bbundy

If I were to spend another few grand or so on parts for my car what would give me the most benefit.
First off my car is pretty good for what it is already.
It is a regularly street driven car that gets driven on long road trips as well while it is near the extreme upper end of performance level for most Miatas.

I can lap most any road course in it significantly below spec Miata lap records. I hold the track record for a street car with doors at a couple outdoor go-kart tracks with it.
And I also kind of went overboard autocrossing it in 2010 with several overall FTD’s in route to several titles.

2010 Western Washington slush series champion – Open Street
2010 Western Washington Series champion – Open Street
2010 SCCA NW region series champion – Street modified Group NS6 (SSM)
2010 SCCA northern Pacific Divisional champion – (SSM)
2010 SCCA Packwood NT 1st – SSM
2010 Chuckanut sports car club series champion – C2 (SSM)

Car has a lot of my own custom handiwork and would take a book to describe everything I’ve don. Basically it is a fairly well sorted 90 Miata with ~360 rwhp ~320 ft-lbs of torque, a decent all around setup suspension, brakes that truly handle a 350 hp Miata on the track, and a bit of aero work. I did autocross to feed my competitive urges but my real joy is on road courses with it though.

Items I’ve narrowed down to more immediate want level.

1) 15X10 ~10.5 wheels-- I ran 275’s on 15X9 6ULs but the wheels really aren’t wide enough. I think the edges are wearing faster due to being pinched on the wheels and I know they would be faster on wider. Drawback is they would only serve autocross duty. It is looking like cheaper alternatives won’t fit my 11.75” brakes so Bogart or Kodiak custom wheels are likely needed. ~$1,800 -$2,000

2) OS Giken Diff – currently running a type 2 Torsen with a 3.909 and six speed. I will be switching to a 3.636 so I’m pulling it apart anyway. I will say at my power level the torsen is severely lacking most notably on the go-Kart tracks and road courses where you touch curbing. A good bump on the inside wheel at an apex while applying power and all the sudden it behaves like an open diff. ~$1590

3) XIDA coilovers – I spent a lot of time 8 or 10 years ago and have developed what I have on my car now (Revalved Koni Sports, 700/400# 2-1/4” hypercoils, custom spherical ball extended travel shock tops, NB bump stops, ISC Racing sway bars, urethane bushings) but the shocks are 10 years old. And I think there is better stuff available now. I’m really liking the features and apparent performance of the XIDA-S or XIDA from 949 can’t see putting anything else together as good for a better price. I got a test drive in the 949 rental to know they are good. $2389 - $3949

Might be able to squeeze out one of these Items from the budget, what’s the biggest bang for the buck? When logic in me starts computing the Diff starts looking better.

Bob

curly

iTrader: (25)

I know you're not dumb, but have you played with tire pressure much? And/or do you really need to run 275's? Plus, as you said, that's two grand for autocross only.

Sounds like your diff performs decently most of the time, no? This option, although the cheapest, just doesn't sound like it would benefit you enough.

Me likey this one. You're going to be on that suspension all the time. Straights, turns, curbs, you'll feel the benefit every where you go.

jacob300zx

The OSG is supposed to give 1-2 seconds on a 2 plus minute track. I also think at your power level the OSG would be needed more. As much as I love the XidaS, I think the OSG plus a revalve on your front shocks (since there older) and your dropping seconds. I dont think you"ll see a big improvement with the Xida over your current setup, maybe .5 second average and way easier to drive at the limit.

bbundy

This is what I am thinking. Kieth from FM put one in his Targa car and took a second off his best time on a track he has a gazillion laps in that car on. The more power you have the more difference it will make I think.

FWIW I think I still hold the Miata record for that Grand Junction track though. My first and only time there at the FM open house and I was on the same full tread RA-1's I drove 1000 miles both to and from the event on. The tire trailer was loaded with camping gear rather than tires.

