imstimpy's 981 S Track Build Journal
07-24-2019, 07:40 AM
#16
OEM 3-point Belts with Race Seats
If you drive your car on the track you should have harnesses for safety, to decrease body movement and fatigue, and to increase your connection to the car. If you drive your car on the street you should have OEM belts for convenience of ingress and egress and, plus, DOT belts are required by law. It is possible to have both a 6-point harness and an OEM 3-point belt for those who drive both the track and the street but don’t wish to swap seats after every event.
It takes a combination of items to successfully utilize both belts on a single seat.
Here is an ideal installation with a Recaro Profi SPG where the BBI side-mounts/rails and the Profi satisfy all conditions:
Here is a sub-optimal installation with a Cobra Imola where 2. is not satisfied and, therefore, the seat belt receptacle is difficult to access and disengage:
If the seat is too wide, or the side bolster is too tall, an alternative approach is to pass the seat belt receptacle through the side of the seat like an OEM lightweight bucket installation.
To follow this approach
Here is an installation with a Recaro Profi XL where 2. was accomplished by cutting the lap belt passthrough (not recommended) and 3. is partially satisfied:
Each installation is a unique combination of seat dimensions and side-mounts/rails. The Sparco QRT-R, Brey Krause R-9075 side-mounts, and Brey Krause R-9044 floor mounts leaves a small amount of room between the seat and transmission tunnel. When initially mounted to the outside, the seat belt receptacle was near impossible to access.
First I attempted to use the OEM seat belt receptacle and the provided boss to place the receptacle on the inside of the seat bolster. The length was insufficient which left the receptacle halfway through the passthrough.
By locating the receptacle beyond the passthrough it became evident the length of the receptacle cable had to be increased. The Brey Krause BK-9541 seat belt extender added some length but some custom spacers were needed. Finally, the 997 GT3 receptacles were used because the cable is slightly longer and bent for a passthrough installation. .
At this stage it is easy to use either belt, ingress is easy, but the receptacle is a little too high placing the OEM lap belt a little high on the hips.
If you drive your car on the track you should have harnesses for safety, to decrease body movement and fatigue, and to increase your connection to the car. If you drive your car on the street you should have OEM belts for convenience of ingress and egress and, plus, DOT belts are required by law. It is possible to have both a 6-point harness and an OEM 3-point belt for those who drive both the track and the street but don’t wish to swap seats after every event.
It takes a combination of items to successfully utilize both belts on a single seat.
- The side-mounts/rails must have a boss for an OEM seat belt receptacle.
- The seat must be narrow enough, and/or the side-mounts/rails must locate the seat away from the transmission tunnel, so a seat belt receptacle can fit between the side of the seat and the transmission tunnel.
- The side of the seat must also be low enough for the belt to cross without floating above the hips.
Here is an ideal installation with a Recaro Profi SPG where the BBI side-mounts/rails and the Profi satisfy all conditions:
Here is a sub-optimal installation with a Cobra Imola where 2. is not satisfied and, therefore, the seat belt receptacle is difficult to access and disengage:
If the seat is too wide, or the side bolster is too tall, an alternative approach is to pass the seat belt receptacle through the side of the seat like an OEM lightweight bucket installation.
To follow this approach
- The side-mounts/rails must have a boss for an OEM seat belt receptacle.
- The seat must have a vertically wide lap belt passthrough so the receptacle can rest as vertical as possible.
- The seat must have a thin side bolster so the receptacle can rest as far away from the hips as possible for ingress.
Here is an installation with a Recaro Profi XL where 2. was accomplished by cutting the lap belt passthrough (not recommended) and 3. is partially satisfied:
Each installation is a unique combination of seat dimensions and side-mounts/rails. The Sparco QRT-R, Brey Krause R-9075 side-mounts, and Brey Krause R-9044 floor mounts leaves a small amount of room between the seat and transmission tunnel. When initially mounted to the outside, the seat belt receptacle was near impossible to access.
First I attempted to use the OEM seat belt receptacle and the provided boss to place the receptacle on the inside of the seat bolster. The length was insufficient which left the receptacle halfway through the passthrough.
