StangEaterSS

iTrader: (41)

I am struggling here getting the car to 60ft correctly. nitrous LS motor with th400 with brake and 3.73 rear gear on 28x10.5 slicks. Leash progressive controller. Car has Madman custom valved afcos in the rear with wolfe spring perches and 150# rear springs. UMI double adjustable LCA's, LCA brackets in the lowest hole. UMI long TQ arm with adjustable front mount on crossmember ( set in middle in the stock location hole) UMI drag bar anti roll bar. front is all race craft tubular chromoly parts. QA1 R series 12 way in front. Travel limiters set with 1-3/4" travel.

Car on small jets will 60ft 1.26-1.27. this is 30% start with 1.25 sec ramp. which is not great but i'm ok with that. on 100 hp more the car wont 60ft better than 1.36-1.38. some passes the car wheelies and 1 car out the back tires break free and its smoking the tires while doing a wheelie and the front slams down. most passes look like the video below. the car bounces alot. it doesn't look right. I have the ramp on the progressive dialed all the way back to 2.0 second ramp and only 16% start on this pass. tried pulling as much power as we could out and still no luck. Is my instant center and anti squat numbers all wrong since I lowered the car this much and added more power? Is this just a shock adjustment problem? I'm clueless here. I haven't measured and figured out and IC numbers with control arm angles or anything since this was a 10 sec car years ago. car is lower now and makes way more power.

ATwelveSec02Z28

iTrader: (17)

Happen to have a datalogger with driveshaft and engine RPM?

Looks like some converter issues and or lean spike

StangEaterSS

iTrader: (41)

No logger. I was suspecting convertor issues since at the top end it was at 8,000rpm thru the traps with a 3.73 gear. Seemed like a lot of convertor slip.

ATwelveSec02Z28

iTrader: (17)

Really need data to know what's happening.

as a guess there may be a lean spike.

Bitemark46

Slow the front down. Looks like the shock tops and and comes down fast. In the vid when your rear tires pass the starting beams the nose already down and bouncing.

What are you shock settings at?

-Mark

lazaris

iTrader: (5)

This the first place to start. Those QA-1R shocks in the front will probably not be enough to slow the front down enough even at full tight. Where are they now?

StangEaterSS

iTrader: (41)

Front shocks 6 out of 12 clicks on rebound. Compression is set full stiff and non adjustable I belive on these R series. The rears are afco double adj. compression right in the middle. If it's 40 clicks it's on 20. The rebound on this pass was 15 from full loose on a 40 click range. Tires 14psi

lazaris

iTrader: (5)

Tighten the front extension all the way. Rear Tire pressure looks low. Are they stiff side wall?

StangEaterSS

iTrader: (41)

28x10.5 stiff. M/T et drag

lazaris

iTrader: (5)

Add pressure till 60' drops.

TTur1996

Get rid of the long torque arm. And get a shorter one that only goes to the tunnel brace. Then get rid of the travel limiters and let the suspension work. You have very good shocks. Let them work. The shorter torque arm will keep the front end down but still transfer the load to the rear tires. Tighten the rear shocks on extension only to the point of spinning. Then back off a couple clicks. Only tighten the front enough on extension to keep the front tires barely touching. The front shocks should be 60% colapsed at ride height so you have plenty of travel on extension. We only have ours on 3 clicks but our car only weighs 3000. The springs on the back shocks should only be preloaded 1/8 inch with axle hanging. Do not crank them up to adjust ride height. Ride height in rear should be adjusted by the spring rate. We have 125's on ours. This will get you real close. Best of Luck.

StangEaterSS

iTrader: (41)

I had some time to scale the car and measure some things. here is what I got last night.

ride height, ground to fender lip:

RF 26-3/8"
LF 26-3/8"

RR 27-1/2"
LR 27-1/2"

scaled corner weights with me in the car with helmet, nitrous bottle, fuel in the car fully ready race weight.

RF 865
LF 894
RR 734
LR 852

total weight: 3,345

Nose percentage 52.5%
Rear percentage 47.5%

Rear control arm angle. 2.5 degrees down hill from body running toward rear axle.

long TQ arm. 60" long.
control arm length 19.5"
height to rear control arm bolt 7.3125"
height to front control arm bolt 7.8125"

wheel base 101.5"

Center of gravity height 19.4375"
Center of gravity length in front of rear axle 53.2875"

Instant center length: 60"
Instant center Height 8.9375"

Anti squat percentage 78%

I used this site for TQ arm calculations for anti squat.

http://www.shopeshop.org/tim.13.htm

These are my numbers and came out with 78%


I don't exactly understand the " horizontal dist. to rear pivot" I'm guessing this is if your rear bolt on control arm is not center with your axle tube. I entered zero since mine are inline with axle.

After playing with numbers and seeing what makes anti squat % go higher, I found that i would have to drop the rear of my control arms over 2" lower to get this to 110%. They are currently in the lowest hole on a bracket that is 1/4" higher than the lip of my rim. This does not seem realistic to add to the bracket and make it nearly scrape on the ground. They next number i played with was TQ arm length. if i shorten the 60" TQ arm to 40" its around 110% also. This seems doable with buying a new TQ arm.

I'm not sure if my math is totally correct or this link to the calculator is accurate, I'm no expert. What do you guys think my target IC and anti squat should be? whats the best way to get there? buy new TQ arm?

StangEaterSS

iTrader: (41)

I think you have this backwards. From my math the shorter arm brings the instant center backwards and that will hit the tires harder. I'm scared it will put it on the bumper if i buy a short arm.

lazaris

iTrader: (5)

Did you try what I posted?

StangEaterSS

iTrader: (41)

Won't be back at the track for a few weeks.

TTur1996

Leverage. If you were able to tie the rear tires to the ground, (which is exactly what your trying to do). Where would it take more force to lift the front tires off the ground, at the trans mount, or the tunnel mount?

SteenH

Wrong.

Bitemark46

The longer the IC the longer the lever/leverage is. But it also means a lower AS. Which is why yours is so low. Longer IC's apply less downforce to the tires but they apply it over a longer period of time. Shorter IC's hit the tire harder (more AS) but do it for a shorter period of time. The key is to find a balance.

Slicks need a different AS than a radial. They need around 100-115%.Then fine tune the shocks/struts or the ARB if it goes left or right off the hit.

If you switch torque arms and shorten the IC, the AS will go up but just make sure still slow the front down. You might end up with a nice wheel stand but they suck coming down. Buying pans and headers ain't cheap.

Hope this helps.

-Mark

StangEaterSS

iTrader: (41)

ok, So I'm picking up a short arm today after work. it puts my IC at 46" from the rear axle. the anti squat goes up to 101% now. I am going to set the front QA1's maxed out on 12 for stiffness and I will run 15psi in the tires instead of 13-14. Id rather have it spin than go on the bumper first pass.

TTur1996

Don't go max effort on the first pass. Sneak up on it. Try 18psi on tires. If you go full tight on the shocks its almost like having travel limiters. You want to control the rise not contain it. Try 3 to start. Ideally you don't want the tires to even come off the ground. Start low on the launch RPM. By letting the front end come up to full shock travel it will transfer the weight to the rear better. In the video you can see the back looks good but the front starts to come up and then it hits the limiters not letting it completely transfer the weight to the rear and then unloads and repeats. You probably had bad tire shake. Video tape what the suspension is doing every pass and watch it closely. It should come up smooth and easy while moving forward the whole time, and hold with the tires just barely touching the ground. Then you got it all. Best of Luck