McLaren replica build base on a Manta

Terry Oxandale

Skinny Man
Sway bar install

I finally decided on a sway bar configuration for the project. I found a couple of sway bars that would fit (Porsche 911 rear bar was one that would fit almost perfectly), but not knowing exactly what I needed in terms of size, I'm not ready to use them. Because of limited sizes from donor-car bars, and not wanting to commit to custom bent bars (unless I knew exactly what I needed), I decided on a NASCAR style bar. They are cheap on Ebay, come in a multitude of sizes, and can provide an almost infinite range of stiffness with the long arms. I chose a medium-sized diameter of splines (1.25") (because of the long list of available diameters), and am using the standard 37.5" length. I was able to purchase a group of the smallest 4 bars on Ebay for real cheap (new), so the only thing left to do was install them. Again, my chassis does not lend well to the addition of yet another piece of equipment in an already very cramped space under the bodywork.

These bars can use a tubular housing, which I chose to insert in place of the existing rear bulkhead crossbar over the transaxle. Thus the bar's housing in essence is a part of the framing. I removed the existing brace, modified the posts that hold the cross-bar, and then machined and welded all the aluminum parts needed to bolt the sway bar housing back in place.

Existing cross-bar:
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After the top of both posts was cut off, I inserted a machined piece of aluminum into the ends (drill press and carbide tipped hole saws make a poor man's milling machine):
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Drill and tap threads to fix plates into each post:
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Then weld saddles (2" square tubing) onto the top of each plate that will hold the bar's housing in place. I welded a long piece in place, and then cut the ends off after it was all done to ensure they were aligned with each other:
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The housing in place, but not yet welded to the saddles. Plastic bushings slide into each end, and then the sway bar slides into the bushings, with shaft collars on each side to hold the bar and bushings in place:
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Completed housing/bulkhead cross-bar:
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With bar installed:
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Looks good mate, will the arms point forward or back? and I guessing a link to the bottom of the upright.

Cheers Leon.
 

Terry Oxandale

Skinny Man
Looks good mate, will the arms point forward or back? and I guessing a link to the bottom of the upright.

Cheers Leon.

Arms will point rearward to the rear part of the upright. I had thought about a lower CG option by placing this behind and under the tail of the transaxle, but the chassis framing in that area was just not robust enough to limit twisting to the bar itself, and increased polar moment was another thought.
 
I love that "Polar Moment" Thinking like a real McLaren man. It is pretty much how the M8s have their sway bars

cheers Leon
 
Terry,

If I understand it, you used aluminum for the sway bar? If that is correct, be aware that aluminum has a much shorter fatigue life than steel. Classic documented example; Porsche built a tubular aluminum space frame for one of its racecars. During the first season the tubes began to crack, so Porsche pressurized the tubular space frame with nitrogen and mounted a pressure gage on the dash to get them through the season. The driver was instructed to return immediately to the pits when the pressure gage dropped. That got them through the race season and they no longer use aluminum space frames. Just so you know.

Best regards,

CJR
 
Terry,

That got them through the race season and they no longer use aluminum space frames.

CJR

Are you sure ??????????????????????????????????????????????????

Porsche Have built a lot of different models with aluminium chassis tubes for years ?
From 1968 to 1971 They built some 908 /02 and 908/03 with aluminium and did not suffer any crack ; then they decided to go onto the very powerfull 917 and all chassis where built with aluminium tubes ; That gauge was there only if there was a big spin and a crash so they could understand if the chassis was or not damaged ?
They also built the 917/10 series for Canam again with 1000 Hp ! and 917/20 and 917/30 driven succesfully by Mark Donohue with more than 1200 HP !!!!
In 1976/77/78/79 Porsche on basis of 908 and 917 drawings built the long serie of 936 with water turbo engines and they win lemans twice with these aluminium Chassis !!!!!!
One modern team in 1980 built a sort of 917 K ( for Kremer ) .. amodern 917 and again they decided to go like in the 70's with and aluminum chassis !!!!

When GR5 "silhouette" rules appear in 1976 Porsche decided to built the 935 ; thes e have been built with a 911 chassis but front and rear frames where only welded aluminium tubular Chassis and the engine was 750 HP !!!
A very long serie of these car where built ( some at Kremer Or Jost where built with complete Aluminium welded tubular chassis ) !!!!!

