Secrets of the Mirage

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Secrets of the Mirage

Postby Native » Wed Nov 14, 2018 7:26 pm

Loren wrote:You pull a spark plug wire and I'll carry sandbags.

:pointlaugh:
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Postby Magooiii » Wed Nov 14, 2018 7:29 pm

Loren wrote:You pull a spark plug wire and I'll carry sandbags.
😂
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Postby twistedwankel » Wed Nov 14, 2018 7:38 pm

Obviously Loren has driven the EVO.
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Secrets of the Mirage

Postby CaptainSquirts » Wed Nov 14, 2018 8:30 pm

Loren wrote:You pull a spark plug wire and I'll carry sandbags.
I can still keep the turbo right?
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Postby Loren » Sun Nov 25, 2018 11:43 am

Got the rear seat out. It was even lighter than expected. Only 35 pounds total. And that's everything! Brackets, seatbelt reels, bolts... it all totalled up to 38.8 pounds. But, I already had some of it out (headrests and spare tire cover).

Photos and stuff here: viewtopic.php?f=18&t=3416

Now I've got an exhaust rattle/buzz that's starting to make me crazy. Need to find that and kill it.
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Suck Less - Drive something resembling a proper racing line.
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Secrets of the Mirage

Postby CaptainSquirts » Mon Nov 26, 2018 11:43 am

From lack of sound deadening or just straight up exhaust getting some metal in metal contact?
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Secrets of the Mirage

Postby Loren » Mon Nov 26, 2018 11:46 am

Oh, it's nothing new. Something is rattling. I hope it's something simple, like a heat shield. But, it could be something broken inside the muffler. That would suck.
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Suck Less - Drive something resembling a proper racing line.
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Postby Loren » Wed Nov 28, 2018 8:36 pm

Got under the car today with my trusty flashlight and rubber mallet. (not to be confused with a spear and magic helmet)

There are two rattles. Unfortunately, one of them is the muffler. Brand new Walker muffler, less than 6 months old. :smack: It's got an internal rattle. The other one is the heat shield above it. Nothing is contacting it, and it's all secure, but there's a very low frequency twang if you smack it in just the right place. I doubt that it's even doing anything, but I'll try to address it when I fix the muffler.

Now I have to order a new muffer. Higher quality muffler. Probably going to end up being a louder muffler. :bangwall: But, if it doesn't rattle and buzz, I'll be happy.
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Suck Less - Drive something resembling a proper racing line.
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Postby Loren » Wed Dec 12, 2018 5:53 pm

New Muffler is in. (thanks, Joe!)

The first muffler was a Walker Tru-fit, which was about the cheapest muffler available in that size. This time, I did some more research and opted for a slightly more expensive muffler, the Walker Sound FX, which is reported to be very quiet. I'm just hoping it stays together and doesn't fall apart in a matter of months like the cheaper one did!

So, the new muffler is a few inches longer. I didn't weigh it, but it might be a 1/4 or 1/2 pound heavier. And now that it's on the car, aside from not having a rattle and buzz... it IS quieter. I'm not going to bother redoing my sound measurements, but, inside the car, it is notably quieter. It wasn't loud before, but had a nice little subtle growl to it. That is gone. It sounds pretty much stock now. There's a little bit of raspiness at high revs that you can hear when the windows are down... similar to what it was before, but probably quieter.

If you're ever looking for a truly quiet muffler: Walker Sound FX. Impressively quiet.

While we had the exhaust off, I cut out the restriction in the exhaust header. It necked down to the stock 1.5" pipe at the flange so that it could use the stock donut gasket and mate up with the stock exhaust flawlessly, which it did. But, since I replaced the 1.5" exhaust with a 1.75" exhaust... that became a bottleneck. So, I finally cut it out.

