Awhit's GPW AP1
04-01-2019, 02:42 PM
#31
Thanks, I appreciate it! The plan is to start taking the car apart for its refresh in June - that timeline should be final at this point. I’ve already got some parts rolling in. I’m stoked!
04-03-2019, 12:33 PM
#32
Some parts for my mechanical refresh have started to come in, so what a great excuse to make a post or 2.
OS Giken Spec-X LSD
When I decided to rebuild the rear differential in the AP1, I immediately dove into the world of limited slip differentials. I settled pretty early on a clutch plate style diff, and focused mostly on the Japanese options like Kaaz, Cusco, Spoon ATS and OS Giken.Of these, I debated mostly between the OS Giken and ATS Carbon LSD. After pouring over how they work, I really believe that the ATS would be the “best” in a strictly performance sense.
While the OS has a slightly more complex design with its negative preload on the pressure ring and special side gears, the benefit of the carbon friction plates in the ATS diff really had me wanting to pull the trigger.Basically, what they advertise (and what the increasingly high adoption among time attack competitors in Japan seems to indicate) is that the Carbon plates allow for a diff to be set up with lots of initial torque and an aggressive 2 way cam which provides lots of stability under braking and power, without the understeer and noise that the combination of those things would lead to with a metal LSD. The added initial torque leads to an LSD that locks very fast too.
It was very clear to me that ATS has done a lot of work to reduce the relative fragility of the Carbon plates, as they offer “Hybrid” LSDs that place metal friction plates on either side of the pressure ring to reduce wear, and offer a differential case that has a lot more paths for oil to be circulated around the plates to further reduce their wear. However, digging through the ATS site I found a few articles of them explaining how initial torque decreases more quickly over time the higher it is set from the factory. This is effect also happens quicker with a Carbon disc compared to a metal disc. The translation even goes as far as basically saying that in high initial torque LSDs, you should set the diff up to plan for some initial torque loss over one race weekend. So, in addition to shorter (~3000 miles or less suggested) oil change intervals than a metal diff, they still advise somewhat frequent rebuilds of the diff to maintain its performance edge.
So….given that my car is a street car and some people would say a plated LSD is not even “needed”, the potential maintenance schedule (not to mention the absolute need to keep fluid temps below a certain level) seemed a little much. Enter the OS which has a reputation for great and consistent performance over a long time and normal OCIs. I opted to go for the Spec-X, which meant OS set up the diff based on information I provided them. May as well have one tweaked for the combination of parts that are on my car!
Greddy big capacity diff cover
Plated diffs create a lot more heat than the OEM Torsen. It seemed like a no brainer to protect the ring and pinion as well as the fancy LSD that will be in the car. I debated between the covers that Spoon and Puddymod offer and this one, and I ended up choosing the Greddy due to its larger capacity and just generally because it’s really nice. This is the same as the EVS cover, I think that Evasive and Trust made some deal where if Evasive designed a cover, Trust would let them use their facility to cast it as long as Trust could sell it under the Greddy brand overseas. Would be interested to know if that is right or not. Trust and Evasive are pretty close, and Greddy does not market the cover in the US so that’s my guess.
OS Giken Spec-X LSD
When I decided to rebuild the rear differential in the AP1, I immediately dove into the world of limited slip differentials. I settled pretty early on a clutch plate style diff, and focused mostly on the Japanese options like Kaaz, Cusco, Spoon ATS and OS Giken.Of these, I debated mostly between the OS Giken and ATS Carbon LSD. After pouring over how they work, I really believe that the ATS would be the “best” in a strictly performance sense.
While the OS has a slightly more complex design with its negative preload on the pressure ring and special side gears, the benefit of the carbon friction plates in the ATS diff really had me wanting to pull the trigger.Basically, what they advertise (and what the increasingly high adoption among time attack competitors in Japan seems to indicate) is that the Carbon plates allow for a diff to be set up with lots of initial torque and an aggressive 2 way cam which provides lots of stability under braking and power, without the understeer and noise that the combination of those things would lead to with a metal LSD. The added initial torque leads to an LSD that locks very fast too.
