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Author Topic: Torque arm question  (Read 6937 times)
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V8Rumble
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« on: July 16, 2007, 01:44:29 PM »

Hi all,

I've been lurking here for a few months trying to soak up all of the info I could, & finally decided that it's time to say hello, join the group, & see if I could get a bit of feedback on my own project.  A bit of info about me & my vehicle first - I live in the Denver area so I'm fairly close to the salt, & I try (whenever possible) to turn my own wrenches.  (Which doesn't necessarily mean that I'm any good at, but so far - knock on wood - they all still run when I'm done, & I don't have too many pieces left over...) cheesy  Finally, last year my buddy "hotrod" Larry & I went out to Speed Week to size things up & try to get a handle on the best ways to do things.

I suppose that I should add that my goal (for the moment at least) is pretty modest - I intend to add my name to the list of people in the USFRA '150 Club'.  (Yes, I know that's a different event & a different organization than what most everyone here runs, I'm pretty much just looking for tech help/advice.) Eventually, I might well try to get myself a red hat - OK, hell, I'd just about kill for a red hat wink - but for now it seems prudent to kind of "dip my toe in the water" & get a bit of experience first.

The car that I'll be bringing to the salt is my '89 Pontiac T/A GTA.  I know that it's supposed to be a decent design aero-wise & I've already started some of the modifications that are either intended to help with aero or dictated by the rules. But the question I have relates to my intention for the car - I really want to keep this as my "street/strip toy" as well as retaining the ability to run the salt.  I was able to score a really good deal on a used BMR "Trak-Pak" torque arm (image below), which is supposed to be a significant aid in planting the tires when it's set up correctly - but I've heard that the flip side of that is that a shorter torque arm can also contribute to brake hop, which is pretty close to the last thing I want when moving at triple-digit speeds. shocked

With all of that out of the way, would I be better off selling this piece & looking for another torque arm option? (I know of a de-coupled torque arm that acts as a shorter arm upon acceleration, but "de-links" upon deceleration, acting like a longer arm, but it's selling for $820, & I'd have to do some fabrication to make it work on my car.)

Thanks all, I definitely appreciate any help/advice you can provide.

« Last Edit: July 16, 2007, 02:23:20 PM by V8Rumble » Logged

I just turn wrenches - and sometimes the car even cooperates!
Glen
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« Reply #1 on: July 16, 2007, 02:01:56 PM »

Welcome to the forum. It's a great place to ask and learn . I don't think you should have a break hop problem as heavy braking is not necessary on the salt. Lots of shut down area and at the 150 speeds stopping is pretty easy. You should have several people in the Denver area including Jon Amo who is the web master of this site. Good luck on the project.
Glen
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Glen
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V8Rumble
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« Reply #2 on: July 16, 2007, 02:18:36 PM »

Thanks Glen, I appreciate the quick reply.  I thought that I'd seen that there were at least one or two others in this area, Larry & I've already spent a bit of time talking with Dave Sarno, & I'm sure that we'll be bending others' ears as well. smiley  Thanks again.

EDIT: Judging by the number of views, I'm guessing that everyone is pretty much in agreement with Glen?  I could go either way, I could sell the torque arm, or I could install it, I don't have a whole lot of opinion either way - I just want to do it right the first time.  Again, I'm grateful for Glen's input, & if anyone else feels like putting in their two cents, I'd be real happy to hear that as well. wink
« Last Edit: July 16, 2007, 10:31:51 PM by V8Rumble » Logged

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revolutionary
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« Reply #3 on: July 19, 2007, 08:40:04 PM »

I'm building some torque arms for mine and a friends 4th gen f bodies that has an adjustable front mount so you can drop it for a better instant center during your 'strip' days and raise it back up for other driving.  I know most of the torque arms are the same 3rd and 4th gen but I don't know whether the mounting location that I am using (same as a relocated BMR or Spohn) is the same on a 3rd gen.  If so I could probably put together a third piece.
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Stainless1
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« Reply #4 on: July 19, 2007, 08:51:29 PM »

V8, you assumption that no one disagrees with Glen is correct.  Never had my foot on the brake pedal at Bonneville, 'cept maybe during my spin/almost flip and then only after the car was going about 30 MPH.
My favorite Al Teague quote, Brakes are used maybe in the pits or during towing, if you step on them at speed, they are like a ripe plum, you know you stepped on something because it was there for a second, then it was gone... (Paraphrased a little but you should get the point)
See ya on the salt  cool
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Stainless
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MSA Bockscar Lakester #1000 my fastest mile 245 and change, 84 ci turbobusa motor... but Corey's 233 MPH H/BFL record is still 3MPH faster than mine.
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« Reply #5 on: July 20, 2007, 12:59:29 AM »

Hi V8
A single torque arm is a good design . The offset to the right of the drive-shaft should be the arm length divided by the ring and pinion ratio . If it is the effect of the bar exactly cancels drive-shaft torque that normally loads the rear tires unequally when you're accelerating . The longer the arm the less the tail will raise with acceleration and squat with braking . It does load the rear tires unequally under braking but as the others have said that's not a problem at Bonneville .
John
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V8Rumble
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« Reply #6 on: July 23, 2007, 02:20:12 PM »

(Sorry for the delay in responding, last week was a rough one...)

Thanks for the feedback, I very much appreciate it.  John, I'll see if I can get some rough estimates of where the arm will be mounted, but I'm curious as to where it's measured. (Since it runs mostly parallel to the driveshaft, perhaps that's a bit flexible?)

revolutionary, I am definitely interested in the torque arm you're making.  Since I've had time to think about it a bit, I've realized that the Trak-Pak could have one significant shortcoming - the increased road noise that it transmits into the cabin.  (And since I like to keep my wife as involved with my hobby as I can, this could be a problem.)
Please do let me know how that works out for you two, & exactly which mounting location you're referring to, & I can very likely get that information for you.  Also, if you could provide a "ballpark" price estimate, I'd be glad to hear that too.

Thanks again all!
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I just turn wrenches - and sometimes the car even cooperates!
John Burk
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« Reply #7 on: July 23, 2007, 03:29:44 PM »

V8
The offset is to the right of the the pinion axis which is usually the drive-shaft axis . Nascar cars have used long torque arms with coil-over shocks in front . GM pickups and cars have come with torque arms . Summit sells replacement bushings .
John
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V8Rumble
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« Reply #8 on: July 24, 2007, 11:30:00 PM »

OK, thanks John, that's more or less along the lines of what I was thinking.  I suppose that if I were to get the measurement using the rough centerlines of each, it'd likely be good enough for what I'm doing.  Thanks again. smiley
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I just turn wrenches - and sometimes the car even cooperates!
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« Reply #9 on: July 25, 2007, 08:05:04 AM »

Just about done making up the first set of brackets.  I've been consulting with a local chassis builder to make sure everything is right and he's giving me a thumbs up.  I don't know anything about pricing on the deal as I'm just buying parts now but I don't think I'll have much more than $200 or so into each set.
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