Yet Another STS MR2! - MR2 Owners Club Message Board
 
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post #1 of 3 (permalink) Old April 17th, 2017, 12:48 Thread Starter
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Yet Another STS MR2!

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.

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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post #2 of 3 (permalink) Old April 17th, 2017, 13:27 Thread Starter
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We had our first event this past weekend (yes on Easter!). And, despite some "old car gremlins" creeping up, things went surprisingly well for our first time out.

The muffler hanger that was welded up snapped, the air intake hanger from the cheap eBay kit snapped, and a coolant line on the back of the motor began to leak. I thought we were going to have to hang it up about an hour into the day. However, with three trips to O'Reillys and AutoZone (all different ones so the staff wouldn't think we were idiots), a few zip ties and exhaust hangers, and some JB Weld, all of those issues we resolved just in time to run. Remarkably the JB weld on the coolant hard line held up perfectly!

So, given that this was the first event in the car, I was nervous about how the car might handle. Was pretty sure our stab in the dark estimates would be off no matter what experience and math they were based on, because I've just never done it on the MR2 yet. In this regard we were quite surprised! Despite some hiccups and minor quirks here and there, the overall balance of the car feels quite good! The corner exit push isn't as pronounced as the stock version, and wheelspin is reasonable. Overall grip seems high. Acceleration was solid. Just lots of good starting points, so we had to get to work seeing what might be improved.

We started at 30psi on the Bridgestones and adjusted up and down from there throughout the weekend. As we moved upward to 32 or 34 the front end started to feel less confident and would skate more in transitions. Lowering to 28 and 26 didn't net time on the clock. However, we started to get the most confidence and results as we transitioned to 30psi in the front and 26 in the rear. This 30/26 split was putting down power better than previously while still maintaining high degrees of confidence in transitions. For now, we're going to use that as a baseline for future testing.

There are still two things I can say I've noticed a bit. We sometimes get a feeling that the car is slow in transitions as if just a bit too much throttle is causing the front to slide, but not in direct proportion to the grip level up to that point. Perhaps a consequence of the sway bar or just that we haven't optimized the shocks yet. We'll see as things continue to develop. It started to get better as the day wore on, but wasn't always predictable. The other behavior is that the rear sometimes has a bit of a feeling of hop while applying power at corner exit. Never uncontrollable, but just a sensation that maybe we could get the shocks settled in to generate less wheelspin or limit the bouncing even more.

I used some of AlexW's shock dynos to give us a ballpark estimate of where to start based on some loose guesses on 65% critical with the weight and spring rates for our car. This led to using 1.5 turns of rebound and 2 clicks of compression up front (measured from full soft) and 1.75 turns of rebound and 3 clicks of compression in the rear. The only shock adjustment we tried in response to the hopping was lowering rear rebound one half turn, but neither of us liked the change's feel, and we went back to the 1.75 for now. With more runs, I think we may try another bump of compression in the rear and see where that gets us.

As for the results? Well, we're fortunate in Milwaukee to have a large group of STS competitors from ours and the surrounding regions. I believe there were at least 6 STS trophy winners in STS cars if I include myself and Andy. In the first half of the day, we were both about .15 seconds behind the top STS car on raw time (I coned of course! ). Second half of the day we kept working and went faster. Andy dropped time while I struggled to drive all the elements of the course to full potential, but in the end the car missed index by only .3 seconds to Adam Barber who finished 3rd last year in Andy Hollis' former STS Civic. Great car and great driving by him and many others. Adam also coned away another .2 seconds (with 5 cones) on his last run.

Overall, we couldn't be happier with this kind of result right out of the gates. There's still some good bits of prep left, and we're just scratching the surface of what to do with tires and knobs. We were also on older tires that may or may not leave something to be desired. Those are not meant to be excuses, but just to build the case that this was a successful start to this experiment. I'd encourage others with MR2's who might think STS is a dead cause for them that it may not be. Even without a win, we were able to be highly competitive, and the low expectations of the car in this class made it quite easy to have fun. Mission accomplished.

We'll hopefully get some video and data hooked up as we get further into the build. We spent a good chunk of the post-winter blitz fixing ball joints and stuck calipers to get ready, so more to come!

Last edited by RyoHazuki; April 17th, 2017 at 13:40. Reason: Spelling and correcting my facts on STS trophy winners.
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post #3 of 3 (permalink) Old April 19th, 2017, 19:54
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Looking forward to reading more about your progress. I was really close to buying this car from you when it was for sale. Glad to see you are putting it to good use now.
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