By locating the receptacle beyond the passthrough it became evident the length of the receptacle cable had to be increased. The Brey Krause BK-9541 seat belt extender added some length but some custom spacers were needed. Finally, the 997 GT3 receptacles were used because the cable is slightly longer and bent for a passthrough installation. .
At this stage it is easy to use either belt, ingress is easy, but the receptacle is a little too high placing the OEM lap belt a little high on the hips.
Last edited by imstimpy; 08-31-2019 at 07:39 AM.
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GentianGentleman (05-30-2022)
08-25-2019, 05:18 PM
#18
Burning Brakes
I am looking at getting Sparco QRT-performance seats. I have been told that you have to use the sparco QRT specific sidemounts. There is no way attach point on the side of them for seatbelt on tunnel side. They say you wont get enough rake unless you use their extra tall side mounts. Are you getting enough rake and not feeling like leaning forward with Hans and Helmet on with this setup?
08-25-2019, 10:22 PM
#19
I am looking at getting Sparco QRT-performance seats. I have been told that you have to use the sparco QRT specific sidemounts. There is no way attach point on the side of them for seatbelt on tunnel side. They say you wont get enough rake unless you use their extra tall side mounts. Are you getting enough rake and not feeling like leaning forward with Hans and Helmet on with this setup?
I've never noticed a seat's rake is affected by helmet and neck restraints. I tend to prefer a more upright driving position, especially when on track. As you can see in the photo below, I achieved my upright driving position using the middle of the three adjustment holes.
08-25-2019, 10:39 PM
#20
Burning Brakes
Who told you that you have to use Sparco QRT-specific side mounts? And why, exactly, are they needed? I just noticed they are adding the QRT monicker to other seats, like the Evo QRT, so bear in mind I'm talking about the QRT-R. The seat's dimensions are a bit unusual in that it is wide on the outside, narrow on the inside, and tall. No matter which mounts you choose you won't have much room for the OEM seat belt receptacle. The Brey-krause mounts I used couldn't offer a more exacting fit.
I've never noticed a seat's rake is affected by helmet and neck restraints. I tend to prefer a more upright driving position, especially when on track. As you can see in the photo below, I achieved my upright driving position using the middle of the three adjustment holes.
I've never noticed a seat's rake is affected by helmet and neck restraints. I tend to prefer a more upright driving position, especially when on track. As you can see in the photo below, I achieved my upright driving position using the middle of the three adjustment holes.
08-31-2019, 07:21 AM
#21
991.1 GT3 vs 997.2 GT3 Brakes
At a glance, the iron front brakes from a 991.1 GT3 and a 997.2 GT3 are similar: both are six piston and 380 mm. The 997.2 GT3 front brake can be adapted to the 981 wheel carrier, as has been done by BGB Motorsports, Rennsport One, and others. I had access to a full set of brakes from a 991.1 GT3 so I wanted to determine if the newer brake is also an option as a brake upgrade.
The 991 calipers (on left) dwarf the 997 calipers. The closed bridge adds a lot of material to the calipers compared to the slim 997 with a removable bridge. The large physical size of the 991 decreases wheel clearance in comparison to the 997; a minimum 19” wheel is required to clear a 991 caliper compared to the minimum 18” of a 997. Further, the closed bridge is of questionable value when stiffness comes at a cost: the caliper must be removed to change pads.
Both brakes utilize a 380x34 mm rotor. The overall hat dimensions are the same which means the rotor centerline is common. The center lock drive pin diameter increased on the 991, however, so 991 GT3 rotors can only be used with 991 GT3s. The 997 era center lock shares the same drive pin diameter as the lug bolts, which remains the same at on the 981 hub. The rotor retaining screws are both M6x12 mm though the 997 uses a unique Torx lens-head, or button head, while most other rotors use a countersunk phillips.
Overall piston area is similar between the two calipers. The 991 pistons are 30-30-30, or 4242 mm^2 per caliper. The 997 pistons are 28-30-32, or 4254 mm^2. The diameter change is negligible in relation to overall pad force. Piston construction is similar, with a ceramic cap over the piston, and rebuild kit cost and availability remain the same.
