Very respectable times. Good job!

Thanks!

Tire plans are coming together.

I went ahead and ordered some of those discontinued Conti/Hoosier wet race tires, in 265/645R18 (Hoosier Racing Tire -- Tires Designed For Champions -> Road Racing -> Discontinued -> bottom of page - $100/tire!).

Ordering another set of 18x10+34 Forgestars to stick them on, too. It'll probably be ~5 weeks to get the wheels in, at which point I'll finally be able to swap between decent dry+wet options in the paddock. 18x10 may or may not be the most-optimal rim size for those wets, but it'll be close enough to work, and in the long term I like the idea of having all my rims the same size and then just keeping an eye out for matching tire deals.

On the dry side, I'm figuring when this current set of RS3's run out of steam (probably mid-Summer?), I'll be ready to try some dry slicks too. My plan there is to pick up random brands of cheap scrubs, it shouldn't be hard to find them in 18x10.

Also, the next long-overdue equipment upgrade on my list is a 1.5-way clutched rear diff. Any recommendations? I don't want to spend forever on setup and go customizing the internals, I just want a reliable diff I can shove in there and change fluid regularly and it works better than the VLSD (well, by now I'm just using an open diff, my VLSD is shot). I'll probably have a local shop that specializes in diff/trans work do the install, I don't have the expertise or patience to sit around trying to shim gears together perfectly (I've done it before on an old truck - it sucked and I doubt we really got it perfect, but it kinda didn't matter on that vehicle!).

My shortlist from remembering older threads: Cabonetics, OS Giken, Nismo.

Look up Cusco LSD
Ive read a lot of good comment about them also they are very popular on the my350z dot com. They arent priced as high as the OS giken and pretty much as tuneable as them plus Cusco wont say no to help you with some tuning info/parts if you ever go that route later on.

I've heard very good things about the NISMO GT Pro. That's what I've got to put in my SpecZ car

Differentials are an entire world of their own. I feel like I could spend 5 years researching diffs and still not make a fully-informed decision :p

Cusco: MZ-vs-RS-vs-Hybrid? And given it's easy to customize before I put it in for the first time, any reason to re-arrange the disks for less-than-full lockup, etc?
OS Giken: reputable, pricey, solid option, not much else to say?
Nismo: GT Pro - Even more expensive than OSG, somehow? Their marketing materials do sound nice, but I don't know if it's that nice.

I had decided a while back (just based on internet research) to skip over the Quaife just because the one-wheel-lift thing seems shitty, and as I get further in my suspension setup, that scenario gets more and more likely. But now I've noticed that there's another torsen type called WaveTrac that claims to be very similar but eliminates the unloaded-wheel problem. That makes me wonder if I should give it a shot. The huge upside of the torsen-style ones is they're basically maintenance-free. Just change fluid once in a while and ignore it. If the WaveTrac really gets rid of the Quaife's main negative point, how much is all that 1.5-way-clutched maintenance worth to me? Does the 1.5-way really feel/drive that much better than a torsen?

About the only thing another evening of research has sorted out for me is I probably don't want any of the Carbon options (from Nismo or Carbonetics). Once you get through all the marketing BS, the bottom line is all the Carbon surfaces do is reduce noise and maybe modify fluid/clutch life, but the metal discs perform better.

Fingers crossed, I still hope with my diff cooler that the OEM can be used fairly well. We know the diff fluid reaches 300* + on the track. That can't be good for the silicone filled VLSD. But if you could keep that fluid always cooler, the silicone might do its job as well as it does on say lap one...all I know is just being on the highway my fluid hits 204* after 45 min. Within 10 seconds the temp drops 40* when I hit the switch. Highest I've had it with the pump on was like 164* I think. Only time will tell now.

Like you. Everytime I do reseach on diffs. I end up with a headache.

In my opinion depending what you want to do if its about track stuff I strongly suggest a clutch lsd in general. As far as longevity with Cusco from what ive seen in the pass on my350z dot com . There has been a lot of them running it for years including drift . I havent seen anybody as far I can tell having to rebuilt it... what they endup doing is changing the locking ratio from 60 to 80 then 100.... dont forget also on the cusco RS you can switch it to a 2way if you want. I cant say for the other one..