Will have to do some acceleration testing, but the butt dyno indicates that it may have actually freed up some torque! I was hoping for more high-end simply without LOSING any torque... but, it feels like it may have done both. Numbers will tell.
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The "Push Harder, Suck Less" philosophy explained:
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Suck Less - Drive something resembling a proper racing line.
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Postby Loren » Wed Dec 12, 2018 9:48 pm

Butt dyno doesn't lie. It's not a huge change, but quick initial testing shows quicker accel from 1500-2500, and from 4000-6000. Unfortunately, there was a dip in the middle, so overall accel from 1500-6000 was nearly the same. Feels good down low, though... and that's kinda nice. And there's a little more top end, which is what I was hoping for.

I'm going to retest a little more carefully, though. And it's about time I did an actual 0-60 test to see where it's at compared to the 11.5 seconds that it started with. It should be something under 10.
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The "Push Harder, Suck Less" philosophy explained:
Push Harder - Drive as close to the limit of your tires as possible.
Suck Less - Drive something resembling a proper racing line.
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Secrets of the Mirage

Postby Loren » Tue Jan 01, 2019 8:49 pm

I guess I should catch this thread up a little bit. Two autocrosses since the last post.

Car is feeling great. December 15th was uneventful, but Philip's photos (and a lot of course worker comments) indicated that we were regularly lifting the inside front tire by an inch in one place on course, and sort of "bouncing" it slightly all along the return side of the course. Not scary, but not good.

So, before the Duel, I thought I'd try a little more experimentation with roll center adjustment. What I did was counter intuitive, and in hindsight, perhaps not a good idea. In an effort to bring the roll center up a little more and get better control arm angles, I raised the front of the car by 3/4". The difference in feel was VERY surprising. Less apparent body roll. Very stable feeling. From a pure "feel" perspective, it's probably the best the car ever felt.

Dan and I both Dueled the hell out of the practice runs, and I think we won every single practice match. I ran competition first, and it was great! The car did everything it was supposed to do, and I don't think I even hit any cones. But, one thing I don't give myself enough credit for... Between this car and the FASTiva, I've been driving "tippy" cars for over 3 years, and I've learned to respect them.

So, Dan got into his competition runs... and decided to try something new. Rather than taking the near-end turn-around that terminates in a walled 90-degree turn (with 25' between the apex and the walls) as a nice, wide arc... he tried to take a tighter line, which required tightening the line A LOT right at that 90. And so that's what he did. And that harsh input was enough to put the car WAY up on two wheels. Thankfully, I don't think there are any photos of it, but I saw it with my own eyes, and I wouldn't be exaggerating to say that it was somewhere between 30 and 40 degrees. It was up there. Kudos to Dan for not panicking, and calmly setting it back down. (and continuing his run... like a boss!) Needless to say, Dan dialed it back from 11.5 to about 9 for the rest of his runs.

Desperate times call for desperate measures. This is clearly a problem that MUST be resolved!

I've got another thread discussing this: viewtopic.php?t=3437

But, in a nutshell: Lowered the car by another 2" or so, and replaced the 226# front springs with 450# springs and a custom progressive bump stop.

Testing it at Sunday's event...
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Suck Less - Drive something resembling a proper racing line.
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Postby Loren » Sun Jan 13, 2019 5:39 pm

Latest round of suspension mods helped some. I further raised the front springs to 500# and added a 2" tender spring to allow for more droop travel. That's all doing a better job of keeping the inside front tire on the pavement. Both front and rear are almost touching the bump stops at static height. It really feels pretty good, but both Dan and I are a little tentative driving it. We're going to have to work our way back up to 10/10ths as we learn to trust the car again.

I feel like I may be at a turning point in the development of this suspension.

There are two ways to go about fine-tuning a suspension for balance between over and understeer. You either take the end that's gripping more and make it grip less, or you take the end that's gripping less and make it grip more. I tend to shun the notion of intentionally making a tire grip LESS, so I've mostly been trying to optimize this suspension to maximize front grip. Rear grip "is what it is", I've done nothing back there with the intent of making the rear grip any better (or worse). And I think I've acheived that. The front has an insane amount of grip. I don't think it can have any MORE grip, as it is... it already has so much grip that it wants to turn itself over!

