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#1072479 - 11/15/21 12:34 AM Re: Front sway bar project [Re: mmc427ss]  
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Have looked at several bar rate calculators to determine bar arm length and bar OD and length to compare combo of parts used.
This one from Fred Puhn:
http://www.gtsparkplugs.com/Sway-Bar-Calculator.html

Another:
http://users.erols.com/dmapes/SWBRCLC.HTM

And Speedway's chart showing rates:
http://1speedway.com/index.php?route=information/information&information_id=18

Lance, where did you get the rate info on your combo?

I lean toward the tube and bar inside the tube mounting of the bar:
https://www.gearheadzproducts.com/howeta2swaybartube.aspx

Two bar mountings done:
https://www.jefflilly.com/build-tips/nascar-sway-bar/

This one a video of fitting the sway bars arms to his unusual build.
https://www.youtube.com/watch?v=aE5FmcaUjW0

If you have nothing to do and want to see how a guy in his garage can do some of the true builder projects he's well worth checking out.
In episode 1 is his introduction to what he's building. A 1966 Volvo 122, with a Toyota Supra IRS in the rear and C4 suspension up front. A Volvo engine with his fabricated carbon fiber intake and his fabbed turbo headers. There are 80 episodes on this build, it's WILD the stuff he has done for this car. Well worth the time to stroll thru his wealth of info he puts out there.
https://www.youtube.com/watch?v=Pq2vR8-e1GM

Bob

#1072497 - 11/17/21 02:45 AM Re: Front sway bar project [Re: mmc427ss]  
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Bob, out of curiosity how much are you estimating to do it "the right way"? I know you referenced 100 rolls of dimes but I assumed to do the whole project it would be more than that.

#1072499 - 11/17/21 04:11 AM Re: Front sway bar project [Re: mmc427ss]  
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In dimes that's 500 bucks. Shopping for all pieces appears to eat that up .
That's why a little more effort in the engineering side needs to be done first. In order to do a very high rate bar it becomes a huge diameter, 1 1/2"+, because of the length of the arms, 13" or so. Lance does it with short 8 1/4" arms, connected to the LCA on the bottom side. I've seen this done before.
On my front suspension, mounting a fat bar is not difficult, but still stuck with 13ish arms. Even with a fat 3 piece bar the rates aren't much higher than a one piece factory type replacement.

I will be, well already, looking at mounting the bar rearward of the stock location. This gets the arm length much shorter, and the bar diameter can be smaller. The difficulty is in the motion of the links. It needs to remain as near perpendicular as possible through suspension up and down travel. A link perpendicular transfers load up and down. As the link changes angle during travel it then transfers some force forward of rearward depending on the angle. As the rate of the bar goes up that forward load increases, stress on the LCA, link mount, LCA pivots can be effected when you have a bar at 1000 lb/in rates. Just something that needs to be factored in when looking for a better mouse trap.

Just a note here that when the 86's stock, well kinda, LCA was relocated to move the LBJ forward 13/16" this effected the angle of the links. Enough to be noticeable but no enough to worry about at that time. Was going to get rid of the Energy Susp links, relocate that connection to the LCA and add a much better link setup. That didn't get done. Always knew i was going to do something other that a 36 mm F-body front sway bar.

Also know for me a huge front sway bar may be intolerable for 99.9% of my 2000 annual miles. Being able to swap in a "soft" bar easily is a necessity. PA roads are unforgiving.
Bob

#1072500 - 11/17/21 04:49 AM Re: Front sway bar project [Re: mmc427ss]  
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I have never looked into any of it but I assumed you would be in it for more than $500. I'm interested to see what you come up with.

#1072504 - 11/17/21 08:05 AM Re: Front sway bar project [Re: mmc427ss]  
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Hi Bob,

In case this is useful - making the links longer reduces off-vertical angularity when viewed from the side, and thus reduces front/rear force impartations. Of course, there's only limited space available to try to exploit this. You could fabricate/weld a mounting nest for the link that places the bottom pivot below the top/front surface of the LCA by as much an or so, or roughly 2" below where you might have it now. The nest would tend to weaken the arm, however, so you'd have to reinforce around the nest to preserve the arm's strength.

Btw, thanks for clarifying that the stiffness is being cited as pounds per inch. This interpretation isn't automatic because it doesn't conform to the British "fps" system as it's often called. I was seeing pounds alone for quite some time in various posts and this was ambiguous.

