REVIEW: SOUL Porsche GT4 Long Tube Street Headers

As written by Rennlist member “mcomet”‘


To start with a little history. I previously owned a 2003 986 Boxster S for a short while, and then a 981 Cayman S for several years. At one point during each, I had an aftermarket exhaust replacing the stock Porsche headers. And in both cases, they were removed fairly soon. Both ended up being one of the louder exhausts, and it was too much for me. With my last Porsche Cayman S, I knew within minutes it was probably too loud after driving home, although it did sound epic. Being in my mid-forties, I don’t quite want the full-on race level exhaust and like the idea of being relatively quiet — at least at points when I need to. At the same time, I wanted something louder for the back road drives.


My goal then with the Porsche Cayman GT4 was to keep the Porsche sports exhaust (PSE) for the tone and sound that I liked but to get “more” volume without being at the point where I’d remove it. With my 981S, I always wanted more volume. The initial purchase of the GT4 afterwards did hit some of that as the GT4 exhaust has no sound deadening and is louder. Still, on back road drives, I wanted something more aggressive so that I’d fit in with people with aftermarket exhausts and other exotics. If the windows were up I had a nice sound, but I naturally wished the GT4 exhaust could be a bit louder. If the windows were down, I wanted to hear my Porsche exhaust more than the wind noise buffeting around the cabin. In addition, the idea of running Stage 2 and having some performance gains was also a nice idea. I have already been running Cobb Off the Shelf (OTS) Stage 1 maps. The hope was to get aftermarket Porsche headers to provide more sound and perhaps some power gains with Stage 2 OTS maps. All the while still retaining the factory Porsche sports exhaust tone and goodness.


Lastly, of course, I was trying to find a way to do this and keep the cost down. Cargraphics have long been the standard for the Porsche header setup and are known for quality. SOUL, however, is a fair bit less expensive, AND they also warranty the same HJS 200 cel cats even if you track the car. (I’ve been to Laguna Seca once, but it was before I had these Soul Porsche headers installed, but I plan to go again). Put both of those together, and I was willing to take the risk with the purchase.



Install and Customer Service

I had a friend who does work as a professional mechanic do the install for me. That meant I wasn’t hands-on with any part of the install, but I did pre-order the proper header gaskets and the extra exhaust gaskets, both of which are needed unless the existing Porsche gaskets are new enough to reuse. Be aware you’ll need to purchase these yourself unless your installer will provide. The shipped Porsche GT4 headers from Soul did include a full color print out of basic instructions (there’s really more detailed instructions on rennlist for general header installation). I also received a red microfiber towel and two white “Soul” stickers. Soul also provides a new nut/bolt setup to connect the back exhaust area of the headers to the exhaust. The actual installation and fitment was good according to my installer, and there didn’t seem to be any real issues.


The only potential concern was the bolts that attach the Porsche headers to the engine. These are supposed to be reused. However, the newer header base is a bit thicker than the flange part of the OEM header. So, there was some concern that the bolt going into the engine wasn’t quite in as far as it would have been previously. That said, it was plenty far enough to be okay, and a small amount of blue locktite (which may not really last with heat) was added to be sure. We’ll recheck bolts at some point in the future once more miles are on the GT4. Other than that, things went perfectly.


In fact, when we were somewhat confused by an installation note about gaskets, I reached out to Soul Performance Products via Instagram and instantly received the information we needed. That’s right. Instagram chat. Instant response and help clarifying. In fact, my entire order, discussion, and decision making took place totally within Rennlist messages, Instagram chatting, and a few emails at the end. I always had very prompt responses and Soul seems to have great customer care and support. In fact I just sent an email Sunday evening as a follow up and received a response soon after. My experience so far is that Soul Performance Products has fantastic customer care.



Initial Impressions and Sound

After the install, I was, of course, eager to get the car and experience it. My installer friend is about 45 minutes away from me, so that meant a bit of freeway and some side streets home. Right when starting the car, I definitely noticed a bit more noise when turning the key. Not a lot, but enough that I could tell the exhaust was more aggressive. That being said, parking lot speeds and low rpms are basically OEM. There’s not a real noticeable change at slow speeds, which is a good thing.


