7 Tips for Making Smart Miata Mods

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Written by The Staff of Motorsport Marketing

From the Jan. 2016 issue

Posted in Suspension & Handling ,Restoration & Renovation

VENUE: The most competitive place to race a truly low-dollar, 1.6-liter Miata is the SCCA’s Street Touring S autocross class. At last fall’s Tire Rack SCCA Solo National Championships, 63 drivers entered that STS class. A Honda CRX driver took top honors, but Andrew Canak drove a 1991 Miata to second place.

TIRES: The high-performance market for 14-inch tires has dried up, but fortunately the Miata easily accepts 15-inch wheels–and they’re legal for the Street Touring class.

If you can’t find something good on the used market, places like Goodwin Racing, Discount Tire, Tire Rack and König offer a great selection of lightweight, inexpensive wheels–some priced near the $100 mark. A 15x7-inch wheel is good, but a 15x7.5-inch wheel takes full advantage of the rules.

The top cars at this fall’s Solo Nationals ran on Bridgestone Potenza RE-71R tires, and Tire Rack charges about $120 each for the popular 205/50R15 size. The BFGoodrich g-Force Rival S, the other contender at Nationals, sells for just a few dollars more. According to Tire Rack’s Chris Harvey, there’s no need to shave either one.

The Toyo Proxes R1R, now available with a 200 treadwear rating, retails for a little less than $120 each in a 195/50R15–the hot size for Miatas in that particular tire. The Toyo was popular in the past, but a rule change legislated it out of the class. The new treadwear rating has now returned it to the street tire fold.

Have less cash to spend? It may not have a win at the Solo Nationals, but the new Kumho Ecsta V720 retails for about $100 apiece.

DIFFERENTIAL: To help those tires grip the road, you’ll want the optional viscous limited-slip differential. If your car doesn’t have one, Treasure Coast Miata can hook you up for about $300. (A more effective Torsen differential became available starting with the 1994 model year, but it’s not legal for the STS class. Treasure Coast Miata sells a Torsen conversion for about $850, and it includes the complete differential plus the axles and driveshaft needed to complete the swap.)

SHOCKS: For autocross–or really any performance driving–you’re also going to want good shock absorbers. Goodwin Racing offers the popular Koni dampers for less than $150 each.

SPRINGS: Stiffer springs that lower ride height are also part of the equation. Off-the-shelf lowering springs start around $200. Adjustable coil-over kits allow more suspension tuning, but that comes at cost. Ground Control’s popular Miata coilover kit retails for about $1250, and that includes the Koni dampers.

ANTI-ROLL BAR: We’d also go bigger on the front anti-roll bar. Racing Beat’s popular hollow front bar usually retails for a tick above $150. It’s available directly from its maker as well as retail outlets like Good-Win Racing and Moss Motors. Just about everyone else in the Miata market offers suspension upgrades, too, including Flyin’ Miata, Moss Motors and Mazdaspeed Motorsports Development, the marque’s own competition arm.

POWER MODS: If you have any budget left, then start looking at things that add power. Cold-air intakes, free-flowing exhausts and ECU upgrades are popular and legal in the STS class, and the usual suspects can help.

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Reader comments:

RedGT
RedGT Reader
May 16, 2016 2:09 p.m.

If you've been autocrossing in sub-par cars and think you might be pretty good, this has got to be the most budget-friendly way (other than picking up a codrive) to get into a "full-prep" car and find out. Mine cost $7k including buying most of the parts new all at once (ouch) and starting with a really nice $3500 chassis (that was not at all necessary).

There is enough prior knowledge out there that you can do a little research, install all the parts, and right off the bat be able to fight for the local win and get into the trophies at Tours/Pros assuming you can, in fact, drive.

Mr_Clutch42
Mr_Clutch42 SuperDork
May 16, 2016 9:45 p.m.

I'm likely to move to a well prepped Miata after running lightly prepped cars in the past (including an E36).

c0rbin9
c0rbin9 New Reader
May 17, 2016 12:02 a.m.

Is there a year/trim to have for an STS Miata? Does it matter?

Thinking of dispensing with my neverending search for the mythical clean E30 and just picking up a cheap Miata instead.

NickD
NickD Dork
May 17, 2016 5:25 a.m.
c0rbin9 wrote: Is there a year/trim to have for an STS Miata? Does it matter? Thinking of dispensing with my neverending search for the mythical clean E30 and just picking up a cheap Miata instead.

