Jnosol

I installed Fabspeed Headers for my buddy's, Shawn, GT4 over the weekend. I thought I would share some insights, tips, and photos.

Overview: The Porsche GT4 is one of the best automotive bargains of the century. It's a true track capable car that's $60k less expensive than the GT3, lighter than a GT3, and the engine is located in the correct location. However, Porsche realizes putting the Carrera S 3.8 into a Cayman chassis without reducing its power would be a mistake (GT3 killer). Porsche de-tuned the engine by reducing the airflow, smaller throttle body/plenum and restrictive headers. The stock power band dips drastically at 3,600rpm. Shawn wanted a single performance mod that not only smooth out the power band, especially at 3,600rpm, but increase the volume of the car without compromising the Porsche signature exhaust sound. Fabspeed Sport Headers was the answer.

Why Fabspeed Sport Headers: Fabspeed has a long reputation in the Porsche community, they have always backed their product performance, great customer service, and Porsche exhaust parts are welded in America using only the best parts. The cats are made by HJS - Germany, the most recognizable brand in catalytic converters so reliability and check engine light will not be an issue.

DIY Information

Tools Needed:

• 3/8" Ratchet
• 3/8" Torque Wrench FT-LB
• 3/8" - 6" extension
• 3/8" - Swivel
• E12 Torx Socket
• 10mm socket (1/4" and 3/8" drive)
• 13mm stocket (3/8" drive)
• 13mm Open Wrench
• 22mm O2 Sensor Crows Foot Socket
• 1/4" - 6" extension
• 1/4" - Swivel
• 1/4" to 3/8" Conversion Adapter
• T-20 bit/socket
• Long flat head screw driver (12-15")
• Jack/Jackstands

Nice to have:

• Small battery powered impact with 3/8" adapter
• Lift

*All will be done under the car. Remove the rear wheels. Let the car cool off for at least 2.5hrs after running before working on it.

Headers Removal Steps:

• Remove the center lower black cover to get to the O2 sensor plugs against the fire wall. (10mm plastic nuts and T20 screws)
• Unclip and Unplug the O2 sensors plugs located against the firewall, and unclip the wiring. (long flat head screw driver needed for the grey wire clip closest to the rear of the car)
• Remove the 2 bolts holding the exhaust side of each headers (13mm nuts).
• Remove the 9 bolts holding each headers to the engine exhaust side (E12 Torx socket and 6" extension)
• Remove the header brackets (3 E12 Torx per side)
• Remove the headers (have a friend to help)
• Remove the O2 sensors (22mm O2 sensor crow feet socket) - *note: Green wire is pre-cat and grey wire is post cat

Installation Steps:

• Swap the O2 sensors to the new headers (22mm O2 sensor crow feet socket, hand tighten)
• Align the headers into position (have a friend to help)
• Install the exhaust side flange first, using the 13mm bolts/washers/nuts supplied by Fabspeed (need to use 13mm wrench, 13mm socket/swirvel, and 6" extention - hand tighten or use impact with 3/8" adapter) *Note: I used the OEM gaskets since the GT4s are almost new *Tip: Don't tighten all the way, leave 1/4-1/3" for wiggle room to align the other end.
• Install the 9 E12 Torx bolts to the header of the engine side, remember to use the OEM gasket (use 10mm thin wall 1/4" sockets with 1/4" swivel/extension. Snug the bolts from the center towards the outer, the come back to torque them in the same pattern). *Make sure you're using 3/8" swivel and extensions for maximum torque transfers. 2 step torque. 11ft-lb then 22ft-lb.
• Finally tighten the 2 13mm flange bolts/nuts on each exhaust side.
• Zip tie the O2 sensors so they're clear of the exhaust/engine. Keep in mind the engine will move slightly so leave some play room. Due to the new O2 sensor locations, you cannot use the old wire clip locations. Reclip the O2 sensor plugs against the firewall.
• Install the black cover (hand tighten, not to over tighten)

*Note, you're not going to need the OEM header brackets.

