When you were talking a while back about the torque arm issue and the length of the arm, you mentioned a shorter attach point from the transmission. How about this setup?http://www.bmrfabrication.com/instru...bottomview.jpg
http://www.bmrfabrication.com/F3-suspension.htm

Jim

 

Yes, that is a good one.

 

I kind of keep flip-flopping on the torque arm length issue. A shorter arm does seem to make sense, but at the same think about when you're trying bust loose or tighten a stubborn bolt.

Here's a couple scenarios I've thought about:
1) When you need more torque to turn a bolt or nut do you grab a stubby handled ratchet and attempt to tighten or loosen it -OR- do you grab the 18" to 24" long breaker bar sitting in your tool box?

2) How about the lug nuts on the wheels. Which works better - your standard length 6" ratchet handle or a 24" long lug nut wrench or breaker bar?

In both of these examples, the longer handle provides more torque. Ever slipped a piece of pipe over the handle of ratchet so as to apply more force? How about torque wrenches. Ever seen a stubby handled one?

Are there any forces or rules of physics that would negate these examples when talking about the rear end of the car when under load? This would support the theory of a shorter torque arm.

 

Bret:
You are way off base. There are two different principals of torque.
In the law of physics, for every reaction there is an opposite or eqaul reaction. Not so when you are applying the torque.
When the rear axle tries to turn from the force exerted by the driveshaft to what the axle is fastened to (the body), the effect is a downward force as it tries to lift the body, thereby creating what in effect, would seem like more weight. Meaning more traction.
Examle: Stick your arm all the way out from your body and try to lift a heavy object. Now, pull your arm in next to your body and lift that same weight and see how much easier it is to lift.
Don>>>

 

Don,
Okay, the more I think about this, the more I think I'm understanding the forces at work. It's making sense now.

Since I've spent so much time involved with fitness and bodybuilding over the last two years, I applied some weight training principles. It comes down to range of motion. The shorter torque arm can generate more force over a shorter distance.

 

Using a huge breaker bar allows you to apply the same work energy over a longer distance. It takes the same work, just spreads it out. This means that power is actually reduced

 

The stock torque arm is way to long for any type of perfromance use. I have a Global west arm and I think it's the most streetable short arm on the market.

Jerry

 

A shorter arm will cause more stress on the chassis(unibody) and will cause greater flex. The longer arm, when solid mounted (not like stock type) will give a more stable and predictable launch. It will also control chassis attitude for handling characteristics (such as better controling brake dive).

Basically- all a torque arm does is controls the pinion angle of the rearend- holding it in as close to static angle with the chassis at all times allowing maximum tire traction and axle lift/thrust to be diverted directly to the chassis without any torque absorbtion to attain maximum weight transfer onto the rear wheels.

The last note I want to add to this is that the shorter the bar is, the more it will resist rear squat under a hard launch. I lifts the chassis under a more rear point behind the cars center of gravity and will "hold up" the rear of the car more under torque squat. Its a balance between the chassis stiffness, the spring rate, and the lift bar mount length to get the right combo.

A snubber on top of the rear differential to limit frame squat would be my choice combined with a longer torque arm for better overall chassis lift and weight transfer.- but hey, I dont drag race- I road race

 

AGood2.8,
I'm glad you brought this up. I've also been thinking about a snubber. The old Mopars ran these.

I'd rather road race myself, so I'll stick with my long torque arm.

 

A snubber only works with leaf springs. And no torque arm.

 

The longer the the torque arm the more brake dive you get and we have to much of that from the factory arm. The shorter the arm the more it pulls down on the rear of car for less dive and better braking. The winston cup guys hate the long arms that the rules call for it has to much wheel hop and brake dive.


A snubber on top of the rear differential on a torque arm car is called a bump stop and you have two of them now that you can use, the factory ones. The diff will not rotate like a leaf spring car (spring wrap) so a snubber on it is just a bottom out stop only.

I have built cars with 20" torque arms to cars with the arm mounted on the front bumper and the factory arm is still to long for a road race car.

Jerry

 

If the arm is mounted closer towards the CG of the car(but not to close under it), then it will "pull down" the entire car evenly under braking and not cause a "nose dive". Yes a shorter arm will help more in braking- but hurt more in accelerating laterally.

Bump stops and snubbers are two different things.
Bump stops restrict suspension bottoming out- a pinion snubber will prevent differential travel but will allow for freedom of outside suspension movement as to not adversely affect handling.

If you were to lower your outside bumpstops to a point where they would help control torque squat, then the suspension would no longer function side to side and absorb road contour. The snubber has to be in the middle under the pinion.

