12-04-2014, 07:31 AM
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#1
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Registered User
Join Date: Oct 2014
Location: Fort Collins, Co.
Posts: 74
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Chassis stiffness
I realize that convertibles are inherently less stiff and that if stiffness is my number one concern then I should probably be in a Cayman but....
It is obvious to me by the noises and feel of the chassis that I am getting flex in my Boxster. Has anyone ever added anything effective that has stiffened up the body in the middle? I added the Schnell strut braces and if anything they made it worse.
I'm sure you track guys that have turned your Boxster into a race car have done something in this area.
Thanks.
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12-04-2014, 08:01 AM
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#2
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Registered User
Join Date: Sep 2013
Location: Chandler, AZ
Posts: 1,796
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I'd also be interested in feedback. One thing is for sure to me is that a hard top provides an extra layer a protection.
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03 Carrera
02 Boxster S Guards Red, black interior with matching hardtop
89 Carrera 4
89 944 S2
78 911SC
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12-04-2014, 08:09 AM
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#3
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Registered User
Join Date: Apr 2010
Location: Canada
Posts: 3,128
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I've heard folks say that the rear strut brace reduces the rattling a bit, but sounds like not working for you. really the race car solution is a roll cage.
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12-04-2014, 08:53 AM
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#4
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Registered User
Join Date: Apr 2010
Location: South Africa, Cape Town
Posts: 131
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I have carbon fibre strut braces front and rear, together with my zeintech hardtop and being lowered by about 30mm, I can say the car feels a lot stiffer than before these mods.
I am planing to build a carbon fibre shell that covers all the 'open' areas when my hardtop is removed with speedster humps, the idea is to build it structurally so that it stiffens the car up when clipped into position. This would be lighter than the zeintop and could possibly offer as much 'stiffness'
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de-snorkeled, clear lights, sports exhaust, zeintec hard top, zein wing, B&M short shifter, DesignTek lowering springs, DesignTek carbon fibre strut brace front and rear, 18'' carerra 5 spokes, semi slick tyres, entire soft top delete, engine cover delete,red console,L&N deep sump, volo performance chip, raptor shift light, de-cat'ed, OEM GT3 bucket seats.
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12-04-2014, 04:08 PM
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#5
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Registered User
Join Date: Dec 2008
Location: Queensland, Australia
Posts: 1,522
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Quote:
Originally Posted by bwillia080261
It is obvious to me by the noises and feel of the chassis that I am getting flex in my Boxster. Has anyone ever added anything effective that has stiffened up the body in the middle? I added the Schnell strut braces and if anything they made it worse.
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If you have added strut braces and you still feel the chassis need stiffening, then you have other problems....
The Boxster / Cayman platform is extremely stiff for a road car (just jack up a wheel and see), so more than likely you have worn suspension like shocks, springs, rubbers and bushes. Adding a strut brace to worn shocks will only exacerbate the problem.
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2001 Boxster S (triple black). Sleeping easier with LN Engineering/Flat 6 IMS upgrade, low temp thermostat & underspeed pulley.
2001 MV Agusta F4.
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12-04-2014, 08:45 PM
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#6
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Certified Boxster Addict
Join Date: Nov 2010
Location: Los Angeles
Posts: 7,669
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As good as the Boxster chassis is, it is no where close to the stiffness of the Cayman. It is amazing how much strength and stiffness that the roof structure adds.
Take a look at the Boxster chassis shown below - the middle of the car is basically the floor pan - that's it! In some ways, its amazing that the car doesn't simply fold in the middle. As such, there is only so much engineers can do to make the floor pan (a mostly flat panel) stiff.
The Cayman adds the roof which creates a very nice box-like structure to greatly improve chassis strength and stiffness.
A Boxster Spec race car achieves the same by using high strength steel tubes to build a box-like "cage" in the middle section of the car. This cage not only protects the driver in a crash, but adds substantial stiffness to the chassis.
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1999 996 C2 - sold - bought back - sold for more
1997 Spec Boxster BSR #254
1979 911 SC
POC Licensed DE/TT Instructor
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12-04-2014, 09:04 PM
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#7
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Registered User
Join Date: Dec 2013
Location: Greenville, S.C.