However, pulling out and getting on gas down the street with sport mode and exhaust on…. AMAZING. This is what the Porsche GT4 should sound like stock. Exactly what I was hoping for. In my opinion, this must be what the engineers at Porsche wanted the car to actually sound like. I feel like they must have designed the engine and exhaust, slapped each other on the back in approval, and then been told by managers they had to put on 800 cel cats, thrown up their hands in disgust and gone to eat some bratwurst. The sport cats amplify the already amazing Porsche sport exhaust sound back to a fantastic level.


For me personally, the volume is basically perfect, maybe slightly on the cusp of entering the loud side. It gives me the “more” that I wanted out of my Porsche exhaust when at mid to high rpms with the exhaust open. I would say maybe 75-80% of race header volume…which is what I was looking for. If race headers on an open road actually sounds like being inside of a parking garage..this is approaching a similar level but not quite to that full amount. Windows up, there’s the amazing tone of the Porsche sport exhaust and engine. Windows down sounds even louder, and I can only imagine how epic it sounds behind the car. I can’t wait to go through a tunnel… If I had to use a word to describe it, I would say the exhaust is more “trumpet” like now with loud revs. It’s still the OEM sounds but just blasted out more.


In addition, I really wanted a smooth pure tone… the Soul Porsche headers are definitely doing that. It’s not gritty or coarse like I was worried it might be, which race headers tend to do as you get fully open flow from the engine. If anything, it is smoother and purer than even my OEM exhaust setup sounded, or maybe I’m just hearing more of it. But it’s fantastic. You get the Porsche 3.8L sound in spades. All I can say is YES YES YES. This is what you want to be hearing when driving your Porsche.

When cruising on the freeway or bumper to bumper traffic at lower rpms, it’s fairly close to stock Porsche exhaust. With the exhaust open, I was getting 76-78 dbA with the windows up/closed. On the gas and higher RPMs with exhaust on and windows up/close, it was 87-90 dbA. I did in fact turn OFF the exhaust for a bit, something I never had to do before. That quiets it more on the engine rev side since OEM Porsche sport exhaust is closed anyhow at low rpms. That said, you can still have a conversation with someone inside. But I felt like it was marginally louder perhaps. Something to consider if you have to use the car for long journeys.



Even without headers, the stock exhaust system has some drone around 2500-2800 rpm…minimal but there. I wouldn’t say that it is worse with the Soul Cayman GT4 headers, but there is more volume overall… so if you are sensitive or doing a long drive, the volume might be a concern. For me, I found the overall volume to be right where I wanted it — loud enough to now hear it and have to maybe turn the radio up a bit more than before…but not so much that it’s overbearing. I took the car to work the other day and honestly I felt like I could easily drive silently just keeping revs down. At 2800 and below it is basically stock. That is sort of my barrier, if I can go to work now and then and not feel self conscious driving. At the same time, I definitely had some fun with hard accelerations, down-shifts etc… you WILL get more attention with these Soul Porsche headers, but I feel like it is the right level for this car.


Being that OEM cats are 800 cell, Sport cats are 200 cell HJS cats, and Race cats are basically no cats… it makes sense. The sport cats let about 75% more flow or volume through. So it isn’t quite race header insanity but up there.


Oh, one other benefit… a bit more “pops” when letting off throttle. The Porsche GT4 doesn’t do this as much as my Porsche 981CS did (which is done by computer). The GT4 doesn’t fake it, so you get way less pops with stock setup. But with the new Soul Porsche headers, I got a handful of nice loud backfires. It is still fairly infrequently … but sounds good when it happens but there are definitely more burbles now overall.


I recorded a video of start up, idle, revs, and some driving with windows up and down below. The numbers are similar to cargraphics sport, which makes sense since they both use the same HJS 200 cell cats. Externally, Soul’s Porsche headers hit about 123 dbA which is within the +/-2 error range for my db reader of what cargraphics were. While I didn’t do freeway driving (less wind noise here) there were still a good level of sound within the car as you can see.