Last edited by MAP; 11/17/21 08:19 AM.
#1072512 - 11/17/21 06:57 PM Re: Front sway bar project [Re: mmc427ss]  
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Another quick thought in relation to lowering the bottom pivot of the end link: you might move this nest forward of the front face of the LCA. This way you could shorten the sway bar swing arms as well as lengthen the end links. The only reservation about moving this nest forward is that twisting the sway bar will put more stress on the front LCA bushings and anchorage bolts. I don't think this is likely to cause problems, but it's hard to gauge the magnitude of the risk.

#1072513 - 11/18/21 07:05 AM Re: Front sway bar project [Re: mmc427ss]  
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A short read on link angles, think it also may be from Fred Puhn.
http://www.gtsparkplugs.com/Sway-Bar-Link-Force-Calculator.html

Lots of thing to consider when trying to squeeze a fat bar into not much room. Here's an example of how complicated the arms can get to fit a fat tire. And the links are under the LCA. "Big Bar Soft Spring Technology"
http://hotrodstohell.net/front_suspension/index.htm

Here's a video from Hotchkis on a method of testing sway bar rate. Yep, pounds per inch. I was going to kinda duplicate their test setup so the four bars I have, stock F41 SS solid bar at 1.25", an Addco solid 1 1/8" bar, a 34 mm (1.34") hollow F-body bar and the 36 mm (1.42") hollow F bar could be tested. If a sway bar rater was made I know it should be able to measure up to 1000 lb/in to test the new three piece bar, now we are getting into explosion territory if something just wasn't up to par.
A while ago had a 36 mm bar mocked up on the bench with a scale and a jack to see what structurals would be needed. A trip to my local steel supplier for sure. But now making a bar rater has moved to a back burner. Testing those front bars I have, maybe.
https://www.youtube.com/watch?v=nzvSdcNtUoo

As a little piece of this project it's time to replace the 20 year old Global West front springs. They were and still are a good spring. Last time they were out a coat of paint made them pretty again. Sold as a 650 and now being a little shorter may be 675, they got a 1/2 coil haircut not long ago. Even with all Delrin for bushings i don't find those spring to uncomfortable.
Big bar/soft springs, small bar/very firm springs, heard those before. It looks like comp cars for autox are running a big bars and big springs.

NASCAR. It seems Roush had produced a trick front sway torsion bar.for his cars, exotic metal and shape. It disappeared one day, it shows up at a rival, Roush was not happy. Trying to learn something about chassis/car setups from the roundy-round cars is hard, they don't share info.
Bob

#1072515 - 11/18/21 01:02 PM Re: Front sway bar project [Re: mmc427ss]  
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We ran a very fast, less technical, all throttle course last Saturday. I rode in a couple fast cars in Group A before I made my runs in B. One was a built S10, big power, 315s square, aero, the whole 9 yards.

There were two fast hard 90 degree right hand turns and 2 of the cars I rode in both released their inside rear tire and spun thru their posi on those turns, my car did not spin the inside rear on those turns. Main difference was my huge front bar keeping the inside rear planted.

The S10 guy is fabbing a huge front bar install right now. It'll be interesting if he gets it done by Good Guys tomorrow.

Pics of the S10 on course can be seen here along with all the other CAM cars we raced with.

https://adventurewife.smugmug.com/Racing/20211113-SCCA-Autocross/

My fastest run here

https://youtu.be/ENZXgHtwsZk


Lance
1985 Monte Carlo SS Street Car
#1072519 - 11/18/21 06:54 PM Re: Front sway bar project [Re: mmc427ss]  
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Those are some good looking cars there. Just curious, do you know anything on that Corvair? Dad had a couple back in the day, including one with a 327 in the back seat. We've toyed with building another one with an aluminum 4.8 in it, maybe one day.
Hard to say from just photos that aren't exactly identical angle etc, but yours seemed to be a bit flatter than most, even the ones that looked to have more money sunk into them. What about that 3rd gen Camaro? He seemed pretty flat through the corners as well.


Shawn

'85 MC with budget 5.3L swap, TH350 with stock 2.14 rear end
It ain't much off the line, but it's nice on the highway
#1072522 - 11/18/21 09:27 PM Re: Front sway bar project [Re: mmc427ss]  
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When braking and turning, and especially with a front-heavy car, nominal heavy understeer works best. Or, accelerating and turning. In other words, anything that puts a heavy demand on the traction circle of each rear tire, is less likely to result in a spinout if we reduce rear roll stiffness in relation to the front.

