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Hello. I'm in the process of building a 1.6l miata DP car for next season.

After reading the rules about rollbars in Prepared it's unclear to me wether i need one or not. I will be running a full stock windshield (unlike most other DP miatas), so would the car still be considered open? would i need one to be legal?

 I do own a legal bolt-on rollbar, but right now the car's about 60 pounds over minimum weight, (1880-1890, will run 9" or 10" wide wheels) and if can get rid of the 40 pound rollbar that'd be great.

Thanks in advance.

Tabor.
 

A Miata has to have a roll bar.  Sec 3.3.2 of the Solo rules says

"A roll bar meeting the requirements of Appendix C, or a roll cage meeting
the requirements of Section 9.4 of the General Competition Rules
(GCR), is required in all A, B, C, and F Modified vehicles, and all
open cars in Prepared Category and in D Modified and E Modified. "

And 12.6 defines an open car

"12.6 OPEN AND CLOSED CARS
A. An open car is a convertible (with or without a full windshield), a
targa-top-type car with less than a full windshield, or a t-top-type
car with less than a full windshield.
B. A closed car is one with a full roof, a targa top-type car with a
full windshield, or a t-top type car with a full windshield."

Your Miata is a open car even with a windshield. 

You don't say what you've done to the car to remove weight, but there are lots of little things that can do to get lighter.   

Like Steve said, you need a rollbar.

Even with the windshield intact, it seems like your car is a bit heavy.  There are CSP cars close to 1900 lbs, and the Prepared rules give you a LOT of additional ways to pull weight out of the car.   Are you leaving the doors & interior intact?

Ok thanks for clearing that up.

First of all the biggest issue i have with weight savings is that the car needs to remain streetable. That means i need to keep the top and the windshield, heater, and i've decided to keep the whole dashboard. As for the doors, I bought a set of doors that i gutted and that i can swap in before i go to the races, and that was about a 75-80 pound loss of weight. The minimum weight is 1822 as i understand with a 1.6l and running wheels over 7" wide. I know the best way to do it is to go below that and add balast strategically to balance out the car and further lower the CG, but my only goal (for now) is to reach that minimum weight.

Here are the mods i've done to remove weight, i may forget some:

Removed all tow hooks

Removed all A/C 

Removed all airbag equipment and sensors

Bought new steering wheel (1.5 pounds lighter than stock w/o airbag) 

Removed most of the interior, including carpet, and repainted the interior light gray (in the process of painting, i started last night, 2nd coat just a few mins ago)

Removed some internal parts of the dashboard

Removed bumper plastic shock-absorbing inserts (kinda risky for street, but oh well)

Removed windshield fluid nossels and bottle

Removed one of the windshield wipers (made center one travel 180 degrees)

Removed plastic engine bottom cover and some other plastics

Fabricated (in the process) an exhaust pipe that I can swap during events that goes right to the header, just straight pipe with a downturn before the rear subframe.

Gutted doors 

Got rid of the pop-up headlights, in the process of installing 2 small (about 4.5 inch) round headlights in the bumper (saves about 14-15 pounds)

Removed trunk linings and metal cover

Bought a 6 pound battery to swap in before events.

Lightweight flywheel (13 pound loss)

Will install a kart seat, getting rid of passenger seat obviously

I know i'm forgetting some stuff. I have debated wether to remove the power steering or not, it is still installed (i've removed it before and didnt like it, I drove an STS2 miata at many events with a manual rack and i dislike it ). Especially with the 9 or 10" wide hoosier slicks i'll be running I dont think I want to take the power steering out. Any comments on this? If I do I think it's about 20 pounds.   I haven't touched the hood or trunk lid, i know there's some weight to be lost there with removing the bracing, but I dont want to have to do that. If I took the car to national events I could probably remove the top, which is about 35 pounds. But i'd really like to reach 1822 without having to take out the top or power steering. I dont really know how much the car weighs right now, it was 2120 (the car is a 1991 long-nose) with a rollbar and power steering before doing all the mods I listed. I just added up the weights of the stuff I removed and i'm getting about 1870-1880 total weight. When i'm done removing all I think i should remove, i'll take it to AIM Tuning and get it corner weighed.

Well i have to go to work now. Is there anything else you guys can think of that would help me remove some weight?

I'll try to post some pictures of the work-in progress tonight.