And yet, the car still understeers a little... well, not so much that... but, it doesn't OVERSTEER at all, which is generally regarded as the "fast" way to set up a FWD car for autocross. Set it up to where it's easy to get the back end out when you're off-throttle, but easy to get it back with a quick jab of the throttle. Which means that I may need to go against my own tendencies and start trying to make the rear of the car LOOSE in search of faster times.

Several ways to do that. Bigger rear swaybar is the obvious. And it's already got a big rear bar. Bigger would just make the inside rear tire lift that much earlier, but once that tire is up, it's up... and it's already coming up.

Higher rear spring rate would resist more body roll, transferring more total cornering weight to the front. Could help, but I'm not willing to get too crazy with the rear spring rate because it DOES have a horrendous effect on street ride quality. Right now I do have a soft progressive bump stop in the rear that is nearly engaged at rest. I could try replacing that with a stiffer bump stop, and tinker with the engagement point of it by using spacers.

Given that my rear alignment is non-adjustable, I can't really do anything with that. (some toe-out would be good)

Adjusting rear shocks stiffer is a thing. But, I'm already doing that. Typical autocross setup is full stiff in the rear. Not much I can do there without spending big bucks on custom valve shocks.

The only other thing I can think of would be the old stock-class cheat of messing with the rear tire pressures. Either going way above or way below "proper" pressure will cause the tire to lose grip. Given that the rear is so lightly loaded, I'm not sure I could go low enough to make a difference. But, I could go way up with the rear pressures and introduce a bit of crown into the tread. That might do the trick.

I've got some experimenting to do...

If I can get the car to where it will oversteer when pressed... then I know I can confidently hammer it into a turn, and it's not likely to get up on two wheels... instead, it will load up that one rear tire until it loses traction, and slide a little bit. Once I adapt to that, I'll be golden!
Loren Williams - Loren @ Invisiblesun.org
The "Push Harder, Suck Less" philosophy explained:
Push Harder - Drive as close to the limit of your tires as possible.
Suck Less - Drive something resembling a proper racing line.
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Secrets of the Mirage

Postby twistedwankel » Sun Jan 13, 2019 8:50 pm

Saroya put her car into "kick ass" mode which was only available a few year ago = discontinued. You must have missed the upgrade from MisterBitichi? You want to change my motor? You're the Man.
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Postby Loren » Thu Feb 14, 2019 5:21 pm

Last event we did try upping the rear tire pressure. Cold pressures were 35 front and 45 rear. Hard to say just how much it helped. The course, while really fun, was almost too easy for the Mirage. Pretty much flat out everywhere, no place to really challenge the tires... except for that one place where I initiated a spin at 56 mph and ended up in the grass. :bangwall:

So, I think the higher rear pressures did what was desired. If you lift in a hard turn, it will come around. Now, I just need to learn to work with it. Can I lift, rotate, and plant the right pedal to catch it?

The good news is that there have been no reports of the car getting up on 2 wheels since the last round of lowering. I don't like the way it feels (bouncy, unstable), but at least it's keeping the front tires on the ground.
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The "Push Harder, Suck Less" philosophy explained:
Push Harder - Drive as close to the limit of your tires as possible.
Suck Less - Drive something resembling a proper racing line.
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Postby Loren » Sun Feb 24, 2019 12:03 pm

Didn't look at tire pressure at Dunnellon yesterday, so should have been about the same as before. Cold pressures around 35F and 45R. Warm closer to 38/48.

Otherwise, autocross prep involved removing the stuff from the back of the car and maxing out the rear shock adjustment.

Oh, I had softened the front shocks at the last event, I think. Noticed that in hard street cornering, I'm getting a significant rub on the front tire. The only place it can hit right now is the top of the inner wheel arch (not a liner, it's actually metal), and that's what it was doing. So, either the shocks are too soft, or the suspension has settled a little bit... or both. Anyway, I jacked the front shock stiffness up from about 6/16 to 12/16. Seems to have helped. I should probably go a little stiffer with it. I did put really stiff springs up there.