But if we have much more roll stiffness in the front than the rear, we have understeer. S10s are particularly susceptible because they have even worse weight distribution than an A/G body.

Last edited by MAP; 11/19/21 01:37 AM.
#1072523 - 11/18/21 11:59 PM Re: Front sway bar project [Re: mmc427ss]  
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That 3rd gen is an up and coming hotshot that got by me late in the runs Saturday. LS power, some UMI parts, and some fresh 660s...plus a lot of seat time.

The Corvair has been racing with us for a while but always in afternoon so I never get to check it out.


Lance
1985 Monte Carlo SS Street Car
#1072571 - 11/26/21 05:20 AM Re: Front sway bar project [Re: mmc427ss]  
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Need to do an update for the couple people following this thread and maybe some like me who still look for info on the internet via forums. Info is very difficult to find on the internet these days. Also this is the easiest place for me to deposit my thoughts so i can look back later and say what was I thinking.

Have been playing with a mock up of a new three piece bar trying to figure out how to get a high rate bar under the car and work efficiently without negative effects. One tool I find invaluable is the Intercomp digital angle gauge, allows getting angles of the installed bar at ride height to the mockup on the bench.

First problem is mounting a bar in the stock location creates a lot of problems. The 36mm F-body bar on the car now is just touching the rubber boot on the idler arm and has bends which offset the bar and make the fit possible. The bar also doesn't interfere with the stock SS diagonal frame braces under the car, they are still installed. The 36 mm bar went in 10 years ago with Top Down Solutions 36 mm poly bushings and Energy Susp end links.

That 36 mm bar arms have been a good fit with the frame and suspension. With a B spindle which moves the track width outboard .400" per side and an XH F-body steering box with internal stops to limit full lock travel I'm able to have no touching of the sway bar by the fat 11" section width of the 275x40x17 tires. All this is a big plus on the current setup.

Now removing the 36 and going to a three piece bar while using the stock location present many problems. Especially if the need is to be to a much higher rate bar setup.
First, the new bar is straight, not doglegged, it would need to be move forward for clearance at the idler arm. Then it would have clearance problems with the diagonal braces.
Moving the bar a little forward would need to have longer arms than the 36 mm bar. The length of the arms needed for very high rates is the huge stumbling point of mounting a three piece bar in the stock bar location. The arm length is a minimum of 12". The 36 mm bar working arm length is close to 12 3/4".
Even if a fat 1 1/2" solid three piece bar was mounted in the stock location on a 12" arm it would be hard to get rates above 800. I could make that happen but look at that choice as a compromise to what rates i think I'd like to end up with initially. Keep in mind with a three piece bar you can always lower the rate with a smaller diameter bar and easily get 300 rate if needed for comfort. One advantage to the three piece bar, just buy a different torsion bar.

Next problem with a three piece in stock location is the arms most likely will be rubbed hard at full lock by the tires, actually limiting turning circle radius, a lot. That arm to bar attachment of a three piece takes up a lot of space and project outboard of the frame, a lot. The 36 mm bar tucks in close to the frame and although designed to fit an F-body chassis fits very well on a G. And needing to add the B-body guys have been also running the 36 mm F bar for years, it fits very well there also.

A simple choice for a little more rate than the F-body 36 mm bar is the 3rd Gen F one piece bar bar from UMI. Pretty sure it is the bar used on the UMI Green Machine when I looked at that car this past Summer. UMI claims I believe 20% higher rate than a 36 mm F bar, and in the neighborhood of a 625 rate. That bar would be a simple swap into the car and fit would probably be identical shape to the 36 mm bar in the car now, Yes it would have a little higher rate than what is installed now, and is reasonable priced, but not really what I'm trying to achieve.

So what is the alternative location for a new three piece bar that will allow the option for a very high rate bar.
Lance installed a three piece on pedestal mounts that drop the bar much closer to the ground and moved rearward to allow an 8" long arm, which attaches to the LCA on the bottom side. I've seen this done on Hot Rods to Hell's Nova front suspension sub frame. I'm sure other have done that before.
http://www.hotrodstohell.net/front_suspension/index.htm
My problem is the clearance between the link'arm and the ground get to only inches. Here in PA we need to be very aware of ground clearance on a vehicle if street driven. A sway bar arm and links below the LCA just doesn't work here. Race tracks, streets with no craters it may work, just not here.

