Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 911 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Registered User
 
Randy Webb's Avatar
 
Join Date: Nov 2002
Location: Planet Eugene
Posts: 4,348
Black Beauty revisited

Hi Jack and Tyson,

I was trolling thru the BB2 threads again and some thoughts came to mind:

Any data on how many degrees of torsional twist on BB2 after the
chassis mods? And do you know how much a stock car has?
-- How much of that is due to the roll cage as vs. the R. shock tower reinforcements?

Some have claimed that a complete strut is needed to tie R. shock
towers together instead of the triangular reinforcements used. Is that not needed with the roll cage? Or do you just disagree with that?

Do you think either type of reinforcement would be noticable on a
street/DE car with no roll cage and stock tire widths?

The engine does not have variocam - is that right? Were any mods made to the engine for lower wt. or increased power?

The F. suspension has the JRZ sturts operating on the stock steel
A-arms? No erp/935 style F. A-arms?

How much wt. did the MG case on the 915 tranny save?

Thanks again for telling the story of this very interesting car!

Old 01-27-2004, 09:42 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Administrator
 
Jack Olsen's Avatar
 
Join Date: Feb 2000
Location: Los Angeles
Posts: 13,203
I can't answer about torsional rigidity. Hopefully Tyson will see this, and correct my errors.

The engine is a stock 1993 964 motor. Stock hp is 247. The only mods are the B&B exhaust and the NBD chip.

The front A-arms have been lengthened by about 1 1/3 inches. The mounting points have also been changed, also.

According to a recent post by Bill Verburg, the mag case 915 weighs 95 pounds (27 less than aluminum). I also have a limited slip, cooler, and some other internal widgets that add to this figure.
Old 01-27-2004, 10:56 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
PRO Motorsports
 
Tyson Schmidt's Avatar
 
Join Date: Nov 2001
Location: Burbank, CA
Posts: 4,404
Randy, I really don't think you'd ever notice the rear shock tower reinforcements. They're really there for strength and long-term durability. I know many guys who have rear coil-overs with no reinforcement whatsoever, with 550# springs or more, who've been tracking their cars extensively with no problems.
The truth is, it's the stiff shocks that cause the super high loads that are transmitted into the shock towers, not the springs. And the rear shock towers do not carry any forces from lateral G's, just jounce and rebound. It's the rear torque tube that takes all the cornering forces transmitted into the spring plates and control arms. That tube's structural integrity is extremely important.

As far as torsional stiffness, it would take a jig and some method of twisting the chassis with a given lever arm by a certain amount of weight, and movement measured with a dial gauge to determine torsional stiffness. Not really something that anyone is going to bother measuring. I don't know if Porsche has ever published these numbers for a stock 911 coupe.

The cage definitely helps. The shock tower braces aren't really for torsional stiffness. (Like mentioned above) But I tied the center tunnel in with the torque tube, and added diagonal braces between the inner rockers and the center tunnel, which no doubt help as well. But their primary function is for stiffening up the rear suspension pick-up points to minimize rear suspension geometry changes during high G-loads.

The triangular rear shock tower braces versus the tube tying them together? Well, that all depends on how stiff the spring/shock combo is, how much grip the car has, how much torque the drivetrain is putting to the ground, and how heavy the car is. We really aren't in that realm yet. I don't think Jack is ever planning on installing racing slicks, and a 750 HP turbo engine into his car. But that could change!
__________________
'69 911E coupe' 2.7E MFI (retired 911-Spec racer)
'72 911T Targa (Formerly "Scruffy")
2004 GT3
Old 01-27-2004, 11:23 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Randy Webb's Avatar
 
Join Date: Nov 2002
Location: Planet Eugene
Posts: 4,348
Thanks guys -- I know some have measure a tub's rigidity by gravity, with a corner tied down and the other corner left to "twist" but I'm not sure where I saw that. It was in a book tho, not a web site.

Let me try a modified question -- Jack has several times pointed out that modern rubber is a lot stickier than the old 70's stuff. Which of the suspension and chassis mods would you do on a car that ran regular width wheels -- 7"?
Old 01-28-2004, 11:53 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
Administrator
 
Jack Olsen's Avatar
 
Join Date: Feb 2000
Location: Los Angeles
Posts: 13,203
That's a good question. I assume this would be for a narrow body car. For the best recipe, I'd look at how the less-regulated vintage cars are setting themselves up. I know different groups allow different amounts of latitude with mods. The least-strict ones would probably have the best ideas.

