Fox body suspension help needed!

I need help figuring why my BB 92 Mustang street/strip car spins the tires hard on launch (leaving at idle) with very little weight transfer. I did some preliminary measurements today and used an online Instant Center Calculator to determine the following:
IC length=38.4
IC height=10.433
Anti Squat=135.181

The car has a tubular x-member w/ 1.5" drop and 1" setback, QA1 coilover struts w/150# springs, double adjustable rear uppers, single adjustable rear lowers, QA1 single adjustable coilover shocks w/ 110# springs. I've been running BFG 325x50x15 drag radials but switched over this morning
to M/T 28x13.50x15 ET Streets. I'm going to have to raise the rear to the next hole on the coilover brackets (about 3/4") in order to gain some tire clearance. I punched in the estimated changes in control arm heights to the formula (not taking into account CG change) and came up with the following:
IC length=48
IC height=12.567
Anti Squat=130.258

What do these numbers mean? Would this improve or hurt traction?
I also experimented with the calculator and raised the rear an additional .75" and raised the front .75" (for addditional header clearance) and came up with the following:
IC length=64
IC height=16.122
Anti Squat=125.334

Would these settings help or hurt?
I'm hoping to borrow a friends digital wheel scales this weekend and get more accurate info. I just need help in figuring which would be the best direction for me to go in. Any help would be appreciated, just realize this is a street car and I'm a novice in the suspension world.

The first set of measurements look way better than the second!

there are a few things to take into consideration

first the 325 BFG sucks, that doesn't mean you cant get them to work you'll just spend a lot of time figuring it out

Second check your struts the QA 1's are notorious for valving irregularities, a $40 rebuild would be money well spent, If you need the name of the company I use let me know!

Third the MT Street radial is a far better tire that the ET street, if you can swap I would highly recommend the radial over the ET street

When you get the car scaled post what you have because this would be useful info!

Good info.... you won't get better input!

I'm trying to get what I have to work, not planning on buying a different set of tires at this time. I have the ET streets because everyone said that the drag radials were junk! A fellow forum member "cobra tom" run's 9.80's on 12.50 ET Streets which are one inch narrower than what I have. I always thought that my car wasn't transferring weight because it wasn't hitting the tires hard enough, but after running the numbers I find that with 135% anti squat I'm hitting the tires too hard and they are bouncing off the pavement and breaking traction. I've been reading in Dave Morgans Doorslammers book, but it's not really geared to a stock unequal length factory four link. I was hoping that someone could give me a little insight into the fox body factory 4 link and how to get it to hook with the tires I have.
Also, my QA1 struts were just rebuilt by Naake Motorsports and the valving was loosened up from the original valving to improve their sutability for drag racing. My struts now at the full tight setting are about the same as they originally were at the halfway setting.
Gary

Naake is who I use so your struts should be fine! 135% anti squat is NOT too much unless you front weight percentage is over 60%, Unfortunately the ET street is not better than the radial, We have tested the tires back to back and the radial always out performed the ET street, but I understand you already have them so run with em'...

As far as your I/C length and height tak a look at a ladder bar set up most of the time it's 32'' length and a 6-8'' height and there are plenty of big block foxes with ladder bars and small tires working.

Get it on some scales and that will help knowing the weight bias front to rear.
Yes "door slammers'' is not really going to help you unless you have a tube chassis big block, big tire car built in 1989...Sorry some people consider it the Bible of chassis tuning, there is a lot of useful information in it to help someone learn about force vectoring, percentage of rise, inertia, and dynamic and static loads, BUT not much applies to stock suspension small tire set ups, yes a 4 link is a 4link but that's where it ends, what I have found building hundreds of these cars and working with even more people who have stock suspension mustangs is there are far too many variables,
Take a pro stock car for instance, big block, tube chassis, big tire, liberty transmission, clutch, most have the same struts shocks, etc. it's far easier to get a set up because most are built the same way and are close in power and gearing. Now take a fox with stock suspension, Tires vary from 26 inches to 30 inches in height, width from 8 inches to 12.5 inches, different shocks and struts because there are too many to choose from, different tire compounds and construction, different transmissions C4's, C6's Glides, turbo 400's, manual transmission, how many different converter and rear gear ratios are there to choose from, What I have found is that unless I build the car there allot of variables that need to be addressed and that there is not one simple set up that works on most cars, like a tube chassis big tire 4 link car with a clutch!
If you go with the theory that the IC needs to be on the neutral line between the center of gravity and ground the car Will work but only at about 70% of what it is capable of!
I could spend hours typing and only scratch the surface of what works and what doesn't. It's not rocket science but rather working with the tools that are available!

