Jeep Engines - Oljeep

480 MOPAR PERFORMANCE PARTSWhat does it take to cut a good light? A big powerfulengine? No way. As long as the engine runs reasonablywell, a stock 4.0L In-Line 6 will cut as good a light as a 426Race Hemi. Remember, the vehicle only has to move a fewinches to start the E.T. clock. A good chassis is the way tolower reaction times. When you release the brake (or linelock) and mash the pedal, the vehicle must move forwardinstantly. No wheel spin. Hook-up every time, the sameway every time. Consistently.Keys to a good chassis are listed in Mopar Chassis-8thEdition (P.5249441). What it takes to hook-up varies withengine and vehicle weight, but the basic rules are: a) racethe vehicle as light as you can, b) make the rear suspensionwork to plant the tires, c) run as much tire as you can.Lighter vehicles react quicker, accelerate faster, allowslicks to last longer, and wear out parts slower. Put yourvehicle on a diet. Instead of buying the latest trick enginepart, spend your money on fiberglass parts. Convert yourvehicle to manual brakes and lose the power booster.Remove the power steering pump and cast iron box and putin an aluminum manual steering unit. Or, better yet, removeany parts that aren’t required. Although a street vehicleneeds a heater and windshield wipers, a race vehicledoesn’t. Back seats are dead weight. If you can’t removesomething, can you move it to the rear? The battery is agood example. Weight moved to the rear will help improvetraction. Lighten up. Not only will your reaction timesimprove, but so will your time slips. Remember, 100 lbs. =.100: that is, every 100 pounds you remove will lower yourE.T. by roughly a tenth of a second (and be easier on yourdrivetrain as well).Before we look at the rear suspension, let’s see what‘shappening when you launch your vehicle. First, the bodywants to move in three directions. It wants to rise in thefront and squat in the rear from weight transfer, and it wantsto roll over to the right (passenger side) from engine torque.The rear axle torques in the opposite direction. It wants topick up the right rear tire. This is because the engine anddriveline run in a counterclockwise direction (as viewedfrom the rear). This means the left rear gets planted but theright tire gets “unloaded.” In this condition, the left tiremust provide most of the traction while the right tireprovides very little. Something else happens, too. Thedifferential wants to flip over backwards! The tires move ina forward rotation and the rear end wants to react in theopposite direction. The pinion wants to “climb’ the ringgear, so to speak. These are basic laws of physics and aregoing to happen no matter what. You can’t stop thesereactions, but you can put them to work for you, and biasedleaf springs do it best.Biased leaf springs mean that the right spring has moreleakes and thus more forward stiffness than the left. Theextra stiffness causes the body’s roll to the right to forcethat right tire back on to the track, allowing both tires tocarry an equal dynamic load and provide equal dynamictraction, making both of your rear tires work equally. Anadded benefit is that, with both tires biting, the vehiclelaunches straight and your E.T. gets better.As for tires, more tire means more stick, but there’s no needto .go overboard. A 12 second vehicle doesn’t need 17inches of Top Fuel rubber, but a little extra is better than notenough. Most 1968 and newer vehicles have prettygenerous wheelwells. Remember that wider is not the onlyway to go. Instead of tubbing your racer out and moving thesuspension inboard, try a bigger diameter tire. Largerdiameter tires have a bigger “footprint” than smallerdiameter tires of the same width. Be sure to keep therelationship of tire diameter to rear axle ratio. Largerdiameter tires give the effect of a numerically lowergearset, but new gears can be less costly and certainly fasterto install than wheel tubs and an all new rear subframe andsuspension.Now that we have you off the line and cutting consistentlylow reaction times, how do you get the vehicle to runconsistent elapsed times? Generally, you’ll find that onceyou have the starting line down, your vehicle should berunning much more consistently already. With the rearsuspension working and the tires big enough to hold thetrack during gear changes, your E.T.s shouldn’t vary bymuch. But how do you get them to settle down even more?The answer: attention to detail.The vehicle must be able to make every pass under fullthrottle for the entire length of the track before you caneven consider getting consistent. This is just goodmechanics. If the vehicle won’t, why not? Let’s look atsome possibilities.Does the ignition system provide enough spark? Need newspark. plug wires, higher voltage ignition coil, better ECU,or new distributor cap? As a rule, ignition systems will actup as engine load increases-high rpm in high gear.However, if the vehicle misses in first but then clears up,the trouble is probably not the ignition.. ..-. T -1