In order to shorten the sway bar arms the approach I'm looking at now is notching the frame and welding in a 2" OD tube over top of the idler and pitman arms. this tube would provide a passage for what ever size bar i would choose and have the added advantage of a structural crossmember. Being it would be in front of the main crossmember that supports the control arms and weight of the engine a notch in front of it should have no ill effects on the frame strength.
That 2" tube placement has to fit in above the steering arms and the arc of their travel and also need to be aware that the engine damper and oil pan are right above the tube. It's a squeeze to get a 2" tube at that location. But a 1 3/8" bar not in a tube and just bar mounts on each side is another option worth looking at.
Already have PVC pipe cut to length to slide into that location to see what is doable, actually already had a 3/4" piece there a couple weeks ago.
Also know that location would be 6" forward of the stock location, now arm length is close to 7".

That rearward location would have zero issues with tires/wheel touch, steering linkage, and a smaller bar diameter could be run to obtain high rates with a 7" arm.
On the bench have a spare 36 bar mocked up as installed in the car and also a 2" and 1 1/4" lengths of PVC to mimic the new bar location.
This allows a visual to see and measure how a links angle changes as the suspension moves through travel. I just need to see a 7" arm at the new location move.
From years of measuring and correcting bumpsteer on this car how much suspension travel it has is a known. Few realize how little compression travel there is on a G after the car is lowered a little up front from stock height. On this suspension at my 26 1/2" ride height, it's now about 1 1/2" compression travel and 4" droop travel measured at the wheel. Again this is a stock LCA, B spindle, modified frame LCA pivot points, and a few other variables.

The sway bar link attachment to the LCA has a motion ratio of about 70% of the wheel motion, will measure that later to know for sure what that number is.
The vertical travel of the sway bar link on 1 1/2" wheel compression travel is near 1". When you would be loading one side of the car to 1 1/2" compression the opposite side of the front of the car is staying near ride height due to a large sway bar, less body roll.
The vertical travel the sway bar arm/link sees is realistically less than 3 inches when asked to run a slalom.
And the only time the sway bar sees all that droop travel, 4", is when both tires are off the ground, and the sway bar is doing absolutely nothing, zero load. So if the link angle isn't that good it's could be a non issue.
Thinking link angle is dialed in to zero at ride height, checked at 1" compression and droop and tweaked to favor compression angle. Where the link attaches to the LCA will require a new bracket so will be able to adjust for/aft/side to side location a little to correct angle.

On the bar mockup can guesstimate how much the links would need to be bent to mate the link to the LCA. Looking like a 40 degree bend in a 7" link to align things, 40 degrees is a lot of bend on a piece of 1/2" steel.

As MAP said earlier it's hard to get real numbers of bar rates. Even when I look at Speedway Eng rate charts they rate at 5 degrees twist. Need to do the math and figure out how 5 degrees with a 7" arm relate.

As with most all mods to this car there was always a long thought process on how to achieve the end results. To often the gains don't come close to expectations and you wasted a lot of brain cells you should have save for late in life. Can speak from experience. The sway bar project is just another one of those. I know i won't be happy as a street car but think as an autox car it will be a good bit better. Decades ago there was the promise of a road course across the field from the 9th hole I played every Fri afternoon. My car build goals back then were to make a few laps over there to see if the car and I were any good. A decade of lawyering and courts and that track never happened. So drag raced a hundred runs in a decade just for a time slip with a few exceptions. Certain cars I needed to get to the lights first, Mustangs, ZL1, some Mopar.
When I autox the first time there was no CAM classes, I ran SM, street modified. I could run Hoosier slicks and the WRX in class could also run slicks. I could care less about class, just wanted to run the car and get experience and see what fixes could help me and the car.
Time constraint, life and a dozen other reasons and only a 1/2 dozen events in 4 years. This past year made the effort to run two events finally with some good tires and between my son and I made 30 runs on the car. The goal for next season is more events and more runs, and quicker times.
And just like drag racing there are a few cars that you need to match yourself up against to see how well you really do. Closing the time gap between your's and their best run times is the same as the pile of time slips in the desk. By the way there are two new 1LE at the last events, fast out of the box, looking at their times to get close to.
An honest goal, old iron verses the new technology.

Had all day between making diner and it's clean up to ramble on here, please excuse me.
Bob

#1072572 - 11/26/21 03:09 PM Re: Front sway bar project [Re: mmc427ss]  
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Interesting approach... I think I like it if it works out as planned. Be sure that nothing will be in the way of getting the center bar out of the tube later (fenders, spindles, rotors etc).

