Chassis Reinforcement

paul_huryk  Mar 31 2006 - 4:44pm   

We all know that the third generation f-bodies are unit body cars thereby having only partial front and rear subframes. Unfortunately,the way GM built these cars to save money cost the cars a lot of chassis flex. I would compare the f-body to a 4' x 8' piece of 1/4" plywood,it is strong,but flexes too much. By adding 2" x 4" wood and attaching it to the outside edges,you make it flex less and have greater overall strength. This is the analogy I use,mostly because subframe connectors are the ' 2" x 4" ' on an f-body. Many people think that stiffening the chassis is unnecessary unless you drag race your car. They are wrong,chassis stiffening is the single most important item in making a car handle better and it also has other benefits also,not without faults too. The mods I suggest will not harm drag racing performance(strut tower and steering brace),and are certainly worth the money and effort.

Subframe connectors are probably the most thought of items when chassis reinforcement pops up. There are many companies that sell subframe connectors for third generation f-bodies,as well as many other cars. You want to buy subframe connectors that are either weld-in only,or bolt ins with the option to weld. I don't like the bolt-ins because the tremendous stress on the bolts causes the holes use to become larger,rendering the subframe connectors less effective over time. I bought the global west connectors because when I bought them,they were the only weld-ins on the market(1991). Unless you are a welder,send the car to a chassis shop or welder with car experience. Figure on spending $125 to $175 for the labor. From experience,every car I know that has had subframe connectors put it inproved handling and that "solid" feel. The bad part about subframe connectors is the weight (usually 20lbs) that it adds to a car,fortunately the weight sits very low,and doesn't make the car handle worse.

Another item that you may know about is the strut tower brace. They were around on mustangs back in the 60's. Those of you with TPI cars have been able to buy strut tower braces for a few years,now Edelbrock has started making them for carb/TBI cars also. You may not realize it,but when you make a turn,your strut towers may move up to 1/2" from the force of cornering. This movement or "flex" alters to alignment of your front end in the negative direction,keeping the towers tied together with a strut tower brace eliminates the flex. I don't have one in my car yet(and I'll get one by x-mas),but a friend with a fourth generation car assured me that the car feels tighter in the front end,but also handles noticeably better. I know that a few companies offer them,but I lean toward the Edelbrock braces because it triangulates the strut towers with the firewall lip,making a stronger front end that just a strut to strut only brace. The braces weigh no more than 6-7lbs,so you the car won't be noticeably slower in acceleration.

Another worthwhile part to get is a steering brace made by Global West. It mounts under your front sway bar using the stock sway bar bushing bolts. It locks the bottom of the subframe from moving side to side,it also makes an improvement in steering response and tightness in the front end. It only costs about $40 and weighs 4lbs. I think everyone should have one,especially at only $40

Suspension and Modifications

Suspensions are the most complex part of the car and are hard to tune compared to engines. Some people like "loose" cars-ones with stock parts,others like "tight" cars-ones that are stiffer and lean less. Truthfully,I don't have any track experience,so I can't say what is better there,but a "tight" car is much better on the street.

Third generation f-bodies were blessed by GM in the suspension department. They are the best handling solid axle rear drive cars ever built period!With only the front end alignment to worry about,the car is perfect for street handling. You may think that cars with independent rears (corvette,928) handle better than solid axle cars. They only do if the rear suspension has minimum deflection(none do),and the rear alignment is perfect (never happen on a street car). The truth is,when you stiffen up a car with a solid rear axle,it will handle better with street tires and street alignment than an independent rear car. It's only because the rear is locked in place,and can't deflect,simple but extremely effective. The front end is also simple,with easily changeable struts and springs-just be careful!

Like I said,"tight" cars handle betteron the street because:the lack of body roll does not shock the tires into losing grip and:street cars are usually aligned to make more effective use of tires(pure street tires) more than a race "loose" car. The tight car has another advantage:better suspension geometry directly related to less "lean" in the turns.

