Ted Brewer

PCA has just made the decision to outlaw from Club Racing the current DAS Sport rollbar for 996s and is presently evaluating the DAS 993 rollbar. No decision has been made either way as of this writting. PCAs concern relates to bolt sheer risk especially where the bar bolts down near the floor.
This must be a difficult decision for PCA since this is a popular rollbar amongst Stock D class 993 racers. My questions for all are, how many of you would be impacted if PCA outlawed this bar and what bar would you go to as an alternative (that is PCA legal)?

Thanks.

Ted

DJF1

I have the Autopower Roll Bar on my D stock. It looks very secure, much better than the DAS because it mounts on the side and floor as well...
I feel safer with this bar.

Karl S

As I understand it, the issue is that the DAS bar (and the Tequipment bar BTW) don't have any support for the foot of the bar. It sits on the floor pan, which isn't that sturdy. The concern is that in a rollover, the bolt will shear and the foot of the bar will puncture the floor pan, collapsing the bar. Apparently the older bolt-in bars were designed to sit on the frame rail rather than the floor pan but this is not possible in the 996.

I think the only acceptable bar will be one that has some sort of steel plate on the foot and bolts through the floor pan to another metal reinforcing plate on the other side of the pan. This is actually how the GT3 Club Sport roll cage is designed to be installed.

Karl

Dick Dobson

I'm guessing you have seen the latest CRN about these bars? If not check it out on the PCA Club Race web site.

Dick

Flying Finn

Idea for DAS:

Why not make plates to the end of the pipes (under the bolt) so that the bar would rest on the floor and be bolted to the seat belt mounts?

Ted Brewer

Dick and FF:

Yes, I have read the latest CRN. I also have a dialogue going with the PCA Tech Stewards as well as Bill and Collin Dougherty. At this time, no decisions have been made regarding the 993 application.

FF, your idea makes sense to me if it is really needed. I have never heard of a real instance where a DAS bar punched through the floor. That said, the PCA folks must know a lot more about actual roll results than I do.

Ted

Anir

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Silver Bullet:
<strong>In a 993, the hoop is attached to a cross bar that is bolted to the seat belt "reel" mounting point. I'm trying to figure out how it would be possible for anything to punch through the floor in this case.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Kim,

I was wondering the same thing.

<img src="http://boards.rennlist.com/upload/DASbarbwebb.jpg" alt=" - " />

The DAS bar has been criticized, perhaps correctly, for the relatively small mounting bolts used at the rear connections to the rear seatback holes. If I were PCA Club Racing, I would probably choose a fully welded-in cage.

Carrera51

A 911 Carrera (87 I think) rolled at a drivers ed last fall at VIR. The car was equiped with a DAS roll bar and it did its job. Didn't punch through the floor or sheer the bolts.

Bill Gregory

The DAS bar on a pre-89 911 rides on the sill for it's feet and has the same last rear bolt arrangement. The 964/993's are as pictured above, where the "feet" actually attach to the seat belt spool bolt in the body, out of sight under the trim, and has the same rear bolts as the pre-89 version. I've used both....

Joe@Fabspeed

Its a bogus rule change.......bolt-in rollbars are sufficient and strong enough. You can use 12 ponit aircraft quality bolts over 250,000psi and nothing will break them nor will the body fail at the rear seat belt or lapbelt attachment points as these are multiple welded reinforced highstrenght sheetmetal attachment points. Some of the welded in cages with redundant poorly placed tubes near a drivers head will easily and quickly kill versus a robust bolted in rear hoop.

Same controversial crap as the SA helmet versus M helmet for DE. You dont need a Winston CUP cage for clubracing.

DanO

993 RS Clubsport,

I'm with on that one. The single shear of a 3/8"-24 bolt is 10050lbs. If 20100lbs of shear strength isn't enough for the PCA tech guys, upgrade to NAS aircraft titanium grade 8+ bolts.

