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NickD
NickD PowerDork
2/18/20 8:43 a.m.

I think I may know the answer to my own question, but I figured I'd bounce it off you guys to see if I'm missing anything. So, my supercharged Miata weighed 2250lbs (without me) when it hit the scales out to the SCCA Champ Tour. That was great because at the time I was running SSM, and my weight minimum was calculated to be 2240lbs. But now along comes this Xtreme Street B class and my minimum weight can be 2100lbs. That is a not insignificant weight difference. So, how do I take 150lbs out of an already light car. 

As the car sits, it has a Rotrex-supercharged 2000 1.8L, 6-speed, '96 Torsen rearend. It still has power steering, but I'd like to keep that because turning at lower speeds with 245-width tires without power steering seems unenjoyable, unless you're Popeye. Air conditioning compressor and lines and condenser are all gone (Evaporator core is still there because I didn't want to yank the dash out). Full interior. All stock body panels. It does have a Blackbird Fabworx GT3 rollbar. Wheels are 15x9 Konigs, which aren't the absolute lightest wheel out there, but at 13lbs are pretty dang close.

Talking to my autocross friends (none of whom are Miata people) netted a few suggestions:

  • Ditch the rollbar. It's fairly heavy and it's weight in a pretty terrible spot. I do like the safety factor though, and if I want to run it at the local private racetrack, they want a rollbar. There was talk about how to make it quick-release, no clue what that would do for safety though.
  • Cut the crash bars and webbing out of the doors. As my friend Scott put it "With all the SUVs on the road, you'd probably die in a T-bone even with them."
  • Carbon fiber body panels. I had my doubts on this one. The stock fenders and hood are pretty dang light, and Carbonmiata stuff tends to fit terrible and be a fiberglass frame with a carbon skin unless you pay a fortune. I suppose I could skin the hood and go to hood pins, like a real racecar.
  • Tubular subframe and control arms. Not a huge weight difference, but I know V8Roadsters sells them. I remember Keith saying that stuff tends to crack though (not V8R, but tubular parts in general)
  • Start gutting the interior. This moves it a bit away from being a street car, but the stock seats I'm sure can be replaced with something lighter, and the carpet has to be worth a pound or two. As well as ditching that now-useless evaporator core
  • Different engine. My friend Randy brought this one up and said it was probably the spot for one of the biggest gains (or losses, I guess). The BP-4W is a cast-iron beast with thick bore walls. I'm pretty sure a Honda K-series has to weigh less.

Am I missing something? I don't think I am. I did have a lightweight battery in it at one point, but it didn't have the capacity my engine needs to crank now. The standalone ECU means its grumpy when starting, and that results in a fair bit of cranking.

slowbird
slowbird Dork
2/18/20 8:48 a.m.

Miata-kart.

NickD
NickD PowerDork
2/18/20 8:49 a.m.
slowbird said:

Miata-kart.

Not legal under Xtreme Street rules. Still has to resemble a car.

Dusterbd13-michael
Dusterbd13-michael MegaDork
2/18/20 8:50 a.m.

On the rollbar: weld nuts to the backing plates, attach backing plates to the body (pop riveted mine)

That makes rollbar removal a LOT quicker and one man doable. 

There isn't nearly as much weight in the interior as one would think.

NickD
NickD PowerDork
2/18/20 8:52 a.m.
Dusterbd13-michael said:

On the rollbar: weld nuts to the backing plates, attach backing plates to the body (pop riveted mine)

That makes rollbar removal a LOT quicker and one man doable. 

There isn't nearly as much weight in the interior as one would think.

That rollbar tip is good. They were suggesting weld a pipe of an OD smaller than the ID of the rollbar and then putting quick release pins through it. Seems like it wouldn't exaclt be safe though.

mrhappy
mrhappy Dork
2/18/20 8:53 a.m.

Smallest battery that will start the car maybe from an rc car or somethin?

NickD
NickD PowerDork
2/18/20 8:54 a.m.

And now that I'm reading the rules again, I don't think I could pull the carpet up anyways.

trucke
trucke SuperDork
2/18/20 8:56 a.m.

Driverless car is the answer.

I'm no help!  Sorry!

John Welsh
John Welsh Mod Squad
2/18/20 8:57 a.m.

