Took my 92 z28 drag car out the last two weekends, stock suspension car, 28x10.5 hoosier slicks. When I bought it last year it had a home made trans crossmember and frame connectors, every thing else is spohn, moser 9 inch 4.56 gears, also had a 1 3/4 roll bar. Over the winter I install a new 1 5/8 cage from s@w and make new round tube connectors and buy a spohn trans crossmember for a powerglide w/driveshaft loop. I checked the pinion angle before I removed all the homemade stuff and to my surprise it is exactly where it was after the new crossmember..the pinion is down 1 degree. The car is not lowered. Last fall on three test and tune nights it went 1.27 60ft and ran 6.19 as its best time, now it's best is 1.37 60 and runs 6.37 et's. I have really thought this over and now see what i missed, The torque arm was solid mounted to the old crossmember and now it can move on the new crossmember. Was it acting like a ladder bar? With no other changes to the car other than removing stock seats and installing a kirkey, it just don't leave like it did. Any thoughts on this, am i grabbing at straws ? Oh I almost forgot we had to let the front end limiters off about an inch to get the weight to transfer. it has 90/10 struts and a PA tube crossmember. Sorry for the long post...
Thanks for your help.

 

The torque arm does act sort of like a long ladder bar. If the front height is adjustable, lower it and readjust the pinion angle then try again. The lower the front mount is, the harder the tires will be hit but too low can cause tire shake. Raising the front mount will lessen the amount the tires will hit which can cause wheel spin but a higher mount also lifts the front of the car more making it prone to wheel stands. Knowing how much to raise or lower depends on where the neutral line is.

Removing the 1-3/4" roll bar and installing a 1-5/8" cage probably added a bunch of weight to the car although changing out the seats may have reduced the same amount of weight.

 

a torque arm is not like a ladder bar.

ladder bars transfer foward motion to the chassis as well as upward twist from the rearend.
a torque arm only transfers the upward twist of the rearend.

the torque arm cannot be solid mounted with no slider joint, since it would cause bind. the lower control arms are much shorter than the torque arm, so they have a different arc of travel.

raising or lowering the front mount on the torque arm will not make much difference since the arm will still be pushing up in the same location on the chassis. what will make a difference is changing the length of the arm. a shorter arm will hit the tires harder than a longer arm.

what is your engine combo? 1.27 is a pretty healthy 60' to just be running 6.2x-6.30's.

 

The torque arm mount is not adjustable..I can move the pinion at the housing though. The engine is a 427 sbc, 13 to 1, roller on alky, glide 5,500 convertor. I did not weigh it before the work, but I scaled it before going to the track and it weighs #2865, 47% rear 53% front, #3142 race ready...

 

If both runs were at the same track then it could be something as simple as track prep. From last year to this year, the track may not have the same good prep. You'll spin off the line and the ET will be slower.

What were the MPH times of both runs? If they were similar then the car is making the same amount of power and it's probably a traction issue.

I was at 2 different tracks this year a week apart. First track had great traction but my 60' time was with the back tires so I can't compare them. The 330' times were 3.708 with good traction and 3.949 with poor traction. Nothing was changed on the car. MPH was actually better on the poor prep track as it was at higher altitude and my fuel mixture was running a little richer and made more power.

 

pinion angle adjustments wont help any either. to improve 60's you will need to adjust lower control arm angle and rear shocks to manipulate how the car hits the tires. then you have weight transfer adjustments like front shocks/springs/limiters...

 

Well you guys have good points..it was at two different tracks but they are usually close. Track prep does make since..memory is a tricky thing ,I pulled out last years time slips and noticed it is down 4 mph from last fall which is a lot...gonna keep looking for the cause.
Thanks for the help..

 

how was the weather in comparison?

 

cool fall air vs. hot and really high humidity.

 

Cool air makes HP. Hot, humid air does not. You're comparing apples to oranges when trying to compare both runs. In the fall, you'll probably run as quick as you did last fall.

 

I hope you are right, my other car is not that different from fall to summer. Will just have to wait and see..

Thanks

 

...I beg to differ. While a tq arm suspension has a somewhat "floating" instant center point due to the floating front mount, changing the height of the front mount does indeed alter the IC which is a big key in suspension tuning.

Altering the control arm mouting certainly increases/decreases starting line traction, but the much shorter arm length means a greater % of change. If you only move the control arms you may get the desired results for 60', but you may also be going the wrong way for traction/handling down track.

 

That was one of my concerns, have I moved it out of the zone, but measuring pinion before and aft says it's in the same place as it was. I probably should try a different track or wait for cooler weather before making drastic moves..

 

https://www.thirdgen.org/forums/post...00-post28.html

from the diagram, you can see the front mount on the torque arm determines the ic of the car in a vertical line. moving that mount up or down wont matter, since it will be on that vertical line. moving it horizontally will matter, however.

 

Are you on race gas or alcohol? If your on race gas then the heat and humidity will hurt it a good bit. Also small tires (28x10.5's) will really struggle on hot greasy track compared to a cooler sticky track in the fall.

 

Alcohol, I think the hot greasy track is most of the prob. I'm not used to the small tires either. My other car has 32x14...

 

I've seen that before and iirc have the book that it's in. From personal experience I consider it to be a flawed "theory", as I've made height adjustments and seen the same reaction as making IC height adjustments on a 4-link, though part of the reaction change in either system would be due to the change in AS%.

I look at it this way - we all understand that the control arms dictate all forward motion transfered into the car, thus if you can keep the control arms level and get the required suspension reaction/traction via altering the tq arm adjustments/mounting point then obviously you're transfering more power into forward motion instead of rotation/planting the tires.





I've been seriously considering a custom "extreme duty" tq arm system in the camaro. I'm going to re-do the back-half when the current chassis cert expires, and could easily incorporate a tq arm system simply by leaving the upper links off the 4-link. Then if I can't get what I want out of it, I can always pull the arm and bolt the upper links back in for the tried & true system.

 

here is a 4 link setup. looks like if you cut your torque arm down to a 1"wide strip and attached it to the top of the rearend with a spherical bearing at each end it would work similar to a 4 link.

on a ladderbar, the ic will always be the front ladderbar mount/hole. (which is kinda how this 4link drawing is done, the blue lines form a ladderbar)

 

Update...went to another track and had the exact same sixty foot, 1.38. I'm thinking my best sixty foots at my old track were incorrect..On another note..took the newly instaled 3 inch flows off and lost 40 lbs. and picked up a tenth..60 stayed the same but It ran 6.28 on a breakout pass. Fall weather may improve on all the numbers..
Thanks

 

flowmaster mufflers are not power makers....been saying this for a while now. glad you found out too! my 3" dual x-piped exhaust with bullets actually decreases my 60' times...might wanna look into it?

 

I love my Magnaflow race mufflers. If I pull the exhaust, I can shed 45 pounds off the car but I like being able to hear things when the engine is running. My exhaust isn't restricting the engine from making power. It just adds weight to the car.

 

^ Side exit FTW! Quiet in the car and no extra weight.

Flow masters suck for power. Their race specific mufflers are ok, but their street stuff is nothing more than a noise maker.



Diggler - what you're talking is a 3-link system. They work well, but the placement of the upper bar is critical(side to side measurement/placement), as there is no way to set any pre-load, thus the upper bar has to be set perfectly to negate any torque steer. That system tunes like a 4-link but w/o any roll steer characteristics.

I'm thinking of running an actual tq arm; attached top & bottom of the rear housing and tied to a shackle type front mount.