Both brakes utilize 225 mm radial mount spacing with M12x62 mm bolts. The through holes on the 991 caliper are slightly oversized compared to the 997; a minimally larger diameter reduces binding during installation and removal. A 140 to 225 mm adapter is required to bolt a GT3 caliper to a non-GT upright. An OEM cast adapter has been used in both 997 and 991 applications and is available for use with one-time use bolts or aftermarket studs. ProSystems sells a machined adapter that includes studs. I suspect the OEM adapter will work directly with either caliper but that remains unconfirmed.
Porsche changed the shape of the radial mounting area and contour of the caliper. The 991 reduced the area between the through hole and the caliper from 10 mm to 8 mm. The ProSystems adapter was designed for the 997 caliper and it is close to 10 mm from stud to edge. It could work if ~2 mm is removed from inside edges of either the adapter or the caliper mounting area.
Overall pad shapes and swept area are similar. The annulus of the 991 is 62 mm and the 997 is 66 mm. Pad thickness varies by manufacturer and application. A 997 street pad is 13.5 mm, the median thickness is 16 mm, and the max of 18 mm is used by the 997. Both pads here are 16.5 mm; the yellow pad is a 991 Pagid RS29 and the black is a 997 PFC08.
The brake line input remains the same thread pitch, M10x1.0, and centrally located on the inside of the caliper. Porsche moved this line lower on some newer calipers, like on the 991 C2S calipers. The caliper is moved outwards approximately 50 mm in either application and a longer brake line is necessary.
In summary, either the 991.1 GT3 or the 997.2 GT3 calipers can be used on a 981 almost interchangeably. The biggest differences are availability (one of my 997.2 calipers was ordered from Germany), minimum wheel diameter, and front loading versus back loading of the brake pads.
At a glance, the iron front brakes from a 991.1 GT3 and a 997.2 GT3 are similar: both are six piston and 380 mm. The 997.2 GT3 front brake can be adapted to the 981 wheel carrier, as has been done by BGB Motorsports, Rennsport One, and others. I had access to a full set of brakes from a 991.1 GT3 so I wanted to determine if the newer brake is also an option as a brake upgrade.
The 991 calipers (on left) dwarf the 997 calipers. The closed bridge adds a lot of material to the calipers compared to the slim 997 with a removable bridge. The large physical size of the 991 decreases wheel clearance in comparison to the 997; a minimum 19” wheel is required to clear a 991 caliper compared to the minimum 18” of a 997. Further, the closed bridge is of questionable value when stiffness comes at a cost: the caliper must be removed to change pads.
Both brakes utilize a 380x34 mm rotor. The overall hat dimensions are the same which means the rotor centerline is common. The center lock drive pin diameter increased on the 991, however, so 991 GT3 rotors can only be used with 991 GT3s. The 997 era center lock shares the same drive pin diameter as the lug bolts, which remains the same at on the 981 hub. The rotor retaining screws are both M6x12 mm though the 997 uses a unique Torx lens-head, or button head, while most other rotors use a countersunk phillips.
Overall piston area is similar between the two calipers. The 991 pistons are 30-30-30, or 4242 mm^2 per caliper. The 997 pistons are 28-30-32, or 4254 mm^2. The diameter change is negligible in relation to overall pad force. Piston construction is similar, with a ceramic cap over the piston, and rebuild kit cost and availability remain the same.
Both brakes utilize 225 mm radial mount spacing with M12x62 mm bolts. The through holes on the 991 caliper are slightly oversized compared to the 997; a minimally larger diameter reduces binding during installation and removal. A 140 to 225 mm adapter is required to bolt a GT3 caliper to a non-GT upright. An OEM cast adapter has been used in both 997 and 991 applications and is available for use with one-time use bolts or aftermarket studs. ProSystems sells a machined adapter that includes studs. I suspect the OEM adapter will work directly with either caliper but that remains unconfirmed.
Porsche changed the shape of the radial mounting area and contour of the caliper. The 991 reduced the area between the through hole and the caliper from 10 mm to 8 mm. The ProSystems adapter was designed for the 997 caliper and it is close to 10 mm from stud to edge. It could work if ~2 mm is removed from inside edges of either the adapter or the caliper mounting area.