  • Springs and Shocks:
  • Like the cam and heads on an engine,Springs and shocks must be closely matched for optimum performance. Springs come in a million different rates(lbs/inch),and are used for different applications from drag racing to road racing,and all imbetween. Shocks can be valved to the rate needed by particular springs(not adjustible,but valved at factory). When you buy springs(from whoever),if the company cannot suggest shocks that are closely matched,buy somewhere else,because your combo needs to be very close. One word about adjustible struts/shocks,they tend to leak faster than non-ajustibles because they are usually higher pressure with more moving (internal) parts.

  • Sway Bars
  • Sway bars are used to control body lean that the springs and shocks can't,and can either help or hurt the handling performance of your car. Usually a car with stiffer springs and shocks calls for larger sway bars,but not always. It depends more on the total package of engine power,car weight,and most importantly driving style(driver's preferences). There were so many different suspension options offered on third generation f-bodies,all with different size sway bars. Instead of spending $150+ a piece,go to a junk yard and buy used ones of different sizes for front and rear(they don't wear out!). One item I would say is absolutely worth the money is changing to polyurethane sway bar links and bushings. The bushings are less flexible and transfer energy to the bar quicker,resulting in better steering response.

  • Tires
  • Tires are without doubt,the single most important item in a car's handling arsenal.

    The largest wheels that came on f-bodies were 16",usually with Gatorbacks. Since the wheels are so cheap now,there is no excuse to get a set,especially if your wheels are 15" or smaller(my car came with 14" wheels!). Cars with a lot of suspension mods need 17" or larger wheels,coupled with wider tires and stickier tread patterns. Through the years,either friends or myself has had almost every brand and style. The best tires for handling I have ever had were the Dunlop D40M2 tires,they offer slightly better performance than gatorbacks at less money per tire. Today,there are better tires than that,I would suggest three tires that are superior to every other(except treadwear): Bridgestone Potenza S02(big money!),Yokohama AVS intermediate,and Dunlop's SP8000. Tires I would not suggest are:Goodyear GSC's(way too much sidewall flex),Michelin MXX3 (tirelife too short),and Pirellis(overhyped and definitely overpriced. Some other good,but less expensive tires are:Dunlop D40M2,Bridgestone potenza RE71,Yokohama A008's.

    If you are planning to go from say 16" wheels with 245-50/16 to 17" wheels,get at least 265-40/17,or your car won't handle noticeably better. Larger wheels serve two functions: To decrease sidewall and increase sidewall stiffeness,and the ability to mount wider tires that offer increased grip. Choose carefully,tires and wheels(aftermarket) are not cheap!

  • Other Useful Modifications:
  • The only other mods you can do are rear suspension. Changing the stock rear control arms and panhard rod to stronger aftermarket items will definitely improve handling. Another item which will help handling(and straight-line traction) is replacing the stock torque arm with an aftermarket one. I think Global West is the only company that offers one for third generation f-bodies,it costs $550. Global West told me(on the phone) that their torque arm will improve handling by keeping the rear axle in the proper place better than aftermarket control arms with a stock torque arm. I was also told that a car will hook better in a straight line because the torque arm acts like a ladder bar when in a straight line. It sounds like a definte for me,I'll buy one in the spring and post results here. Another item which is worth mentioning is aftermarket tie rod sleeves. They are stronger than stock,but are also easier to adjust alignment with. They go for about $40.

  • Driving:
  • I want to warn those of you who don't have modified suspensions not to think suspension work will let you "fling" the car around more than the stock suspension was capable of. A "tight" suspension is meant for smooth driving,jerk the wheel and you'll put the car off the road. The car will certainly handle better,but it needs to be driven properly or you'll wreck it. Sometime next summer I plan to go to a professional driving school,just to teach me how to control the car in high speed situations. As it is now,I get nervous driving fast,mostly because the car's limits are so high getting over my head could kill me.

     
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