Still on stock seats?  Bolt-in, bolt-out lightweight seats seems like an easy way to shed weight for events but with the ability to return to street seats when wanted

NickD
NickD PowerDork
2/18/20 8:59 a.m.
John Welsh said:

Still on stock seats?  Bolt-in, bolt-out lightweight seats seems like an easy way to shed weight for events but with the ability to return to street seats when wanted

Definitely on my consideration. Seats are easy to swap in Miatas. My friend Scott joked about giving me one of his old shifter kart seats to put in the passenger side ("Hey, it's a seat!") but definitely not legal. And it wouldn't allow me to terrify passengers

the_machina
the_machina Reader
2/18/20 9:00 a.m.

The lithium ion batteries are super light and still crank hard. They just don't have a ton of capacity for parasitic loads or for leaving accessories running without the car running. Might want to add a battery tender pigtail and a battery tender that's lithium ion compatible.

NOHOME
NOHOME MegaDork
2/18/20 9:01 a.m.

Lets pretend it is going to stay street-driven.

AC Evaporator

Lighter seats/shells

Carpet

Console

Convertible Top

crash bars under bumper cover.

Washer squirter bottle

Lighter wheels ( diminishing return point alredy)

alloy brake hats

lighter calipers

Wheel well liners

license plate frame(s)

Radio

Glovebox

Closing panel for dash ender steering column

Airbag components

fixed headlights, lose the motors

Tin shield over the tank in the trunk and under the carpet behind the seats

 

Pete

 

 

 

FuzzWuzzy
FuzzWuzzy HalfDork
2/18/20 9:08 a.m.

Smaller battery, radio system, swap out stock seats.

Idk how much you weigh, but you can go on a diet yourself during race season?

NickD
NickD PowerDork
2/18/20 9:12 a.m.

In reply to NOHOME :

Carpet isn't legal.

Convertible top I don't want to ditch, because I don't have a hard top and it sits outdoors. And I don't want a hardtop because I like the flexibility of putting the top down on the fly.

Crash bars, yeah, could probably chop down. Like the door bars, with all the trucks and SUVs,, in the event of an accident, this thing is likely toast anyways.

Washer bottle. Didn't think of that. They haven't been hooked up for two years anyways, since I broke the Y-coupler and haven't found another since.

Brakes, I really need better ones anyways, because I kill them in short order at Pineview.

Wheel liners, already chopped down to the bare minimum.

Plate frames, gone. No front bracket either, or front plate.

Radio, I like it for the hour+ drives to events and roadtrips. Could probably go to some sort of TrAccord setup though.

Airbag stuff: All gone already. Never had a passenger side one, and running a Nardi wheel on the driver's side.

Tin shields: Largely gone trying to chase a rattle.

 

NickD
NickD PowerDork
2/18/20 9:13 a.m.
FuzzWuzzy said:

Smaller battery, radio system, swap out stock seats.

Idk how much you weigh, but you can go on a diet yourself during race season?

Reducing driver's weight helps, but the weight is sans driver. I'm also 6'3", so I'm never going to be a lightweight.

captdownshift
captdownshift UltimaDork
2/18/20 9:27 a.m.

Ditch the hydraulic power steering and get a Prius rack to modify

Seats 

Battery

You'll still be lucky to save more than 60lb though. I didn't realize that it's much easier to get a BG chassis under 2100lb then a Miata. This new class does make picking up a Fiesta tempting (if I had the space and time). 

spacecadet
spacecadet SuperDork
2/18/20 9:27 a.m.
NickD said:
  • Different engine. My friend Randy brought this one up and said it was probably the spot for one of the biggest gains (or losses, I guess). The BP-4W is a cast-iron beast with thick bore walls. I'm pretty sure a Honda K-series has to weigh less.

K20 and K24 are heavier compared to the little 1.8BP ... 400+lbs.
 

a BP appears to weigh under 300lbs... so you can make more power on the K series.. but it's also going to require going to the BMW trans to do it and it that's also going to have a weight penalty. 

https://www.locostusa.com/forums/viewtopic.php?f=4&t=12804

on top of the fact that K swaps get into 5 figure territory quickly.. 