I would say '94-'95. It's still the classic lighter NA chassis cars. But it adds a bigger more powerful engine, bigger brakes, extra chassis bracing and a stronger rear differential with Torsens available, all while staying OBDI.

RedGT
RedGT Reader
May 17, 2016 8:53 a.m.

I have a different opinion - specifically for STS competition, buy the nicest one you can find in either engine size.

To go out and have fun, any 90-97 without a Torsen works (Torsen goes to STR)

To get super serious, avoid 96-97 because of issues maintaining OBD2 functionality with megasquirt and other tuners, like you said. But I'm 3 years into this and I can't justify the cost of a megasquirt yet. Last weekend I was solidly within "just drive better you idiot" distance (0.017 and 0.24 sec) of the reigning prosolo champ, and I have no tuning system installed except a chipped ECU to raise the rev limit.

90-93 - VLSD, less power, less weight.

94-95 - Open diff, more power, more weight.

Suspension stuff you do to them is essentially identical between the two.

90-93 are the only Miatas that have actually won nationals in STS. But then...one blue Miata driven by andrew canak is the only miata that has actually won nationals in STS.

A friend has just built a '94 to the limit of the rules and I look forward to trying it against my equally built '90 but right now the guy is in just-had-a-baby limbo and not racing for a bit.

KyAllroad
KyAllroad UltraDork
May 17, 2016 9:01 a.m.

A friend has a '91 STS car built very close to the limit of the rules. It's exceptionally quick and usually our fastest road tire car locally. My '97 suffered badly on a tight course due to the lack of a torsen diff.

My vote for the best STS car would be to get a 1.6 car with the VLSD diff. Weight and traction will trump raw power in autocross.

Bear in mind, built to the limit of the rules the car will have no radio, no AC, race seats, MS tuning, 750/550 springs, and Konis race shocks. It will not be a pleasant DD car anymore.

NickD
NickD Dork
May 17, 2016 9:08 a.m.

Huh, I guess I have the hot ticket for STS and didn't realize it, with my 1990 1.6L with VLSD. In fact, I was told several times (on here even) that the '90-'93 was rubbish for autocross and I oughta sell in and get either a 1.8L NA or an NB. Granted, mine is a B-Pack, so it has all the heavy stuff you wouldn't want for an STS car. And now I'm running it in C/SP to already better results.

RedGT
RedGT Reader
May 17, 2016 11:41 a.m.

Yeah, you do. It's also a hot ticket for CSP when fully built. I don't know where all the 'Buy a 1.8' rhetoric comes from in this case. On the street? Sure buy a 1.8 or an NB. Plan to leave it bone stock? Ok, buy a 1.8 or NB. Have a cranky spouse that wants it to feel like a 'real car' from this millennium? Definitely buy an NB.

But if you plan to start throwing coilovers and bolt-ons on it and go seriously autocrossing? Then a 1.6 NA is perfectly adequate and in specific cases arguably better.

Canak's is a '91. At nats last year the next highest placing Miatas were 90, 90, 92, 91, 92, 92, 90, etc. The first 1.8 car was 38th place. Now, I am not saying 1.8's are bad. There are plenty of them running around doing very well in STS too, they just didn't happen to make it to nationals. What I am saying that 1.6's can totally get it done.

I am actually anxious to try with the 1.8 as mentioned because the newest tires have great longitudinal grip and the required open diff will be less of a handicap. But "it miiiiight be better" does not correlate with "abandon 1.6 and buy 1.8 right now!" that I often see and that you encountered. I don't get it.

cmcgregor
cmcgregor HalfDork
May 17, 2016 11:43 a.m.

In reply to NickD:

What do you have on your car that puts it in CSP? Just curious.

STS is a lot of fun, but is really the only "home" where a 1.6 car is the one to have (arguably). Getting a 1.8 opens up ES, but STR is pretty tough for an NA. General consensus seems to be that a 1.8 car is a "better" street car, but in reality it's just slightly less slow than a 1.6.

NickD
NickD Dork
May 17, 2016 11:50 a.m.
RedGT wrote: I am actually anxious to try with the 1.8 as mentioned because the newest tires have great longitudinal grip and the required open diff will be less of a handicap. But "it miiiiight be better" does not correlate with "abandon 1.6 and buy 1.8 right now!" that I often see and that you encountered. I don't get it.

