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Yet Another STS MR2!

7K views 33 replies 7 participants last post by  RyoHazuki 
#1 ·
So, I've had the good fortune to own one of the old hardtop '93 MR2s from the ES days of yore for quite a few years now. It's been in and out of retirement, driven occasionally, and I even listed it for sale about three years ago. Just seems like the MkII has been fading out of consistent autocross use at the National level (outside some SSM successes and a bit of FP appearance), and there are always other cars and ideas that kept it in the garage a good chunk of the year. This past off season, my co-driver and I were discussing doing something different, and I threw out the idea that I'd like to either do something with the MR2 or sell it and free up the space. Somehow that transitioned into the idea of doing something different and low pressure like building an STS MR2. Thought I would start a thread to document our progress, results, and share any info that we can in case others wanted some ideas.

Over the past few years, there have been a few discussions about STS MR2 builds, most notably I think was Jimmy's build last year. Even prior to that, I know we've had some discussions on the board here about what might work and some of the handicaps that an MkII would have to overcome. As such, I had considered doing the STS build as a side project a while ago just for fun, and if I hadn't had some of the surprise success in ES in 2015 it would have happened already.

Anyway, here's where we're at so far:

Cliff Notes version:
- '93 n/a MR2, PS, ABS, cruise control, no power options
- 15x7.5" wheels w/ 205/50/15 Bridgestone Re-71r's
- 550/800 spring rates with DA Koni coilovers and top hats from AlexW (Thanks Alex!)
- -4.5f/-3r degrees of camber, 1/8" toe out front, 1/8" toe in rear
- ST front sway and removed rear sway
- Stock size battery
- Stock seats
- OBX header from eBay
- Magnaflow cat (200-cell)
- Magnaflow HP-2 muffler
- Stock ECU

Wheels & Tires
I have managed to locate two 15x7.5" sets of wheels by watching eBay and HondaTech like a hawk. There are a few options in DB8's for sale thread on the OC here, too. We're using spacers to get them to a +25mm stance in the front right now. It looks stance-y, and is pretty hilarious. Seems to work though!

So far we're just using 205/50/15 Bridgestone RE-71r's, but the plan is to do some testing of BFG's and new Bridgestones in Lincoln for Spring Nationals next month. I'd like to think the 225 would be useful to the heavier car, but not sure if 7.5" wheels justify that yet.

We also have a set of 17's in the wings waiting for a tire decision. We have considered running a taller 17" tire in the rear on some courses where we need taller gearing. Something for the "bag of tricks" to reduce our course dependency.

Suspension + Alignment
At first I wanted to just do a cheaper option like KW's or Teins and chalk it up to the experimental nature of this STS build, but in the end I was lured toward AlexW's built Koni coilovers. Not only would this support someone doing a lot of great work to keep helping the MR2 and its owners, but the top hats are easily the best/most optimized design available for the MR2. Additionally, the Konis are the only shocks readily available that would handle the spring rates we need to run to limit body roll on our McStrut machines.

For spring rates, I'd been reading the barless setup threads that Steve helped to provide, and I'd thought about going that route for quite a while. However, when faced with the decision of what rates to run, I began to think long and hard about what I really thought worked. My preference was to maintain the front bar from my ES experience, and to remove the rear sway bar to try to minimize wheelspin. The primary advantage that the MR2 may have in STS is torque and weight on the drive wheels, so what I'm looking toward is applying power earlier during corner exit than most of our competition. The bar-less setup recommendations seemed to lean toward 850f/550r spring rates, and I was very intimidated by the 3.5+ Hz front frequencies that resulted from that setup. So, my rough "stab in the dark" estimates settled on 550f/800r lb/in spring rates while maintaining the hefty ST bar from ES. Just a starting point to get out and drive, and I assume(d) it will likely change.

For alignment and corner balance I turned to a trusty local shop out here called Big Bear Tire (can't say enough good things about them). My co-driver and I slammed the car as low as the coilovers would go and made the drive out there, only losing one fender liner in the process. On arrival, we settled on some numbers and dialed in camber to -4.5 front and -3 degrees in the back. Toe was set with a pretty traditional autocross alignment of 1/8" out in the front and 1/8" in at the rear. It's an attempt to balance power down, front/rear balance, and making sure we don't bandaid poor spring rate choices with dramatic alignment settings. We needed something to get the year started and see where we're at.

Weight Loss
The corner balance revealed that with our limited prep we are currently at 2435 pounds. Slightly portly and disappointing, but there's still some work to do. Weight will be a priority as we go, but given that our car already has no AC and comparing weights with Jimmy's car last year, it's safe to say that the T-Top cars without glass in could have a slight weight advantage to the hardtop cars.

We did a lightweight Ballistic battery... and I promptly killed it leaving the trunk open and not disconnecting the battery. Lesson learned. So, still stuck with the large stock battery for now and waiting on a replacement. Quick disconnect for the battery will go in with the new one. :smile2:

The stock passenger seat weighed in at 31 pounds on my bathroom scale, and I'm guessing the drivers side will be identical. So, we still plan on replacing the seats with 25 pound equivalents. Just not installed yet.