When I drove Emilio’s rental car it had just a torsen in it we had the same spring rates and pretty similar alignment. his car felt tighter and hooked to the track better in the corners but mine felt like I could put power down better off corners even though I had allot more power to put down for some reason. I drove both cars back to back in the same session.

Bob

jacob300zx

Honestly, if you have the cash the OSG and XidaS combo would be mint. How much can you sell your torsen's, ring gears, coilovers for? I bet the OSG gets the most time but the Xida's would be a joy to own esp since you daily your miata. Forget the rims since you"ll probably be on 245 NT01's soon.

bbundy

I've got a set of 4:10's I will be swapping out my 3.909 from an 80's RX7 for a 3.636 from an 82 626 that just arrived today.

Another issue I have though is I seem to already be dam fast on the track and there is not much competition it's just for fun. Autocrossing is hard and I have some very competent competition so going faster autocrossing brings more glory unless we get some sort of Miata challange going on up here. I think the OSG will be the ticket at the local Kart track lap attacks though. putting down power is real difficult on it. The only street licensable car that has beat me so far is a 300 hp Areal Atom on 275 hoosiers.

Bob

jacob300zx

Sounds like OSG and a cheap front revalve/refresh is the ticket.

y8s

iTrader: (8)

here's a crazy idea and I'm not sure what the bang for the buck is but you said "road trips"

swap everything into a 2001-2005 shell. oh and seam weld it first and get all the bracing.

jacob300zx

What? Have you been drinking?

bbundy

What would that achieve?

I've already seam welded and replaced welded in some of the extra unibody chassis bracing from an NB. I welded in stout backing plates for my roll bar and door bars so they are much stiffer as well. I have also added stratigic bracing to the chassis. If people didn't like me or knew id likely get protested for this stuff that was done to make it a better track car with less shakes and rattles on the street that is not quite legal for SSM at the national level.
I dont think any of it makes me faster at an autocross most of it just adds weight for that use.

Bob

bbundy

One downside to the diff option is no visible bling.

Bob

90R

iTrader: (4)

2 sec a lap isn't bling?

:dons flame suit: Torsens suck :flame suit off:

hustler

iTrader: (6)

Xida, then the new diff. I've driven Johnwag's car with the Cusco diff and it's pretty awesome and amazing how the car turns. However, the (non-xida) AST 5100's let me put the power down at what felt like similar positions and the car is damn faster.

I was talking the Brian who runs AST-USA. He told me Stevenson Racing (Grand AM) had a set of AST's made with an idential shock dyno to their Koni shock. I don't remember the numbers but the team was happy and went substantially faster. Piet Kreeft (AST HQ) watched the car on the track and ordered a few more changes (shims and valves) overnight from Holland (nobody likes the tuna) and the car went even faster the next day. AST is doing something special apparently and 949 has done all the fine tuning.

I know I jock these dampers pretty bad, almost embarrassing to be posting this again, but the stuff I'm doing on track with these shocks is amazing. A local BMW switched to AST and set 3 class records in TT on the 5-tracks we run in the season. I was within .2 to the Miata record set by 290whp and 275 Hoosiers at Hallett this year, and he and I both have tons and tons of experience on that track...I was making 232whp, ran 225 Nittos. There was some discovery going on with me (fear of grip), then John got in the car and bested that record by 1.1-seconds. Also, I'm not that good of a driver, my lap times really started to take off at the end of this season though.

Badass instructor guy in a C6Z recently let me know that I was "turning in way too early". What he didn't realize was that I was going 3-seconds faster than him at ECR, and doing it with overheated brakes. I think I'm hitting more corners 1-gear higher than not.

