Secrets of the Mirage

[Loren]

If it will start repeatedly? Somehow I cannot imagine a small battery being able to survive the output of that alternator or running an AC compressor at idle to make up the difference in amps.

I'll let you know if it becomes a problem. Miata guys run the same battery, and the only problem they have is with cold starts. VERY cold starts, not Florida cold. I think it will be fine for my purposes.

[Loren]

Sorry if I missed this, but what safeguards are being put in place to prevent the engine killing down shift from happening again?

I wish there was a safeguard! There's really not much you can do other than what Jamie said. Stay in 2nd.

Well, that's not true. For purely whimsical purposes, I have considered making a Ferrari-style gated shifter plate. Just out of aluminum, nothing heavy. I just think they look cool. (How often does something get done on my car JUST because it looks cool?) If I did that, it would be easy to incorporate a 3rd gear lockout if I wanted to. Or, it would also make it quite obvious whether you were in 1st or 3rd.

Hmmm...

[nathanwilliams617]

I see.
Maybe you can engineer an optional first gear lockout on that aluminum gate. You'd engage while in 1st right before launch, and once you shift out of 1st it locks it out. Maybe spring loaded... Shouldn't have to reset or disable till you get back to grid.

Idk, but It needs something though

[Loren]

Neat idea. Sort of where I was going with the 3rd gear lockout... but, I didn't quite get there. I like it! Spring loaded lock-out for first. You don't get into first without specifically "asking" to get into 1st.

And, honestly, it's probably worth spending a few bucks on!

[Loren]

I liked this idea so much that I went out to the garage to take some measurements. Quickly remembered that the transmission is not in the car, thus I have no idea where the gearshift lever positions really are! But, I did take some measurements, and can assume for now that the limits of the shifter movement are where the 4 corners are. Center is spring-loaded, so that's easy. I can mock this thing up!

Thanks for the nudge, Nate!

[Loren]

Here's a fun fact. I can't do a gated shifter on the Mirage. The shift lever is 13mm diameter. The distance from the center of one gate to the next is only 15mm. If I did a gated shifter, the material between the gates would have to be about 1mm wide!

I guess that's kinda cool in a way. I can't do a gated shifter because the shift pattern is too tight! But, that's misleading. The lever is long, and the throw is a lot longer and wider up where your hand is. I COULD do a gated shifter if I built up the shifter pedestal to be taller, and hide more of the lever. Meh.

But, I CAN still do a first gear lock-out pawl. I'll work on that idea.

[nathanwilliams617]

Cool!

[Loren]

Another sub-topic is born: Gating the Shifter

[Loren]

Flywheel is back. Unfortunately, they only took .8 pounds off of it, bringing it to 14.3 pounds. They milled the fat outer ring off of the back, so the weight they took off was some of the most relevant weight because it's further out. Won't be a night-and-day difference, but for $45, I'll take it.

[CaptainSquirts]

With the small hp addition from the engine and an almost pound from the flywheel it'll all add up!

[Loren]

Got the last of the brake upgrade parts today. (they forgot to include the caliper brackets with my salvage parts order)

I'm not messing with the rear brakes yet, but I do have a larger drum kit to go back there if I feel like I need them. A project for another day.

The front rotors are going up from 229mm (9") OD to 251mm (9.9" OD). Rotors are 1.57 pounds heavier. (boooo!)

The brackets are 0.23 pounds heavier, that's not so bad. Everything else is the same.

[twistedwankel]

So did they have to rebalance it or was it a machined surface to begin with? Just asking because if I were to use an aftermarket flywheel for my RX8 with the similar outer weight removed I have to buy the "bolt on" automatic flex plate version counter weight to keep the crank in balance (9200rpm). It weighs about 3lbs I think? Maybe your engine doesn't care?

[Loren]

It is a balanced flywheel, and the ring they machined off was already a machined surface. So, no need for rebalancing.

[Loren]

Here's what the engine side of the flywheel looks like now.



I didn't take any before photos, but here's a stock one that I found:

[Loren]

I just re-read a great article about brake bias and reminded myself of what I already knew, but was being stubborn about.

A typical stock car has brakes that are pretty heavily front-biased (5-10%). That means that, by design, the front tires should always lock up before the rear tires... which is a good thing. My car has ABS as standard in all markets, so it may have a little less front bias than some.

From there, lowering the car shifts the bias more to the front. Taking weight off of the front (like the 28 pounds of battery that I'm removing) shifts bias to the front. Putting better pads in the front (Hawk HPS) shifts the bias to the front. And when I put the bigger rotors on the front... yep, even more front bias.

So, the rear disk brake upgrade that I was doing to drag my feet on and "wait and see" if I needed... yeah, I'm gonna go ahead and install it.

Ordered a new set of shoes to go with the larger drums. Should be able to get that done while the car is down.

[Loren]

Today's project. I swear sometimes I'm the worlds slowest fabricator. I spent over 4 hours on this. Modified the battery tray to fit the ETZ10S motorcycle battery.

Here's the final fit-check before paint:



And this is how the stock positive battery cable fits. The terminals are supposed to be on the back side of the battery, but the battery is so much smaller that they'll fit even on the front.



All I did was weld a rail on the right side (left in the photo) of the battery tray, and another on the back side. Then I made a corner bracket that bolts in. This will allow some flexibility should the next replacement battery not be exactly the same size.

If you look in the first photo, you'll see a notch cut in the center of the tray right next to a bolted on bracket. That's where the stock tie-down J-bolt hooks. There's one just like it on the back side. So, I used the one on the back. And then I drilled a hole for the one on the front. Had to make a pair of shorter J-bolts.

And then the top plate I made from a piece of 1" square aluminum tubing that I cut in half.

It all buttons up super-snug, and looks nice. In theory, the battery will be enough to reliably start the car (in Florida). We shall see.

Oh, the important part. The reason for doing this. The weight!

OE Battery = 34#
OE Battery shelf/tray/tie-down = 2.8#

New Battery = 6.11# (+.1 lug terminal adapters)
Modified battery shelf/tie-down = 2.16#

Total battery weight reduction: 36.8 - 8.37 = 28.43 pounds!

[twistedwankel]

The best part is that it's on the driver's side where you don't need the extra weight. Is all that aluminum on the + pole a heat sink? I have electric power steering with a 60amp fuse and it's not anywhere that big. Those type batteries would reliably start my '81 750cc - 4 cyl Suzuki for about 3-4 months if I forgot to put it on the 1.5amp trickle when not in use. Notoriously weak alternator on those bikes. I've found I only get 4 years out of a lead acid autocross battery. Invariably a plate will break from slamming the car around on sticky tires and I get a discounted new one as guaranteed for 5 years.

[Loren]

I honestly haven't looked at the mess on the + terminal closely enough to see what's there. Probably some kind of fuse, or relay or switch... Idunno.

[dbeng]

Total battery weight reduction: 36.8 - 8.37 = 28.43 pounds!

Well that pretty handily offsets the weight gain of the larger brakes Plus the center of gravity is now lower since the battery sits high and the brakes are low.

Not to mention, larger brakes coupled with net weight loss equals even further reduced stopping distance. More time on the throttle, less time slowing down

[Loren]

I wasn't really seeking better stopping distances. Mostly just better feel and fade resistance.

I'm still leaning heavily towards pulling out the back seat, too.