My drive home was mostly traffic, even on the freeway. But the car definitely pulled nicely. Not that it was horrible before. After arriving at home, I transferred on the Cobb OTS Stage 2 map with my accessport and did a quick drive around town. It was hard for me to register much with the “butt” dyno and just street driving. I will say when I had stage 1 on my Cayman S it was similar… I couldn’t tell a difference from stock to Stage 1…until I got used to it and one day took it off. Then I was like wow I miss all this high-end power on the freeway. So I didn’t really expect a big change for me. I’ve only had the Porsche GT4 a few months and am already running a tune and feeling like the car is fast enough, so I didn’t expect anything.


After taking the car to work and back, I definitely noticed some more mid range pull. If you are sitting closer to 4k rpm and get on the gas, you can often get a bit of shove into the seat. It’s still not a torque monster, but it is noticeable a small bit. Honestly, I had a hard time registering it the first day or so I had the car. So it may be that the ECU had to adapt or that it’s just harder to tell coming from stage 1. Clearly if you want max gains you’ll be doing Porsche race headers, intakes, and a pro-tune. In my case it is solely the Soul Porsche headers, tune, and 91 octane. The 3.8L GT4 is really perfect for me speed wise. I always want more torque but don’t care about speed. Apparently the way the Soul Headers are designed is for more midrange torque, which jives with what I was noticing, even if subtly. Low range / low rpm is still pretty anemic, but that’s Porsche NA engines for you.

I asked SoulPP about air filter changes/intakes etc. for more gains, they replied that would be more minimal additions vs the headers. Doing a proper ProTune would be the best which makes sense. Overall Cobb Stage 2 with 91 Octane does yield a difference over stock for sure. So I am positive there are gains here. I hope to get a dyno at some point. We can run some numbers off of the Cobb website below…

Just looking at the Cobb Tuning website:
Stock GT4

385hp @7400rpm
309 ft-lb tq @4750rpm

MAX GAINS 91 oct
GT4 Stage 2 13.19%hp 13.33%tq

Mathematically would be around:
(+50.7 / +41)
435 hp / 350 ft-lb tq

Assuming that Sport Cats are 25% less efficient than race header this would make my stage 2 delta more like for MAX gains:
430hp / 345 ft-lb tq

GT4 Stage 2 6.70%hp 5.60% tq

Mathematically would be around:
(+26 / +17)
411 hp / 326 ft-lb tq

Assuming that Sport Cats are 25% less efficient than race header this would make stage 2 delta more like for MAX gains:
407hp / 323 ft-lb tq

So, in reality, I would venture to say even without a proper dyno, my Porsche Cayman GT4 should be around probably over 400hp… not a bad place to be for mostly street driving.

Longer Drive Testing

The day after getting the car back I decided to do a run up Mt. Hamilton. I actually connect to a back road drive from where I live, which is about 30-45 minutes, to the actual drive up Mt. Hamilton, which is easily another 1.5 hours of twisty and some straight bits of country road and some semi highway bits in-between. It was the hottest day of the summer so far at 107 degrees. I left early, and by the time I arrived for the “main” part of the drive the temps had risen from 67 to 84 degrees. I did a mix of driving with windows up, windows cracked and windows down despite the temperature. I hadn’t yet had the GT4 on this road, although I’ve driven it with my other cars. Overall I spent over four hours of actual driving time there and back.


There is no question the Soul Porsche headers were a great choice with tons of fun volume and sounds. Amazing tone and feel. And apparently there is in fact more power as I seem to be able to get wheel spin in some cases now with second gear at the right rpm. But mostly for me it was about sound. With much of the drive being narrow and some spots of gravel I didn’t push super hard. Except for some areas with good visibility and no one around driving was more moderate. The video below has a number of bits from slow to fast. Be aware the sound from the external mic is a bit “gritty”. That’s not at all what it sounds like in reality from inside the car. It’s loud and aggressive…but has a really good smooth tone. The noise you here is probably due to my microphone and sound placement. At some point, I will attempt to get some other video externally and with other devices.