Jerry, I respect that you have raced sprints for years and am not trying to bash your ideas, I'm am just giving engineering points to this subject. The Winston/Nascar guys are regulated under strict rules and can not alter many many things because of rules- If they could they would- thus theirlonger TQ arms cause havoc with the lighter cars and more rear positioned CG. Your car appears to be lightened more in the front than an average thirdgen F-body- thus a shorter bar is looking more favorable to you than most others with your setup- (I am not schooling you by any means- I am just explaining to others reading this post as to how things need to be married to configuration they have.) Average full bodied full weighted stock frame street cars will favor the longer arm with a solid front mount.

Dean.

 

[Average full bodied full weighted stock frame street cars will favor the longer arm with a solid front mount]
Dean:
If you're talking street drag cars, a long torque arm will render the snubber useless and prevent weight transfer. There is an artical in one of the magazines this last month that spells it all out.

 

Guys, I should at this point clear up what I think we are all debating eachother on- Torque arm length.

When I am refering to a longer torque arm, I am not refering to longer than stock. Stock is too long. A unit like Spohn's I refer to as "long" even though it is shorter than stock, and GW or BMR is a short for reference.

I personally feel that the "shorter" arms on a non lightened unibody car causes too much stress on the frame(or lack of). Now if the car is lightened, equipped with a rollcage, and frame stiffened, then the shorter torque arms will function as intended and provide better weight transfer. On a heavier full weight streetcar the chassis is going to flex way too much and the arm needs to mount more forward like the Spohn unit onto the solid inner subframe, closer foward to the car's CG to lift and transfer the weight more with less chassis stress. We all know the race cars are tube chassis- stiffer and lighter than a stock f-bodies.

Now what I've seen of Jerry's car- he's build a Rodeck Block, has a lightened K-menber, lightweight front suspension and brake components and I believe he has also lightened his bumper assembly if I am not mistaken.- I don't consider his car "full street weight" anymore. He has lightened several hundred pounds of the front of the chassis and will promote a stiffer, more reactive weight transfer due too a more rigid frame(Via less weight and flex). He will benefit from a shorter torque/lift bar assembly and not cause weakening of the chassis, especially over time.

Edit: Also to all, Please understand that I love a good debate and am being the utmost respectful to all when I expess my opinion- My intentions Is not Ill directed towards anyone- just a friendly debate. Just don't want anyone to misconstrue this as a pissing contest This kind of debating helps me sharpen my knowledge.

Dean

 

'nuff said:

 

Don your killing me here, Thats not a full weighted car. Its a striped down(lightened) race car. Doesn't compare to what I am trying to educate people with heavy street cars that are completely nose heavy- they will not get the weight transfer with a heavy weak unibody car that is nose heavy- they will loose potential grip because the instant center is too far back on a flexible frame heavy weight iron V8 3rdgen. Unless they are running awesome power and huge slicks, the pivot point of the shorter BMR TQ arm will not lift and rotate back the heavy nose weight as well as a little longer TQ arm like Spohn's.

I promise that the guy up top(globalco) who asked about the BMR TQ arm for his car is not running a lightened drag car with huge slicks and frame work like yours in the picture- Merely stating that he will get better results with a Spohn Tqarm on a heavy nose street car on so-so drag/street tires with o.k. traction and normal 3rd gen frame flex.

I hopre you'll still talk to me next time I drop by your shop

 

You need the torque arm mount way rear of the CG to counter the brake dive and power on squat. Do you know on a stock car the location of the CG to the torque arm mount.

True.

True.

Wrong... A pinion snubber is for leaf spring cars to counter act the spring wrap.

True.

You can call a stop in the middle of the car with a torque arm a snubber but in real life it's a bump stop in the middle of the car. A snubber moves up when the rear axle housing rotates under power. On a solid front mount torque arm car ( we don't need to talk about 5th coil moving torque arms now.) the rear axle can't twist up so the stop will not hit the body the only way it will hit is have the body go down "Bump" and hit the stop and thats a "Bumpstop" mounted in the center of the car.

A stock third gen is lighter than a Winston cup car.

The point is the stock arm is way to long.

Jerry

 

Gee, all I was doing is noting that I had found a short torque arm setup similar to the one Don and I had been talking about.

Yes, eventually I would like to add subframe connectors, tower braces and a after market torque arm. Probably after I rebuild the engine.

Apparently I should use the Spohn unit per a previous responce correct?

I do not intend to lighten the front end other than a fiberglass hood.

Jim

 

Now who told you that the car in the picture weighed in at 3200 lbs....stock frame and front suspension with roll up windows and full dash. In those days they were called Heads up Super Stock.
No problem, I'll still talk to you