121 replies to this topic

[Alberto]

When one's moral conscience is altered with beer, it still don't make them holes in the trunk bracing legal. 

 

Actually, where is the rule for that?  Just went through the GCR and didn't find anything.

 

Otherwise, I guess I'll fill the holes with titanium plugs - after I get a sponsor ship 

 

 

 

misspelling was intentional... 

[Alberto]

So, I removed the dashboard over the weekend to see what lurked behind that I could remove.  

 

The dash skin itself is very light.  Not much to gain there.  There was an odd small metal plate on the back of the dash skin near the passenger side that I removed.  Maybe 1 lb at most.  Popped out the remaining eye ball vents while I was there.  The only fasteners holding the dash in place was the 4 for the instrument cluster and 2 holding the center console to the metal structure behind it.  Hopefully, it stays in place when I reinstall it.

 

Behind the dash, you can find some scary looking snakes of wiring bundles.  There is no way in hell that a hack like me could pare the harness and remove the airbag wiring w/o screwing something up.  Ain't touching that.

 

Apparently TC Design removed all the ducting when they installed their dash bar.  Thankfully, I've never had to use the heater controls and the heater box is bypassed anyway so it wouldn't have done much.  I guess it would be nice to have the ducts in place but oh well.  Dave would not approve of the bar location btw.

 

The big, black, heavy noise padding stuff that Dave mentioned in the Spec Miata constructors manual was removed when I first took the car apart for the cage.  

 

I think the only locations I have left to lose some weight is to cut some more ounces maybe 1-2 pounds max out of the doors and remove the big rubber gasket between the hardtop and the body.  I understand that weighs 1-2 lbs.  

 

Also, I finally upgraded my 8 year old suit to a nice lightweight Sparco (yea Black Friday sale) so I'll save a couple of pounds there.

I can switch to some lightweight oils too....

[Bench Racer]

So, I removed the dashboard over the weekend to see what lurked behind that I could remove.  

 

Behind the dash, you can find some scary looking snakes of wiring bundles.  There is no way in hell that a hack like me could pare the harness and remove the airbag wiring w/o screwing something up.  Ain't touching that.

 

 Thankfully, I've never had to use the heater controls and the heater box is bypassed anyway so it wouldn't have done much.  

 

I think the only locations I have left to lose some weight is to cut some more ounces maybe 1-2 pounds max out of the doors and remove the big rubber gasket between the hardtop and the body.  I understand that weighs 1-2 lbs.  

IMHJ, hacking the under dash wiring harness would be illegal. The under dash wires for the airbag have no separate number as compared to the number you would use to reorder the under dash wiring harness. 

 

By heater box, do you mean heater core? Either way if the heater core is bypassed, illegally poke a hole in the heater core and allow the liquid to drain.

 

Maybe asked and answered, have you removed the triple thick metal at the door top from rear of door to the vent window support.. May folks including Mr. Wheeler remove it.

 

I back tracked, wall thickness .120 wall x what diameter? And compare to .095 x 1.5 O.D. by say 80 feet of tubing. I forgot how many feet I used to build my 2020 pound 1990 with .095 x 1.5 wall tubing. and I have approx. 14 feet more tubing than minimum required. 

[dstevens]

Like Benchy says your cage may be a bit heavy.  My bending software says I used 71' @ 106# 1.5x.095 DOM.  Using 80' as an example a 1.5 x.120 DOM cage would be 141#, .095 would be 114#.  If you wanted to save more weight you could buck up to 4130 (chrome-moly) and use smaller tubing, 1.375x.095 it would bring it to about 104#.  That extra 10# between 4130 and .095 DOM comes at a cost.  4130 is 2-3 times the cost of DOM, at least where I buy it.  Best practice on welding 4130 would be TIG, (slower, more labor) but it could be welded with MIG though that's another discussion.

 

Bottom line, if you could do the work it would cost about a grand for a DOM kit to lose roughly 27#.  It doesn't look like you weld so it may be another grand or so depending on your area.  If you wanted those extra 10# it may be another couple grand on top of that as I don't know of any 4130 Spec Miata kits.

[Bench Racer]

If you wanted to save more weight you could buck up to 4130 (chrome-moly) and use smaller tubing, 1.375x.095 it would bring it to about 104#.  

 

Logbook earlier than 2007, alloy steel 1.375 x .095 for 1500-2500 lbs.

 

Logbook issued after 2008, alloy steel 1.375 x .095 for weight up to 1700 lbs.

 

 

[davew]

I do not have time to find it, IIRC all SM's are required to run 0.095 x 1.500 roll cage. There is no difference in size requirements for Chrome-moly tubing. Plus it takes special procedures and welding techniques to do it properly.

 

We all get away with clipping off some unused wire, but modifying the wire harness is specificly not allowed.

