhaust is a weird animal in that you just have to try different stuff. So many combinations and variables it is hard to say what it is going to sound like.

m05fastbackGT

From my understanding the prochamber helps toning down rasp and trumpeting sort of like a resonator, but doesn't have a perforated core as a resonator does.. The main purpose of the prochamber is to scavenge exhaust gases along the lines of an exhaust header so that gases flow more efficiently and smoother.. The design is an open chamber with flanges that supposedly provide a smoother/deeper exhaust tone over a traditional H or X mid pipe crossover.. So I suppose in someway it does function as a tuned resonator, but isn't designed to change or cancel out certain frequencies as a resonator would that once again has a perforated core with layers of exhaust dampening material for the sole purpose of reducing and cutting down resonance drone..

I suppose that I can try out the prochamber first without the resonators and find out if it cuts down any of the resonance drone and if doesn't, then I'll add the Vibrant resonators with the prochamber and then see how everything turns out

07 Boss

Well yeah, it's not your traditional resonator. I forgot the name of the type of resonator they call it but it's design uses the frequency of the exhaust pulses for better scavenging and flow which is also going to change the sound.

m05fastbackGT

This is Mac's description of it's prochamber design.. So perhaps this will provide a clearer understanding of what type of resonator it's considered as

The MAC Patented Pro Chamber™ has made the current intermediate systems obsolete all together. Split (one each side) manifold or exhaust headers on any engine, need to be balanced to each other. On a V8 motor for example, the exhaust pulses enter respective collectors at uneven intervals of 0-90-180-270 degrees of engine rotation. This process hampers the full benefits of any exhaust header system or manifold by the long intervals between exhaust pulses. Balancing of exhaust gases in mandatory for optimum power. Balance tubes between exhaust, on opposite side, helps transfer exhaust pulses for side to side to smooth out the exhaust pulses and flow. This results in more Power and a broader Torque band.

The MAC Pro Chamber goes even futher than the Traditional X & H-Pipes to produce More Torque and Horse Power by merging the Exhaust Pulses into one area. Merging of all Exhaust Gases creates Higher Temperatures which creates a Boost in Exhaust Velocity and allows the Exhaust Gases to see and use both Outlets.. "Your Exhaust will think it's a 180° Fully Tuned Header"

07 Boss

Helmholtz resonator. That what it's called. made to enhance some frequencies and squash others. That is why you get such a nice tone out of them.

m05fastbackGT

From a couple of you tube videos I viewed, the description of a Helmholtz resonator seems to have more in common with a bottleneck type over the prochamber.. The Prochamber is more along the lines of an X pipe design inside of a closed box/open chamber, also referred to as a Helmholtz chamber..

Anyway here's a you tube video of a homemade designed Helmholtz resonator..


Update.. Spoke with Manny from Mac performance regarding the design of the prochamber.. According to his description, the prochamber is NOT a resonator nor is designed to dampen or cancel sound frequencies associated with resonance drone.. The Prochamber's sole purpose is to increase torque and HP by merging the exhaust pulses/gases into one area in order to smooth out the exhaust pulses and improve exhaust velocity and flow.. Also the Prochamber design has no tubing in it's enclosure whatsoever, but rather uses 3 reflector plates instead to help balance the exhaust gases for optimal power..

At any rate, that was the info provided straight from the manufacturer..

Clark Kent

I have slp loudmouths and I am afraid to add anything else to the exhaust setup. It hibk it will just make them abnoxious and too loud

m05fastbackGT

I was actually considering SLP loudmouths before finally deciding on the Borla S-types, as I was concerned about the loudmouths producing even more drone over the Borlas. For my particular application, I returned the Vibrant resonators back to Summit Racing after discovering they would only muffle/deaden the sound of drone, but not get rid of it. So for the time being, I'm just running the Borlas with the off-road pro chamber and plan on having Solo Performance fabricate and weld-in a pair of adjustable J-pipe resonators which are considered as a Helmholtz resonator design that's been actually proven to cancel out the frequencies that produce interior resonance drone.

But if I were in your place, I wouldn't run the SLP loudmouths without cats, and possibly without resonators as well, otherwise they may end up sounding obnoxiously too loud, just as you mentioned