Hi All, I just did a TH350 swap and decided to put on my MAC torque arm while doing so.

This arm mounts about a 18" back from the original one and to the floor pan on a big plate. I went to test and tune, and it wasn't as much help as I had hoped for.

Anyone have direct experience with the shorter arm vs a longer one?

Anyone see a four-link setup on our cars?

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-- Tim
http://tim.mindriot.net

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[This message has been edited by MisterGuru (edited August 20, 2002).]

 

AFAIK, Arm length should be a *minor* issue (There are some issues with length but I wouldn't worry about it, guys have gone much faster with the more common "shorter" TAs), the main emphasis would be:

a)Adjustability of Pinion angle, which doesn't make for better traction, just a more efficient, reliable drivetrain when setup correctly.

b)Instant Center. THIS is where it gets tricky. *Most* Torque Arms do not have an Adjustable Instant Center, and so this is not something you should have to worry about. The Only "Traction" Benefit I see coming from most of the Torque Arms is its strength, and lack of flexing under load. Thats why Stock Eliminator cars have been able to do so well with even the stock TA in place.

For now I'd count your track visit as nothing until you get onto a Better prepped track. If you're still having problems, then there might be an issue somewhere.

All JMO.




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Kurtis Tamez
LT4-396.com
97 Z28 LT4-396
94 Firehawk LT1-396
Team NW F-Body

 

What KT said! I'll add that if you want to change your instant center you well need to beable to move the front TA mounting point up or down. Look at it like a four link with only one top bar and non-adjustable bottom bars (boy, that sucks)

 

The length of the TA will have a direct impact on the instant center point for your rear suspension.

Imagine a vertical line (or line perpendicular to your vehicle) that intersects through the torque arm mounting front point - got it? Now imagine a line that is defined by your two LCA mounting points.

The intersection of these two lines will will be the instant center - so a shorter torque arm will move it rearward, etc. The vertical aspect of the ic will be a combination of the ta length and the lca anglularity.


Chris

 

OK - clear as mud now :-)

It hooked about the same as ususal last night... a little wheel spin on the 4th pass.

I just need a 4 link.

 

If you don't have LCA lowering brackets get those ASAP.

In general a shorter TA is going to give you a harder initial "hit", then go back to normal weight distrubtion quickly - a longer one will have the tendency to "average out" the "hit" over a longer time domain.

The LCA angle will determine the height of your IC, and how high this is above (or below) your center of gravity will determine the amount of anti-squat (rear end lifting instead of squatting) on your launch.

If you hook initially then break loose - a longer t/a may help - if it's initial spin then a shorter one is the ticket (this is a VERY general statement). But get the LCA brackets in there asap. If they don't spray the track buy your own bottle of VHT and do a burnout in it.


Chris

 

I'll just head down to the farm supply store and get a pressurized bottle w/solenoid controlled nozzles and rig them in the fenderwells to mist the tires.... nah I never had that thought

I have read continually that LCA brackets only help lowered cars, but I will get some and try them. I assume bolt on work as well as weld on?

 

Yeah, me too. But I always wondered about this. What will LCA Brackets do for a non-lowered car?

 

I had a long conversation this morning with a guy at BMR who explained much of it to me. I don't know how well I can relay it, but it makes sense that the lower the rear mounting point is, the more the car's weight plants the tire under acceleration.

I wanted to get the BMR Brackets, just to pay for my education, but Spohn makes a Moser-specific bracket. I am trying to reach them now, but they are not answering.

It's just square metal with holes! I am sure I can fab it for $10, but the convenience is good I suppose!

[This message has been edited by MisterGuru (edited August 20, 2002).]

 

When you lower the LCA rear mounting point you increase the angularity of the LCA - they point "UP" more - since the instant center is the intersection of the line they define and a line running perpendicular to your torque arm mount increasing LCA angularity (raising the front mounting point or lowering the rear) will cause the instant center to be higher vertically - when your instant center is higher than your center of gravity your car begins to pick up "anti-squat" -- that is the rear end raises instead of squats - this is good for traction. the higher the instant center the more the anti-squat.

On a lowered car the brackets allow you to move back to stock geometry (lca mostly parallel to the ground) - on a stock car they allow for drop. This can sometimes cause wheelhop problems on breaking, but will depend on the rest of the suspension also.

If that doesn't make sense think about it this way - imaging you are the rear end pusing forward on the LCA (only place the rear end pushes forward on the car). If it is perfectly horizantal all the force you are pushing forward with goes straight to forward force. Now if we lower the car the front end is being pushed down - so was we push forward we are also pushing down - this causes the rear end to squat - but the reactive (opposite force) is the car picking up on the rear end - not a good thing.

Now if we make the back portion lower than the front when we push forward we also push up on the car raising the rear end - the reactive force is the car pushing back down on the rear end - giving better "traction".


Chris Bennight

 

I realize how old this thread is, but had a bunch of success with F Body torque arms at the drag strip, of course, after sub-frame connectors, LCA relo brackets and shorter TQ arms with dedicated crossmembers...

Regardless, here is an updated video I did on F Body Drag Racing Suspension mods. Hope it helps in some way...

 

i only got 80,000 miles on my car only drive few thousand a year a 98 z28 ls-1 i believe the arm bangs some up ,down upon stepping on and off the gas, as long as theres no danger of the bar knocking the exhaust down and catapulting its driver and passengers im ok w/ lil banging stock arm

 

You sure it’s not a broken trans mount?

 

im not saying its a transmission mount im saying i believe these arms w/ rubbermount will bang some w/ gas on and gas off and that there prone to it ,now of course if the tranny mounts busted rubber from the mount thats reallly gonna sow up

 

I know you didn't say it was a transmission mount, You said "on my car only drive few thousand a year a 98 z28 ls-1 i believe the arm bangs some up ,down upon stepping on and off the gas," Sound like you were describing your car. If so:

Have you looked under the car to see if the trans mount is OK? Have you checked the torque arm bushing to make sure it hasn't rotted and fallen out? The torque arm should not be banging on anything if the trans mount and torque arm bushing are intact.