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Thread: Autocrossing a Mirage

  1. #11
    Still Plays With Cars Loren's Avatar
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    Did a lot of work this afternoon. I've had it all apart enough times now that it really didn't take long. (I've also had it apart enough times, and been over-torquing the lower strut bolts enough that I destroyed the threads on them and had to replace them... but, I saw it coming. I had replacements on hand when one of them finally seized today!)

    So, I lowered the rear to match the front. I set it a half-inch from as low as it would go. (I like to leave a little on the table) I've got some rattles back there now, I need to go back and look and see if I can figure out why.

    And then I took the front apart and stuffed my 450# springs in there while raising it up about an inch. (half inch with coilover height adjustments, the rest due to the springs being stiffer and compressing much less than the old springs) Quite proud of myself, too. I did all the math last night, so I knew that the replacement springs would compress 1.3" under the weight of the car... and another 1.3" at 1G cornering load. So, I knew exactly where I needed to be in my shock stroke. I was able to set things up perfectly the first time! And I was able to trim a custom bump stop so that it is right about a half inch from making contact at static ride height. It all fell together perfectly! There's something to be said for experience and understanding what you're doing.

    Here's today's gratuitous "moar low" photo. All nice and level.



    Something important that I learned today:

    If you lower the car so much that the front tires rub against the fender liners, YOU'VE GOT A SERIOUS PROBLEM. I was ready to let it go, and just allow the tires to "self clearance" against the fender liners. Often this isn't a big deal. But, I wasn't going to let it go for too long without checking it. And it's a good thing I did!

    There are three problem areas. One is at about 10-11 o'clock on the wheel arch. As you rub through the fender liner, you expose the metal tabs where the fender meets the bumper. Yes, I did take photos.



    That little metal tab will SERIOUSLY gouge a tire. It looks like I only hit it once or twice, but it took out some nice 1/8" strips of rubber. Good thing it's a brand new tire with plenty of rubber to spare.

    You could address that one pretty easily by removing the fender liner and either grinding off the offending metal, or bending it out of the way. But, that's not going to fix the other problem.

    If you're hitting there, you're ALSO hitting the top of the fender well. Not the fender liner. The actual TOP of the fender well. I guess you could get medieval with a big hammer and maybe improve that situation a little. I chose not to go that route, myself.

    This wasn't a sharp edge like the other one, so it didn't take chunks out of the tire. But, it's still not a good thing.



    The third area of concern is a lot less critical. It actually has less to do with the car being low, and more to do with running a much larger diameter and wider tire (while also being low). This is a contact point that I'd noticed before, but it's DEFINITELY a lot worse just after one evening of driving around "super low" than it was after a year and a half of autocrossing. Curiously, it's only on the left side. The right side doesn't rub.

    I'm talking about the rear edge of the fender well where the inside corner of the tire makes contact at full lock. I could probably fix this with a wheel spacer, but it's not enough of a problem to worry about.

    This photo doesn't give a lot of visual reference, but the round hole is the bottom of the "frame rail". It's just the back side of the fender well toward the inside.



    Looks like I ought to pull the front wheels off and get back in there with some paint on that bare metal, eh?


    Simplify and add lightness.

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  3. #12
    Still Plays With Cars Loren's Avatar
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    BTW, the current ride height with the 8k/3k spring rates and the shocks set at 8/16 actually rides nicely. Previously, I'd been riding around under sprung and over damped. Now that I have enough spring rate, I can run proper damping and the ride is surprisingly smooth.

    As I used to say about my first Miata (similarly modded), it's "firm, but not harsh".

    Will know more after the autocross this Sunday.

    Oh, and I need to check my alignment tomorrow. I doubt that it changed a whole lot, camber should be about the same, which means toe should also be about the same. But, the steering wheel is slightly off-center, so I'll need to at least tweak it for that.
    Simplify and add lightness.

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    Loren,, that looks so sweet,, love the color and stance of your car..
    kinda takes me back to fun with a departed friend..
    think you have previously mentioned a spitfire before..
    my friend started pushing his street spitfire in auto cross but the bug bit too deep..
    soon he had to add a non street-able spitfire to the stable just to play with at the auto cross tracks..
    looks kinda like you are hitting that area,,, where cost vs gains doesn't really equal out..
    first gains always come cheaper and with more bang for the buck.
    trying to keep it a street-able car, everything becomes more of a trade off.
    i got drawn in as a wrench... i had a 69 gt6. so was familiar with triumph and between us had about another 4 cars worth of parts lol. and machining capabilities..
    we would b.S. the night away wrenching and laughing...
    i love the idea of pushing small displacement to its limits, vs large displacement.. its easy to go fast with too tons of power.. but try doing it with none... that why i have several small displacement bikes still kicking around lol
    just wanted to say thank you for taking the time to post, and just pose the question what about a cheep wrecked mirage just for autocross?

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    Still Plays With Cars Loren's Avatar
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    Oh, I've had all sorts of thoughts about cheap Mirages and what to do with them. Chopping tops and back halfs and removing glass to get rid of another 200+ pounds. Using one as a donor for a rear-engine Locost. Stuff like that.