The nismos lsd was also quite popular in the pass because it use to be very cheap 800-900$ the only issue some guys were complaining about the noise of it more than other clutch lsd...

I can say for the os giken. They are a brand name and all I know is some guys had problem getting info and parts to tune the lsd.

This is why I went to a cusco rs .. 2 of my friend is running it . One use to have a kaaz which is another clutch lsd in similar price range as the cusco .. unless it changed in the last year or two.

From what I've gathered:

OS Giken - Smooth, Reliable and most expensive
Nismo/Cusco - Practically the same. Might want use WPC treatment on clutch packs. Parking lot speed/turns will make the car sound broken
Quaife/WaveTrac/Torsen - Might boil fluid, a little cheaper than the clutch types, low maintenance, quiet/unnoticeable.

From speaking with you, you said you wanted to remove the rear sway bar, and that would help with getting the rear wheel to droop more and stay on the ground.

The purple Z had a Cusco, dunno if you heard it or not.

Don't care about noise, since this car isn't driven on the street at all anymore.

Well, either way I'll probably do a diff cooler, though it may come later than the diff install itself. That aside, though: if we ignore the wheel droop issue, does the torsen-style action actually perform/feel better or worse on-track than a 1.5-way clutched when cornering hard? I know that's a somewhat-subjective question, but it seems to be the key question in deciding whether the maintenance/cost/complexity of the 1.5-way is worth it, and nobody ever answers it in a straightforward manner. I'm willing to give WaveTrac the benefit of the doubt on killing the wheel droop issue, their solution sounds reasonable.

Yeah, I guess that's true as well. Although, on the other hand, in general with my JRZ's there's very little available droop in the rear to begin with. When I put the car on the lift the fronts droop as expected, but the rears droop very little, relatively speaking. I'm guessing if I up the spring rates a bit when I remove that bar, that will help a little as well.

This mean using the Z on the track only , then a clutch LSD is the only way to go !
If it was 50//50 street /track then maybe yeah that wavetrack could fine good enough

don't worry on the maintenance cost on the Cusco,,, like I said I haven't seen/heard anyone yet having to rebuilt one.

This has been a really informative thread on the subject (well, after you filter out the stupid posts): Quaife vs Wavetrac vs OS Giken

How convenient that this post appeared today!
MY350Z.COM Forums - View Single Post - New NASA Class for 2012: Spec Z

Track cars still have to maneuver around the grid or your driveway etc! Still worth noting minor inconveniences that will always exist.

Heh, I had just about convinced myself I should just go Cusco RS, then you post this pro-WaveTrac link :P I guess, at the end of the day, I'm not really competitive at this point anyways. Best case maybe I start doing NASA TT late this year or early next year, but even then I'm not planning on actually winning anything anytime soon. So maybe I'll do the WaveTrac for now, and if it's really inferior on laptimes it's not the end of the world. If a year or two from now I actually think it's holding me back, I could always upgrade at that point. Lower-maintenance is worth something. I already spend an inordinate amount of time on car prep stuff.

Posting this here for posterity: since I'll probably have to buy a 6MT pumpkin for whatever diff anyways, I've been researching my rear-end ratio options and trying to rationalize the differences on-track between the options. (Keep in mind the 7AT's transmission ratios are substantially different than 6MT...).

Stock 7AT is 3.357, Stock 6MT is 3.692, and there's also a 4.08 available that people have done. I'm estimating my tires at 789 revs-per-mile for 275/35R18 (although it will vary by tire options of course), and the 7AT's first 5 gears are 4.924, 3.194, 2.043, 1.412, 1.000 - I hope to rarely ever use 6, and never 7, as they get weaker up there. I guess we can pretty much ignore first gear too, I can't imagine needing it on any track.