I do have a 2000 BP-4W that I yanked from a junkyard that will be getting overhauled, built up and put in the car this winter, just because I would like a little more power. Although I autocross my car, it does see primary use on the street so ~160 crank horsepower would be nice

cmcgregor wrote: In reply to NickD: What do you have on your car that puts it in CSP? Just curious. STS is a lot of fun, but is really the only "home" where a 1.6 car is the one to have (arguably). Getting a 1.8 opens up ES, but STR is pretty tough for an NA. General consensus seems to be that a 1.8 car is a "better" street car, but in reality it's just slightly less slow than a 1.6.

I have the 15x8" Jongbloed wheels, a FM/Cannon rear subframe brace and a high-flow catalytic converter, all illegal for STS. I'm not actually building my car with any class in mind, I just build it into my image of a fun street Miata and let it fall in whatever class it falls in. The advantage to being in C/SP in my region is the only other car in C/SP is a '92 Miata, so it's a close dogfight.

oldeskewltoy
oldeskewltoy UltraDork
May 17, 2016 12:14 p.m.

headwork not saying its legal... just saying it helps

KyAllroad
KyAllroad UltraDork
May 17, 2016 12:31 p.m.

In reply to NickD: I suspect it's the subframe brace that's throwing you, otherwise you should be STR. CSP prep pretty much starts with R-comps, everything else supports that.

Unfortunately an NA in STR will be in over it's head against the S2Ks and NC Miatai.

NickD
NickD Dork
May 17, 2016 12:36 p.m.
KyAllroad wrote: In reply to NickD: I suspect it's the subframe brace that's throwing you, otherwise you should be STR. CSP prep pretty much starts with R-comps, everything else supports that. Unfortunately an NA in STR will be in over it's head against the S2Ks and NC Miatai.

That's the major thing. But 15x8" wheels are also not kosher in STS (15x7.5" maximum) and the high-flow cat is also a no-go. STS rules state it has to have an OEM catalytic converter.

cmcgregor
cmcgregor HalfDork
May 17, 2016 12:41 p.m.

In reply to NickD:

As long as the cat is over 100cells/inch, it's OK. It's actually in the first sentence of the section on catalytic converters - "Any catalytic converters are allowed". You're right on the wheels though. I'm not sure on bracing, I've always found that to be confusing, but I'm not altogether sure that it's allowed in *SP either.

KyAllroad:

As far as I know, there's no provision for running a 1.6 car in any configuration in STR.

All of this is academic anyway, as long as you're happy running in the class and have some competition, good for you.

KyAllroad
KyAllroad UltraDork
May 17, 2016 12:50 p.m.

Oops, my bad. I saw the bit about the 1.8 he was planning to put in. Yeah no 1.6's in STR.

NickD
NickD Dork
May 17, 2016 12:51 p.m.

In reply to cmcgregor: From the SCCA Classing guide for ST classes: Full exhaust system may be modified (except cats). I read that as no high-flow converters.

It almost seems like the rear subframe brace should be allowed in lower classes, considering the rear subframe had a brace from the factory later on. Everyone I talked to said it is SP legal though. In fact, the guy in a B/Street Z3 M Roadster was saying he the only change he wanted to make to that car was he wanted to add a rear subframe brace due to the BMW propensity for subframes tearing out, but that would bump him all the way to SP.

Flight Service
Flight Service MegaDork
May 17, 2016 1:02 p.m.

In reply to the staff of Motorsport Marketing:

Well that is an interesting name...did you get that from your Mom or Dad's side of the family?

RedGT
RedGT Reader
May 17, 2016 2:26 p.m.
NickD wrote: In reply to cmcgregor: From the SCCA Classing guide for ST classes: Full exhaust system may be modified (except cats). I read that as no high-flow converters.

Whatever guide you are referencing is just that, a guide. "Run whatever exhaust you want but you still need a cat" is good for classing newbies who don't know where to start. The actual rulebook says:

  • E. Catalytic converters: Any catalytic converters are allowed, but must attach within 6” (152.4 mm) of the original unit. Multiple catalytic converters may be replaced by a single unit. The inlet of the single replacement converter may be located no further downstream than 6” (152.4 mm) along the piping flow path from the original exit of the final OE converter. The extents of an OE converter are defined by the expansion chamber in which the catalyst is contained, regardless of placement within larger exhaust sections. Replacement converters must have a minimum catalyst density of 100 cells per inch and minimum substrate length of 3” (76.2 mm).
NickD
NickD Dork
May 17, 2016 2:52 p.m.

