Secrets of the Mirage

[Loren]

Scratch that.

I just measured. It's the rear tire clearance that's tight. Maybe 1/2" on the inside, but nothing on the outside. The front has 1/4" on the inside... and if I pull the fender liner, there's an inch of clearance on the outside.

So, when the time comes, it would be easiest to run a staggered tire setup. 205's front, 195's rear. Increase the front offset (or add a spacer).

Can even gain about another 1/4" be giving the front fenders a slight "pull". They're very soft and bendy.

So, yeah... "easy button", I could get a set of proper 1/2" spacers for the front right now. That would allow me to still fit 205's later. (it's on 195's now)

Of course MORE front grip isn't really what it needs just yet.

[Loren]

Just for reference...

The smallest bolt-in spacer I could find is 20mm. https://www.amazon.com/gp/product/B00TY63MF6/

Smaller than that would be a sandwich spacer, and I'd have to fit longer studs.

20mm + 5mm tire width (half of 10mm) moves things out by 1". Could still work. As long as my wheel studs aren't LONGER than 20mm.

Why does every possible modification always go in circles? I'm getting dizzy.

[mymomswagon]

Just for reference...

The smallest bolt-in spacer I could find is 20mm. https://www.amazon.com/gp/product/B00TY63MF6/

Smaller than that would be a sandwich spacer, and I'd have to fit longer studs.

20mm + 5mm tire width (half of 10mm) moves things out by 1". Could still work. As long as my wheel studs aren't LONGER than 20mm.

Why does every possible modification always go in circles? I'm getting dizzy.

these guys look like they have 15mm?

bloxsport-4x100-cb561-forged-6061t6-hub-centric-wheel-spacers-p-1478.html

I have a set of their wider size for VW. The hubcentric fit is very precise. Needed a little anti-seize to get them on the hub lip


[IMG]https://uploads.tapatalk-cdn.com/201712 ... f894be.jpg[/IMG]

[Loren]

Gotta take some measurements and draw some pictures. Got nothing else on my agenda for today.

Shuffling this off into a "theoretical discussion":
viewtopic.php?f=3&t=3064&p=53493#p53493

[twistedwankel]

Once a Rabbit always a Rabbit. First it hopped and now it hikes a rear tire. Change the hood ornament to a playboy bunny.

[Loren]

I'm really starting to miss the days when my suspension tuning was limited to playing with springs, swaybars and alignment. Things get really thick and dark the further you go down the rabbit hole. ESPECIALLY when you're talking about FWD. Misinformation runs rampant, and "real" engineering data is scarce.

Anyway... Let's reframe the current situation with the current suspension:

Feel: Great! Turn-in could be crisper, but it gets there.
Balance: Very neutral. No easy lift-off oversteer, no understeer when driven properly. It does have some understeer if you overpower the front too early coming out of a turn. (typical FWD)
Grip: Amazing! Hangs a turn tight, and puts down power nicely.
Rear Wheel Lift: 2-3", but only when pressed VERY hard
Front Wheel Lift: Nothing like the previous setup. Didn't even realize it was happening until I saw a photo... it's lifting like 1/4" when pressed VERY hard

So, what exactly am I trying to do here? Well, "optimize", I guess. It is TRULY amazing that 195 RE-71's have enough grip that even when 99.5% of the weight has been transferred to the outside tires, it still stays confidently stuck! It's also a hint that the setup can't be THAT bad. But, it could still be better. We just need to figure out how.

Things that should help (in no particular order):