    If I was young, I'd be a holy terror with the amount of knowledge, skill and willingness to engineer and build things. (hanging around with 24 Hours of LeMons people and a few local fabricator types has changed my perspective) But, I don't really want to trailer a car to an autocross. Just not my style. So, whatever I build/drive needs to be fully streetable. And I'm over the whole convertible open-top thing. Realized when I started daily driving a Yaris 10 years ago that it's kinda nice not being sunburned all the time, plus 20 years of mostly open-top driving on top of some serious over-exposure when I was younger has left me with very annoying tinnitus and I don't want to make it worse. So, it's closed top cars with AC and quiet exhausts for me!

    And I'm terrible with things like paintwork and detail finish work, so I'm not likely to build a "Locost" type of scratch-built car that would meet my requirements for street driving. At least... that's where I'm at now. Who knows. When running Mirages hit the $1,000 mark, and I'm bored, maybe I'll buy a good MIG welder and do something stupid?

    There's something about a complete engine and transmission that weighs under 200 pounds that appeals to me. If you can build an 800 pound frame... you've got an easy 1,000 pound car with 12.8 pounds per HP. That wouldn't be so bad.

    But, for now... I just want to play with the Mirage. Comfortable, reliable, daily drivable, quick enough. Just gotta get the suspension sorted... if it CAN be sorted. There are fundamental physics of height vs width that do not work in our favor.
    Simplify and add lightness.

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    Your mirage looks great Loren.

    How about an EVO next if you want a change? Obviously a stock one would work your mirage hard with ease.

  8. #16
    Still Plays With Cars Loren's Avatar
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    I know a guy who autocrosses a very nicely prepared Evo. The Evo, much like the STI, any a lot of other cars is simply not "me". It's everything I don't want in a car. It's too big, too heavy, needlessly complex with turbochargers and all-wheel-drive, etc. These are my thoughts every time he asks me to take a run in it. And every time I come back with the same thought: "This car does not suck!" I actually set the fastest time of the day at one event that he let me drive it. It's a handful to drive, but it's fun.

    But, lightness, simplicity and a little bit of absurdity are my trademarks.

    Showing up with a nicely prepared Evo would be no different than showing up with a nicely prepared Miata. You are expected to be fast because of what you're driving. "Look at that bad-ass Evo go!"

    Show up with something silly, slow and unassuming and somehow manage to make it fast... and people's heads explode.

    Combine all of that with my budget-mindedness (cheapness), and affinity for not wasting fuel needlessly, and you get a Mirage autocross car. A car that I can get 45+ mpg driving TO an autocross, have fun and make people scratch their heads AT the autocross, and get 45+ mpg on the way home... with the AC on. All on a set of tires that costs me about $500 rather than $1200.
    Simplify and add lightness.

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    Yeah I get what you're saying. It's fun to have the unique car. One of the reasons I like the mirage too, especially the 5spd one. Pretty unique

  10. #18
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    Quote Originally Posted by Fit View Post
    Oh yeah btw its a CVT too! How she did it is to reflash the TCU to operate at a higher pressure and therefore instantaneous response when you accelerate.
    And this is where you tell us that this custom flash is available to flash for those of us with CVTs ...

    Is there any major downside to running a higher pressure? Wears the fluid faster? Risk blowing seals?

        __________________________________________

        click to view fuel log View my fuel log 2017 Mirage GT 1.2 automatic: 37.5 mpg (US) ... 15.9 km/L ... 6.3 L/100 km ... 45.0 mpg (Imp)


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    Quote Originally Posted by phaux View Post
    And this is where you tell us that this custom flash is available to flash for those of us with CVTs ...

    Is there any major downside to running a higher pressure? Wears the fluid faster? Risk blowing seals?
    LOL! I believe in Thailand they have done this a while ago. I am just lucky to get to know about it’s existence after chatting with the owner of the gymkhana space star. It costs SGD$600 to flash it. I haven’t tried it yet. I will do this last. After my cams will have to do tuning and perhaps with this flash I can get it on a dyno.

    As to how Long the cvt will last running like these is a question mark.

  12. #20
    Still Plays With Cars Loren's Avatar
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    UPDATE:

    In short, the 450# (8k) springs don't suck. With the shocks set towards the middle of their adjustment, street ride is pretty good. And autocross performance was better. Feels good and isn't lifting the front tire like it did. It's "almost" lifting, but nobody saw any air under it yesterday in the 12 runs that were taken in the car. So, definite improvement. No indication of any tire rubbing, either.

    I ordered a set of flat-wound tender springs last night. They are 100# rate, 2" free length, with .94" of travel. With the rate being that low, they compress fully under the weight of the car and are basically a spacer at static load. But, when the inside wheel droops in a turn, instead of that wheel lifting, it will have an extra inch to droop travel. Yay!

    I'm going to install those with a pair of 4" 500# springs that I have in the garage. That will give me about 2.3" of droop travel, and 1.2" of compression travel. And with that, I should be able to lower the front of the car another half inch from where it is. All of that should help even more!


    Simplify and add lightness.

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