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Drag Racing IRS In-Here, Need tips
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<blockquote data-quote="ClubVenom1" data-source="post: 15155552" data-attributes="member: 47265"><p>A lot of interesting comments here. I noticed some say "I think"... don't think, KNOW. Do some research. This is info taken from proven setups from real drag racers. This might shock some of you, but like I said... do some research.</p><p></p><p style="text-align: center">Drag Racing an IRS 101</p><p></p><p>Solid-Axle VS IRS</p><p></p><p>Under most circumstances, rigidly mounting the differential assembly to the chassis in an IRS-equipped car is a good thing since it reduces unsprung weight. This arrangement allows running softer springs rates and shock valving, which improves ride quality without sacrificing handling. However, planting thousands of horsepower from a standstill falls outside the realm of most circumstances, and the huge drawback of an IRS is that it limits the amount of anti-squat built into the suspension in a drag-racing application.</p><p></p><p>As a car accelerates forward, weight transfer causes the rear suspension to squat. Since the rearend housing and differential assembly are not mounted directly to the chassis in a solid-axle car, the rearend can separate (move downward) from the body to resist squatting. That’s what suspension designers and drag racers refer to as anti-squat. The icing on the cake is that the torque of the engine in a solid-axle car is transmitted through the suspension, which drives the rearend assembly and tires into the ground to enhance traction. According to legendary suspension engineer Herb Adams, manipulating the instant center allows a solid-axle car to achieve over 100 percent anti-squat, whereas an IRS is typically limited to about 25 percent anti-squat.</p><p></p><p>Suspension Recipe</p><p></p><p>Now lets get to the meat and potatoes. Setting up an independent rear suspension like a solid axle suspension is a recipe for disaster. An IRS requires a completely different suspension setup than a solid-axle car, and managing weight transfer is way more important. With a solid-axle car, you can adjust the instant center to make the body separate from the rearend, and smash the tires into the track. Solid-axle cars don’t squat at all, they just separate, lift the rearend, and take off. You can’t do that with an IRS. Instead, you have to MAKE THE CAR SQUAT, and transfer the weight rearward.</p><p></p><p>The Squat Factor</p><p></p><p>A solid-axle car and an IRS car work completely opposite of each other. A solid-axle car works on the premise of separation to plant the rearend into the ground, but the only way to get an IRS car to launch is to transfer the weight to the back and keep it there through the entire pass. <strong>Since you can’t adjust the instant center on an IRS car, the most effective adjustment you can make is the shock valving</strong>. The initial hit at launch doesn’t drive the tires into the ground nearly as hard as in a solid-axle car, so the goal is to valve the shocks so the car squats very quickly. From there, you need to control the extension of the shocks to prevent the weight from transferring back up to the front.</p><p></p><p>Double Adjustable Shocks</p><p></p><p>Setup the rear shocks compression valving soft enough so that the car can squat evenly at a very rapid rate out of the hole but not so much that its going to drag the gas tank. Once the car squats evenly, adjust the rear shocks to tighten up the rebound. Normally, the rear shocks will try to extend back up at a faster rate than what you want thus unloading the rear tires and result in immediate tire spin. Double adjustables shocks in the rear are a must have for effective and repeatable 60 foots in an IRS equiped vehicle.</p><p></p><p>The front shocks also rely on correct shock valving, but for the exact opposite purpose as the rears. The goal with the front shocks is to control the rate of extension. You need to keep the front shocks extended over a very long period of time, and don’t use travel limiters. </p><p>A good double adjustable rear shock can help get your 60-foot times down to 1.5 seconds or less depending on car weight, tire type, and HP/TQ numbers.” Although more exotic shocks are available for more extreme applications, off-the-shelf double-adjustable shocks have proven effective in many 8-second combos.</p><p></p><p>Weight Distribution</p><p></p><p>If weight transfer is so important in an IRS car, why not just put more weight in the rear of the car in the first place? That’s exactly what George Farkouh decided to do with the ARH/Farks Supercars Camaro, and the results... Well, I will let him tell you. Notice what he says in a magazine article I pulled online......