Overall pad shapes and swept area are similar. The annulus of the 991 is 62 mm and the 997 is 66 mm. Pad thickness varies by manufacturer and application. A 997 street pad is 13.5 mm, the median thickness is 16 mm, and the max of 18 mm is used by the 997. Both pads here are 16.5 mm; the yellow pad is a 991 Pagid RS29 and the black is a 997 PFC08.
The brake line input remains the same thread pitch, M10x1.0, and centrally located on the inside of the caliper. Porsche moved this line lower on some newer calipers, like on the 991 C2S calipers. The caliper is moved outwards approximately 50 mm in either application and a longer brake line is necessary.
In summary, either the 991.1 GT3 or the 997.2 GT3 calipers can be used on a 981 almost interchangeably. The biggest differences are availability (one of my 997.2 calipers was ordered from Germany), minimum wheel diameter, and front loading versus back loading of the brake pads.
Last edited by imstimpy; 09-19-2019 at 07:49 AM.
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CaptainSlowly (12-24-2023)
08-31-2019, 09:53 PM
#22
Rennlist Member
Thank you Stimpy for the super detailed thread! I'm doing similar on '14 981 S, PDK. My brake caliper options same as yours; plus - the expensive AP Radi-Cal CP9661, or stay with stock 4 piston caliper and switch rotors to Girodisc. The ability to easily change pads with the open bridge concept on the 997.2 GT3 and AP calipers is very compelling. Decisions, decisions.
09-01-2019, 08:33 AM
#23
Thank you Stimpy for the super detailed thread! I'm doing similar on '14 981 S, PDK. My brake caliper options same as yours; plus - the expensive AP Radi-Cal CP9661, or stay with stock 4 piston caliper and switch rotors to Girodisc. The ability to easily change pads with the open bridge concept on the 997.2 GT3 and AP calipers is very compelling. Decisions, decisions.
Last edited by imstimpy; 09-01-2019 at 08:50 AM.
10-01-2019, 08:09 AM
#24
Bleeding the Brakes, ABS, and Clutch
Bleeding the brakes is a common enough procedure that it ought to be well documented and well understood. During my research and execution I found some misunderstandings as well as some tricks.
Basic Bleeding
The Porsche service document recommends bleeding using the pressure method at 29 psi. Porsche also recommends cycling the pedal slowly while each valve is open- a combination of both the pressure method and the assisted method.
The common rule of thumb is to bleed each caliper in sequence from furthest away from the master cylinder to closest. Porsche, on the contrary, says there is “no prescribed sequence”. There are two bleeder valves on each brake caliper and Porsche recommends bleeding both starting with the outer valve.
I use a Motive Products 0109 Black Label European Power Bleeder and a generic brake bleeder bottle. I keep a bottle of rubbing alcohol nearby to cleanup spills. If brake fluid gets on the calipers I first splash some water on it then go back with rubbing alcohol.
Nothing special here so I’ll be brief:
Porsche recommends bleeding the ABS hydraulic unit only when the unit is replaced. If air is introduced into the system by letting the brake fluid reservoir get too low, replacing brake lines, or replacing calipers, changing fluid brands, bleeding the ABS unit should be considered. This process requires access to a PIWIS II.
Using the PIWIS, select “PSM”, “Maintenance repairs”, then “Bleed the brakes” and follow the on-screen prompts. The process asks for 2 bar of pressure at the reservoir and cycling the pedal slowly while each valve is open.
The procedure follows this sequence and duration:
Leaking Vent Valves
When going to the track after every brake bleed I found fluid on the caliper near the bleeders for the first few sessions. At first I thought I was under-torquing the bleeder screw; over-torquing the bleeders had no effect. Next I thought it was fluid left inside the bleed screw. As you can see in the picture below, a measurable amount of fluid can be extracted from within the bleeder screw after it has been closed. Despite extracting the fluid, I still cleaned fluid off the calipers after a hot session.
Some 993 discussions left me with a theory that fluid was pooling around the threads of the vent valves. As it turns out, the vent valves have remained the same Brembo part through the years. I bought a bottle of Speed Bleeder thread sealant to seal the threads (don’t use Teflon tape!). The only way I found to replace the vent valves without brake fluid pouring down the calipers (which I learned the hard way) is to disconnect and cap the brake lines before replacement.
