what is the purpose of the torque arm? is it basically to hold the rearend in place? does the shape of the torque arm matter as long as the rearend is held in place at the correct angle? I guess what I am getting at is.....has anyone ever thought of making one that is the same principal as the sphon but shorter? It would still connect to the same place as the sphon. the mounting bracket would made to connect there and the actual torque arm would be about 2 or 3 inches shorter. I am wanting to keep my x-pipe and my fiance's dad suggested that I make one like he did on his 32 coupe. any ideas?

 

Are you talking about A Torsion Bar?

 

I have always called heard it called the torque arm.....It is the triangle piece of metal that is attached to the rearend housing and the transmission. I now know the function of this piece and am now needing to know if shortining the sphon design by 3.5 inches will surverely increase my traction?

 

The torque arm (TA) resists the torque applied to the rear axle by the driveshaft, hence the name. The pinion is trying to "climb" the ring gear and rotate the whole rear end housing in the opposite direction the rear tires are going.

There are other ways to resist this torque. With leaf springs, the torque tries to wind up the leaves, but the front portion of the springs resists the torque. With a 4-link or 3-link, the top and bottom links resist the torque.

Yes, the TA also sets the pinion angle. It also helps determine where the "Instant Center" (IC) of the rear suspension is located. The location of the IC determines how much anti-squat you get. This relates to bite especially at launch. A side effect can be wheel hop or brake hop.

In order to answer your question, you should be familiar with IC and anti-squat. Here's an explanation of IC on a Camaro:

This diagram is VERY helpful.

http://www.jonaadland.com/Ta.jpg

In a stock Camaro rear suspension with a fore/aft sliding front mount of the torque arm, the side view IC is found as follows:

Extend a line from the rear pivot of the lower control arm (LCA)thru the front pivot forward past the transmission mount. Next a line is drawn perpendicular to the front end of the torque beam where it is attached at its rubber slider joint. This is basically a vertical line with the car at normal ride height. Where this vertical line crosses the line of the lower control arms is the side view Instant Center.

This is quoted from Terry Satchell, a GM suspension engineer very familiar with this subject.

Note that you can easily raise the IC by dropping the rear pivot height of the LCA. Note also that different ride heights (lowered or raised car) change the IC height. Note that lowering the rear drops the IC, and therefore reduces the anti-squat unless LCA pivots are relocated.

My thanks to Jon Aadland for the picture.

If you move the front mount of the TA rearward, you'll note thet the IC also moves rearward. How does this effect anti-squat? Draw a line from the center of the tire where it contacts the road thru the IC. The steeper this line is, the more anti-squat (and probably brake hop) you'll get, and the harder the tires will "hit".

Aftermarket TAs are shorter so they move the IC rearward. Going even shorter than the Sphon TA may just get you into many more problems than it solves. Remember that the shorter the arm, the more load it puts into the mount on the body/chassis.

I'd advise against going any shorter that the Sphon. A much better idea would be to modify the exhaust system. A good Y-pipe and a 3 inch single behind it should be sufficient for your engine unless you get WELL past 450 rwhp. Then just increase the size of the single pipe and muffler of course.

Sorry to go against your future father in law's advice, but your car ain't a 32 Ford. One of the reasons the Camaro didn't have true duals was the torque arm rear suspension design uses up a lot of the room. Everything is a compromise, especially packaging. Either leave the stock TA in place, which isn't all that bad an idea if you are not drag racing weekly, or go to the Sphon (or equivalent) and run the exhaust around it.

My $.02.

 

The image appears to be the one from Racecar Vehicle Dynamics by Milliken&Milliken

I suggest every race vehicle enthusiast own a copy! The workbook also helps a great deal.

 

I understand about instant center. My thinking is that with the sphon TA the torque arm is relocated ~8in rearward increasing the IC. The desireable pinion angle is -2* this also increases the IC. studies have shown that with a sphon TA adjusted at -2* the 60' will drop ~ 2 tenths on a stock spring stock height car. This is like moving the IC ~ 1" rearward. I am thinking that I could further move the TA rearward by ~3 inches keeping my pinion angle at 0* causing the ic to move > in. I don't think that it will be too much for the car to handle...my main purpose for doing this is to remove the TA from the transmission. My car will be making 450+ hp very soon and I would like the reasureance that the transmission is safe. Any more input would be greatly appreciated. I need to learn as much as possible before we start this project.

 

The IC is a point not a length. It has nothing to do with determining pinion angle. It is merely the point about which the rear axle swings at a particular vehicle ride height. If the car lifts or drops due to acceleraton or a bump or braking the car the IC moves. I believe you are referring to anti-squat whe you mention "increasing the IC".

If you are concerned only about the trans case, check with other folks running the kind of rwtorque you expect. Remember available traction determines load on the torque arm. If you are planning to see sub 1.50 60' times the torque arm might be the least of your rear end problems.

My advice is to not design your own torque arm. Either use the stock one, or buy a well-proven aftermarket one. When you upgrade to a stronger rearend would be the time to change torque arms, IMO.

Good luck!

 

Yes, it certainly is. Chapter 17 was written by Satchell in language most folks understand. I'm not sure every race vehicle enthusiast would fully understand a lot of the stuff in the book, but I may be mistaken...that happend once before.