Redline speeds in gears 2-5:
3.357: 52, 82, 118, 167 (current)
3.692: 47, 74, 107, 152
4.080: 43, 67, 97, 137

Thinking about straight lengths and speeds at my most-typical local tracks: generally I'm in 3 and 4 almost exclusively right now with only the big straight at TWS requiring a move to 5th. My end-speed on that straight is ~135 now on a good lap, but that might get higher as I learn to exit onto it faster, and it's almost certainly a bit higher in the less-common CW direction, so probably plan on 150 as a soft "top speed" that I'll rarely exceed anywhere (and if I do, it won't be for long or matter much). On most of the more-typical straights (e.g. back straight of MSR-H, back straight of TWS), on a good lap I'm sometimes bumping the redline in 4th right at the end, so ~115-120, but it's not worth upshifting before turn-in currently (but I might have to if I get faster eventually). Only COTA has really required 2nd gear, and I won't hit that often.

4.08 seems like it's not a good option right off the bat. I'd be using up a substantial portion of 5th gear on a regular basis (multiple times per lap typically), and I'd be shifting to 6th halfway down the big straight at TWS going CW eventually. I'm not sure I trust the strength of 6 or 7 on this trans to be in them hard every lap on my closest course :)

3.692 is a little bit of a wash with stock on shift points, maybe slightly better. I'd definitely be able to carry through some corners staying in 4th where I currently have to drop to 3rd to keep revs up, and that's worth a lot. However, straights that I can currently stay in 4th through (TWS back, MSR back) would now definitely require a 4->5 upshift partway down the straight. 5th should last me all the way to the end of the big TWS straight.

I used to think the universal "Lower is better" argument for rear-end ratios only really applied to drag racing, but I finally managed to convince myself it's true in the general case for road-racing as well (ignoring shift-points above). What it boils down to is this: the lower the rear end ratio, the shorter each transmission gear's speed range gets. The shorter the transmission gears get, the more time you spend higher in the power band (given equivalent shifting strategies using both rear ends). So, I think I'll take the stock 6MT ratio when I switch diffs.

I just realized there's a 3.917 gear available from Tomei as well, and the 4.08 is actually 4.083 (not that it matters rounded to mph below):

Redline speeds in gears 2-5:
3.357: 52, 82, 118, 167 (current)
3.692: 47, 74, 107, 152
3.917: 44, 70, 101, 143
4.083: 43, 67, 97, 137

I think I may have to do some more analysis, since the gaps between the trans gear ratios aren't linear, either. Maybe somehow graph this all out into a map of overlapping gear powerbands. Then I could figure out, essentially, my ideal shift points (probably all at redline, but it doesn't hurt to check), and then figure out whether the widening gear gaps in the higher gears means I'm losing effective power by pushing some of my "normal" speeds out into that range, and whether the torque gains from the gearing offset that or not at various speeds. Then maybe I could also pull in some notion of average speeds from my track data to find out which ranges are more important as well, if it comes to that.

Now that I've tinkered with the data a bunch, all I've done is further convince myself that lower is always better :) So much better in fact, maybe it's worth the risk of destroying 6th gear on my trans just to put 4.08's in there. It can always be rebuilt :)

Contrary to my intuition, the gears don't get wider as you step up, they get narrower when graphed as Horsepower vs Speed. In other words, the higher you are in the gearbox, the less rpm/power drop there is when you upshift again. This is especially true if I can move some of my shifts out into the 6th gear range, because the 5->6 shift is *very* short. Here it is visually:

http://www.the370z.com/members/wstar...d-vs-power.png

And again with only the outer two datapoints (less clutter):

http://www.the370z.com/members/wstar...ed-clarity.png


Note there are a lot of loose approximations in the data that lead to these graphs (e.g. I didn't have exact-enough dyno figures per-RPM and didn't feel like interpolating, so I stole someone else's dyno graph that had nice grid lines - but the rough shape is all that's important there).

Dude you really inspire me with the things you do and the thought you put in it.

But when and where would you need 6th. Isn't that like over 160? Super long straight away. For the other gears. I'd love to have it. Some tracks it would help. Others I assume it will be just another shift. But it's all a benefit.

Having different rear diff setup does help on different track ;) I used 3.91 and the 3.54 with good success
ive seen somebody with a 4.3 I should start looking for this for next year ! Depending on budget.