Btw, how much does a hoosier 22x10x13 c3000 slick weigh?

 

I thought min. weight was 1832#, 1757# plus 75# for wheels, but I could be wrong.  If I'm right, then your closer to your goal

I love my power steering!  I didn't have it at first and then was talked into putting it on the car.  That was the first thing I should have done when I bought the car! 

Love to see some pics.  And welcome to DP 

I'd recommend leaving the power steering in the car.  I started out with manual steering and ended up putting power steering back in my car.  (apparently a common theme with Prepared Miatas)

It doesn't sound like your car is all that streetable any more, but I know it's a big step to saw off the windshield frame.  FWIW - the windshield, frame, and remaining dash should add up to about 40 lbs.

A few other weight saving ideas:
Get a hard top and ditch the soft top (this is your single easiest way for major weight reduction)
drill the brake rotors
remove dust shields (if you haven't done so already)
remove hood & trunk bracing.  (it makes the hood a bit floppy, but you won't even notice the difference on the trunk)
lighter Wilwood brake calipers
aluminum-bodied shocks & shorter 5" or 6" springs

Good luck with the build!

 -Steve

Steve (well you're both steves...) you're right:    1597x1.1 = 1756.7   +  75 = 1831.7 or 1832     I guess I am closer than I thought!

I'd be more than willing to remove the windshield if I could, but I definitely cannot. The hardtop is $800 or so that could I otherwise dump in the engine build (maybe later). So I guess I'll be a few dozen pounds over, but that's ok. I was hoping there was a secret lead compartment in the miata housing 70 lbs of lead for no reason that only DP guys knew about, but i guess not, haha.

I'm gonna go give the interior/trunk a third coat and then I'll try to post some pics.

I guess my definition of streetable is different since i'm only 18 years old... 

Steve how much can i shave if I gut the hood and trunk?

This one is the Miata I drove at Nationals this year, it's Geoff Chamber's car and I co-drove with Jon Tak. 

Here's my car in my garage that I turned into paint-booth for the weekend... I'm doing 4 coats of DTM Alkyd.

http://www.we-todd-did-racing.com/files/1041003_qmt9x/DP%20prep%202.JPG

And here's the stuff I removed (some's going back in) getting flooded outside. Not a good day to paint. 

gripfreak89:

Steve how much can i shave if I gut the hood and trunk?

I believe I cut approx. 5 lbs out of the trunk, which included removing all but the perimeter support ribs, the trunk release, and the hinges.  Note:  I use 4 fairly heavy stainless steel pins to fasten the trunk down, so the savings would be a bit more with aluminum pins.  You could probably save close to 3 lbs by simply trimming out the supports.  Even gutted, the trunks are pretty heavy, as they're steel.  A lightweight carbon fiber trunk would save another 5-6 lbs, but IMHO isn't worth the expense unless you're made of money.

 I have an NB, so my hood weight savings really aren't applicable.  However, the NA has more to gain from hood lightening, if you eliminate the pop-up headlight mechanisms and get a hood that covers the openings, like this one: 
http://www.iscracing.net/miata_airdam.htm

If you just remove the hood bracing, you'll be lucky to save a couple lbs, as everything is aluminum.

-Steve

p.s.  Don't discount any unsprung weight reductions you can accomplish.  While things like drilled rotors, shorter springs, removing dust shields, etc. don't seem like big savings - they achieve weight savings that will more directly impact the car's performance, versus most modifications.  
 

I weighed some of the parts on my NA Miata and finally found the list!

Aluminum hood weighs 15# without hinges and light doors.  My fiberglass hood weighs 14#!!

Power steering pump, 11#.  Power steering rack weighs 2# more than a manual rack.  Windshield frame is 14#, glass is 18#. 

Steve G. is spot on, unsprung weight is bad.  Get the lightest wheels and shocks you can afford.

But the most important thing is to get the car running and then go have fun 

Feel free to contact me privately if you have questions.

Good stuff. So the power steering isnt as heavy as I thought, I bet it's like 15-16 more than manual rack with fluids.

Thanks for the tips.

Partial interior should be going back tomorrow, the oil-based paint takes time to fully cure. I might be back here once in a while with more ???'s or concerns, or just for the heck of it, and will post some more pics as I get stuff done.

I'm having fun already.