Impression: At first startup the car sounds 20% louder and deeper. On day 2, the car pulls much smoother at lower RPM (ECU finally recognized the mod). At high RPM range, the car sounds like an F1. It's probably one of the best exhaust note I've heard. I highly recommend this mod for all GT4 owners. Don't touch the exhaust, start with the headers first as you can see the OEM headers have many odd bends/kinks/smaller. You'll get more gains and better sounds with just the headers. Pair this with COBB/IPE Plenum and you'll have a GT3 killer.

Also, I believe the weight savings is closer to 12lbs. I should've weigh them with a more accurate scale to be exact, but the OEM headers + brackets are very heavy.

Let me know if you have any questions... Exhaust clips are coming. Overall, my buddy is super happy with the result. I'm doing this same mod for my 991 GTS soon. Selfishly I'm doing this to gain experience for my own car install. =P

user1029

My 'friend' has the same setup and I do agree with him that Fabspeed (race) header + stock exhaust is just purrrrrrrrrrfect

John@Fabspeed

Jimmy that is a beautiful write-up, thank you very much! I might just add this to our installation guides haha. Please give Shawn my best regards when you see him next Here is a link to a GT4 with just our Sport Headers installed for reference.

Jnosol

We thought about Race Headers for our cars, but only needed mid-range gains and not too crazy about the smell since it's nearly a DD. Race headers would sound crazy awesome and offer more top end gains.

What tune is your "friend" running?

user1029

he's on stock tune but I'm persuading him to get a Plenum/TB/Cobb

Jnosol

No CEL running race headers and no tune?

Jnosol

Thanks for the initial instructions, John. It was helpful to get me started.

tstafford

Had Fabspeed cats/exhaust on my 997TT. Sounded awesome. Was planning to leave the GT4 stock, but this thread has me rethinking.

Jnosol

Our group of friends in KC has 3 GT4s. Shawn was the first to do this mod. After just the initial impression of sound and power, the rest are going to order the same setup.

I seriously do not think you need to replace the OEM muffler, which has the signature Porsche sound. Just sport headers will give you more "engine" sound, volume, and throatiness that you're looking for. At low RPM, it's not much louder than stock so your neighbors won't hate you. Then next would be IPE Plenum and Cobb tune to completely free up the power that Porsche held back on the GT4.

With a car lift and Ryobi Lithium Impact with 3/8" adapter, the project takes about 3hrs (subtracted 2hrs for the car to cool off). The next time we do should be a lot quicker.

DrPhil Gandini

I've been running this setup (with a few other mods) for 6000 miles now and it's as fantastic as Jnosol says!

usctrojanGT3

That's why I bought CG race headers and will throw it on the OEM exhaust. For cruising around town it should be fine sound wise but at the track when I'm going flat out it'll sound great.

Jnosol

Race headers with stock exhaust would sound intoxicatingly good. Some tracks might force you to use turndown muffler tips due to noise ordinance.

John@Fabspeed

Big improvement, especially with the Cobb/Protune. Let me know what your friend needs to get started

None so far, our new catted O2 spacers are doing a great job haha.

No problem, glad to help!

Great to hear you have worked with us before! The headers are laughably restrictive on the GT4, start with our Sport Headers and get ready to have some fun! I'll reach out to you shortly and we can chat about it for a bit

Tell your guys to give me a call at their convenience, i'll be sure to get them set up

The factory center muffler sounds fantastic with just upgrading the headers. However, it is necessary to replace if you are after the most power out of the car as we have seen huge additional gains upgrading the PSE system to our Valvetronic Exhaust system.

Thanks for chiming in Phil. You modification threads and videos are fantastic Let me know if there is anything else we can do for you!

Martin you are going to love the race headers with factory center muffler. If you need a tuning solution to shut off the CEL and take full advantage of the increased exhaust flow please let me know (the GT4s/991 GT3s love some more fuel in the higher RPMs). We have a superb protuner in house that will take care of you

GT4Life

Thanks for the thorough write-up! Looks like I might have to get these headers sooner than I thought

Scottykenneth

Wow. I likes!