Good luck with trial fit...


Lance
1985 Monte Carlo SS Street Car
#1072574 - 11/27/21 06:54 PM Re: Front sway bar project [Re: mmc427ss]  
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Spend some time yesterday laying on cardboard on that ice cold concrete floor. Have a 140K BTU hot air furnace that make things very pleasant to waist height, but the slabs stay ice cold all day. I installed 1400' of tubing, 6 zones, in the floor when I poured it 20+ years ago and never had the need to push some hot water through it. Now the bones are old and laying on cold concrete is something you pay for later. Just something else on the bucket list that I'm looking at finishing, toasty floors.

Did some more ciphering of numbers, made a template of the arm, had 1 1/4" OD plastic pipe and the arm under the car to see how it may possible fit.

Observations:
There no way of getting a 2" tube where I was hoping to do it, 6" rearward of the stock bar location. Idler arm and pitman dominate the space. And the engine damper and timing cover would need to go it a 2" tube was installed in the necessary space above the linkage. So 2" tube is out.

A 1 1/4" OD bar can be installed there. It would need to be centered between the timing cover and damper and be about 1/8" below them. It would clear the steering linkage and the arcs of them as the steering is turn L or R full lock.

Was able to mock up the arm on the bench and measure just how much travel an arm moves at 7" length with a 5 degree movement of at the bar. I need this info as Speedway gives their bar ratings at 5 degrees deflection, as rated on a Longacre sway bar rater. This info i need to be able to understand what size bar to put in that space. All the stock type bar replacements are sold in lbs per inch of twist. The three piece bars don't give you that info, it's lbs at 5 degrees. I find that a 7" long arm at 5 degree is 1/2" movement at the 7" location. So logic tells me with 1" of compression you double the bar rating at 5 degrees using the 7" arm. This info really helps with bar size selection.

With the 1 1/4" plastic pipe and an arm attached to it able to slide that above the linkage, the car sitting on jackstands, full droop. The sheetmetal arm was bent to mimic what is needed to get the arm to align with the LCA attachment point. That is all well and good, no problems with alignment of the arm. My old tires, a little less section width, are on the car right now. Those new RT600 are basking in the warmth here at home for the Winter. When the tire is turn inward at full droop I can see that a 37 1/2" length bar may present a problem touching the fatter RT660. Maybe a slightly shorter length bar may work, didn't play with at comb yet.

Mounting the bar to the frame would require cutting the frame and letting in plates to attach the bar. This would move the bar as high up close to the damper and timing cover. No problem doing that, just can't bolt the bar mounts to the frame without that being done.

So at this point I feel a 1 1/4" bar could be done at that location, maybe even a 1 5/16" bar may fit.. So what is the rate of a 1 1/4" bar? From Speedway Eng charts a solid 1 1/4" bar has a rate with an 8" arm of 617 lb at 5 degrees twist. So at 7 - 7 1/2" it would be slightly higher, it i go with a slightly shorter, say 36 1/2" bar it goes higher. If that is 1/2" link movement at that 7" for 5 degrees would the rate be twice at 1" movement of the link. All something I need to sort out.
http://1speedway.com/index.php?route=information/information&information_id=18

Measure the motion ratio of the sway bar location on the LCA. I was way to low at guesstimating it at 70%. The math yesterday says 86% of motion of the ball joint.
So if wheel compression is 1.5" total, link vertical is 1.3" in compression.
With the 36 mm bar install and resting at full droop you can see how much the angle of the link changes as the suspension moves to full droop. But i really think this is a moot point as there is no load on the sway bar/links when both wheels are at full droop. The operation range of the LCA when driven hard is what is important. That is what will ultimately dictate arm length and how the link angle changes through suspension operating travel.

While looking at available arms I thought I saw 1/2" thickness, nope, 3/4" thick. Also 1 1/4" spline the norm, whether 48 or 49 up front for us wanna-be NASCAR bar guys. But when you look at what the real NASCAR guy use it's 1 3/4" or even 2" spline. I assume this because of the sometimes really high rate bars they run. I wonder where that smaller 1 1/4 has met the limit of strength. Also there is even a square spline plug that goes into some arms they sell. Have also seen available arms that use two instead on one clamping bolt at the spline engagement. So arms are still something to figure out.