I skipped over 1st gear in my graphs, so those peaks are gears 2-6 (the very end of the whole line is the redline in 6th). So, if drop down to 4.083 rear end, my 5->6 upshift will be at 137mph (probably more like 134, because I tend to short-shift a bit by default unless I'm really pushing it). I don't think I'll hit 6th at MSR-Houston with that ratio, but I probably will on TWS-CW and COTA under this setup, given the speed help from the lower gearing earlier in the straight. I almost wish I could go even lower and get to that very short 5->6 shift even more often. It seems there are, in fact, gear sets for 4.364 and 4.636, although I'm not 100% sure they're compatible on our 6MT-R200V rear end. Might be interesting to add that to my data as well...

Here's those even-lower drives vs 4.083:
http://www.the370z.com/members/wstar...nal-drives.png

In that 4.636, the 4->5 upshift would be at ~87mph, 5->6 at ~122mph, and 6->7 at ~142mph

I've now found mention of a 4.90 that came in the 2004 Xterra, which might also fit in our diff :)

New graph of just those lowest-two found so far (4.636 + 4.900), with 7th gear added since max speed limit is (finally) becoming an issue at these ratios. I have feeling there are probably other tradeoffs I'm ignoring if I push this too far, also (like time lost to the 7AT's relatively-fast shifts if I'm shifting much more often), and that aside my max speeds in 7th with those gears are ~160 and ~150. I'm not hitting 150 anywhere yet, but I probably could eventually (esp, again, with the gear change itself helping out).

http://www.the370z.com/members/wstar...-4-636-4-9.png

^- you know at some point you're gonna be spinning the tires because you got so much torque with the low ratios! IMO I wouldn't want to go too low or else you're gonna have to have more throttle control... even worse in rain. maybe i'm just lazy and like to put the pedal down as soon as possible :)

Well, I was planning to re-work my throttle map for better control in the bottom half of the pedal anyways, but, yes :) There are actually a whole lot of reasons not to go extreme on the final drive ratio. More-so than the traction issues I worry about the wear-rate fallout with the 7AT.

According to those who've run FI on their cars, 6 and 7 (and maybe 5, too) aren't as strong as 1-4 in terms of torque-handling and get burnt up when you put too much power through them. I have no idea if moving a larger percentage of my track-time to redlining in those gears will have a similar effect even though I'm NA, over time, and eventually kill those upper gears.

And again - more shifts = more time lost to shifting, and I can't always shift mid-corner if I'm on the edge of traction, so a strategy that requires more shifting may result in more delayed shifts waiting for the car to straighten up and be a net loss.

Still, it's tempting to just slap in that 4.90 and see what happens. It would be a fun experiment, but possibly a costly one if I have to go back and put a different gear in soon afterwards :)

^- that's what gran turismo is for! they need to get that gps overlay stuff in there asap so we can get the texas tracks in the game lol.

Got any thoughts on 3.5 gearing? I have a 3.5 vlsd pumpkin taking up space... I could sell it to you for pretty cheap.

Another thing is a lot of my analysis with regard to upper speed ranges is based on TWS because (a) it's my closest track now and (b) other than *maybe* the back straight of COTA (which I probably end up doing once a year tops), it has the fastest straights around here for my car. If TWS goes away, that probably has significant effect on what speeds I care about on a regular basis :(

I think I have to pick up a used pumpkin no matter what I do, either off someone or off a junkyard. I need to look into that more, but it seems like there's some minor difference in the interior shape of my 7AT pumpkin vs the standard 6MT pumpkin on 350's and 370's, which is why a lot of the LSD mfgs only make it for the 6MT? It could also just be that it's a problem with gear circumference on the gear I'd be swapping out anyways, I don't even know yet.

My diff is from a 6MT, and there is the exterior flange that bolts up to the drive shaft that's different, but swappable.

http://i451.photobucket.com/albums/q...ps92f14071.jpg

Review 4.08 Ring & Pinion Swap, she's alive! - MyG37

Here's a compiled list for VLSD drop ins:
List of aftermarket LSD for VLSD cars - MY350Z.COM Forums

For the wavetrac, looks like you need an open stud and a different stud (which might work with one side of the vlsd stud)
nasaforums.com • View topic - Wazvetrac issues/discussion

So, to sum up the (perhaps obvious to some!) things I've confirmed from looking at gears lately:

Given the shape of all VQ horsepower graphs, the things that really matter in the end, once you've seen the data, is "How do the gear gaps relate to each other" and "what's my max speed in top gear". As long as the gear gaps get shorter as you go higher in the box, and you don't run out of top speed, you're winning by going to a lower rear end ratio in terms of area-under-the-curve on the HP-vs-Speed graph (subtleties about shift points/delays notwithstanding).