Posts: 2,670
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I have a hard top and a slipped drive into the garage that I take at a diagonal, this gives a fair amount of body stress and the lack of stiffness can be heard in the hard top. It creeks until the car settles on even ground. I think these cars fare pretty well as apposed to coupes made into convertibles like a crossfire or Zcar, but they do suffer from a lack of stiffness.
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12-05-2014, 06:28 AM
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#8
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On the slippery slope
Join Date: Mar 2014
Location: Austin and Palm Springs
Posts: 3,796
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Just drop a Viagra into the tank at every fill up
That will make the car plenty stiff when you give it a good workout
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2004 Boxster S 6 speed - DRL relay hack, Polaris AutoTop DIY
2004 996 Targa Tip
Instructor - San Diego region
2014 Porsche Performance Driving School
2020 BMW X3, 2013 Ram 1500, 2016 Cmax, 2004 F-150 "Big Red"
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12-05-2014, 06:36 AM
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#9
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Registered User
Join Date: Feb 2013
Location: Cranston RI
Posts: 902
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If you really want to experience "flex" you should have driven my 78 Fiat X 1/9! I have jacked up my Boxster and thought the car to be quite stiff and structurally sound.
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99 Porsche Boxster
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12-05-2014, 07:22 AM
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#10
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Registered User
Join Date: Oct 2014
Location: Fort Collins, Co.
Posts: 74
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Quote:
Originally Posted by JayG
Just drop a Viagra into the tank at every fill up
That will make the car plenty stiff when you give it a good workout
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LOL!!!
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12-05-2014, 08:40 AM
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#11
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Track rat
Join Date: Nov 2006
Location: Southern ID
Posts: 3,701
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As I understand it, the only way to address Boxster torsional flex is with a cage. Strut braces support areas of the car that are already quite stiff so don't add much. I still find the Boxster to be pretty stiff and precise compared to most cars. The only time flex becomes a real problem is when using very stiff springs so the torsional body flex becomes the new effective spring rate. The Cay is definitely stiffer and more precise though.
So many other areas of the car to derive performance before body flex becomes the low hanging fruit...
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2009 Cayman 2.9L PDK (with a few tweaks)
PCA-GPX Chief Driving Instructor-Ret.
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12-05-2014, 11:47 AM
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#12
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Registered User
Join Date: Oct 2014
Location: Fort Collins, Co.
Posts: 74
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Quote:
Originally Posted by thstone
As good as the Boxster chassis is, it is no where close to the stiffness of the Cayman. It is amazing how much strength and stiffness that the roof structure adds.
Take a look at the Boxster chassis shown below - the middle of the car is basically the floor pan - that's it! In some ways, its amazing that the car doesn't simply fold in the middle. As such, there is only so much engineers can do to make the floor pan (a mostly flat panel) stiff.
The Cayman adds the roof which creates a very nice box-like structure to greatly improve chassis strength and stiffness.
A Boxster Spec race car achieves the same by using high strength steel tubes to build a box-like "cage" in the middle section of the car. This cage not only protects the driver in a crash, but adds substantial stiffness to the chassis.
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Thanks for the awesome graphic! Love it.
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12-08-2014, 01:54 PM
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#13
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Registered User
Join Date: Feb 2013
Location: Land of naught
Posts: 1,302
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While it's true that there's much that can be more easily improved, stiffness IS the foundation with which all else rests. Can 'we' feel it as we enter or exit a corner or flow over a dip or bump? I think so. I test drove a 911 a while back and was surprised at the noticeable improvement- I went over some train tracks at 40 km and swear I could Feel the roof rails! Ever since I've been wondering how to improve the otherwise spectacular Boxster chassis. Those excellent pics don't show 2 major structures along either side of the floor. These are used when jacking the car up and/or for jack stands. Perhaps they could be fortified. Also I think adding an additional bar ( with triangulation) in the lower door openings perhaps 6-8" above the sill would be of the most benefit. Entering and exiting wouldn't suffer much- it's just the install--weld, bolt or bond?
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Death is certain, life is not.
