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Scca STX autocross build

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Bucks
#21
...winning in STX may be a long shot.
Ive been doing "toilet seat" thinking about this since you started this. Also, since September, Ive been wondering how a mini won stx... when you see a brz/frs whiz by you, you cant imagine a fwd car beating it. So, it is possible, and whoever does it will go down as a legend.
Have you thought about maybe a getting the rear a little lower... reverse rake? Or, going with a smaller dimensioned rear tire?... Like they do in CRX-land.
 


OP
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Thread Starter #22
I don't know Craig Wilcox or his car, but I understand that he is a solid driver with a well developed car. The Mini beating the rest of the STX class is partially due to course design. Day 1 times were close, with several cars within a second of Craig, and on the 2nd day, he beat everybody by over a second. I read that there were places on course that Craig didn't touch brakes where everyone else did. I understand that the Mini was on 225 tires. I'm guessing that the Mini's short wheelbase doesn't make it a paragon of stability, and with 225s the Mini isn't winning on outright grip. I've got to believe that light weight and narrow width were the 2 biggest advantages the Mini had over other cars in the class. The FiST has both of those, but slightly narrower and slightly lighter. The Mini does have a very well designed suspension over the FiST.

I have run mis-matched tires on the FiST, but not with the goal of changing overall balance, but because I was trying to limit my risk when finding out how much tire you could run on the FiST. When I first bought the car, I ran with Dunlop Z2 and BFG Rivals. Like I said before, the Rival was too much tire, but I still drove them till they were used up. I switched between the Rival or Dunlop up front based on the course walk, using the Rival to get the most speed out of 2nd gear, and using the Z2 on slower/ tighter courses. I wasn't able to tell meaningful difference in balance when I switched.

It hasn't been my experience that the FiST has trouble rotating though. In slow corners it helps to toss the car a bit for rotation, but unavoidable understeer is not a problem for me. In my mind, the most difficult part about driving the car fast is wheelspin. At slow speeds and very tight turns, the inside wheel lights up every time. The e-diff is a piss poor substitution of a differential. This causes 2 problems- the first is that the e-diff works the hell out of the brakes. I've come in after 2nd runs and sprayed the tires; the brakes were so hot, and transferring the heat to the wheels that water on the wheels was sizzling off. The second problem is that we can't get enough camber (in Street class) and so the car really overworks the outside edges of the tire. When the car spins the inside wheel, the tires are just too easy to overheat. I've come back from events with the edge of the tire turned purple from the heat.

To address the e-diff, I'll be installing a true LSD. Well, a torque biasing differential anyway. I'm also going with a set of offset LCA bushings to improve the camber curve when turning. I think that the lsd is going to be a huge improvement. I'm hoping that improved bushings help to minimize the bad things that happen to macpherson suspensions in corners, and get more out of the tires.
 


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#23
What camber were you able to achieve in stock form? And did you notice the wear on the fronts or front and rear from too positive of a setting?

Also, I'm loosely considering the Koni STR.Ts if I do any mods to the suspension at all. Any experience or advice?

Thanks!
 


OP
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Thread Starter #24
In Street class I was able to get maybe an extra 0.75? of camber by loosening the upper strut bolts and pushing the strut inwards; probably not a meaningful amount but sometimes you take what you can get. I don't have a camber gauge so I can't give you a number, I just tried to get as much as I could. It was not enough to be detrimental to the tire wear on daily driving.


Not long ago, we put a Koni STR-T lowering kit on my Miata after it had spent a years on adjustable coilovers and crazy stiff springs. The STR-T kit is a nice setup for around town driving. If you are going to go to the trouble and expense of changing shocks, I would go with Koni Yellows over the STR-T. You may not need the adjustability, but shocks aren't something that you should fiddle with often anyway. But if you want to improve the ride and handling, the yellows are not too expensive and give you options in the future if you make other changes. I've made mods like that in the past and went with the cheap option and then decided I wanted more down the road. That's just my experience and opinion, you know your needs better than anyone.
 


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#25
Thanks for the explanation of your experience!

In all honesty, I'd like to get rid of the bounce-house ride and stay in HS. Otherwise, I'd be going with MeisterR coils.
 


M-Sport fan

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#26
If you are going to go to the trouble and expense of changing shocks, I would go with Koni Yellows over the STR-T. You may not need the adjustability, but shocks aren't something that you should fiddle with often anyway. But if you want to improve the ride and handling, the yellows are not too expensive and give you options in the future if you make other changes. I've made mods like that in the past and went with the cheap option and then decided I wanted more down the road.
^^^+1!!

I would even take them over the 'street' Bilstein options, as good as those dampers are as well. [wink]
 


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#27
Interestingly, can't seem to find fronts of the Yellows or the STR.Ts. And I understand the yellows have to be adjusted while off the car? And do the yellows get as good or better handling on-course as well as eliminate the bouncehouse feel?

Sorry if I'm dragging this off-topic...
 


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#28
Interestingly, can't seem to find fronts of the Yellows or the STR.Ts. And I understand the yellows have to be adjusted while off the car? And do the yellows get as good or better handling on-course as well as eliminate the bouncehouse feel?

