Guest bastaad525 Posted November 27, 2004 Share Posted November 27, 2004 Just a quick one. I was thinking on how, when you go to the track, your trap speed, rather than your ET, is the number that is considered the de facto number to go by, when trying to determine your true wheel hp. BUT, what I don't get is, how can you use trap speed to determine this, GIVEN the fact that trap speed isn't your final speed when you cross the finish line, rather it's an average of your speed over the last however many (I think 60?) feet of the track? So, especially in the case of high powered cars, which may still be accelerating quite a bit during that last section, wouldn't using trap speed as a rule for figuring wheel hp be inaccurate? Quote Link to comment Share on other sites More sharing options...
Guest Phil1934 Posted November 27, 2004 Share Posted November 27, 2004 The formulas were changed when NHRA quit averaging the last 66' before the line and 66' after as cars were driving hard past the finish line on minimal tracks. Now it's just the last 66' before the line. That's a pretty short diatance. At 120 MPH you cover 176'/sec so this is only 1/3 of a sec. If you were accelerating at 1G, that's only 32'/sec/sec. You are probably doing about .15 G at the finish line, so over 66' the difference between coasting and accelerating is less than 2 MPH. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted November 28, 2004 Share Posted November 28, 2004 Well that 2mph is actually a pretty significat difference. Let's say my 2600lb w/driver car finishes the 1/4 mile with a trap speed averaged over the last 66' of 104mph. This would equate to about 228rwhp. Now if my actual terminal speed at the instant I cross the line were only 2mph faster, then that would equate to 242rwhp. That, to me... is a pretty significant difference. In a heavier car the difference would be even more. Just nitpicking one of the little things I wonder why no one else wonders about... could be worth some 'free' bragging hp to some Quote Link to comment Share on other sites More sharing options...
onovakind67 Posted November 29, 2004 Share Posted November 29, 2004 As noted, the typical acceleration of a 100 mph car at the end of the quarter is about .15g's or 4.82ft/s/s. If you assume a constant acceleration over the last 66', your speed on the time card would actually be the speed at the 1287' mark. 100 mph is about 147ft/s, so you would cover the last 33' in about .22 seconds, accelerating to about 148 ft/s in that time. This would make your actual speed about 100.7 mph. According to the web-cars calculator it takes about 4 more rwhp to achieve this extra .7 mph in a 2600# car. There are a lot more factors involved, such as frontal area, tire drag, etc. I notice on these 'bragging' calculators they never ask you if you're driving a barn door or a belly tank. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted November 30, 2004 Share Posted November 30, 2004 I notice on these 'bragging' calculators they never ask you if you're driving a barn door or a belly tank. Another good point... especially since most of us drive an S30 Z which are very well known for their horrible aerodynamics. Quote Link to comment Share on other sites More sharing options...
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