Thanks for the reply TeamZ. I don't have an all out racecar, so I'm not looking to get every last bit of ET out of it anyway. The car is mostly a street cruiser that will see occasional strip use. I'm just trying to find out what I can do to improve the hook so that I can get a starting point to get it to go down the track somewhat consistently. I'm going to try and get it on the scales as soon as I can. I think I'll adjust my ride height front and rear to see if their is an improvement in traction at any of the possible alternative IC locations. I figure to try and soften the hit on the tires some and see if I can get better traction, and then try to fine tune it and add in some more antisquat back in. My preference is to retain the stock suspension locating points so that the car would be legal for True Street if I want to try that in the future. I'm going to try to make it to Milan Dragway within the next few weeks, do you ever go there?
Gary

I finally got the opportunity to put my car on the scales. These are my preliminary readings of my car (with my big A** in the drivers seat) before making any suspension and ride height adjustments.
LF=1004
RF=915
LR=738
RR=715
Right now it shows 56.9% on the front wheels. I plan to make sure that my rear wheels are centered in the wheelwells and also measure the tire diameter to make sure the rollout is close. I'm going to raise the ride height a little for tire clearance and reset my pinion angle and sway bar adjustment before scaling the car for the final time.Do I have the adjustment procedure correct?
1) Unhook left upper control arm from rearend, and unhook swaybar from rearend on passenger side and leave hanging.
2)Set pinion angle w/ upper left control arm.
3) Adjust upper right control arm until the bolt can easily be slipped in and reconnect.
4) Adjust passenger side swaybar link until bolt can be easily slipped in and reconnect.

According to what I've been told this would leave my rear suspension neutral- without any preload. Then after a few practice launches I could determine if any preload is needed to get it to launch straight? Which should I use to put preload in -with the upper right control arm or the sway bar link. Does this procedure make sense or does someone have a better way to do it? What else do I need to check or do? It's a 5 hour drive to Milan Dragway, so I want to have everything sorted out before going.
Gary

bump

Wow, been gone from here a while and look who shows up. Dave Zimmerman.

Dave is the man on stock suspension, builds the best pieces and best of all he understands how to make them work.

Dave helped me through the setup on my stock suspension BB car and I'll pass it along.

The back of these cars are not that complicated nor can you do much with the adjustments. For example you can not preload with the control arms (these are not true 4 links) and you can't make major ic adjustments like you can with a true racing 4 link.

1. First and foremost weld everything related to the torque boxes, weld everywhere the mig nozzle will fit, and then weld some more. If the body and torque boxes are flexing around you will never get the car to work (and you will break stuff). Dave told me to weld until I was tired and then weld until I was tired of it 3 more times.

2. Set the ride height of the car so that the lower bar is level or slightly (1 deg.) up at the front. If you want the car to "work" the "look" will have to come second. With my lower bar level the car is slightly higher than I really want, but I want the car to "work" so it stays as is.

3. Center the rear (in the car and in the wheelwell), set your pinion angle, and tighten the crap out of the bolts. I mean tighten them like there is no tommorow. Loose rear suspension bolts cause most of the bending and breaking you see.

4. Set your sway bar for no preload as you described. Make a hit or two and see where the car wants to go. If it goes a little right put 1/8 turns of preload in the right sway bar link (make the link longer). You can not add preload to these cars with the control arms. Do not put more than 1/8 of a turn in at a time, you won't believe how much difference that little of a change will have on the car. Obvious to this is making sure your rear tires have the same rollout, same airpressure, etc.

5. Set your rear shocks at halfway and see what happens. If you are hitting the tire too hard, back the shock off a little bit. Remember the shock is a "dampner" and the tighter it is set the less dampning it will do resulting in hitting the tire harder.

Now for the business end of a stock suspension Mustang. The front.

6. If you are not transferring any weight you need to keep loosening the front struts up until it starts to "work". With as much front strut travel as these cars have they will almost "jump" off the ground if the struts are loose enough. if you are full loose and the front is still not transferring you need a smaller spring. I run the 150 spring also but have more front weight than you.

This should get you close and atleast going down the track. You will have to fine tune it from here. Every car reacts somewhat differently to changes. Make changes one at a time until you have a good handle on it.

There are some varibles you haven't covered yet:

1. Is it a 8.8 with stock mounting points? If not is it a 9" and who built it? I ask because Dave and Strange are the only guys (that I am aware of) who are building the 9" Mustang housing with the mounting locations in the right places.

2. How much air pressure? Not sure what the street tire likes but with 28 x 10.5 slicks these cars like quite a lot of airpressure. Almost double the airpressure I ran in my other car with 31 x 10.5w's and ladder bars.