AngryCorvair
AngryCorvair MegaDork
2/18/20 9:30 a.m.

anything you say you don't *want* to do, for whatever reason, is something you need to either:

1. get over it

or

2. give up.

is it a racecar or not?  the answer to that question is the answer.

John Welsh
John Welsh Mod Squad
2/18/20 9:35 a.m.

How about a smaller (smallest) battery added for events but back to a street battery for the street.  If concerned that the small battery wont be enough at events then bring a jump box too.  Actually, bring your big battery and cables as the jumper.  

NOHOME
NOHOME MegaDork
2/18/20 9:46 a.m.

Can carpet be replaced with a lightweight carpet? At least remove the padding while the dash is out? Any noise-dampening tiles to remove?

 

Do you need heat or just defrost? Lose the heater core if you dont need heat. Lose the whole HVAC stack and ducting if you dont need defrost.

 

Ipod/headphones  will do the music chore and you can add the speakers to the list of stuff to remove.

 

Exhaust heat shields ( cause racecar)

Detachable mirrors for inside and outside.

lightweight muffler

Can I introduce you to titanium hardware? Slightly more expensive than cocaine, but if you must lose weight.

 

 

 

Snrub
Snrub HalfDork
2/18/20 9:57 a.m.

None of the weight loss is going to be without compromise for a street car. Here's a decent link to get you started: https://www.lightweightmiata.com/beast/lightness/ 

Cooter
Cooter UberDork
2/18/20 10:00 a.m.
AngryCorvair said:

anything you say you don't *want* to do, for whatever reason, is something you need to either:

1. get over it

or

2. give up.

is it a racecar or not?  the answer to that question is the answer.

Harsh, but exactly what I was thinking.

Ditch the top, and make or buy a tonneau 

NickD
NickD PowerDork
2/18/20 10:20 a.m.

A little clarification: This is not to make my car absolutely perfect to the letter of the rules. I was just trying to see if I was missing any spots to get some weight out of the car with a brainstorming session to see if there was anything I was missing. I've won SSM two years in a row simply due to showing up frequently. I imagine I'll likely do the same in XSB. Or I won't. I was just trying to find a little more competitive edge. And it did bring up some decent points. I didn't think about the washer bottle. And while I was thinking of brakes for improved stopping power, it didn't click that that'll shave weight. The electric power steering I'm considering, not just because it might cut weight, but because it'll simplify my engine bay and get the lines and pump and cooler out of my way (engine bay is full science project effect). Can probably jettison the cruise control bits, since no amount of parts-swapping seemed to revive it and no one seems to know how to diagnose it. 

Rodan
Rodan Dork
2/18/20 10:28 a.m.

Mostly good suggestions, and you're probably going to have to sacrifice streetability for performance at some point.

As a point of reference, my NA was 2050 last time I weighed it:

stock body panels

15x9 with 225/45-15 rubber

1.8 VVT engine, stock 5 speed

Xida suspension

Big wilwood brakes

AC removed

No interior except for top half of dash and door panels, no HVAC

Lexan 'wing' windows, stock power windows still intact

Snugtop hardtop, no soft top

Corbeau FX1 seats/ 6pt harnesses

stock type battery

Since the above weigh in, I've removed the headlights, power steering, and power windows.  IIRC, the headlights were ~18lbs, windows ~ 25lbs.  Power steering I didn't weigh, but probably 30lbs once I got the cast iron bracket off the engine.

 

If your ruleset allows the removal of the interior, there's gains to be made but you'll be sacrificing streetability to get anything serious.  A race seat, will save a few pounds, and you can leave the pax seat in the paddock if the rules allow.

 

IIRC, the stock soft top was ~30lbs, so if you remove it and go to a race hardtop, you can probably net ~15lbs high up on the car.  That's my next step, but it's an expensive 15lbs to remove.

I would not remove the rollbar.

These threads from MT.net may help:

Track car weight loss

Where to remove weight

 

captdownshift
captdownshift UltimaDork
2/18/20 10:30 a.m.

Do you have garage/basement storage space for an additional set of doors?

Picking up a second set and purging them on Windows, regulators, crash bars, cards, everything short of the latch, aluminum skin and pull. Would save a good amount of weight, but you'd likely want to swap them on the evening before an event and obviously stay parked in the garage until the complete doors were refitted. 

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