Posts by GTS Dean
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14,258 Posts
Let's talk about air boxes then. I've dyno'd my GTS on 4 different machines since '99 and from 11k to 25k miles. With the exception of a mustang shop in SA that wasn't properly altitude corrected, every one indicated between 410 and 413hp with a fully warmed engine. New u-joints and diff made no measureable difference on my car from my March and December '03 pulls. Stock airbox with smoothies and K&Ns dyno'd the same on a hot, humid day in Houston as the HMS CF box did on a cold, dry day in SA. However, at TWS, my front straight speeds are about 4-6mph higher with the HMS box, and my trap speeds at the strip are up from ~116mph to consistently around 121+ mph. I don't give a rat's ass how much fan you blow at the front end, you will not duplicate the pressure differences at the airbox in real life. Saturday, my cool engine made 8hp more than my warm engine. It was the only time I've seen this "magic" 420hp number for my filters and tubes car.John Hennessey said:
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14,258 Posts
Jerome,
The severe wrinkle-wall phemomenon on a drag slick helps increase net torque at the tire by shortening the rolling radius (effective lever arm) between the axle and the ground. After a few revolutions, the tire begins to grow circumferentially. This raises the axle center from the ground and lowers torque, but the tire is covering more distance in one revolution than at rest, or low rpms which accounts for the huge mph gain. A shorter tire will accelerate the dyno rolls more quickly than a tall tire. I believe that should raise the indicated power levels.
Steel belted street tires exhibit very little "growth" and maintain circumference. HP street tires (Pilots, not E/Ts) have very stiff sidewalls and there's not much energy wind-up in them at recommended inflation pressures. That's why we have to run such low pressures at the strip to make them work well. Flexing stiff sidewalls creates heat and wastes energy. That's why you should run plenty of air in them on the chassis dyno. Some of the "cheater" boys' cars were moving around laterally a good bit - wasting power. Probably should cross the tiedown straps to minimize that.
The severe wrinkle-wall phemomenon on a drag slick helps increase net torque at the tire by shortening the rolling radius (effective lever arm) between the axle and the ground. After a few revolutions, the tire begins to grow circumferentially. This raises the axle center from the ground and lowers torque, but the tire is covering more distance in one revolution than at rest, or low rpms which accounts for the huge mph gain. A shorter tire will accelerate the dyno rolls more quickly than a tall tire. I believe that should raise the indicated power levels.
Steel belted street tires exhibit very little "growth" and maintain circumference. HP street tires (Pilots, not E/Ts) have very stiff sidewalls and there's not much energy wind-up in them at recommended inflation pressures. That's why we have to run such low pressures at the strip to make them work well. Flexing stiff sidewalls creates heat and wastes energy. That's why you should run plenty of air in them on the chassis dyno. Some of the "cheater" boys' cars were moving around laterally a good bit - wasting power. Probably should cross the tiedown straps to minimize that.
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14,258 Posts
If there wasn't a lot of useful energy stored in the tire sidewall, they wouldn't need beadlock screws to keep them from slipping on the rim. You can either do it with screws, or internal pressure. The correct engineering term for this phenomenon is "rimpull."
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