Then again, Tyson can probably answer this pretty easily. He sets up all kinds of 911's.
Old 01-28-2004, 12:03 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
PRO Motorsports
 
Tyson Schmidt's Avatar
 
Join Date: Nov 2001
Location: Burbank, CA
Posts: 4,404
Randy, tell me what you've done to the car so far, and what you plan for the suspension and drive train.
__________________
'69 911E coupe' 2.7E MFI (retired 911-Spec racer)
'72 911T Targa (Formerly "Scruffy")
2004 GT3
Old 01-28-2004, 12:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: Aug 2002
Location: Galivants Ferry, SC
Posts: 10,551
Can I take a stab at this ???

For a dual-puprose car, I think a shock tower brace ( by itself) is of some...but little value. Why? Because severe side loading will :
-- compress the lower A-arm suspension bushings, if still rubber.
-- compress the upper shock mount bushings, if still rubber.

And the shock brace ties the *metal* shock towers together. See the picture? I think Chuck Mooreland even has a nice animated video he posted here.

To get fat ( or even *any*) tire to stick well at whatever suspension settings you choose ( always a compromise), maybe the best bet is to first go with non-compliant A-arm bushings ( Properly machined poly or polybronze), combined with a monoball top side for the shocks. Then...even later...go with a triangulated shock truss bar to tie the two pieces together..but now you're going for "finer cuts" on where the problem is, because the whole front suspension has more predictable geometry under load.

IMHO....

Wil Ferch
__________________
Wil Ferch
85 Carrera ( gone, but not forgotten )
Old 01-30-2004, 02:44 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
PRO Motorsports
 
Tyson Schmidt's Avatar
 
Join Date: Nov 2001
Location: Burbank, CA
Posts: 4,404
Quote:
Originally posted by Wil Ferch
Can I take a stab at this ???

For a dual-puprose car, I think a shock tower brace ( by itself) is of some...but little value. Why? Because severe side loading will :
-- compress the lower A-arm suspension bushings, if still rubber.
-- compress the upper shock mount bushings, if still rubber.

And the shock brace ties the *metal* shock towers together. See the picture? I think Chuck Mooreland even has a nice animated video he posted here.

To get fat ( or even *any*) tire to stick well at whatever suspension settings you choose ( always a compromise), maybe the best bet is to first go with non-compliant A-arm bushings ( Properly machined poly or polybronze), combined with a monoball top side for the shocks. Then...even later...go with a triangulated shock truss bar to tie the two pieces together..but now you're going for "finer cuts" on where the problem is, because the whole front suspension has more predictable geometry under load.

IMHO....

Wil Ferch
Wil, just wanted to point out that we're talking about the "rear" shock tower reinforcements here in regard to using coilovers. Not sure if you were aware of that.

But I agree about the front end, with exception to Cabs and Targas, which benefit from a strut brace by the chassis stiffening effect it provides.
__________________
'69 911E coupe' 2.7E MFI (retired 911-Spec racer)
'72 911T Targa (Formerly "Scruffy")
2004 GT3
Old 01-30-2004, 07:02 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #8 (permalink)
Registered User
 
Randy Webb's Avatar
 
Join Date: Nov 2002
Location: Planet Eugene
Posts: 4,348
Tyson -- It'sa 1973 with a hotrodded 3.2L engine (250hp on the engine dyno with a ruler flat torque curve using SSis, Monty, PMO carbs, and various tricks to the valve train). Suspension/brakes all from a Carrera (various cars actually). I've replaced all the suspensin bushings with new rubber (nothing stiffer). It does have a strut brace in front -- there was one lying around so I put it in. It has a sunffor, which I'm keeping. I plan to put a 901 tranny in, and remove the rear seats and fire wall undercoating and put in new, lighter undercoat on the fire wall. I may go with CF or FG rear bumpers and deck lid. Basically, I am trying to lighten it up a bit while wtill keeping it a good street cruiser/GT and that's the intended use -- maybe some DE's but no racing.

Thx. - Randy

Old 01-30-2004, 10:00 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #9 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 06:08 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2020 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.