Porsche 981 GT4 Acid Green – ALL IN
Its not very often we get one of these projects, but oh what fun it is. At BRracing, we always want to ensure that we match the objectives / target / results, with the enhancements that are to be implemented. Not all cars need all the enhancements possible, and one of those objectives that we have to work within is making the most with the budget we have.
But, in this case…we were given free reign. The objective, just make it the best car possible for both street driving and track use. We had some unusual requirements, as the customer is very tall, and has very long legs. This would mean a different approach relative to seat / steering wheel fitment, even though the base car has some adjustment, they were not sufficient to allow a comfortable driving position.
As we have mentioned in our other write ups about the GT4, the base platform is very good….but not perfect. There were lots of small enhancements implemented by Porsche in the GT4 platform, but some areas were left wanting. We know also that Porsche purposely took some power away, to prevent the performance of the GT4 to encroach too much on the 911 territory, so that is an easy target. Plus…we wanted to create some excitement, make people go “oh wow” when they see the car.
– Software tune
– Body / Graphics / Protection
The good news, great news is that Porsche put the 911 3.8L engine in the GT4. However, to ensure the proper marketing position, Porsche “de-tuned” the 3.8L engine when put into the GT4. What did they do? Simple exterior changes…changed the intake, changed the tune, and changed the exhaust. By limiting the engine in these areas, Porsche took some grunt away…but, the great news is that those are all easy changes to make, and we can restore the lost power. When we raced the GT4 Clubsport in its first year of racing (2016), we found that Porsche had restricted the intake, exhaust, and software tune. Therefore, for street cars, we don’t have to follow the rules, we can unleash the beast hiding within. The first step then was to alter the intake system (intake plenum, throttle body). IPD has the pieces, and on some other Porsche engines, they don’t have that big of an impact, but on the GT4, they are just what we needed.
The throttle body is the other element of the intake that needs to be upgraded…and the parts bin of Porsche provides us the solution in the stock GT3 throttle body. It’s a perfect fitment, and mates well w the new silicon hose of the IPD plenum.
So, we have enhanced the intake side, to allow the bigger engine to breathe better, but that’s only half the equation. If we make the engine breathe better, then we also need to let it exhale better. That would be the logical response, but there is also a factual response. Again, with the racing experience we had w the Porsche GT4 Clubsport in 2016, and the chance to work directly with Porsche Motorsport at all the events, we had several discussions about the exhaust system of the GT4. We encountered some issues during the year, and to the point that Porsche Motorsport issued a change in the engine exhaust system mid-season. Taking this into consideration, we reviewed the exhaust systems out there, and also those designed by the same people we played with on the Pirelli Cup series, GMG fully understood what needed to be done, and provided the solution in their exhaust header system for the GT4. it flows better, protects the ignition coils better, protects some of the suspension / drivetrain better…..a win / win / win solution. Oh, and by the way, it sounds AWESOME as well.
We believe there is a little misconception in the market….with the thinking that a software tune will unlock some hidden power in the engine. For the most part, that is NOT true. The normal stock elements of the DME / ECU, the thermal sensors, the O2 sensors, the cam sensors, the variable valve timing and the knock sensors allow the engine to manage itself within a relatively wide range of conditions, fuel trims. The stock engine can fully detect what “octane” rating the fuel is, and adjust appropriately for the cam timing and the ignition timing. If you push ignition timing forward (one of the normal “tune” parameters), the knock sensor will detect the change, and often retard the timing automatically, and therefore, take away any power a “tune” tries to implement.
However…if you make sizeable performance changes, then the stock engine performance window will be different than the target, and you need a tune to take full advantage of the changes. Hence, if it is a turbo engine, and you dramatically change the boost, then a tune will be needed to unlock the power.
With the addition of the intake plenum, intake hose, and throttle body…plus the exhaust to be talked about later, a tune was what the doctor ordered. If we are going to implement a tune, then the tune we like more than any other is the Cobb Tuning solution….its a hand held “access point” device, that offers a lot of features besides just being a hand held tuner. No tune is ever perfect, and no project is ever done, and the Cobb unit allows you to alter, change, update, and upload a different tune at any time, and also to restore to stock at any time. Many other tune solutions, require the ECU to be pulled, “flashed” and then installed….that’s often a three day experience…whereas the Cobb is a five minute effort.
The stock suspension in the stock GT4, is, for the most part, just fine. Other than the attroxious alignment. We have written about the horrible stock alignment…and the variety of setup options (Phase 1 to Phase 4) that we have defined depending on the specific needs, type of tires being run, and aggressiveness of the customer. To achieve anthing beyond the Phase 1 settings, you need to replace some of the suspension pieces….and to do it optimally, you want to replace the front upper strut mount with the Porsche Motorsport unit. The other piece is the rear toe link, as there is not enough adjustment range in the stock unit to achieve the toe setting in the rear, once rear negative camber is set in the target range. One of the other pieces that goes a little beyond this is the ride height itself. Most don’t know of the change needed, or the reason needed, but the ride height and rake of the car can be changed (great news here is that the stock GT4 comes with adjustable height coil-overs…so making this change can be done with the stock suspension), and should be changed to optimize the handling of the car.