</p><p></p><p>“Since you can’t drive the tires into the ground with an IRS car, the percentage of static weight over the rear tires is very important. That’s why we put the intercooler core, water tank, and ballast in the back of our car to keep as much weight over the rear tires as possible,” says George. “When you get an IRS car setup right, it squats and stays that way the entire pass. Our best pass to date is 7.67 at 179 mph on 275mm drag radials, which makes it the fastest IRS-equipped, fifth-gen Camaro in the world. This combo started out pulling 1.32-second 60-foot times in its first season, but now we have that down to 1.20 seconds.” </p><p></p><p>Yeah I know its a Chevy quoted here but the exact same principle applies to ANY IRS equipped car. And note that he did this on Drag Radials folks. Thats impressive. So stick your battery, intercooler tank, nitrous bottles, water meth tank, and girl friend in the trunk of your car. Well maybe not your girl friend... but possibly your EX instead.... LOL.</p><p></p><p>DEFLECTION PREVENTION</p><p></p><p>Compared to a solid axle, an independent rear suspension relies on a multitude of control arms, links, and rods to locate the rear wheels. These links utilize bushings to prevent road noise and vibrations from being transmitted into the chassis. The downside is that as these bushings deflect under load, wheel control is compromised.</p><p></p><p>With the stock suspension, the entire spindle and differential moves back and forth during a hard launch. This causes wheelhop and tire spin. To prevent this from happening, install a quality bushing kit, replace the stock rear toe links with stronger pieces, and upgrading the stock anti-roll/sway bar to a much larger/stiffer bar than stock like 1.5 inches. Now all the alignment specs don’t change at all during launch, and your 60-foot times will be very consistent.”</p><p></p><p>Full Tilt Boogie Racing sells a complete IRS bushing kit with delrin and aluminum bushings, but any other quality bushing kit will work to your advantage in this area. Even Polyurethane is better than the stock rubber ones.</p><p></p><p>Rear Camber</p><p></p><p>To assist with cornering grip, the negative camber in a modern IRS system increases as the suspension is compressed. While this increases the contact patch of the tires while cornering, it actually decreases the contract patch during hard straight line acceleration. Dialing in some positive camber seems like a logical solution, but some tips are hard to come by.</p><p></p><p>I don’t know how many secrets I want to reveal to the world as far as alignment settings are concerned. What I will say is that how a car looks at a rest is completely different than how a car looks while going down the track. All that matters is how the car looks as it’s going down the track. With that note..... Hint, Hint... put some positive caster in the car, but not that much. It’s less than one degree.</p><p></p><p>STIFFNESS</p><p></p><p>Let’s say you want to try your hand at going fast with an IRS, but have no intentions of running 6s. Custom race shocks aren’t always necessary for less extreme applications. In fact, experimenting with modestly priced springs and shocks are a good starting point for managing weight transfer.</p><p></p><p>Compared to a solid-axle car, an IRS car benefits from softer front springs. This gives them more stored energy, which helps with weight transfer. The front shock valving should be similar to a solid-axle car, but the rear shocks in an IRS must have much stiffer rebound valving. Some IRS drag racers I read about online went through a phase with their cars, it would hookup on the initial hit, then go up in smoke ten feet into a run after the rear tires unloaded. By stiffening up the rebound valving, most were able to keep their cars squatted and hooked up the entire pass. Now their cars just squat and go.</p><p></p><p>Anti-Roll/Sway Bar.... Good To Have</p><p></p><p>Big anti-roll/sway bars in an IRS-equipped car perform the same function as they do in a solid-axle car. In addition to loading the left-and right-side tires evenly at launch, they help force the tires downward into the pavement. This is one of the few ways an IRS can generate at least a small degree of anti-squat.</p><p></p><p>I thought this was very interesting info so I looked at numerous videos of IRS and SRA cobras launching and noted the HUGE amount of squat that the successful suspension tuned IRS guys got. NONE of them lifted and planted the tire like the solid-axle cobras did.</p><p></p><p>I'm sure most of you have had good success with the tried combos that got you the 60' times, and in no way am I saying that those combos don't work. Just posting the research I scoured from reading.</p><p></p><p>I dont take any credit for this information. Its from multiple articles I have read on the subject both online and in magazines and books.</p><p></p><p>Hope this helps everyone and happy track times.... Now Go Kill a Few Chevys at the track.</p></blockquote><p></p>