Have looked for accurate rate calculators and find the Fred Puhn is what i will be using. Using 36 width, 8" with 8 3/4" actual length, and a 1.25 solid bar it calculates to 1081 per inch of twist. Same dimension except a hollow bar with .250 wall is 941 lb/in. Note the 36" number, that is what a 37 1/2" bar width is imputed at.
http://www.gtsparkplugs.com/Sway-Bar-Calculator.html

Will be soon laying under the car with a full scale model of the new 1 1 /4" bar with 3/4" thick arms just to see if this all fits as hoping. The net if it all works out is a new bar about doubles the rate of the 36 mm bar, into the 1000 lb/in area.

Something needing to be mentioned is what the front weight heavy pig my car is, it was 58.75% several years ago and like old things, me, put a pound or two on since. So front roll, big bar to counteract the weight was the reason for the 36 mm bar years ago. This huge bar project is like putting another hole in your belt.
But as mentioned you can always put a lower rate bar if not happy with very high rate bar. Tune for the biggest I can fit initailly.
Bob

#1072575 - 11/27/21 08:43 PM Re: Front sway bar project [Re: mmc427ss]  
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Now you can see why I went under... laugh

Have you explored how big of a bar you'd need with 12" arms to get that same rate? Remember, you can do a step bar to get a higher rate with similar bushing size. Just curious if it would save you some fab and consternation vs jamming it in where there wasn't room meant for it to be?


Lance
1985 Monte Carlo SS Street Car
#1072578 - 11/28/21 03:20 AM Re: Front sway bar project [Re: mmc427ss]  
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A 1 1/2" solid bar with a 12.75 arm nets 950. The problem is that three piece would really interfere with turning radius, especially with the fatter tires. Because of the idler location you can't just move the bar back a couple inches without doing pedestals like you did. 6" rearward nets short arms, smaller bar OD would be used to get near 1000.

Do you know that there are bars in the 2" range. A hollow 2" bar with the 12.75" arms is calculated at 2050, that a lot of bar.

Will model all the possible locations over the coming weeks to see it there is a viable location with less compromise. The good thing about the 6" rearward location is the original stock bar location could always be returned to and the old 36 mm just bolted back in if not happy with the three piece setup.
Bob

#1072584 - 11/28/21 04:13 PM Re: Front sway bar project [Re: mmc427ss]  
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As with any of your post I learn a lot, even though I'm not at the handling stage of fixing on my car I will tuck the info away for later. Good stuff Bob.

#1072588 - 11/29/21 03:57 AM Re: Front sway bar project [Re: mmc427ss]  
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Hi Bob,

I was gone a few days, so apologies for the delay. Linear deflection at the end of the arm could be interpreted a few different ways, but they would yield very similar numbers. Try r*sin(theta), so with a swing arm length of 7" and an angular deflection of 5 degrees, you'd get 0.61" of linear deflection. Your estimate of half an inch isn't very far off. Sway bar stiffness goes almost exactly as the inverse square of the swing-arm length, so this parameter has a dramatic effect on stiffness. 7" is nearly three times stiffer than 12", for example (assuming all other parameters are left unchanged.) 12" is 13% stiffer than 12.75".

Bob, what about relocating where the end link attaches to the LCA per my earlier suggestions? A forward-projecting perch mounted on the lower edge of the LCA would but you roughly 2" of height reduction and 2" of swing-arm length reduction, provided there wouldn't be any interference issues (again, my memory of this area is fading, so this may not be feasible.)

Also, what about a combination of using stiffer suspension springs and a different bar? Changing the former, depending on your tolerance for a stiffer ride for all kinds of bumps, could provide relief for the latter, which affects only difference-mode stiffness.

Last edited by MAP; 11/29/21 04:01 AM.
#1072591 - 11/29/21 03:28 PM Re: Front sway bar project [Re: MAP]  
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Originally Posted by MAP

Also, what about a combination of using stiffer suspension springs and a different bar? Changing the former, depending on your tolerance for a stiffer ride for all kinds of bumps, could provide relief for the latter, which affects only difference-mode stiffness.


My experience shows that going from a 600# front spring to a 700# front spring had a much greater negative effect on ride comfort than going from a 500# front sway bar to a 1500# front sway bar.

The softer front springs Bob has not only provide a much nicer ride for everyday driving (wife acceptance factor) but also allow for easier compression to get to the sweet spot of caster\camber gain. I'd lean toward the softer spring every time for this application. I often threaten to put the 600s back in the front of my car but basically, I'm too lazy. If or when I ever get tired of trying to be competitive with this car, that'll be my first change back for sure.