3. Double check everthing front and rear to make sure it is not binding, esp the front A arms. Are they stock or race pieces with rod ends instead of bushings? Either way they must be completely free moving. I.E. if you jack up the car and take the strut loose the wheel should drop freely.


Hope this helps some atleast.

BTW, Dave is good people. You can not go wrong either buying his stuff ( http://www.teamzmotorsports.net/ ) or listening to him for advice.

wow, good stuff, quality info:D

Jamie, thanks for your detailed description of stock suspension setup, it will give me a good starting point.
1) Its a narrowed stock 8.8.
2) So far I've run them with 14# which is probably a little high, Cobra Tom says his work best at around 11.5#.
3) The control arms are PA Racing chromemoly w/ delrin bushings. The wheel will drop free if the strut is unbolted from the c/c plate. Everything seems to be free, I removed the springs from the rear shocks and cycled the rearend up and down to check for free movement and everything seemed ok.
The torque boxes were welded up by Pande's Performance in Livonia when they put in my rollbar, they did a pretty good job. It's not "continous" weld but I'd say it's at least better than 60-70% coverage. I'll try to weld everything up completely this winter and maybe install battle boxes, better safe than sorry!

Again, thanks for the help!
Gary

BTW, Dave is good people. You can not go wrong either buying his stuff ( http://www.teamzmotorsports.net/ ) or listening to him for advice.[/QUOTE]

Jamie could not be more correct, Dave is one of the nicest people I have ever met and he graciously took the time to give me some pointers on my Mustang at the NMCA race in Milan, not many people that will take the time to do this in this industry. Dave will get all of my future business.

Very, very good info here guys! Great stuff.

I may have missed this, but,

1 It is stock suspension right?

2 What is the pinion angle? This is VERY important

3. It may work better if you don't leave at an idle in order to shock the suspension and load the tires. I have seen some n20 promods drive like crap when making motor passes because the suspension isn't loaded.


just my 2 cents

I may have missed this, but,

1 It is stock suspension right?

2 What is the pinion angle? This is VERY important

3. It may work better if you don't leave at an idle in order to shock the suspension and load the tires. I have seen some n20 promods drive like crap when making motor passes because the suspension isn't loaded.


just my 2 cents
1) Stock suspension locations, double adjustable uppers w/ spherical housing bearings, single adjustable lowers, single swaybar, and coilovers.
2) It was set at 1 1/2 degrees.
3) I did 1 practice launch leaving at 3,000 (in the driveway!) and it seemed like tire spin wasn't too bad, but I had the sway unhooked and it wanted to turn hard right. After I get everything checked and reset I plan to head to the track in a couple of weeks for some testing and I'll experiment with this again.
Thanks for the help, I'm sort of new at this ( I was a country road street racer back in the 70's!) and the car has never been to a real dragstrip!
Gary

I think you need more like 3 degrees on the pinion angle. You really can't compare what its gonna do at the track to the driveway. I had a stock suspension fox with a 514 in it and I left at about 5200....you gotta really "hit" that suspension.....just my opion

You really can't compare what its gonna do at the track to the driveway.
Actually, the place I'll do most of my racing at is quite similar :D!
http://gov.boynecity.com/government.phtml?catid=293
The return road is a city street and you get to drive down it with open headers and slicks, and the Police just wave and smile!:cool:

As far as pinion angle it was set to what was recommended by Wolfe Racecraft for a car with spherical bushings and heim joint control arms. Cobra Tom says his car which has a similar setup w/ ET Streets likes 3 1/2 degrees best, I'll probably experiment with 3 to 3 1/2 degrees and see what it likes. When get to the track (hopefully soon!) I'll be able to experiment with launch rpm and see if it likes to leave with more rpm. I'm open to any advice given.
Gary

i run 3.5 and my car sixties 1.28 9 out of 10 times ,or 1.30 thats it -- car weighs 3300 with a BBF th-400 stock style suspension

i run 3.5 and my car sixties 1.28 9 out of 10 times ,or 1.30 thats it -- car weighs 3300 with a BBF th-400 stock style suspension
Have you ever plotted out your IC with your current setup?
Gary

Adjusting "pinion angle" is not a chassis tuning tool to "hit" the tire in most drag cars, that's an ancient myth. It can only have an effect on cars that rely on a pinion snubber type traction device. And even then it's not the angle that has an effect, but the size of the air gap between the pinion housing & the snubber.