The sealed vent valves, along with extracting the excess fluid from within the vent valve itself, yield completely dry calipers after track sessions. I’d call it a success!
Clutch Bleeding
The clutch uses the same fluid reservoir. Porsche recommends bleeding using the pressure method at 1.3 bar.
Tools and torques
Brake caliper vent valve 10.5 ft-lb, 11 mm
Slave cylinder bleed valve 3.5 ft-lb
Bleeding the brakes is a common enough procedure that it ought to be well documented and well understood. During my research and execution I found some misunderstandings as well as some tricks.
Basic Bleeding
The Porsche service document recommends bleeding using the pressure method at 29 psi. Porsche also recommends cycling the pedal slowly while each valve is open- a combination of both the pressure method and the assisted method.
The common rule of thumb is to bleed each caliper in sequence from furthest away from the master cylinder to closest. Porsche, on the contrary, says there is “no prescribed sequence”. There are two bleeder valves on each brake caliper and Porsche recommends bleeding both starting with the outer valve.
I use a Motive Products 0109 Black Label European Power Bleeder and a generic brake bleeder bottle. I keep a bottle of rubbing alcohol nearby to cleanup spills. If brake fluid gets on the calipers I first splash some water on it then go back with rubbing alcohol.
Nothing special here so I’ll be brief:
- Pull the wheels
- Top off fluid
- Pressurize to 15 psi
- Select a corner and bleed until the bubbles stop and fluid color is restored
- Repeat for other valve at same corner
- Repeat for other corners
- Clean vent valves and calipers
Porsche recommends bleeding the ABS hydraulic unit only when the unit is replaced. If air is introduced into the system by letting the brake fluid reservoir get too low, replacing brake lines, or replacing calipers, changing fluid brands, bleeding the ABS unit should be considered. This process requires access to a PIWIS II.
Using the PIWIS, select “PSM”, “Maintenance repairs”, then “Bleed the brakes” and follow the on-screen prompts. The process asks for 2 bar of pressure at the reservoir and cycling the pedal slowly while each valve is open.
The procedure follows this sequence and duration:
- left rear for 30 seconds
- left front for 30 seconds
- right front for 130 seconds
- right rear for 120 seconds
Leaking Vent Valves
When going to the track after every brake bleed I found fluid on the caliper near the bleeders for the first few sessions. At first I thought I was under-torquing the bleeder screw; over-torquing the bleeders had no effect. Next I thought it was fluid left inside the bleed screw. As you can see in the picture below, a measurable amount of fluid can be extracted from within the bleeder screw after it has been closed. Despite extracting the fluid, I still cleaned fluid off the calipers after a hot session.
Some 993 discussions left me with a theory that fluid was pooling around the threads of the vent valves. As it turns out, the vent valves have remained the same Brembo part through the years. I bought a bottle of Speed Bleeder thread sealant to seal the threads (don’t use Teflon tape!). The only way I found to replace the vent valves without brake fluid pouring down the calipers (which I learned the hard way) is to disconnect and cap the brake lines before replacement.
The sealed vent valves, along with extracting the excess fluid from within the vent valve itself, yield completely dry calipers after track sessions. I’d call it a success!
Clutch Bleeding
The clutch uses the same fluid reservoir. Porsche recommends bleeding using the pressure method at 1.3 bar.
- Open the valve 1-2 turns
- Depress the pedal by hand and and leave depressed for 30 seconds
- Cycle the pedal by hand 10-12 strokes over 60 seconds
- Close valve then ensure proper function while checking for leaks
Tools and torques
Brake caliper vent valve 10.5 ft-lb, 11 mm
Slave cylinder bleed valve 3.5 ft-lb
10-01-2019, 03:21 PM
#25
Great thread, thanks for sharing all this. What part numbers did you use for the longer 997 receptacles? Also did they have the wire harness? How much longer are they than stock?
10-03-2019, 07:05 AM
#26
They come with the wiring harnesses, however, the connectors are not compatible. It may be possible to re-pin it but I didn't bother.