[QUOTE="ClubVenom1, post: 15155552, member: 47265"] A lot of interesting comments here. I noticed some say "I think"... don't think, KNOW. Do some research. This is info taken from proven setups from real drag racers. This might shock some of you, but like I said... do some research. [CENTER]Drag Racing an IRS 101[/CENTER] Solid-Axle VS IRS Under most circumstances, rigidly mounting the differential assembly to the chassis in an IRS-equipped car is a good thing since it reduces unsprung weight. This arrangement allows running softer springs rates and shock valving, which improves ride quality without sacrificing handling. However, planting thousands of horsepower from a standstill falls outside the realm of most circumstances, and the huge drawback of an IRS is that it limits the amount of anti-squat built into the suspension in a drag-racing application. As a car accelerates forward, weight transfer causes the rear suspension to squat. Since the rearend housing and differential assembly are not mounted directly to the chassis in a solid-axle car, the rearend can separate (move downward) from the body to resist squatting. That’s what suspension designers and drag racers refer to as anti-squat. The icing on the cake is that the torque of the engine in a solid-axle car is transmitted through the suspension, which drives the rearend assembly and tires into the ground to enhance traction. According to legendary suspension engineer Herb Adams, manipulating the instant center allows a solid-axle car to achieve over 100 percent anti-squat, whereas an IRS is typically limited to about 25 percent anti-squat. Suspension Recipe Now lets get to the meat and potatoes. Setting up an independent rear suspension like a solid axle suspension is a recipe for disaster. An IRS requires a completely different suspension setup than a solid-axle car, and managing weight transfer is way more important. With a solid-axle car, you can adjust the instant center to make the body separate from the rearend, and smash the tires into the track. Solid-axle cars don’t squat at all, they just separate, lift the rearend, and take off. You can’t do that with an IRS. Instead, you have to MAKE THE CAR SQUAT, and transfer the weight rearward. The Squat Factor A solid-axle car and an IRS car work completely opposite of each other. A solid-axle car works on the premise of separation to plant the rearend into the ground, but the only way to get an IRS car to launch is to transfer the weight to the back and keep it there through the entire pass. [B]Since you can’t adjust the instant center on an IRS car, the most effective adjustment you can make is the shock valving[/B]. The initial hit at launch doesn’t drive the tires into the ground nearly as hard as in a solid-axle car, so the goal is to valve the shocks so the car squats very quickly. From there, you need to control the extension of the shocks to prevent the weight from transferring back up to the front. Double Adjustable Shocks Setup the rear shocks compression valving soft enough so that the car can squat evenly at a very rapid rate out of the hole but not so much that its going to drag the gas tank. Once the car squats evenly, adjust the rear shocks to tighten up the rebound. Normally, the rear shocks will try to extend back up at a faster rate than what you want thus unloading the rear tires and result in immediate tire spin. Double adjustables shocks in the rear are a must have for effective and repeatable 60 foots in an IRS equiped vehicle. The front shocks also rely on correct shock valving, but for the exact opposite purpose as the rears. The goal with the front shocks is to control the rate of extension. You need to keep the front shocks extended over a very long period of time, and don’t use travel limiters. A good double adjustable rear shock can help get your 60-foot times down to 1.5 seconds or less depending on car weight, tire type, and HP/TQ numbers.” Although more exotic shocks are available for more extreme applications, off-the-shelf double-adjustable shocks have proven effective in many 8-second combos. Weight Distribution If weight transfer is so important in an IRS car, why not just put more weight in the rear of the car in the first place? That’s exactly what George Farkouh decided to do with the ARH/Farks Supercars Camaro, and the results... Well, I will let him tell you. Notice what he says in a magazine article I pulled online...... “Since you can’t drive the tires into the ground with