Reduce Front Roll Couple: This is done by raising the front Roll Center closer to the CG by lowering the ball joint pivot point. (modded lower control arms with heim joint ends) The effect should be less body roll. This might keep more weight on the inside front tire, and ultimately more front grip.
Increase Front Track: Wheel spacers. This VERY slightly raises the Roll Center, but is also supposed to help stabilize the front end and decrease understeer.
Increase Rear Roll Center: It's already pretty high relative to the front. But, the car is pretty level, could raise the rear a bit. Increasing that Roll Axis Inclination should make the rear roll happen quicker, increasing corner-entry oversteer, and keeping the front end planted. (Philip will like that one)
Decrease Front Bump Steer: This is mostly a "feel" thing, and I'm not really "feeling" it. But, the tie rods are DEFINITELY angled upward significantly at the ends. And with my steering rack being on the back side of the axle, that means that as the suspension compresses, toe is pulled outward. The more the body is rolled into a turn, the more this effect should be. So, hitting a bump mid-turn could unsettle the car. The fix would be custom tie-rod ends.
Lower CG and shift weight Forward: (yes, Forward, to load the front tires more) This, of course, is the fundamental problem that causes the excessive body roll that's causing the front wheel lift. Lots of things can be done here, even within M4 rules.
- The battery is really heavy, and mounted pretty high under the hood. Could easily fit a battery about 1/3 the size significantly lower in the car.
- Start autocrossing without the spare in the back. (yeah, I'm lazy, it usually stays in)
- The jack is located under the driver's seat... probably no benefit to taking that out except for just weight.
- Remove the back seat. I'm on the fence about that one, it's pretty light, anyway. Could easily flip it down to lower the CG a tiny bit, though.
- Fit a lighter driver's seat LOWER in the car to put the DRIVER weight lower in the car. (or look at modifying seat brackets to just mount the stock seat lower) That's 180 pounds that could be lowered by 3".
- Remove the rear wiper, I never use it, anyway.
Remove Front Swaybar - This could help with inside front wheel lift. Should also help the front end stick better. But, I don't really want to do it without adding some spring rate or at least a taller bump stop in the front. Less front roll rate means that when the rear wheel lifts, it lifts all at once. Need some spring rate to "catch" it.
Larger Front Swaybar - I'm not going to do this because I have the inside front wheel lifting already, and I don't want to lift it more. (plus, nobody makes a front bar for this car) But, the theory is that most McStrut front suspensions gain positive camber in a turn... eliminating body roll with fat bars stabilizes the camber and is said to be faster on some cars.
Taller Progressive Front Bump Stops - The bump stops that came with the kit are fairly short. They are progressive, but they start "stiff" and get "stiffer". I'd like to find something like the ones I've played with on Miatas. Taller bump stop that is almost engaged at static ride height, so it engaged IMMEDIATELY, and starts progressively adding to spring rate. (really, could use stiffer front springs, but I want to try not to do that to preserve street manners) This would provide the roll resistance to handle the rear wheel lift, but without pulling UP on the inside front wheel like the swaybar does.
More Front Droop Travel - The problem before was that I had almost no droop travel and it was pulling the inside wheel up... always. It's not doing that any more, but the only things that can pull the inside front wheel up (short of honestly getting way up on 2 wheels) are the swaybar or the shock. I've got the shock travel centered now, could easily adjust that for a little more droop travel.

I'm sure there's more. But, those are some of the easier things to do. Some are even free. NONE of it should have a dramatic effect, but over time, ALL (or most) of it combined could make a significant difference.

[JasonS]

Larger Front Swaybar - I'm not going to do this because I have the inside front wheel lifting already, and I don't want to lift it more. (plus, nobody makes a front bar for this car) But, the theory is that most McStrut front suspensions gain positive camber in a turn... eliminating body roll with fat bars stabilizes the camber and is said to be faster on some cars.

It seems the National level guys driving DS WRX's are going the LFB route for this reason. Seemed counter intuitive to me for a while but with the already camber limited front end camber of these cars it makes sense to me now. Supposedly a LRB causes excessive rear lift. Just would have figured a LFB would have caused even more push, and I guess it does, but most say that it is worth the trade off for less camber loss and enhanced transitions. Been toying with picking one up.

[Loren]

Further meditation has occurred.

Here's the epiphany: I've been messing with suspension modifications since about 1997. I've lowered um... at least 7 of my cars that I can think of. And I've NEVER given any consideration to Roll Centers before now. I just took the positive benefits of lower CG and stiffer springs, and ran with it. And as long as I kept things in proper balance, it generally worked. (I learned a lot about screwing up the balance of a car with my first two autocross cars)

I'm not saying that Roll Centers don't matter. But, I'm saying that maybe I can continue not worrying about it much. Maybe I'll deal with it later... maybe I won't.

So, maybe bringing the roll center up would reduce body roll some. And maybe that would help with the tendency to want to lift a front wheel. Or maybe it won't make that much difference because the weight transfer is GOING to happen, anyway. See, that's the part that doesn't come out in any discussion that I've read. It's supposed to reduce body roll due to reducing the Roll Couple. That's as far as anyone goes. It's all about "theory" and "reducing body roll". Meh. I can live with body roll, it's all part of the game.