The front tires are at 109 runs now, so I took the car to Carl and had them flipped. They should be good for at least another 80 runs. The rears are still fine. I could have had them flipped, they are finally showing some wear. I'll get 'em next time. Those rear tires have 244 runs on them now. They're in it for the long haul!
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The "Push Harder, Suck Less" philosophy explained:
Push Harder - Drive as close to the limit of your tires as possible.
Suck Less - Drive something resembling a proper racing line.
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Postby Loren » Sun Mar 10, 2019 8:17 pm

Raised the front of the car up by about 3/8" Friday. Trying to get it to stop rubbing the top of the inner fender when pressed. Curiously, it doesn't seem to do it at autocross. But, it still happens on certain turns on the street. So, I need to go up a bit more... or I need to fit a bump stop stack that just prevents it from going there.

Anyhow, that's all that changed since the last event. Didn't even check the tire pressure. We're running something like 35 front and 45 rear, or whatever they get up to when they're warm.

Three drivers in the car yesterday. I was 30th overall with a 41.9 (in the Mirage!!!), which was good for 18th in PAX. The PAX index is not at all friendly to the Mirage, so that's good. Co-driver Dan Brentnall ran a 43.4, and special guest driver Mike Redmond did 42.5 on his last fun-run.
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Push Harder - Drive as close to the limit of your tires as possible.
Suck Less - Drive something resembling a proper racing line.
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Postby Loren » Sun Apr 21, 2019 10:24 pm

What? Oh, yeah... we're still driving the Mirage!

The only thing that's changed is that we experimented with going low on the rear tire pressures rather than high. Didn't make a notable difference, but low pressures ride better than high pressures on the street, so left it that way. Current cold pressures are around 35 front and 30 rear. They are what they are when they are warm. Car feels good.

The last ride height change seems to have fixed the tire rubbing problem.

And I think the lower setup with the stiffer front springs did solve the "getting up on 2 wheels" problem. But, I've already decided that I will never fully trust this car. And I don't like driving a car that I can't fully trust. So, it's definitely retiring from autocross (at least on my dime) come the end of July. It's a shame. I think I've finally got the thing figured out!

Of course, the big pain in the ass right now is that there are at least 5 more events in the season, and the front tires are done. I'd give them 2-3 events with one driver. Two events with two drivers would be pushing it. 5 events... ain't gonna happen! So, I need to order new front tires.

The good news is that 205/50-15's will work on a Miata. :thumbwink:
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The "Push Harder, Suck Less" philosophy explained:
Push Harder - Drive as close to the limit of your tires as possible.
Suck Less - Drive something resembling a proper racing line.
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Secrets of the Mirage

Postby Loren » Thu May 09, 2019 12:36 pm

Carl mounted the new front tires today. I stuck with exactly the same 205/50 Dunlop ZIII's because I know they fit properly.

There was still a hint of the two center grooves in the old front tires, but upon close inspection, there was about a 3" strip of cord starting to show on the inside edge. They were done at 186 runs!

The rear tires are still going strong with 321 runs.

5 events left in the season. With two drivers, that should be around 60 runs or so. Then the Mirage retires from autocross.
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The "Push Harder, Suck Less" philosophy explained:
Push Harder - Drive as close to the limit of your tires as possible.
Suck Less - Drive something resembling a proper racing line.
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Secrets of the Mirage

Postby Loren » Sat Jun 15, 2019 7:49 pm

It's days like today that make me think I should have just stuck with that plan to put a supercharger on this car.

It's still huge fun to drive, but to finish better than 19th overall (out of 40), it needed some quicker acceleration.
Loren Williams - Loren @ Invisiblesun.org
The "Push Harder, Suck Less" philosophy explained:
Push Harder - Drive as close to the limit of your tires as possible.
Suck Less - Drive something resembling a proper racing line.
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Postby CaptainSquirts » Sat Jun 15, 2019 8:55 pm

Loren wrote:It's days like today that make me think I should have just stuck with that plan to put a supercharger on this car.

It's still huge fun to drive, but to finish better than 19th overall (out of 40), it needed some quicker acceleration.
Well at least it looked great on the course. How much power could a super charger add anyways?

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