New Porsche Motorsport front upper camber / strut mount unit on the left, stock unit on the right (below).
We also need to adjust the alignment to our custom track type specs. To get there, besides the front upper camber strut mount, we also need to replace the rear lower toe links with adjustable units. We selected Porsche Motorsport versions for this car (important to use the “pinch” style rear toe links, not the “jam nut” style.
Now, for this customer…he wanted to go beyond, to get the best. We have to keep in mind that this is still a street car, daily driven, on the freeways in our local area. If this were being made into a racing “ClubSport” model, we would take a different approach. Therefore, we replaced the stock coil-overs w KW Clubsport units with remote reservoirs. To do this, we would need to eliminate / defeat the EDC system as well (electronic dampening control that comes with the car, and the selectable shock setting from the centner consule). Along w the KW Clubsport, we also implemented KW’s EDC delete kit.
Body / Graphics / Protection
This is one of the fun areas of the project. We wanted to make a tasteful statement, an “oh wow” type of statement with the body and graphics, and yet look perfectly wtihin the normal Porsche design methods and styles. We have loved the Porsche Acid Green color, and the silver color of this car is the perfect match, so we designed some graphic elements, additions to add to the style, and we would use the “acid green” (from the Porsche 918 hybrid). The customer also wanted full body protection….so, how do you combine both full body protection and graphics? We did the full body / clear bra to every surface of the car first (and we mean every surface), and then had the graphics installed / applied.
Now, with the body and style elements addressed, we turned out attention to the rear wing. There are a couple of approaches to dealing with the rear wiing (Vorsteiner, SalterAero), and we have implemented both. The pricing and methods are a little different, but the results nearly the same. Both will raise the rear wing, get the wing into cleaner air, and make the rear wing more efficient (you don’t really need more rear wing, but the rear tends to feel unstable at very high speed sweepers…and this helps). For this customer, we went with the Salter Aero replacement rear wind uprights. Very well made, and they get the wing up, and also out of the rear view mirror obstruction.
The stock brakes are just fine, for either street driving or track events. But, if the car has the Porsche Carbon Ceramic brakes (PCCB), we are still seeing too much degradation and wear to warrant long term track use. The PCCBs, once up to temp, offer great braking results and feel…but the cost to replace is just too high. So, for almost all our track junkies w PCCBs, we recommend replacing the PCCBs w steel.
For this customer, the current brakes were steel, not PCCB, so they offered another benefit to the overall design….we could make them AID GREEN just like Porsche’s hybrid cars….and that would match exactly to the current project color scheme. We pulled the brake calipers, had them completely cleaned, prepped, then powder coated ACID GREEN to match the color scheme of the car, and then added the stock Porsche brake caliper decal to resemble the stock hybrid brake calipers. Sweet!
Often when customers come in, and talk to us about their cars about track use, the first thing on their mind is performance, but the first thing on our mind is safety. In this case, the good news was that the customer ordered the car with the Porsche Carbon Fiber Sport Bucket Seats, with integrated airbags, shoulder harness seat back openings (and multiple height options), center submarine hole, and deeper side cutouts for the waist seatbelt elements.
We have written about the various approaches to the rear harness bar / roll bar for the GT4. This customer is very tall, so we needed to ensure that the rear roll bar would not inhibit, or limit the full movement to the rear of the seat. That further reinforced our decision to go with the GMG bar solution, and we would use our traditional approach of putting the shoulder harness mounts on the rear firewall (ensuring proper location, angle, strength, and prevents us from having to cut up th interior pieces like many of the other bar solutions do…and the GMG bar has better rear view mirror view (or less obstruction). The GMG bar also, we believe, is stronger due to the angles of the downbars, cross bars.
There is one item in the drivetrain that most would like to change…the 1st / 2nd gear ratio. They are too long, or too tall. However, the stock 1/2nd gears, in the transmission, are a once piece assemlby, and can not be changed. We contemplated having a custom, billet new transmission shaft built w a new 1st / 2nd gear, but the time and expense was too great. Some companies out there are changing the 3rd gear, which can be changed, but for street and track use, we don’t believe that is a smart move, we think that actually makes the current 1st / 2nd gear even worse.
But, a piece that can be upgraded is the stock rear differential. Not many have taken a look at this, and few know of the supplier of these units, but this is another track soft spot for the GT4. We grabbed a Drexler racing rear diff, and implemented that for better traction, on throttle, for corner exits.
There you have it….a complete project upgrade in every way. Just what the customer wanted.
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BRracing – bringing JOY to our customers
Great write-up of a welcome set of modifications for the GT4. I’m interested in getting estimates for the replacement of the rear wing uprights, the rear limited slip differential, and the intake and exhaust upgrades.
Can you send me more information on those costs?
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