And now I'm thinking... I want to introduce some more rake. That should shift weight toward the front to help keep it planted, and change Roll Axis such that the rear will react quicker, and theoretically be more inclined to oversteer. But... I'd be better off lowering the front. I don't REALLY want to be any lower. But, it's the thing to do. It will drive the Roll Center further into the ground, but I DON'T CARE. Lowering CG is certainly better than raising it at thish point.

Maybe I'll get motivated and do that tomorrow?

[Loren]

Instead of messing with ride height, I decided to start experimenting with no front swaybar. I've been meaning to do that for a while. So, I removed an end link.

As expected, steering response suffered. Overall, the difference is pretty significant and "weird". Will take some getting used to. I don't hate it. In fact, in a lot of ways I like it. It REALLY smoothed out the front ride compliance. Steering response is "okay", transitional response is what really suffered. It definitely feels more planted in the front. Less "on edge", more in control. I just need to make steering inputs a bit earlier.

Went full stiff on the rear shocks (autocross mode!) and that helped the steering response some. Still wasn't quite it. So, I went stiffer on the front shocks. I'm just past half-way on the front shocks. Feels pretty good. Striking that balance between compliance and steering response now. I WANT the compliance. The more front grip you can get out of a FWD car, the better. But, I also like steering response. We'll have to see how it feels driving slaloms at an autocross.

Need to add some front tire pressure, too. And, I read some stuff from Andy Hollis that has convinced me to lower my rear tire pressures a lot. (I usually err on the side of raising rear tire pressure to reduce grip, he goes the other way) So, I'll do that. Probably end up somewhere around 38 front and 30-32 rear.

I've got time today, I could monkey with the front ride height. But, I try not to break that fundamental rule of "change one thing at a time". I'm already changing shock settings and tire pressure to go with removing the front bar. That's enough for one round!

The net take-away here is that removing the front swaybar should help me by:
- Removing some of the force that's pulling the inside front tire up in a turn.
- Shifting the bias of the car toward oversteer, maybe causing the rear tires to give up slightly before the front even thinks about lifting.

I generally don't like the idea of making one end of the car lose grip... I'm a max grip kind of guy. But, if max grip is making the car want to roll over, I guess giving up some rear grip isn't such a bad thing.

[twistedwankel]

Baron Loren Von Williams is a busy man. Interesting reading.

[Loren]

Mostly busy just researching and thinking, unfortunately.

But, I just made some free horsepower.

Being a modern economy car, this car is designed to take in WARM air. It helps the fuel atomize better, and gives the bestest fuel economy. So, the air intake tube hangs right off the top front of the engine and sucks in air from directly behind the radiator.

Of course, for best power, we want cold air. Fortunately, there's GOBS of empty space under this hood. And among the crap I have cluttering my garage was an intake tube leftover from my Spitfire project... I think it's from a 90's Escort. Just a 3" diameter accordion tube about 3 feet long. Nothing fancy.

So, I stuffed this tube around the itty bitty intake snorkel, didn't even bother sealing it. Routed the tube down and around to the front of the radiator where the fresh air is.

I didn't do a proper "before" test. But, on a warmish day, I've seen 140-150 degree intake temps on this car. Today, ambient temp was 75. And after letting the car warm up for a few minutes, I was seeing 92 degrees on the OBD app. Time to go drive. Instantly dropped 3 degrees into the 80's, and as I got up over 40, it dropped down to 80-82. As long as I kept moving over about 20 mph, it stayed stable. I even saw 78 at one point. Get close to a stop, it starts rising.

After my drive, I let the car idle in the driveway for 5 minutes. In that time, the intake temp reached 100 degrees.

Even on a cool day, I'm seeing some significant cooling of the intake charge down to within 5 degrees of ambient. And that's without sealing the duct so that it can't pull under-hood air. Also without any attention to "pointing" the duct forward. It's just jammed in there in front of the radiator.

So, if I'm seeing 140 degrees on a 90 degree day, and I can get that down to 95 in the first few seconds of an autocross run... that's 40+ degrees cooler air. What's that worth? Who knows??? A common number that gets thrown around is 1% for every 10 degrees. So, maybe I'm getting 4% more power. Hell, even if it's 2%, I'll take it... it's free!