I'd go for a ride in a Xida car before I dropped the coin on anything.

bbundy

I already mentioned I drove Emilio’s track rental car back to back with mine at Laguna. It felt freaking awesome but the very one thing I felt my car did better was putting power down coming off the apex of corners. I’m not sure what subtle things we had going on that made this so but the most significant thing was probably dampers might have been somethig else I got right by accedent. My car had significantly more power to put down as well. My car felt more floaty and skippy on steady state cornering with a slower turn in and tended to skip more on the curbing and feel unsettled on uneven surfaces but setting that *** down under acceleration it would stick very well. I also noticed it watching youtube in car videos of Emilio and Bellwilliam and VegaXt all on XIDA’s Most evident in VegaXt’s video trying to follow me I’m launching off the corner in front of him while he is struggling to put power down with the rear end itching to step out and having to do a lot of correcting. I watched Emilio and bellwilliam fast laps and it looks like they having the same issue. And that is what I felt in Emilio’s Rental car prior to seeing any video. My car also felt like the suspension had a smoother ride even with the same spring rates.

Bottom line is I know they are better but my current setup aint too bad either. Fastest car there was Savington on Koni Race shocks probably not hugely different from mine other than being more stroke challenged in the rear. I might have been second if my lap timer hadn’t gone **** up I could tell. So I am not sure how much better.

Bob

emilio700

iTrader: (3)

Bob,

VagaXT was on MonoFlex. William's car had an OS Giken diff with some experimental diff settings. Fast but edgy. The Rental is set up to be driven through the apex with the tail a little out under power similar to a Spec. With me driving it at least, it does 1:42's there without a draft. If you are accustomed to driving off turns with no slip angle at the back as you would want in a higher powered car, then it's no surprise the Rental's set up would feel loose. That is not a strength nor weakness of the Xida's. That's just the way I set the car up as that's what's fastest at that power level with no aero and that tire/wheel combo. Double the power, add aero and that is no longer the fast way around a racetrack but I'm sure you already knew that

Any corrections you see while I'm tracking out at full power in the youtube videos I post of the Rental are because I'm generally driving the snot out of it and uh, sliding a bit.

hustler

iTrader: (6)

Well, you're not going to go wrong with the diff, that's for sure. I've found my Torsen does a pretty good job until I'm turning while going up a steep hill...and then it's all or nothing. I was really surprised to see how well the torsen still works after putting real shocks in the car even over curbing.

bbundy

Honestly where the Torsens weakness really shows up for me is on the little go-cart tracks. Quick second gear turns on a race course like track that has different banking and curbing and such and it feels like a open diff sometimes. You feel like the car is not at the limit of grip or slip angle and you apply power but nothing happens just the inside rear tire spins up and the engine revs the car doesn't speed up or get tail happy untill after you are fully off the corner.

Bob

jacob300zx

Here ya go! This plus Xida...

bbundy

I figured the edginess on power off corners was setup. It just wasn’t obvious to me what caused the difference in our setup. Shocks are different, I think I have bigger bars both front and rear (ISC 1 notch from full stiff up front and ISC full soft in rear) plus some added aero. I am quite confident I could get the XIDA's set up too my liking on my car. My best lap where my timer work in session 2 was a low 1:40 but I am also quite confident that wasn’t my best lap time. My lap timer quit working. Perhaps a Data acquisition system should be in my toy budget in the near future.

My car rotates under power it just didn’t seem as edgy. I did manage to do a nice controlled drift in the rental without lifting coming off turn 2 and I’m not much of a drift driver so it definitely gave me confidence control wise just seemed like it did it with less power level than I felt I could be using to go faster. Maybe with my driving style just wasn’t entering the corner fast enough to begin with however, the rental car gave me a lot more confidence in the first part of the corners than did mine. In my car however the biggest drops in lap time I have seen once I got the general setup working pretty good for general high cornering grip have been in trying to get it where I can apply more power sooner coming off corners. The current aero setup seems to make it push a bit more the faster the corner is but it seems like it just allows the use of more power and the car is still faster with a bit of steady state push at high speed corners with a bit more rear end grip for the slow speed corners. I seem to have enough power to overcome a bit of extra drag.

Anyway you didn’t answer the question or take a guess. Which do you think would help lower my lap times more the OSG or XIDA’s.

Bob

bbundy

OK where did he post this?
I have a Torsen II with a 3.909 and a spare 4:10 gear set that might work as a trade.

Bob