Power Stuffs
So, uncertain if any of these make power. Mostly just weight savings in disguise. But, we've thrown some bolt-on bits at the car.

For the intake, I just ordered the eBay intake kit that Jimmy dyno-ed last year. I replaced the restrictive silicon elbow from the eBay kit with a nice smooth one that I found on Amazon, and we stuck this gigantic 6" filter with a velocity stack on the end. (found from BPI - BPI Performance Velocity Stacks) Supposedly Honda guys have used similar and seen gains. Figured anything that helps the top end breathe better might be worth a shot. Plan is to do some dyno shootouts with the intake bits to see if this actually makes any difference. For now, bigger must be better! Also, the intake saves 9 pounds off the stock system!

For exhaust, I ordered an OBX header off eBay. Watch out because the one I received was mild steel that was painted despite being advertised as stainless -- I believe there may be two versions floating around, so look carefully. After getting a 100-cell cat from a race shop and discovering the 13 inches of packaging was too long to fit the exhaust bends under the engine and over the subframe, we settled on a more readily available Magnaflow 2.5" 200-cell cat from Summit. It weighs 2.2 pounds and easily fits at the flange right after the header. I was also concerned about how loud the car might get, so we installed a reasonably packaged Magnaflow HP-2 muffler that weighed in at 6.6 pounds. Heavier than needed maybe, but I really don't want an obnoxious car. End result is a car that sounds pretty good actually, and will almost certainly have no issues meeting sound. Other than having to tap rusted head studs, not a bad project. Also, this shaved about 10 pounds from the car. The car does feel reasonably peppy with all these bits installed, so likely they do something even if the gains aren't massive or optimized yet.

ECU is stock for now. Have a Greddy eManage and just putting together the wiring harness so we can do some dyno tuning. We'll probably advance timing at the distributor as well, but really hoping to do some work with the rev limiter and try to reduce the gearing issues Mk2's typically deal with.

Getting lengthy, so I will post our first event results separately. Stay tuned!
 

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#29 ·
Thanks Alex! We're still battling to try to get the eManage working to raise the rev limiter last minute here. The wiring harness is all soldered together now, and we're learning the software. Coming down to the wire! Got a passenger seat in, and Andy pulled off the rear wing. Basically, I think we're about as light as we can be without some more stupidity in the brake caliper area.

Hopefully catch you down there, gigglehurtz. We're somewhere in the mid-20's I think. It's the Milwaukee Region area, but I'm not sure I know where that is yet. Stop by any time!
 
#30 ·
GotCone took some great shots of the STS MK2 at Nationals. I got a chance to watch a handful of STS runs and I really enjoyed seeing/hearing the SW20 out on course and doing so well. Brought back fond memories from my ES days in Nerves Of Teal!

Seems like it's a really fun STS car. Shame there aren't more of them!

2019 SCCA TireRack Solo National Championships » STS » 3g7a9174-2.jpg: GotCone Autocross & Rallycross Photos

2019 SCCA TireRack Solo National Championships » STS » 3g7a9177-2.jpg: GotCone Autocross & Rallycross Photos

2019 SCCA TireRack Solo National Championships » STS » 3g7a4118.jpg: GotCone Autocross & Rallycross Photos
 
#31 ·
Great to meet you in person Andrew! Wish I had a little more time to pick your brain, but such is Nats...
I'm hoping to start development on my MR2 on the off season, hopefully it'll be ready for next year. I'm delving into the depths of the internet to see if there any room to make power up top with a 5S, and figuring out how to fit a Megasquirt.

If the setup is promising, maybe I'll have it out for Nats? If not, definitely a couple of ProSolos.
 
#32 ·
Ah, yes, the bicycle picture.... Turns out that when your car is bouncy and you hit big bumps you get crazy stuff like that going on!

We felt pretty good being (if I'm remembering correctly) 3rd and 8th on day 1. The car was definitely still in the mix. Day 2 it was one of those courses where rev limiter seemed to hurt us worse than we thought it would. There just wasn't much we could do. Still had fun, and always nice to throw another car in the mix. The MR2 is definitely a fun time in STS and it's a great class/group top to bottom, though I think our STS journey is going to be on hiatus for a bit. I've been considering a K-swap for giggles, and maybe some other new projects down the road. We'll see how the offseason goes. We also still lack a truly local site for Milwaukee region, so not sure if maybe ChampCar or something else is in the cards instead.

Btw, gigglehurtz, this is Chris, not Andrew. Pretty sure Andy wishes we still had his old STS Miata. ;) I've owned the MR2 for the past 10 years now. Andy lurks on here sometimes, but not sure he posts much. Hope the car prep goes well! Feel free to hit me up or post here if you need anything.
 
#33 ·
Whoops, my bad Chris! Eventually I will remember names and faces. My RX-8 is helping make the decision to go deep into STS prep on my MR2, since parts are not as expensive for the MR2. I just have to resist the urge to buy parts cars and stockpiling miscellaneous parts...

I'll probably end up making another thread to document what route I end up going with my MR2.

-John
 
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