[Loren]

Well, I can't say if my cold air intake made a difference or not, but disconnecting the front swaybar seems to have further tamed the front end. Guess I'll have to follow through with removal. No sense keeping that unused swaybar weight on the car!

[Loren]

Since I guess I'm starting "phase one weight reduction", I decided to start a spreadsheet to track weight. All of the easy stuff should get me close to 1,930 pounds. Kinda disappointed that I can't get under 1900 without getting crazy. But, it's just a number, I try not to get too worked up about it. It's a solid 120-pound reduction from stock. Estimated weight reductions at this point, so I could be off.

I just ordered a 6-pound YTX9-BS AGM motorcycle battery. 135 CCA for $22 shipped. Should be ample to start the car in Florida. (I considered going with a YTX7 to save another pound, but it was only 90 CCA) The factory Group 35 battery weighs somewhere around 38 pounds. So, there's 32 pounds (plus a little bit of bracketry) that I'll be dropping when I install that.

If I get weight down from 2050 to 1930 lbs, and power up from 74 to 78 hp (with the cold air intake), my 0-60 time should go from about 10.9 to 10.1 seconds. Every little bit helps!

[twistedwankel]

I hate to admit it but the Mirage does have a great sound to it when wound up. Must be the gutted cat? Or the nutted one on the treadmill?

[Loren]

Haven't touched the exhaust on this car yet. There is a long tube header available that eliminates the first cat.

I like the sound it makes, too. Reminds me of the ridiculously long stroked 1500 Spitfire engine.

[Loren]

Poked around under the hood for a minute today.

Found that there's a removable plastic piece that covered about 6" of space right next to the radiator. (the radiator is offset to the left) Two screws and that piece came out, giving me the perfect opening for my air intake. Maybe I'll get fance and duct up tightly to it for a slight "ram air" effect. Maybe I won't. So far, I haven't.

Also looked at the battery. I'm probably going to be lazy and keep the stock battery bracketry. There are some other things bolted to it. So, if I pulled it out and recreated something for the new battery, I'd have to account for all of those other things. It would be a hassle, and ultimately, probably wouldn't save much weight, anyway.

If I *did* build a new battery bracket, I could probably mount the battery a little lower. Instead, I think I'll just mount the new battery on the existing tray rotated 90 degrees forward (connector lugs toward the front). There's enough slack in the cables to deal with that. And it's a sealed AGM battery, it won't mind being sideways.

OE battery is approx 9x7 and 9 inches tall. Replacement battery is roughly 3.5x6 and 4 inches tall. Turn that battery sideways and it's 4x6 and 3.5" tall. So, I'll have lightened it by 30 pounds, and lowered its center from 4.5 to 1.75"... so, almost 3" lower mass. Little block of wood to keep the battery from sliding sidways. Custom upper bracket to hold it down. Done!

[Loren]

Getting below 1900 pounds with this car is going to be harder than I thought. Everything is already light!

Removed the rear wiper today. 1.7 pounds. Oh well, the back of the car looks cleaner without it. Took all of about 3 minutes to remove.

Removed the front swaybar. 5.9 pounds of bar, 1.5 pounds of brackets and end links. As expected, that convoluted bar was a pain to remove. I was faced with the choice of dropping the front subframe or cutting the bar. I took the easy out and cut the bar in half to remove it. If it needs to be reinstalled, I can get a piece of tube to sleeve it and weld it back together.

The car is now 0.5% lighter. It all adds up!

[Loren]

Well, my new battery showed up the other day. What kind of moron ships a lead/acid liquid-filled battery in a PADDED ENVELOPE? Sure enough, it arrived with a bent lug (I could deal with that), and a very slight leak. It's a shame, too. It's got a perfect 12.8V charge. So, I requested a replacement, but I can't return it. We shall see. If I have to buy another one, I might just run down to Wal-Mart and spend a couple bucks more for it.

So, this won't be done before Saturday.

And I ended up with an acid-hole in one of my favorite pairs of shorts.

[Native]

moron

Exactly.

[lddavis91]

I hate to admit it but the Mirage does have a great sound to it when wound up. Must be the gutted cat? Or the nutted one on the treadmill?

Its the 3 banger, triples make a nice little I6-like snarl, you should hear Matt's Triumph or my Seadoo.