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I was just going through your whole build process, love it. My car still has a long way to go, once I get better parking situation I want to buy a daily and strip my GT3 to make it a little more race orientated. It's a shame here we don't have the same support as you guys do in America for aftermarket parts, really want that guard LSD but unsure how to go about getting one from Japan.
Thank you for reading. For me, the fun is in the build process of personalizing the car then followed by the satisfaction of experiencing the improvements. Buying a fix-er-upper is very much ideal for me because had I able to afford a brand new or low-mile pristine car I'd probably be more inclined to not modify it and drive it as is, which there's absolutely nothing wrong with that, but that's just not my style. LOL
Originally Posted by Luke Huxham
It's a shame here we don't have the same support as you guys do in America for aftermarket parts, really want that guard LSD but unsure how to go about getting one from Japan.
I can help you out with that. Part of my job is to provide specialty products and support remotely. I export parts almost daily via FedEX to Asia, Europe, and Middle East. Just email me. tchan@tpcracing.com
I did experienced huge corner exit understeer that I didn't have before having a highly effective locking diff that wants to propel the car straight, so I adjusted my driving on entry by turning more getting the car tucked in to be more in line to the exit then hammer down! The locking diff is so effective that I even reduce the rear wing angle from 7 degrees down to 4.5 degrees. I also stiffened the rear sway bar to attribute to less exit push.
For the second track day, I knew there's more time by getting rid of the exit understeer so I throw the kitchen sink at it- soften front bar, replaced 70/130nm spring with 100/150nm and raised the rear height 3mm. I uprated the rear springs for two reason- 1) to reduce weight transfer to the rear during exit throttle and I was thinking the cup replica rear wing was too much for old springs seeing photos of my car squatting. With adjusting my driving some more to setup changes was worth 1.4 second! I know there's more on tap with more seat time.
Tom, quick question, isn't the differential upgrade supposed to reduce corner exit understeer? On the weight transfer, couldn't that be fixed with dsc?
Tom, quick question, isn't the differential upgrade supposed to reduce corner exit understeer? On the weight transfer, couldn't that be fixed with dsc?
(yes, me very curious noob)
On Road Racing Circuits limited-slip differentials are for primarily for improving putting the power down during corner exit. Another words, reduce corner exit oversteer by locking the inside and outside wheels to deliver engine torque. Some drivers find that it helps to calm rear instability during hard straightline braking but there are other variables involved and the differential isn't the cause of that. Suspension tuning such as DSC and/or adjustable sway bars will improve the car's balance to a good extend, usually its enough for street and light-duty track use, but for hardcore track use a well-built diff is essential as part of a system on a well-sorted track car. For example, a 100% factory spec 997.2 GT3 RS runs impressive lap times and the handling was a benchmark for that era. DSC and other suspension setup will make this car quicker on track. Diff work will make this car even quicker. So it depends on how good you want the car to be and if you are willing to drive the car at the limit and be satisfied or want to push the envelope further.
On the weight transfer, couldn't that be fixed with dsc?
After drinking my Sunday morning coffee I have a better answer for you-
DSC is in the category of weight transfer management in a vehicle's chassis dynamics system(aka the setup), this is the same category as adjustable coilovers except that DSC is active, not passive, so DSC can do more.
Differential is in the category of torque(or power) transfer management.
While weight transfer and torque transfer are two different variables, they both influence a vehicle's balance of understeer and oversteer. And often these two variables intertwine to shift the the balance scale to some degree. But neither one of the two is a true substitute for the other, i.e., using one of the two can produce a very good handling car but using both properly will produce a supremely good handling car. Usually differential is not talked about as a chassis tuning device chassis tuning because it more difficult and costly to make an adjustment and some considers it as somewhat a black art so weight transfer management devices(DSC, shocks, sway bars) is more prevalent. Through this prevalence is born the market for proven bolt-on solutions for consumers to avoid extensive testing & tuning.