[dstevens]

Benchy is right, I looked at the wrong dates but the bulk of the weight is going from .120 to .095 DOM.  It's non trivial at about 1/3# a ft.  But it's still a couple grand or better to change the cage if you can't do the fab.  We're basically a Brownsburg or Charlotte of large pro desert racing teams and a bunch of recreational offroad so everyone and their dog has either a small shop/team or a garage operation that does fab.   You can get a kit installed and welded pretty inexpensively around here but he probably isn't going to be as lucky in the Bay Area.

 

As for 4130 if you are doing .120 wall and under, no pre heat or stress relief involved.  Most don't even back purge.  It's straight ahead DC TIG.  The applications I see around here are mostly suspension components.  Only the high buck cars and buggies are built with 4130. The deal with high carbon steels is you have to control the heat application more precisely.  Back 4-5 years ago I got certification training from an AWS affiliated local college and Lincoln has an excellent motorsport specific program.  Back then the Lincoln program was cheap but we had to stay in Cleveland for a week in the winter.      

[Alberto]

I definitely won't be re-doing my cage but useful info about cage weight that would be helpful to people adding a cage to a new car.  I wish I had known to ask about that when the cage was going in.

 

Bench - I did indeed remove one of the three layers of sheet metal at the top of the doors.  That was worth 2.5 lbs per door.  I may remove the second layer as well.  I'm reluctant to remove too much from the door making it flimsy.  I lean on the open door often when I need to get in or out of the car when loading it on the trailer so I need some structure there.

 

 

We all get away with clipping off some unused wire, but modifying the wire harness is specificly not allowed.

 

FWIW, I found a bunch of old threads (esp on the old specmiata.com site) where some people included wiring in their interpretation of "Air bag systems".

As written in the GCR on p.772:

 

c. Air bag systems shall be disarmed and may be removed.

[Mark]

That gasket between the hardtop and the body needs to remain in place. Nothing in the gcr says that it can be removed and I believe it has been the target of tech inspections at a few of the races this year. If this is not the case please correct me so I can take ours off the cars

 

Mark

[davew]

Mark, you are correct it is not allowed to remove the w/s to roof gasket.

 

It has been determined that modifying the wire harness is not legal. Remember the old specmiata.com site has been dead for many years (about 8 IIRC). Lots has changed since then

 

Dave

[Johnny D]

[Bench Racer]

[Alberto]

Mark, you are correct it is not allowed to remove the w/s to roof gasket.

 

It has been determined that modifying the wire harness is not legal. Remember the old specmiata.com site has been dead for many years (about 8 IIRC). Lots has changed since then

 

Dave

 

Glad I asked this time  Saved me some work.  

May I ask what the rationale for that is?  

[Bench Racer]

I do not have time to find it, IIRC all SM's are required to run 0.095 x 1.500 roll cage.

Logbook issued 2008 and after 2008:

 

F. TUBING 1. Seamless or DOM mild steel tubing (SAE 1020 or 1025 recommended) or alloy steel tubing (SAE 4130 or T45) must be used for all roll cage structures. Alloy and mild steel tubing may not be mixed. ERW tubing is not allowed.

 

2. The following table shows the minimum allowed tubing outer diameter and wall thickness by vehicle weight:

 

GCR Vehicle Weight, Up to 1700 lbs. Tubing Size (inches) (outer diameter x wall thickness) 1.375 x .080

GCR Vehicle Weight, 1701 - 2699 lbs. Tubing Size (inches) (outer diameter x wall thickness) 1.500 x .095 1.625 x .080

 

Logbook issued 2007 and earlier:

 

Vehicle Weight Material Without Driver     Mild Steel             Alloy Steel

1500-2500 lbs.                                         1.50 x .095             1.375 x .095

[davew]

From what I found in a quick google search

 

1.5 x 0.095 mild steel is 1.426 pounds per foot. Using 60 feet of tubing that would weigh 85.56 pounds

1.375 x 0.095 chromoly weighs 1.299 pounds per foot or 77.94 pounds for the same 60 feet.

 

Savings of less than 8 pounds. Chromoly is stronger and heavier, but you used to be able to use thinner/smaller tubing which netted a weight savings. BUT, it costs a lot more.

 

FYI the 1.625 x 0.080 weighs 1.319 per foot

[Ron Alan]

Glad I asked this time  Saved me some work.  

May I ask what the rationale for that is?  

Same reason we dont take out the heater core or fan?!! I you look close in the paddock you will find some that have removed the gasket piece out of the hard top and or created a gap by some means between the hardtop and the car...reduces drag(and not legal)!

[Johnny D]

I guess you can't do it in SSM (IDK, interesting to find out) but you could go up on weight (in class) if you went .010 over bore on the engine.

 

J~

[Alberto]

Same reason we dont take out the heater core or fan?!! I you look close in the paddock you will find some that have removed the gasket piece out of the hard top and or created a gap by some means between the hardtop and the car...reduces drag(and not legal)!

 

Didn't think about aero/drag.  I get it now.

heater core and fan are not related to aero though

[Johnny D]

I assuming if you can remove your brake handle (which you don't want to) you could lighten it.

just saying.

 

J~

[Alberto]

yeah, i know but it makes it harder to drift w/o the e-brake.

 

 wait...

wrong car