Lance
1985 Monte Carlo SS Street Car
#1072593 - 11/29/21 05:07 PM Re: Front sway bar project [Re: mmc427ss]  
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Thanks Lance.
Being old I've read over the years big bar-soft springs verses the big spring-small bar debate. As far as the wife riding in the car thing she has hated it for years now so ride quality isn't an issue anymore, she doesn't ride but a few miles to shows if anything. I've had 640 springs in the car for 20 years, when the LCA relocation was done a 1/2 coil was cut off to adjust ride height, so that should have added a little higher rate. Fortunately with DA shocks up front and TA in the rear you can tweak the ride a little and make it tolerable. I personally don't mind the higher rate front springs. Only when the new RT660 are on the car does harsh show it's face, but that I've learned to live with. Going higher than 650 rate springs isn't something i really want to do.

Today will have time to start the process of seeing if I can get that new bar located above the steering linkage. Will make up a working model under the car and see exactly where it may be able to mount and make full scale arms to see if I can squeeze them in and not impact turning radius/tire rub. Thinking a slightly shorter bar, 36", can be used to move the arms inboard a little.
Being I live in roundy-round stock car country, Grandview Speedway 10 miles up the highway, will do a little research using some of my connections to that side of the sport. Being their season is done here I may be able to borrow some knowledge or parts to have something in hand before purchasing my parts. As with most all parts today shortages are everywhere, assuming getting a torsion bar may have the same problem.
Calling Speedway Eng which seems to be the go to for these three piece bars parts will happen soon to answer availability and some tech of what I'm trying to achieve.
May even give Ramey a call to discuss his thought on the huge bar thing.
Bob

#1072595 - 11/29/21 07:17 PM Re: Front sway bar project [Re: mmc427ss]  
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Sounds about right: springs affect both sum and difference-mode bumps; bar only difference, so the bar will tend to ride smoother other things being equal. However, going from a 500lb/in bar to a 1,500lb/in bar, assuming a 0.86 motion ratio, would yield a 740lb force difference for a one-inch, one-wheel bump, while a swap from 600 lb/in to 700 lb/in spring would yield only 25lb force difference for a one-inch, one-wheel bump, assuming a 0.50 motion ratio. That's a ratio of nearly 30:1, so it's a little hard to believe that the stiffer bar is the smoother option. OTOH, there could be other NVH things going on with the stiffer springs that the stiffer bar tends to obviate or diminish. And. this is where the chassis' torsional compliance could be partially masking and "undoing" the bar's inherent stiffness. I know in the past with my own A/G bodies, I also preferred the soft-spring/stiff-bar combination as the best overall solution. So did Herb Adams.

Incidentally, any particular reason why no comment about the end-link relocation scenario for the LCAs? Shortening the swing arms by about 2" buys a sizeable increase in bar stiffness.

Last edited by MAP; 11/29/21 08:21 PM.
#1072599 - 11/29/21 10:52 PM Re: Front sway bar project [Re: mmc427ss]  
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I was wondering when you would jump in here Mark.
The arm length of a stock and most all the bolt in bars is 12 3/4" measured from the center of the link hole in the bar to the centerline of the straight section of bar. The perpendicular off the straight section is 12". The Puhn calculator can then input those measurement to determine effect on rate.
http://www.gtsparkplugs.com/Sway-Bar-Calculator.html

Moving the bar reward from stock location will shorten the links into the 8ish range with a large rate increase for the shorter arms.
Once I'm done figuring out if I can squeeze a bar into the new location the length of the arms can be determined and the rate calculated.

As it is now a 1.3" solid bar may be able to be mounted in the new location, with 8" arms, 8.75" effective length, 36" bar length puts rate at 1080.
Shortening the effective to 7 3/4" with a 1.3" solid bar is 1672 lb/inch.

So yes arm length is a huge factor in rating the bar.