After drinking my Sunday morning coffee I have a better answer for you-
DSC is in the category of weight transfer management in a vehicle's chassis dynamics system(aka the setup), this is the same category as adjustable coilovers except that DSC is active, not passive, so DSC can do more.
Differential is in the category of torque(or power) transfer management.
While weight transfer and torque transfer are two different variables, they both influence a vehicle's balance of understeer and oversteer. And often these two variables intertwine to shift the the balance scale to some degree. But neither one of the two is a true substitute for the other, i.e., using one of the two can produce a very good handling car but using both properly will produce a supremely good handling car. Usually differential is not talked about as a chassis tuning device chassis tuning because it more difficult and costly to make an adjustment and some considers it as somewhat a black art so weight transfer management devices(DSC, shocks, sway bars) is more prevalent. Through this prevalence is born the market for proven bolt-on solutions for consumers to avoid extensive testing & tuning.
First of all, thank you for your responses. On the differential, I understand that there is more to the car dynamics than a differential upgrade, my question is, if your car was already sorted (I think) regarding understeer, why did it get more after the diff upgrade?
Then my other question why not tune the dampers rigidity, instead of swapping springs, given that it is possible to do it and might sort the weight transfer (that usually is one of the biggest culprits of understeer)?
If you had increased the rigidity wouldn't you get at the end of the day similar results to what you got by swapping the springs? And why not make the opposite wheel at the front softer (in this case the left front wheel damper) and the other harder so there is less torsion of the chassis, that would result in less understeer?
To me, that was the beauty of the Tractive/DSC setup, to basically tune the suspension to various conditions, without having to swap springs.
On the differential, I understand that there is more to the car dynamics than a differential upgrade, my question is, if your car was already sorted (I think) regarding understeer, why did it get more after the diff upgrade?
Before the diff was one-wheel-drive. After the diff is true two-wheel drive. I should have clarified that the exit understeer was only on certain turns that are long duration on exit where unwinding the steering wheel and throttle are simultaneous. In which case, the diff is locking the two rear wheels as it is suppose to while the car is not driving in a straight line. With the two rear wheels locked the car naturally wants to go straight, hence understeer. If I were to "square the car" before or at the apex then exiting straight or almost straight would not understeer but for me that'd be slower.
Originally Posted by RennOracle
If you had increased the rigidity wouldn't you get at the end of the day similar results to what you got by swapping the springs?
I did increase the rear damping commands via DSC before the spring change. That did reduced exit understeer for those turns. But I wanted stiffer rear springs to complement replica Cup rear wing + Gurney flap anyway. And I wanted the stiffer spring rates to add to the DSC + Tractive suspension; I wanted to increase the compound stiffness to like a real race car as oppose to an extremely capable dual-purpose car.
Originally Posted by RennOracle
And why not make the opposite wheel at the front softer (in this case the left front wheel damper) and the other harder so there is less torsion of the chassis, that would result in less understeer?
In theory this would work to an extent. In my case I have a pretty stiff 29mm TPC front bar that I like so I adjusted the roll stiffness on the bar. I am accustomed to and enjoy tuning with sway bars as well as the DSC; just making use of all available adjustments at my disposal.
Originally Posted by RennOracle
To me, that was the beauty of the Tractive/DSC setup, to basically tune the suspension to various conditions, without having to swap springs.
Tractive and DSC suspension do indeed have a huge performance range using the standard 60/110kg-mm(336/616 in-lbs) springs to satisfy the most discriminating drivers. And then there are those who are never satisfied and keep raising the bar for themselves, making their GT3's less appealing and less valuable to the masses...like Moi!
Before the diff was one-wheel-drive. After the diff is true two-wheel drive. I should have clarified that the exit understeer was only on certain turns that are long duration on exit where unwinding the steering wheel and throttle are simultaneous. In which case, the diff is locking the two rear wheels as it is suppose to while the car is not driving in a straight line. With the two rear wheels locked the car naturally wants to go straight, hence understeer. If I were to "square the car" before or at the apex then exiting straight or almost straight would not understeer but for me that'd be slower.