In reply to RedGT:

Oh, oh well. The wheels and rear brace still put me in C/SP. I think a Miata that runs in STS is going to run in C/SP just to have other people to play with, because our STS rarely has more than 3 cars, and he is usually the only person to show up enough to be eligible win the class.

cmcgregor
cmcgregor HalfDork
May 17, 2016 2:57 p.m.

In reply to RedGT:

What he said

The first mention of chassis bracing I can find in the rulebook is all the way in Prepared - which is obviously a little ridiculous, you're not gonna run in DP just because you put on a subframe brace. That said, I don't think anyone cares, especially at the local level in a car that's not exactly built to the maximum extent of the rules.

Anyway, my intention is not to get into a technical discussion of the SCCA's classification rules or call you out for doing anything wrong - just want to clarify for future internet searchers (and myself, if I'm mistaken as to the actual rule interpretation). If you're happy running in CSP you should run in CSP.

cmcgregor
cmcgregor HalfDork
May 17, 2016 2:59 p.m.

In reply to NickD:

That's a good enough reason alone for switching classes. Locally we had 11(!) people in STS for our last event. I was 8th, so I'm not exactly tearing up the field out there haha

NickD
NickD Dork
May 17, 2016 3:12 p.m.

In reply to cmcgregor:

Most of our classes are 1-2 cars. The only class of any size is H/Street. For example, at Sunday's event, we had 1 car in B/S, 1 in C/S, 2 in G/S, 1 in STS, 2 in C/SP, 2 in STX (1 of which was XSTX), and then 12 in H/Street (including 2 in NH/S and one in XH/S). Of the 31 cars present, 12 of them were H/S.

RedGT
RedGT Reader
May 17, 2016 3:22 p.m.

Yeah, at the start of 2014 there was no competition in STS locally and you can only win by 2+ seconds so many times before it gets old. I started having fast friends codrive so they could beat me and I could learn from it...then a few more quick people showed up and bought/built cars so now in an STS class of 6-10 there are usually 3-4 fighting for the win and it is good fun.

Dang, you also only had 31 cars. Our 'small' region around here has 50-60 on a slow day and ~100 is typical. Hey, is 8 runs/70 seconds fairly typical? Maybe I will head up there sometime.

cmcgregor
cmcgregor HalfDork
May 17, 2016 3:28 p.m.

Yeah we average around 120, and our first event this year had ~190. That was a lot.

STS was a smaller class last year and the year before, but I think lots of people picked up cheap Miatas for this season. Everybody is just trying to catch Wagstaff though.

RedGT
RedGT Reader
May 17, 2016 3:39 p.m.

That's true everywhere he goes. I was within 0.017 on Saturday and I was ECSTATIC. But the thing about pros is there's...two courses...and I totally sucked at the other one all weekend :(

revrico
revrico Reader
May 17, 2016 4:03 p.m.

As far as I have seen so far, I'm the only car in my local STS. Which is fine for my first year as a novice and trying to learn. I wasn't even going to run for points this year, just fun, but might as well make it count. The best advice I've been given so far is STOP working on the car(aside from regular maintenance) and work on the driver this year. Learn how to drive on course, then learn the cars limits, and from that, take the off season for upgrades or tuning.

But I have been wondering, if I got say an MS3 or a used MS2, I could do whatever to the tuning? I know there isn't much there to get but I'd like to get what I can, eventually.

moxnix
moxnix HalfDork
May 17, 2016 5:52 p.m.

Not exactly.

The problem with ST rules and megasquirting miatas is that most megasquirted miatas run speed density and require a MAP sensor that you can not add under ST rules (this is the vacuum line you run to the megasquirt)

Specifically for 90-93 miata's the stock manual TPS (that again you have to use for class legal reasons) is just a on/off switch. The later miata's and automatic miata's came with a variable TPS. Also the AFM is a bit weird in it's voltage outputs with something near 4.5V without airflow and near .4V at WOT and at the time I think this required a bit of custom code.

Some of those problems may have been fixed in the last 7 years since I looked at it closely or just running it as a "piggyback" might make it easier to deal with some of those issues now.

KyAllroad
KyAllroad UltraDork
May 17, 2016 6:01 p.m.

For tuning a 1.6 contact http://aimtuning.com in Indianapolis. There is power to be had from them but apparently it takes some work.

RedGT
RedGT Reader
May 17, 2016 6:04 p.m.

I believe the current state of things is that you can legally get the midrange power with a piggyback AEM FIC and appropriate harness, however this setup does not let you legally change the rev limiter. You'd need that custom coded megasquirt in order to have both. So right now I have the rev limit ($0.80) but not the power ($800+)

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