It was very clear to me that ATS has done a lot of work to reduce the relative fragility of the Carbon plates, as they offer “Hybrid” LSDs that place metal friction plates on either side of the pressure ring to reduce wear, and offer a differential case that has a lot more paths for oil to be circulated around the plates to further reduce their wear. However, digging through the ATS site I found a few articles of them explaining how initial torque decreases more quickly over time the higher it is set from the factory. This is effect also happens quicker with a Carbon disc compared to a metal disc. The translation even goes as far as basically saying that in high initial torque LSDs, you should set the diff up to plan for some initial torque loss over one race weekend. So, in addition to shorter (~3000 miles or less suggested) oil change intervals than a metal diff, they still advise somewhat frequent rebuilds of the diff to maintain its performance edge.
So….given that my car is a street car and some people would say a plated LSD is not even “needed”, the potential maintenance schedule (not to mention the absolute need to keep fluid temps below a certain level) seemed a little much. Enter the OS which has a reputation for great and consistent performance over a long time and normal OCIs. I opted to go for the Spec-X, which meant OS set up the diff based on information I provided them. May as well have one tweaked for the combination of parts that are on my car!
Greddy big capacity diff cover
Plated diffs create a lot more heat than the OEM Torsen. It seemed like a no brainer to protect the ring and pinion as well as the fancy LSD that will be in the car. I debated between the covers that Spoon and Puddymod offer and this one, and I ended up choosing the Greddy due to its larger capacity and just generally because it’s really nice. This is the same as the EVS cover, I think that Evasive and Trust made some deal where if Evasive designed a cover, Trust would let them use their facility to cast it as long as Trust could sell it under the Greddy brand overseas. Would be interested to know if that is right or not. Trust and Evasive are pretty close, and Greddy does not market the cover in the US so that’s my guess.
04-03-2019, 01:10 PM
#33
Holy crap this is cool.
You're going to easily have the neatest underside of an S2000 on this site.
You're going to easily have the neatest underside of an S2000 on this site.
04-08-2019, 04:59 AM
#34
04-08-2019, 05:15 AM
#35
Community Organizer
Nice choice on the OSG LSD Alex, although it's surely overkill for the street. This should go without saying, but you absolutely need to use the proprietary OS Giken fluid and not the Motul stuff that's an acceptable alternative. I've used both with my OSG diff and the Motul stuff simply isn't up to the task. It breaks down quickly, and is not heavy enough to adequately lubricate the clutch type LSD the way the OSG fluid does. I think the motul shit is like 70w-140, and the OSG fluid is 80W-250.... With the motul fluid in there, it's gonna sound like the diff is falling out of the car (ask me how I know lol).
I considered the higher capacity case as well, but decided I wanted more heat sink vs. higher capacity after a good discussion with puddymod. Basically, once the fluid in there gets too hot, it absolutely won't get back down to temp unless the car is parked. Because of how little heat sink that rear cover has, the fluid in the diff tends to get hotter quick despite the added capacity. Puddy makes a best-of-both-worlds solution now with a modified OEM cover with extra capacity AND as much heat sink added that the subframe will allow that I probably would have gone with if it was available at the time.
TL;DR, looking forward to hearing your thoughts and seeing this thing on the road post-rebuild.
I considered the higher capacity case as well, but decided I wanted more heat sink vs. higher capacity after a good discussion with puddymod. Basically, once the fluid in there gets too hot, it absolutely won't get back down to temp unless the car is parked. Because of how little heat sink that rear cover has, the fluid in the diff tends to get hotter quick despite the added capacity. Puddy makes a best-of-both-worlds solution now with a modified OEM cover with extra capacity AND as much heat sink added that the subframe will allow that I probably would have gone with if it was available at the time.
TL;DR, looking forward to hearing your thoughts and seeing this thing on the road post-rebuild.