Again looking at NASCAR, Winston Cup cars of old, ARCA for what they do with front sway bars. The combo I see is the long arm, 12" or longer and huge diameter bars, some as big as +2". Trying to figure out what those boys run is all like top secret. Very little help with tuning from those guys who race at the highest levels.
Bob

#1072602 - 11/29/21 11:47 PM Re: Front sway bar project [Re: mmc427ss]  
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Other things being equal, I prefer the shorter-arm approach to increase stiffness. For one thing, it makes for a lighter bar. The effective swing arm length should be taken as the side-viewed distance from the centerline of the front, transverse portion of the bar, to the effective center of the top pivot of the end link. That's dimension "A" in FP's diagram. At least, that's the case if we assume that all of the bar stiffness comes from torsional shear within the central section of the bar. If we factor in bending of the swing arms, it gets very messy, and closed-form algebraic expressions for this stiffness will be nearly impossible to obtain. That's when we resort to mechanical FEA for an exact answer.

I think you'll get more than close enough to a reliable answer just by looking at twisting of the central section. Sanity check: in FP's equation, look at the magnitude of the A^2 term versus the C^3 term. Guaranteed that the C^3 term will be tiny compared to the A^2 term, meaning we can safely neglect swing arm bending.

But, what of end-link relocation on the LCA? It's low-lying fruit, pun intended.

Last edited by MAP; 11/29/21 11:57 PM.
#1072603 - Yesterday at 07:37 AM Re: Front sway bar project [Re: mmc427ss]  
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Mark the link will be located on top of the LCA, in almost the same spot as stock, and thinking link length will not be short and will be rod ends. Making and installing new link attachment points on the LCA is a given. Will be able to minimize link angle load with a relocation of that point.

Spent some time again under the car.
With a 1 5/16 bar (1" pvc conduit, 1.3" OD) slide over the top of the idler and pitman and moving the steering full lock left and right there is no issues with clearance on the idler side. The arc of the idler has plenty of room to squeeze the bar in there. On the pitman side plenty of clearance when turned L or R but with the wheels straight ahead the pitman is pressing hard against the plastic pipe. So that is my point of interference and everything fitment wise will be based on having the pitman move freely under the bar.
A 37 1/2 standard length bar is to long. In order to have the tires not hit the new arms on the bar the arms need to hug the frame. Modeling so far says with a shorter bar, 36", the fat 275s should not touch if the arms can be kept close to the frame. The front wheels are hanging now at full droop, jackstands.
Next is find a 36" x 1 1/8" rod, make two 3/4" arms out of plywood, hang assemble in the new location and go through all the travel in full droop and then drop the car back on the ground, on turnplates, and see how the arms up and down movement works out being so close to the frame. That is the make of break of this bar swap. The arms need to not be touched by the tires. As part of the new wheel fitment, 17x9 and fat 275s i made adjustable spindle stops on the LCA to be able limit, tires not touch anything when at full lock. The turning circle of the car was slightly effected but still was 40' at full lock, OK. I could adjust them a little more, increasing that circle but that is not a consideration at this point.

Already know to position the bar's bearing mounts the frame will need to have about a 3"x 6" section cut out of the bottom of the frame and a flat plate welded back in. Fortunately there is plenty of room on both sides to cut and weld things back together, and be stronger than before. That plate will need to be slightly recessed into the frame to compensate for the height of the bar bearing mounts, and need to be flat to mount the bar bearings. No big deal, just dirty work laying under the car.

Still playing with the Puhn calculator to guess at rate. Thinking the arms functional length "C" is close to 8", bar length for "B" will be 34 1/2" (36" bar). Using the largest OD bar I may be able to get in the space would be 1 5/16". If a solid bar rate would be 1684. WOW. Dropping the bar down to a 1 1/4" hollow bar (.750" gun driller ID) with the same arms would be 1215. Even going smaller bar to solid 1 1/8" would be 915. What that tells me is if I can maintain that 8" arm length the largest OD bar I need to fit is 1.25".

If I was to abandon the new location and mount a three piece bar back in the stock bar location a 1 1/2" solid bar would net about 1000 due to the long arms, 13" needed as the large 1 1/2" bar would need to move forward to clear the idler. And that bar would be 5' of 1 1/2" solid steel hanging under the radiator at 6 lb/ft, 30 lbs. there is already to much weight on the front end now.

Bob

#1072607 - Yesterday at 04:21 PM Re: Front sway bar project [Re: mmc427ss]  
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MAP beat me to it, but I drew it out in CAD to double check my math and memory.
5° gives:
7" arm - .61" vertical movement.
10" arm - .872" vertical
12" - 1.045"
12 3/4" - 1.111"

Nothing more to add, just following along.


Shawn

'85 MC with budget 5.3L swap, TH350 with stock 2.14 rear end
It ain't much off the line, but it's nice on the highway
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