an IRS car, the percentage of static weight over the rear tires is very important. That’s why we put the intercooler core, water tank, and ballast in the back of our car to keep as much weight over the rear tires as possible,” says George. “When you get an IRS car setup right, it squats and stays that way the entire pass. Our best pass to date is 7.67 at 179 mph on 275mm drag radials, which makes it the fastest IRS-equipped, fifth-gen Camaro in the world. This combo started out pulling 1.32-second 60-foot times in its first season, but now we have that down to 1.20 seconds.” Yeah I know its a Chevy quoted here but the exact same principle applies to ANY IRS equipped car. And note that he did this on Drag Radials folks. Thats impressive. So stick your battery, intercooler tank, nitrous bottles, water meth tank, and girl friend in the trunk of your car. Well maybe not your girl friend... but possibly your EX instead.... LOL. DEFLECTION PREVENTION Compared to a solid axle, an independent rear suspension relies on a multitude of control arms, links, and rods to locate the rear wheels. These links utilize bushings to prevent road noise and vibrations from being transmitted into the chassis. The downside is that as these bushings deflect under load, wheel control is compromised. With the stock suspension, the entire spindle and differential moves back and forth during a hard launch. This causes wheelhop and tire spin. To prevent this from happening, install a quality bushing kit, replace the stock rear toe links with stronger pieces, and upgrading the stock anti-roll/sway bar to a much larger/stiffer bar than stock like 1.5 inches. Now all the alignment specs don’t change at all during launch, and your 60-foot times will be very consistent.” Full Tilt Boogie Racing sells a complete IRS bushing kit with delrin and aluminum bushings, but any other quality bushing kit will work to your advantage in this area. Even Polyurethane is better than the stock rubber ones. Rear Camber To assist with cornering grip, the negative camber in a modern IRS system increases as the suspension is compressed. While this increases the contact patch of the tires while cornering, it actually decreases the contract patch during hard straight line acceleration. Dialing in some positive camber seems like a logical solution, but some tips are hard to come by. I don’t know how many secrets I want to reveal to the world as far as alignment settings are concerned. What I will say is that how a car looks at a rest is completely different than how a car looks while going down the track. All that matters is how the car looks as it’s going down the track. With that note..... Hint, Hint... put some positive caster in the car, but not that much. It’s less than one degree. STIFFNESS Let’s say you want to try your hand at going fast with an IRS, but have no intentions of running 6s. Custom race shocks aren’t always necessary for less extreme applications. In fact, experimenting with modestly priced springs and shocks are a good starting point for managing weight transfer. Compared to a solid-axle car, an IRS car benefits from softer front springs. This gives them more stored energy, which helps with weight transfer. The front shock valving should be similar to a solid-axle car, but the rear shocks in an IRS must have much stiffer rebound valving. Some IRS drag racers I read about online went through a phase with their cars, it would hookup on the initial hit, then go up in smoke ten feet into a run after the rear tires unloaded. By stiffening up the rebound valving, most were able to keep their cars squatted and hooked up the entire pass. Now their cars just squat and go. Anti-Roll/Sway Bar.... Good To Have Big anti-roll/sway bars in an IRS-equipped car perform the same function as they do in a solid-axle car. In addition to loading the left-and right-side tires evenly at launch, they help force the tires downward into the pavement. This is one of the few ways an IRS can generate at least a small degree of anti-squat. I thought this was very interesting info so I looked at numerous videos of IRS and SRA cobras launching and noted the HUGE amount of squat that the successful suspension tuned IRS guys got. NONE of them lifted and planted the tire like the solid-axle cobras did. I'm sure most of you have had good success with the tried combos that got you the 60' times, and in no way am I saying that those combos don't work. Just posting the research I scoured from reading. I dont take any credit for this information. Its from multiple articles I have read on the subject both online and in magazines and books. Hope this helps everyone and happy track times.... Now Go Kill a Few Chevys at the track. [/QUOTE]
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