04-08-2019, 07:19 AM
#36
Nice choice on the OSG LSD Alex, although it's surely overkill for the street. This should go without saying, but you absolutely need to use the proprietary OS Giken fluid and not the Motul stuff that's an acceptable alternative. I've used both with my OSG diff and the Motul stuff simply isn't up to the task. It breaks down quickly, and is not heavy enough to adequately lubricate the clutch type LSD the way the OSG fluid does. I think the motul shit is like 70w-140, and the OSG fluid is 80W-250.... With the motul fluid in there, it's gonna sound like the diff is falling out of the car (ask me how I know lol).
I considered the higher capacity case as well, but decided I wanted more heat sink vs. higher capacity after a good discussion with puddymod. Basically, once the fluid in there gets too hot, it absolutely won't get back down to temp unless the car is parked. Because of how little heat sink that rear cover has, the fluid in the diff tends to get hotter quick despite the added capacity. Puddy makes a best-of-both-worlds solution now with a modified OEM cover with extra capacity AND as much heat sink added that the subframe will allow that I probably would have gone with if it was available at the time.
TL;DR, looking forward to hearing your thoughts and seeing this thing on the road post-rebuild.
I considered the higher capacity case as well, but decided I wanted more heat sink vs. higher capacity after a good discussion with puddymod. Basically, once the fluid in there gets too hot, it absolutely won't get back down to temp unless the car is parked. Because of how little heat sink that rear cover has, the fluid in the diff tends to get hotter quick despite the added capacity. Puddy makes a best-of-both-worlds solution now with a modified OEM cover with extra capacity AND as much heat sink added that the subframe will allow that I probably would have gone with if it was available at the time.
TL;DR, looking forward to hearing your thoughts and seeing this thing on the road post-rebuild.
While this is still going to be a street car the vast majority of the time, once this and the refreshed motor gets dropped in I am going to start taking the car to the track a few times a year. I doubt you'll get any insight from me outside of "yeah it seemed to work well until I drove into the wall" but the temp monitoring and stuff should be interesting. I know this cover will hold 1.5 to .8 more qts of fluid then either of Puddy's covers, I wonder what the "extra time before thermal runaway bought in heat sink vs fluid capacity" chart looks like.
04-08-2019, 09:43 AM
#37
Community Organizer
You think I would turn down a chance to buy some fancy fluid??? I picked up some OS-250R as well as some OS-GT01R fluid to use in this thing so we will see how they work. I'm also probably going to stick a fluid temp sensor in the diff cover and see what happens when it gets driven hard.
While this is still going to be a street car the vast majority of the time, once this and the refreshed motor gets dropped in I am going to start taking the car to the track a few times a year. I doubt you'll get any insight from me outside of "yeah it seemed to work well until I drove into the wall" but the temp monitoring and stuff should be interesting. I know this cover will hold 1.5 to .8 more qts of fluid then either of Puddy's covers, I wonder what the "extra time before thermal runaway bought in heat sink vs fluid capacity" chart looks like.
While this is still going to be a street car the vast majority of the time, once this and the refreshed motor gets dropped in I am going to start taking the car to the track a few times a year. I doubt you'll get any insight from me outside of "yeah it seemed to work well until I drove into the wall" but the temp monitoring and stuff should be interesting. I know this cover will hold 1.5 to .8 more qts of fluid then either of Puddy's covers, I wonder what the "extra time before thermal runaway bought in heat sink vs fluid capacity" chart looks like.
05-16-2019, 12:32 PM
#39
I got to spend some time up in the mountains last week with a few friends - despite being close to getting a few upgrades it's crazy how much fun it is to drive the AP1 as it sits. Even though my Evo was much faster, I have so much more fun driving the AP1 even in its fairly close to stock form. I'm continuously impressed by the Nitron dampers in particular, how much they smooth things out as the pace increases while still feeling super controlled is very impressive to me. The only thing that feels wanting is the power between 4000 and 6000rpm. I wish it had a bit more go in that rpm range, but that should be addressed soon.