I did increase the rear damping commands via DSC before the spring change. That did reduced exit understeer for those turns. But I wanted stiffer rear springs to complement replica Cup rear wing + Gurney flap anyway. And I wanted the stiffer spring rates to add to the DSC + Tractive suspension; I wanted to increase the compound stiffness to like a real race car as oppose to an extremely capable dual-purpose car.
In theory this would work to an extent. In my case I have a pretty stiff 29mm TPC front bar that I like so I adjusted the roll stiffness on the bar. I am accustomed to and enjoy tuning with sway bars as well as the DSC; just making use of all available adjustments at my disposal.
Tractive and DSC suspension do indeed have a huge performance range using the standard 60/110kg-mm(336/616 in-lbs) springs to satisfy the most discriminating drivers. And then there are those who are never satisfied and keep raising the bar for themselves, making their GT3's less appealing and less valuable to the masses...like Moi!
Now I got it all, thank you. Yes the springs make a lot of sense given all the extra aero.
P.S. Did you thought about doing something to remove air pressure from the front fenders? That should dig the front to the tarmac at every instance.
Tom, it looks like I have a leaky power steering line. Since I need to drop the motor to replace the leaky lines, I'm considering the Cup steering pump swap instead. From your photos, everything looks to be done with the engine in? It also look like one would need to buy either a set of Cup .1 or .2 PS lines in order to get the PMNA compression fitting?
Tom, it looks like I have a leaky power steering line. Since I need to drop the motor to replace the leaky lines, I'm considering the Cup steering pump swap instead. From your photos, everything looks to be done with the engine in? It also look like one would need to buy either a set of Cup .1 or .2 PS lines in order to get the PMNA compression fitting?
I did the conversion with engine in. The original PS lines in the engine compartment are still on the car because I haven't had a reason to drop the engine to remove those lines. For the conversion lines that go into the steering rack, you could buy Cup lines or have a hydraulic hose shop make you a set of lines using the original line ends. I kept my original line ends for in case I need to replace the lines in the future.
I did the conversion with engine in. The original PS lines in the engine compartment are still on the car because I haven't had a reason to drop the engine to remove those lines. For the conversion lines that go into the steering rack, you could buy Cup lines or have a hydraulic hose shop make you a set of lines using the original line ends. I kept my original line ends for in case I need to replace the lines in the future.
cool, thanks for the info. and as a follow up, can you get me cup lines?
cool, thanks for the info. and as a follow up, can you get me cup lines?
Welcome. We do have PMNA account. Be happy to provide the numbers via email but prob won't be that good because we'd have to ship the parts from west coast to east coast and then back to the west coast.
Still haven't put it on yet. Its too pretty! And I've been too busy. I ended up getting 996 GT3/Cup stub axles instead of using longer bolts with 997 stubs to pair with the Guard GT2 Pro diff. Not that there's anything wrong with the latter approach. Checking the breakaway torque, it ~20% higher than the standard Guard rebuild kit for OEM housing so I'll play with this some on the bench.
PS- its just an excuse for me to post another photo.
Welcome. We do have PMNA account. Be happy to provide the numbers via email but prob won't be that good because we'd have to ship the parts from west coast to east coast and then back to the west coast.
thanks, appreciate it.
curious, are there any marking on the PMNA line fittings? maybe I can source those fittings from elsewhere when I make my own line. seems like a waste to buy the PMNA lines, then convert them to PMNA->AN couplers
curious, are there any marking on the PMNA line fittings? maybe I can source those fittings from elsewhere when I make my own line. seems like a waste to buy the PMNA lines, then convert them to PMNA->AN couplers
None that recall seeing. The line ends look the same as for all OEM 997/987 street car.
09-16-2017, 09:17 PM
I know there's more on tap with more seat time.