Well i planned to use the kart seat as the driver's seat and no passenger.

Also I was looking at the diamonds as my last resort if i cant find some used aluminum wheels.

I got the car back together yesterday and took it for a drive, i couldnt believe the difference the weight loss made in acceleration with my still stock STS2 (not for long) engine, and im not even at target weight, so it's only getting better. Lateral force, turn-in, and even braking were improved noticeably.

I think you may find a kart seat won't work so well with a rollbar.  You're going to find that things are a LOT more violent in a DP car, versus an STS2 car - and using a bolt-in bar designed to fit under the stock top puts it a lot closer to your head than the custom rollbars you'll typically find in a Prepared Miata.  When my car was in SM2 without a rollbar, I could get by with just a lap belt.  In XP trim with a cage, I use a full harness, just to keep from getting bruised up on the bars.

You may have a tough time finding 13" x 10" wide wheels used, as that is a pretty unusual size for Miatas.   Most of the CSP guys are running 13" x 8.5" or 13" x 9" wheels, and I believe most of the DP cars are running 13" x 7" or 15" x 7" with cantilevered slicks.  If you're interested in a good set of 13" x 8.5" 3-piece Panasports (awesome-looking wheels), here's a set available at a very reasonable price:  http://forum.mnautox.com/forums/showthread.php?t=8069

BTW - Hoosier lists a weight of 16lbs each for the 22.0 x 10.0 - 13's. 

gripfreak89:

Well i planned to use the kart seat as the driver's seat and no passenger.

Please don't use the kart seat.  Two reasons:  1) you will hate it.  A DP can be as violent a car to drive as any production based car in autocross.  You will likely find you are being thrown arround too much, and as Steve G noted, you will likely get beat up by the roll bar.  2) its very unsafe, despite the fact that a member of the SEB used Kart seats in his CSP Miata      Note that you really can't use a full harness with a kart seat.  Your upper body is left unrestrained which allows you to flop arround in the seat alot and that means bouncing off the roll bar. 

There is also another issue.  If you use a kart seat, and the SEB finds out about it, they will feel compelled to screw up the Prepared seat rules as badly as they have the Street Prepared seat rule.  I don't want them to do that.  

A proper race seat isn't that heavy so please use one.  You will keep us all safer that way.  

I agree with what everyone's said about the kart seats.  They really don't belong in anything other than a cart and since your car is remaining streetable, it really would be a danger on the street.  The wieght savings aren't worth getting yourself (or someone else) hurt.  Design your roll bar to use the minimal amount of tubing and be tidy with the welds.  I know I used about 20 pounds too much wire welding in my cage.

I think you'll find the DP folks are extremely supportive and helpful when it comes to questions.  We finished our car right before Nationals and had an absolute blast in Topeka.  I can't say that the Street Mod class was ever as much fun...

Kart seat. This is clearly my ignorance making you all worried. I used to race karts, so i had a perfectly fitting seat, the kart puts out more g force than the miata will and I find them comfortable.

However, I thought everybody in DP was using kart seats, I was clearly wrong. I have my own opinions about safety of the kart seat and safety of autox in general, but I dont want to start any drama/dicussions about it so I'll keep them to myself. For the sake of keeping all of you as friendly as you've been I'll just install the Kirkey I had for STS2.

I got my tires today. They're huge! 22 x 10-13  R35 C3000. From the research i'd done it seems like not too many people are running this size, but once they get some heat they should be excellent (I think).

 

gripfreak89:

However, I thought everybody in DP was using kart seats, I was clearly wrong. I have my own opinions about safety of the kart seat and safety of autox in general, but I dont want to start any drama/dicussions about it so I'll keep them to myself. For the sake of keeping all of you as friendly as you've been I'll just install the Kirkey I had for STS2.

1. Unlike karts, cars have a lot of metal parts above the top of the seat.  If you get thrown around in a kart, there's nothing for your head or upper body to hit.  However, there are all kinds of protruding bits in a Prepared car that can beat the heck out of you if you're in a low-backed seat.

2. I wouldn't even consider using a kart seat on the street.  Yes, a kart generates more lateral grip than a Prepared car, but an accident will generate FAR more g-forces than you'll ever see in a kart.   A race car seat is designed to handle the kind of violent forces generated by automotive accidents.  Kart seats aren't.