You only set the pinion-to-driveshaft operating angle (or "pinion angle") in a drag car (and slip yoke-to-driveshaft operating angle) to a given number to keep the U-joints happy under launch loading. "Happy" in a drag car means under launch loading there's no unwanted binding/frictional losses (it's working as close to zero degrees operating angle as possible). Excessive binding/frictional losses caused from too much angle under load (either too much "nose down" pinion vs driveshaft, or "nose up" the other way) can tear up U-joints in a drag car.


The reason Wolfe suggests 1* to 1.5* pinion-to-driveshaft operating angle with all metal bushings is because their not going to squish/deflect like a rubber or urethane bushing will. Less bushing squish/deflection means less pinion rotation will happen under launch loading with solid bushings, and so less "at rest" static pinion angle is needed. Rubber/urethane bushings will squish/deflect more under load so they require more "at rest" static pinion angle adjusted in to prevent the pinion from rotating the U-joint operating angle up past zero degrees under load.

http://www.wolferacecraft.com/pinionangle.aspx (http://www.wolferacecraft.com/pinionangle.aspx)

Dave, thanks for the clarification on pinion angle. I'll leave it at 1.5*.
Gary

what is the proper way to measure the angels? can it be done on either end of the installed drive shaft or must the shaft be removed?

i am 58 % front and 42% at the rear my car works awsome -with a 1/4 turn on my front passenger strut spring i went from 62 % to 58 % havent touched it since

i also went from 1 on pinion angle to 3.5 and have never touched it - but what do i know my car only sixties 1.28 :(

i am 58 % front and 42% at the rear my car works awsome -with a 1/4 turn on my front passenger strut spring i went from 62 % to 58 % havent touched it since

i also went from 1 on pinion angle to 3.5 and have never touched it - but what do i know my car only sixties 1.28 :(

Have you ever plotted out your rear suspension IC? I've been experimenting with changing the front and rear ride heights and then measurng and plotting everything out using an online IC calculator. That way I'll have an idea of what effect it will have if I want to make changes in the future.
http://inductionmotorsports.com/im/ic.html
I'd be interested in seeing what your settings are since your car 60's so well. I wish someone would write "Fox Body Suspension for Dummies", I'd buy a copy!
Gary

im not expert-by far but i think some people try to over analize it-

im not expert-by far but i think some people try to over analize it-
My car didn't hook very well to start and then I put in a bigger engine with 100 more hp and even more torque, I wonder why it just wants to spin the tires:rolleyes:? I guess I'll just have to wait for the "Dummies" book to come out.
Gary

what rear suspension are you running- whats your pinion angle- there are many issues is the car transfering th weight shock settings front strut settings ?

what rear suspension are you running- whats your pinion angle- there are many issues is the car transfering th weight shock settings front strut settings ?
I'm running a Wolfe rear suspension- double adjustable uppers, single adjustable offset lowers, single swaybar, and QA1 coilovers w/ 110# springs. I've got a set of QA1 adjustable struts w/ 150# springs that were rebuilt and revalved by Naake Motorsports. The valving now at full tight is about the same as they were originally at halfway. I usually run the struts full loose. I was running the rear shocks at 3 clicks from loose, but lately have been trying them from 5-7 clicks to soften the hit. I'm not trying to overanalyze the whle thing, I just want to have my "ducks in a row" when I get it to the track. I've been unemployed for 10 months and don't have alot of money to waste. There are no dragstrips close by, and a trip to the strip becomes quite an expensive roadtrip with gas and a motel.
Gary

i think some people try to over analize it-
Pro Mod racer Bill Kuhlman once wrote in a drag magazine article that people worry too much about I/C placement and should just basically pick any I/C point and go with it. But that might be more true for them since they are going to be doing a lot of tuning for launch hook with the clutch. Gerry your good hook & 60's are more likely the result of your good I/C placement choice & shock/strut valving choices than your pinion operating angle choice.


Now back in ancient times some drag racers did use excessive pinion angle to purposely introduce U-joint binding & frictional losses as a way to "steal away" some of the engine power reaching the tires to help a car that spun at the launch try to hook. But this is a dangerous idea and can lead to dramatic U-joint failures.


Don't remember which driveshaft site these numbers are originally from but they show how max U-joint operating angle has to decrease as max drivshaft RPM increases.

DRIVESHAFT RPM vs MAX. NORMAL OPERATING ANGLE.........
5000 = 3.25º max
4500 = 3.67º max
4000 = 4.25º max
3500 = 5.00º max
3000 = 5.83º max
2500 = 7.00º max
2000 = 8.67º max
1500 = 11.5º max


what is the proper way to measure the angels? can it be done on either end of the installed drive shaft or must the shaft be removed?
The driveshaft being in the car is the best way to accurately get the front & back U-joint operating angles (and to tell if they are positive or negative). You just need a way to get under the car while it's full "race weight" is sitting on the front/rear suspension compressing it so the car's sitting at it's race ready ride height. The front & rear U-joint operating angles are the difference between the combined angles at each U-joint. At the front it's the engine crank/trans output/slip yoke centerline vs the driveshaft centerline, and at the rear it's the driveshaft centerline vs the pinion shaft centerline.