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12-08-2014, 02:59 PM
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#14
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Track rat
Join Date: Nov 2006
Location: Southern ID
Posts: 3,701
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Quote:
Originally Posted by woodsman
While it's true that there's much that can be more easily improved, stiffness IS the foundation with which all else rests. Can 'we' feel it as we enter or exit a corner or flow over a dip or bump? I think so. I test drove a 911 a while back and was surprised at the noticeable improvement- I went over some train tracks at 40 km and swear I could Feel the roof rails! Ever since I've been wondering how to improve the otherwise spectacular Boxster chassis. Those excellent pics don't show 2 major structures along either side of the floor. These are used when jacking the car up and/or for jack stands. Perhaps they could be fortified. Also I think adding an additional bar ( with triangulation) in the lower door openings perhaps 6-8" above the sill would be of the most benefit. Entering and exiting wouldn't suffer much- it's just the install--weld, bolt or bond?
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A bolt-in cage might be the most cost-effective way to improve Boxster chassis stiffness. It also offers a lot more driver protection for motorsport. I favor a custom welded cage for safety but they are also a lot more $$$.
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2009 Cayman 2.9L PDK (with a few tweaks)
PCA-GPX Chief Driving Instructor-Ret.
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12-09-2014, 05:16 PM
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#15
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Registered User
Join Date: Aug 2004
Location: Alta Loma, CA
Posts: 1,334
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I have a chassis stiff kit we are testing and TomS? The cage is good.. but stress analysis told me to "add a tube". The first time I pitched a SPB into T1 with our extra tube? HUGE difference and 20+ deg. tire temp increase on the right front (at WSIR where the right side of the car is mostly on vacation) I won't share any pics.. but feel free to stop in and look at the cars
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Engine Builds, Transmission Builds, Engine Conversions, Suspension Installs, Suspension Tuning, Driver Coaching, Data Acquisition, Video, SCCA/PCA/POC/NASA/GRAND AM/ALMS.
We have worked with amateur and professional drivers for over 26 years. In house machinist, In house fabrication. Our cars, our parts, our engines, our transmission's run nationwide at events every weekend. We work side by side with industry names developing parts.
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12-09-2014, 06:09 PM
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#16
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Registered User
Join Date: Feb 2013
Location: Land of naught
Posts: 1,302
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Those of us that are street-bound need a solution that's works for us. Track cars need a cage for safety anyways but we want our soft top option intact. How about it Brad-- do you have a fix?
__________________
Death is certain, life is not.
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12-09-2014, 06:20 PM
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#17
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Registered User
Join Date: Feb 2013
Location: Land of naught
Posts: 1,302
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And lets not forget that as these cars age, the weakest areas are weakening!
-- if we could know the 2 points of the greatest flex ( cowl and rear bulkhead?) then we could fix 'em good and retain chassis integrity into the 2-300 000 mile range...
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Death is certain, life is not.
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12-09-2014, 06:56 PM
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#18
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Registered User
Join Date: Aug 2004
Location: Alta Loma, CA
Posts: 1,334
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I have a kit we are testing. It welds in under the stock carpet/pad/thing. It's multiple pieces and helps tie the center tunnel to the side rails and engine mount bulkhead.
It's very similar to what I developed with Engman for the 914 inner frame rails, but a lot more elaborate.
(Engman/Mark is no longer with us)
B
__________________
Engine Builds, Transmission Builds, Engine Conversions, Suspension Installs, Suspension Tuning, Driver Coaching, Data Acquisition, Video, SCCA/PCA/POC/NASA/GRAND AM/ALMS.
We have worked with amateur and professional drivers for over 26 years. In house machinist, In house fabrication. Our cars, our parts, our engines, our transmission's run nationwide at events every weekend. We work side by side with industry names developing parts.
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12-10-2014, 07:12 AM
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#19
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Registered User
Join Date: Oct 2014
Location: Fort Collins, Co.
Posts: 74
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Quote:
Originally Posted by Brad Roberts
I have a kit we are testing. It welds in under the stock carpet/pad/thing. It's multiple pieces and helps tie the center tunnel to the side rails and engine mount bulkhead.
It's very similar to what I developed with Engman for the 914 inner frame rails, but a lot more elaborate.
(Engman/Mark is no longer with us)
B
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Sounds promising and exactly the kind of solution I expected to hear. Keep us informed. Need a test car?
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12-10-2014, 07:42 AM
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#20
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Registered User
Join Date: Apr 2010
Location: Canada
Posts: 3,128
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