Beside these stories it's exact that using aluminium is something to be carefull on where this material is used and what kind of material is used
There are 2 sort of ; one ( AG3Mc) weldable but soft and not advisable and one(AU4G) very stiff that can be only drilled and machined ( no bends , no welds )

In fact watching at Terry pics I can notice that the sway bar is steel ?? it's the black part splined to receive arms . the only part in aluminium is the tubular housing welded on brackets ?
So I don't see any possible issue with those !
Seems to be a nice set up .....
Keep up your good work ....Terry

If you are not sure of what torque you have to choice the sawy bar you can have one of the arm done in 5130 tube welded on a splined female busch and then have some sliding rod attached to that tube and linked to the suspension ?
You can have too ( but pricy ) some blades done machined in V300 steel that yo can turn
more or less to soften one side of your sway bar ?
Eventually I can draw for you some similar part ?
 
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Terry Oxandale

Skinny Man
Thanks for the feedback guys. The bar is steel, but the housing is aluminum. I've got 4 bars of progressive sizing to allow me to do a lot of experimenting before choosing a permanent hollow bar(s), as well as allowing me to shave some amount of material off of the overly large and thick (19mm x 42mm) aluminum arms for the sway bars. I've done the same thing to the front of the car, so now I'm ready to make and install the links. Then perhaps get it on a track to push the limits a bit and dial it in. I'm going to start off with some settings similar to what some of the members here are using for their projects, and work from there, with the larger one up front, and a fairly soft in the rear.
 

Terry Oxandale

Skinny Man
Well, I feel a little better, because the pre-swaybar existing X-bracing that I was using to improve rigidity in the rear half of the chassis, was just now fabricated and installed...out of aluminum tubing. Yes, I'm finally feeling pretty good about welding aluminum.

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Yes Terry
Very nice arrangement !!
You know there are mathematics formulas to evaluate swaybars but as usual it will be quicker to do like you plan instade to start pages and pages of sophisticated calculation to then understand that track test is always necessary !!! LOL
 
Michel,

Pg.90, "Race Car Chassis Design and Construction", by Forbes Aird, documents Porsche's experience with aluminum space frame cracking as I described it.

Best regards,

CJR
 
CJR
Ok you're right ; cancel all what I wrote , apologise !

so now let us come back to Terry original thread ....
"hacking" other's thread is not my cup of tea

Terry your rear alu tube rinforcement start to be very nice !
 

Terry Oxandale

Skinny Man
Arms installed with links. They are a bit bulky, so I'm looking at where they can be milled down to cut some weight, yet still be strong enough to do the job.

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Randy V

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Looking really good Terry..
Had you considered bolting the heim joint in shear directly to the arms? While I wouldn't do it that way on a truck, it is done that way on many of the racing cars I've worked on over the years. It would reduce some of the unsprung weight as well as some of the bulky appearance.
 
Looks good Terry,
I agree with Randy re the method of mounting for simplicity, not so concerned with the weight. Once you have found the ideal rates you may find you never need the last few holes on the arms so could simply remove the unneeded ends, this would reduce the bulky look you are concerned with.
Should have that pontoon and tanks done for you next week, not that I'm feeling any pressure
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Cheers Leon.
 

Terry Oxandale

Skinny Man
I had considered the single shear, but I don't have experience in aluminum arms. These are huge, and I'm planning on milling them down once I find a length-range that works. I didn't know if the single shear, with its off-axis forces, would be an issue when I fabbed all this up. Since then, I've inserted one of these arms in a press, and using a very large Crescent wrench, tried to twist the aluminum arm with all my weight. It didn't budge, so I will definitely be looking into the single shear linking on these arms. Doing this would greatly simplify adjustments, and a 3/8" grade 8 bolt should work just fine, especially through a 3/4" thick arm. Thanks for the feedback!
 
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Terry Oxandale

Skinny Man
Leon, Randy,

Your comments had a positive affect on the rear bar. I like this much better. Can't beat simplicity. Drilled out the 1/4" holes to 3/8", and mounted them right up. My unfounded fear was an overwhelming twisting force on the arm, but these things are pretty beefy.

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