Aaron Pfadt

I'm with you guys (993 RS Clubsport and DanO) on this one. There must not be any engineers in operation over there in PCA tech world right now. I suggest you send a note to Lance Weeks expressing how you feel on this one. LWeeksPors@aol.com

Oh, I believe that most seat belt mounting bolts are 7/16-20 which makes the shear numbers even higher. 13,600 lb to yield (not failure) in shear on a single grade 8 (SAE) bolt.

"Consequently, only the horizontal bolt into the seat belt mount secures these roll bars - not very reassuring and certainly not safe in a rollover" - Donna Amico, CRN March/April 2003, Page 7.

save the children ;-),
Aaron Pfadt, BSME (actual engineer)
'73 911S w/welded in bar

Joe@Fabspeed

Hi Aaron Pfadt........SAE grade 8 bolts are rated to 150,000psi. I hope there are engineer racers like yourself out there that can shed some light............there are many many clubracers whos cars will be removed from clubracing due to NEW RULE CHANGE which is "safety overzealousness not matching up with engineering reality". Bolted in rollbars are perfectly safe and if clubracers have to buy NAS hardware to upgrade and satisfy PCA Clubracing then that should be an option.

All Porsches use big 7/16" bolts for the rear seat belt bolts and seatbelt anchors that are at your hip-bone. What kind of ACCEPTABLE shear in pounds/KG would you have if PCA Club Racing had a SPECIFIED NAS Milspec bolt.

There are many sources for super strong bolts listed with AN (army/navy) MS (military Specification) NAS (national aerospace standard)surnames. I went to a hardware specialist and put in NAS external wrenching 12 points with washers and he showed be the appropriate engineering data and they were rated if my memory serves me correctly to withstand over 200,000psi.

Given that the multiple hi-strenght steel welded triangulated panels that comprise the seatbelt anchoring points areas in these 911s/964s/993s/996s........these are areas that are never ever going to fail and super quality NAS bolts arent going to fail! We dont need a rule change to sideline several 100 PCA clubracers. Ill have to drop out and buy a GT3 Cup car if this mess goes awry.

Skip Wolfe

993 RS Clubsport

The bolts that are being used would be grade 8.8 and not grade 8 which is for SAE. Also the 150,000 psi is for tensile strength and not yield strength. And since the mode of failure would be in shear, we need to look at the the yield strength in shear of a bolt, which is equal to 50% of the yield strength.

Yield strength of a grade 8.8 bolt = 95,726 psi

Yield stength in shear = 1/2*95,726 = 47,863 psi

Shear stress = Force/area
Force = shear stress*area

So for a bolt with a 7/16" shank

Force = 47,863 psi*0.15 in2 = 7,195 lbs per bolt

Geo

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Skip Wolfe:
<strong>So for a bolt with a 7/16" shank

Force = 47,863 psi*0.15 in2 = 7,195 lbs per bolt</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Anyone want to risk their life to that? I don't have a clue what these cars could weigh, but even if you assume an ultra light 2,000 lb car, these would barely cover a 3.5 G force.

Also, the implication being made by saying "per bolt" is that you can somehow add up the numbers per bolt. Perhaps with certain impacts that evenly distribute stresses to more than one bolt, but such is seldom the case with a racing accident.

I think those of you who think bolting a cage or bar to a seltbelt mounting point is adequate are way off base. Start thinking forces of 30-75 Gs and then you are in the right ballpark. Welded cages have been known to be ripped out of cars, let alone those bolted to seltbelt mounting points. We don't protect against the odds in motorsports, we protect against the severity of an incident.

If you really want to take up a noble crusade, rail against the recent SFI recommendation for belt webing replacement every two years. It's a scam. It's based of 35+ year old tests of fibers that aren't even used in racing belts under conditions they won't be subjected to. It's truly outrageous. SFI is supported and more or less run by the manufacturers in the safety industry. This is just a not so clever attempt to sell more belts.