On a side note, I also initially lost the audio recording GoPro during the drive. I opted to move cameras around for more interesting positioning. The main audio camera I placed on the right rear fender came loose probably because I forgot to wipe the dirt/dust off first, and had it over an arc on the body work… which meant it wasn’t quite suctioned well enough. After a long high speed area it came loose, and eventually fell off after it disconnected from the wire holding it to the microphone. Luckily I managed to recover it almost an hour later on my return drive, finding it right in the middle of the road. The case I was using was damaged but the camera was ok. I put all this near the end part the video for amusement sake… I guess if people want to know if a GT4 with Stage 2 is fast…the answer is yes…it will rip your cameras right off!


The Soul Porsche GT4 headers overall get two big thumbs up from me. Exactly the sound that I wanted and not crazy but definitely “louder”. I have no doubt behind me it must be pretty fun now. Not race header obnoxious, but approaching it in a good way. I am pretty sure my wife will hate it, but she already hated the suspension and noise of the GT4 compared to the Cayman S anyways. Cruising with the new Porsche exhaust setup, which already sort of got on my ears with the stock setup, shouldn’t be too bad as it is similar to OEM and it is worth the trade off to get the extra noise for the back road drives and open exhaust sound. I really use this car for weekend fun…it’s the balance I was looking for. Livable enough for the long part of the drive and exciting enough for the rest. I also believe I will still pass sound at Laguna Seca by doing the up-shift and half throttle trick one has to do with stock setup since I know other sport cats are able to do that. Or maybe I will get some Laguna Pipes. Mix great customer service, overall value for the price, sound, and ability to run Stage 2, and I’m very very happy with the Soul Sport Cats. If you are in the Bay Area and want to check it out, feel free to drop me a PM… Just another happy Porsche owner and Soul customer.

Additional Follow Up

DEFINITELY louder AND more powerful. The car was quick before…it now feels properly fast. There’s one back road by me I used to go from stop sign to a small bridge flat out. I am pretty sure car was easily several (7+?) mph faster today maybe even more, and I hadn’t even done a super aggressive start. Crazy. Mid range pull is nice.


There have been a few times where I was like hmmm I wonder if I actually want louder. But when the windows are down I am like nope, this is the proper level of loud from outside the car. I am sure there are probably people outside who think it is too loud. It’s amusing I can now grab people’s attention by just downshifting or getting on the the throttle. Just give it a little gas and heads will turn. In addition just driving under any sort of overpass is pretty amazing. Even freeway speeds, windows down, wind noise… just get on gas a little under a normal totally open underpass… it’s pretty amazing sound level. If any car or sort of wall is near you the echo / sound is even more. Tunnel now sounds like double what a tunnel used to be. And as mentioned tone above is just perfect. Sounds like a proper exotic car or race car. Friend of mine with the F328 below drove with me this am. He said he could hear my car even when he was in front of me just fine haha. There’s definitely some more mechanical or other sounds from the engine too but at high rpm it’s just lovely flat 6 sound. And the pops are just awesome. The best loud backfire seems to happen most often letting off of 1st gear quickly at 5-6k rpm or so.


On the flip side just up shift to a higher gear and lower throttle and you can totally fly under radar. Did that with several cases of either slow traffic, or police coming opposite way on some drives. The car will be basically stock and near silent. With the valves closed it’s also decently quiet even when on the gas. That said I am driving with sport mode and exhaust on ALL the time and windows down. Because…race car. Anyhow best mod I have ever done to my Porsche, or any car for that matter. Despite accidentally curbing one of my wheels today (that sucks) it’s still so fun. The Porsche GT4 itself is just amazing too… the only car I’ve owned where I’ve felt like writing about it every time I drive it. The Soul Porsche headers just add to that enjoyment.

>> Porsche GT4 / Boxster Spyder Long Tube Street Headers <<