In both the 6MT case and the 7AT case (ignoring the useless 1st gear, anyways), the gaps do get smaller all the way up the gearbox. While both exhibit the same basic narrowing of the gap as you go higher, the 7AT has significantly wider gears at the bottom and narrower at the top, vs the relatively-stable profile of the 6MT's gears, meaning there's probably less advantage to extreme gearing in the 6MT (but it's still there).

The percentage change in gearing per upshift looks like this:

7AT: 35.1% -> 36.0% -> 30.9% -> 29.2% -> 13.8% -> 10.4%
6MT: 38.7% -> 30.1% -> 21.7% -> 21.3% -> 20.6%

Top speeds in top gear with various rear ends discussed above, assuming 275/35R18 and a 7500rpm redline:

7AT:
3.357 -> 220
3.692 -> 200
3.917 -> 188
4.083 -> 180
4.364 -> 169
4.636 -> 159
4.900 -> 150

6MT:
3.357 -> 214
3.692 -> 194
3.917 -> 183
4.083 -> 175
4.364 -> 164
4.636 -> 154
4.900 -> 146

Some of those things change between the G37/370/350. I'm pretty sure both 6MT and 7AT 370Z rear ends have the same input flange on the driveshaft side. And no matter what pumpkin I'm using, I need at least one axle-shaft if I'm switching from VLSD to aftermarket LSD (but not open to aftermarket LSD). But for some reason other than those issues, there's a difference between the 7AT and 6MT 370 rear ends (enough that LSD mfgs generally are 6MT-compatible only, or make a separate model for 7ATs). It's either that the much-higher ratio in the 7AT is actually a different diameter (in which case I don't care, that gear set is being tossed anyways), or it's that the inside of the pumpkin has an odd shape for some reason I can't fathom. In any case, though, it seems the common solution others have employed is to grab a used 6MT pumpkin and slap it into their 7AT car. I think the 350Z and G37 6MT pumpkins both work in that case. Anyways, I really don't know, something to research later in the week :)

My rain tires arrived! These are the discontinued Continental-brand "Wet Radial Race Tires" that Hoosier's selling for $100/tire in 265/645R18 (if you order these, be sure to note there's a Left and a Right, get two of each!):

https://lh3.googleusercontent.com/5F...I=w506-h851-no

https://lh4.googleusercontent.com/ff...c=w900-h851-no

Now the interminable wait for the wheels to mount them on. I can't wait to see how these feel in the rain.

I just bought 5 sets of the continental 285/645 slicks!

Nice!

Any idea how the 285/645 slicks compare to DOT tire sizes? I've heard that the slick sizes vary quite a bit from what one sometimes expects, sometimes wider? I'm *hoping* my 265/645 wets will fit well on 10's, but I wasn't sure enough to bet on the 285 slicks yet until I see how this looks.

Those look wide for 265.

Yeah. Both my RS3's and Conti DW's are 275/35 on 18x10. When I compare the unmounted 265/645's to the mounted DW's (just lining them up with each other on the floor), the width looks identical. But we'll see what happens when they're mounted. If they do fit, and the sizing is consistent between dry+wet, that makes me think 285/645 might be a tad wide for 10's, but I have no idea. I guess the smart thing to do would be to call Hoosier and ask :)

I didn't find time to call Hoosier, but I did find rim sizing elsewhere on their site for new Hoosier slicks, which is probably identical to this stuff (the Conti is just branding, I think Conti actually owns Hoosier and Hoosier makes all slicks with Conti written on the side?).

In any case, in "recommended rim width" for new Hoosier dry slicks, 265/645R18 is 9-10 and 285/645R18 is 10-12. So they probably work on 10's, maybe a little fat-looking :)

I run 295/40 Hoosiers on my 9.5s and my 10s, so I plan on the same with these.

On the sizing, the 645 is the total tire height, 25.4", which would make the 265s roughly a 35 and the 285s roughly a 32 in common aspect ratios.