Sorry if I'm dragging this off-topic...
The Yellows will be for a standard Fiesta(no specific application for the FiST). and only the rear shocks need to be unbolted from the lower bolt to be adjusted. And for feel, they are much better than stock. FWIW
 


Superman

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#29
It hasn't been my experience that the FiST has trouble rotating though. In slow corners it helps to toss the car a bit for rotation, but unavoidable understeer is not a problem for me. In my mind, the most difficult part about driving the car fast is wheelspin. At slow speeds and very tight turns, the inside wheel lights up every time. The e-diff is a piss poor substitution of a differential. This causes 2 problems- the first is that the e-diff works the hell out of the brakes. I've come in after 2nd runs and sprayed the tires; the brakes were so hot, and transferring the heat to the wheels that water on the wheels was sizzling off. The second problem is that we can't get enough camber (in Street class) and so the car really overworks the outside edges of the tire. When the car spins the inside wheel, the tires are just too easy to overheat. I've come back from events with the edge of the tire turned purple from the heat.
Were you running a big front swaybar? Or did you opt for a rear swaybar and still have traction problems in the front?
 


OP
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Thread Starter #30
I haven't changed/ added sways on my car. Conventional wisdom is to stay away from big bars up front on FWD. One of the local FiST drivers swapped on the Fiesta SE front bar onto his car in HS and was happy with the results. That bar is only slightly bigger than the ST (22mm vs 19mm). I have strongly considered doing this and I haven't decided to pull the trigger or wait after I've put on some of the parts I already have lined up.

Speaking of which, pretty stoked that M-Factory is running their group buy on the lsd. I had already decided that theirs was the one I was going to buy so saving $150 is great. I can't wait to started with that.

My plan is to install several parts when I have the car torn down for the lsd. Unfortunately that probably won't be in time for the first local event. I still have some good stuff to do before then though. I'll be updating this in the next few days.
 


greyloop

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#32
Anyone know what the best wheel/tire setup is for running in HS without any rubbing going on? 205? 215? 225?. 16 inch or 17 inch wheels?

Any advice would be very helpful.

Thanks!
 


OP
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Thread Starter #33
My experience is on 16" w/42mm offset wheels, 225/45R16 fits fine. 225/50R16 rubs, and in unsettling ways.

Somebody else can probably chime in about 17" options.
 


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#34
Anyone know what the best wheel/tire setup is for running in HS without any rubbing going on? 205? 215? 225?. 16 inch or 17 inch wheels?

Any advice would be very helpful.

Thanks!
The fastest (HS) FiST at nationals last year was on 205 45 16. The fastest people go with a 205 in 16". They complain about running out of gear but would rather have a crisper response. I played with 215/45 17 RS3's last year due to the low cost and because i got the car at the end of the season and didnt know what size wheel to use... No rubbing, even while tripoding. So far, the best evidence is 205/45 16 re71s on a 42 offset wheel.
 


Plainrt

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#35
Yeah I ran 225 on 16x7 the first year and it felt horrible. 205 re71r's as said. Especially bet.
 


OP
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Thread Starter #36


Alright, start getting excited. New tires got delivered to the house late yesterday. A full set of the new Rival S 1.5. I'll get them mounted later this week.

This marks a couple of high points to the Fiesta autocross efforts. First, this is the first time since early 2014 that I have had 4 new tires for autocross. In 2015 I only bought 2 new and rotated the old to rear duty only. I didn't have any new tires for 2016, and my times reflected the worn out rubber.

Perhaps more surprising, this is the first time ever that the FiST will be competing on the same make/ model at all 4 corners. My first set of tires were a Rival / Z2 combo, then a Z2 /Z2* combo.

I wish I had a few more weeks before the 1st event. I won't be able to get everything on the car before ax#1, but that may give a good contrast of the contribution the mods make.

 


M-Sport fan

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#37
^^^I would definitely like to know how those (215/45-16) tires are on a 7" wide wheel, since they are one of the donuts I would put on a 16x8 IF they existed!! [wink]
 


greyloop

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#38
The fastest (HS) FiST at nationals last year was on 205 45 16. The fastest people go with a 205 in 16". They complain about running out of gear but would rather have a crisper response. I played with 215/45 17 RS3's last year due to the low cost and because i got the car at the end of the season and didnt know what size wheel to use... No rubbing, even while tripoding. So far, the best evidence is 205/45 16 re71s on a 42 offset wheel.
Great. Thank you for this info. Do you happen to know what brand of wheel they were running? O.Z? Sparco? Enkei?
 


OP
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Thread Starter #40
Nothing new today, but now that tapatalk is letting upload pictures again, here are some pictures of the strut housing I built for the front. The important part is the Koni double adjustable strut insert.


Then I took a set of the oem struts (thanks again Rick) and after degassing them, I cut the tops off and removed the damper.


Then we welded a short length of tubing with a threaded ID. After cutting the tubing down to the correct height, the threads were a bit boogered up and I had to chase the threads with the tap. Another forum fellow helped me out with both the threaded tubing and lending me the tap (a $100 tool) after I damaged the threads. Thanks Greg!


Then a strut nut from an E30 BMW to hold the insert in place.


And that's it. Now I have front struts which are individually adjustable for rebound and compression. If I rebuild for adjustable spring perches, I can probably lighten the assembly by a couple of pounds, but for now, these get the job done.
 


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