10-03-2019, 06:35 PM
#27
Thanks! I suppose leaving the stock buckle under the seat with a dummy latch inserted would be fine to get rid of the seat belt warning. Not sure when you bought these, but the parts site is saying only 997.803.183.11 is available, replaces .04.
10-04-2019, 07:36 AM
#28
Leaving the receptacle unplugged bypasses the chime. However, if you replace your seats with aftermarket buckets you have more than just the chime to contend with. The seat belt receptacles generate two of seven airbag codes. It is possible to disable them via PIWIS.
Airbag
002004 Driver's belt buckle, open circuit
002104 Front passenger buckle, open circuit
000404 Thorax airbag driver's side, limit value exceeded
000504 Thorax airbag passenger side, limit value exceeded
002804 Seat position sensor driver 5%, open circuit
002B04 Seat position sensor passenger 5%, open circuit
00611F Seat occupancy detection, open circuit
Seat occupancy detection00611F Seat occupancy detection, open circuit
10-04-2019, 03:58 PM
#29
It sounds like you are you worried about the chime. These buckles should be nothing more than an open circuit that goes closed or vice versa. It would be easy to put a multi-meter on the buckle and figure out how to spoof it electronically without the buckle and a dummy latch in the car.
Leaving the receptacle unplugged bypasses the chime. However, if you replace your seats with aftermarket buckets you have more than just the chime to contend with. The seat belt receptacles generate two of seven airbag codes. It is possible to disable them via PIWIS.
Airbag
Leaving the receptacle unplugged bypasses the chime. However, if you replace your seats with aftermarket buckets you have more than just the chime to contend with. The seat belt receptacles generate two of seven airbag codes. It is possible to disable them via PIWIS.
Airbag
002004 Driver's belt buckle, open circuit
002104 Front passenger buckle, open circuit
000404 Thorax airbag driver's side, limit value exceeded
000504 Thorax airbag passenger side, limit value exceeded
002804 Seat position sensor driver 5%, open circuit
002B04 Seat position sensor passenger 5%, open circuit
00611F Seat occupancy detection, open circuit
Seat occupancy detection00611F Seat occupancy detection, open circuit
10-22-2019, 02:10 PM
#30
Rennlist Member
[QUOTE=imstimpy;16074096]991.1 GT3 vs 997.2 GT3 Brakes
Both brakes utilize 225 mm radial mount spacing with M12x62 mm bolts. The through holes on the 991 caliper are slightly oversized compared to the 997; a minimally larger diameter reduces binding during installation and removal. A 140 to 225 mm adapter is required to bolt a GT3 caliper to a non-GT upright. An OEM cast adapter has been used in both 997 and 991 applications and is available for use with one-time use bolts or aftermarket studs. ProSystems sells a machined adapter that includes studs. I suspect the OEM adapter will work directly with either caliper but that remains unconfirmed.
Porsche changed the shape of the radial mounting area and contour of the caliper. The 991 reduced the area between the through hole and the caliper from 10 mm to 8 mm. The ProSystems adapter was designed for the 997 caliper and it is close to 10 mm from stud to edge. It could work if ~2 mm is removed from inside edges of either the adapter or the caliper mounting area.
Do you happen to have a Part # for the OEM adapter?
Both brakes utilize 225 mm radial mount spacing with M12x62 mm bolts. The through holes on the 991 caliper are slightly oversized compared to the 997; a minimally larger diameter reduces binding during installation and removal. A 140 to 225 mm adapter is required to bolt a GT3 caliper to a non-GT upright. An OEM cast adapter has been used in both 997 and 991 applications and is available for use with one-time use bolts or aftermarket studs. ProSystems sells a machined adapter that includes studs. I suspect the OEM adapter will work directly with either caliper but that remains unconfirmed.
Porsche changed the shape of the radial mounting area and contour of the caliper. The 991 reduced the area between the through hole and the caliper from 10 mm to 8 mm. The ProSystems adapter was designed for the 997 caliper and it is close to 10 mm from stud to edge. It could work if ~2 mm is removed from inside edges of either the adapter or the caliper mounting area.
Do you happen to have a Part # for the OEM adapter?