Take for example a common "point the crank C/L 100% directly at the pinion C/L" drag racing use only setting for a full chassis car with a low crank nose height number & a tall rear slick diamiter. Lets say with the car sitting at race ready ride height the engine is sitting nose down in the chassis & measured at 1* nose down with an angle finder (so crank nose= -1* down & tail shaft= +1* up from level). Now lets say that the drive shaft C/L is also 1* nose down measured with an angle finder (ds front= -1*down & ds rear= +1* up from level). This would give you a front U-joint operating angle (or "slip yoke angle") of 0.00* (+1* & -1* = 0.00*). Now contuning on lets say the rear pinion shaft C/L is sitting nose down at 2.5* with an angle finder (pinion front= -2.5* & pinion rear= +2.5* from level). Now using the previous driveshaft numbers this would give you a rear U-joint operating angle (or "pinion angle") of -1.5* (+1* & -2.5* = -1.5*).

gtmustang- call me ill try and help 330-730-3491 gerry

Thanks Dave that is the best explination I have had yet

Larry


Pro Mod racer Bill Kuhlman once wrote in a drag magazine article that people worry too much about I/C placement and should just basically pick any I/C point and go with it. But that might be more true for them since they are going to be doing a lot of tuning for launch hook with the clutch. Gerry your good hook & 60's are more likely the result of your good I/C placement choice & shock/strut valving choices than your pinion operating angle choice.


Now back in ancient times some drag racers did use excessive pinion angle to purposely introduce U-joint binding & frictional losses as a way to "steal away" some of the engine power reaching the tires to help a car that spun at the launch try to hook. But this is a dangerous idea and can lead to dramatic U-joint failures.


Don't remember which driveshaft site these numbers are originally from but they show how max U-joint operating angle has to decrease as max drivshaft RPM increases.

DRIVESHAFT RPM vs MAX. NORMAL OPERATING ANGLE.........
5000 = 3.25º max
4500 = 3.67º max
4000 = 4.25º max
3500 = 5.00º max
3000 = 5.83º max
2500 = 7.00º max
2000 = 8.67º max
1500 = 11.5º max



The driveshaft being in the car is the best way to accurately get the front & back U-joint operating angles (and to tell if they are positive or negative). You just need a way to get under the car while it's full "race weight" is sitting on the front/rear suspension compressing it so the car's sitting at it's race ready ride height. The front & rear U-joint operating angles are the difference between the combined angles at each U-joint. At the front it's the engine crank/trans output/slip yoke centerline vs the driveshaft centerline, and at the rear it's the driveshaft centerline vs the pinion shaft centerline.

Take for example a common "point the crank C/L 100% directly at the pinion C/L" drag racing use only setting for a full chassis car with a low crank nose height number & a tall rear slick diamiter. Lets say with the car sitting at race ready ride height the engine is sitting nose down in the chassis & measured at 1* nose down with an angle finder (so crank nose= -1* down & tail shaft= +1* up from level). Now lets say that the drive shaft C/L is also 1* nose down measured with an angle finder (ds front= -1*down & ds rear= +1* up from level). This would give you a front U-joint operating angle (or "slip yoke angle") of 0.00* (+1* & -1* = 0.00*). Now contuning on lets say the rear pinion shaft C/L is sitting nose down at 2.5* with an angle finder (pinion front= -2.5* & pinion rear= +2.5* from level). Now using the previous driveshaft numbers this would give you a rear U-joint operating angle (or "pinion angle") of -1.5* (+1* & -2.5* = -1.5*).

A long read but well worth the time!

http://www.yellowbullet.com/forum/showthread.php?t=172353

A long read but well worth the time!

http://www.yellowbullet.com/forum/showthread.php?t=172353
Thanks Dave, definitely a long read- but exactly the info I was looking for. I guess I'm not the only guys with traction issues. Just as in the yellowbullet post, it looks like adjustment of ride height is the key to traction if you can't move the locating points. I'm going to play with my current setup and see what it will do, and then maybe go to your relocated lower mount (the one with the adjustment notches like a nascar track bar). I've been checking out weather.com and hoping that we get alittle warmer weather. I'd like to take my car to Milan on the 21st for it's first 1/4 mile test n tune.
Gary