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Old 06-29-2009, 09:41 AM   #1
Rudywrx04
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Default Please teach me about Trap speeds.

I have been kinda of an oval track guy, but am going to the Drag Strip for the first time.

My question is what does your Trap Speed really tell you?

For example if I ran a 12.6 second quater mile would the trap speed always be the same?

Could you run a 12.6 several times with different Trap Speeds?
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Old 06-29-2009, 09:47 AM   #2
Jack
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At the ending point of the dragstrip, there are 2 sets of sensors. That's where you're timed for your trap speed. You can indeed run the same time and have different trap speeds......but it'll usually be close.

For an extreme example, say you line up against a top fuel dragster. You both start at the same time.....the dragster smokes the tires up and just about stops.....then starts going again and catches you right at the finish. You both run 13.0......but you're at 98mph and he crosses at 250mph.

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Old 06-29-2009, 09:55 AM   #3
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Most people use trap speeds to get a good idea of what kind of power a car is really making. You can bog the launch, an still end up trapping fairly consistenly.

ET's will vary considerably, but traps should always be fairly close.
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Old 06-29-2009, 09:56 AM   #4
Rudywrx04
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Thanks Jack,

Makes sense. What RPM is usually best to launch at?
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Old 06-29-2009, 10:02 AM   #5
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Think of trap speeds as an indicator of power/weight, or general acceleration.

ET, while certianly indicating acceleration, takes into account the launch, etc.

WRX's, and other AWD cars, tend to have very low trap speeds compared to their ETs. AKA, they launch hard, but aren't accelerating very hard.

A typical 2.0l WRX is really a 15 second 1/4 mile car with a great launch, so it runs in the 14's (but has a typical 15 second trap speed).
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Old 06-29-2009, 11:01 AM   #6
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Quote:
Originally Posted by REX8 View Post
Think of trap speeds as an indicator of power/weight, or general acceleration.

ET, while certianly indicating acceleration, takes into account the launch, etc.
Right

Basically, you can have any launch in the world, and as long as your power and shifts stay consistent, you'll trap at basically the same speed. Power and aerodynamics control your trap speed, your launch controls your ET. That's why most people compare trap speeds, because for the most part it's driver and launch independent. Throw an awesome driver in there and he could drop a half a second off of the ET with some kind of crazy launch from hell, but it will still trap at roughly the same speed.
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Old 06-29-2009, 01:24 PM   #7
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et = driver skill
mph = power/tq the car is making.
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Old 07-09-2009, 11:22 AM   #8
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Your trap speed generally goes up when your launch is not good. A good launch will cover ground quickly giving you less time to build speed. In 1/2 and full-mile runs, people do not launch their cars as they're going for a top speed and not an ET.

Other than that, I agree with the above.
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Old 07-09-2009, 11:54 AM   #9
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Quote:
Originally Posted by Rudywrx04 View Post
Thanks Jack,

Makes sense. What RPM is usually best to launch at?
this is how i launch and its worked extremely well for me

There are two things you need to accomplish to get a good launch in the wrx.
You need to launch under some boost,
and you need to control the load on the engine so it stays near max torque rpm for the first few feet without banging the clutch and shock loading the drive train.

There are several variations on the theme and each person will discribe it slightly differently but you want to engage the clutch quickly and smoothly so it slips just a bit with out just side stepping the clutch, or frying the clutch by holding it at partial engagement. The newer 2003 cars have a flow limit valve in the clutch line so you cannot just let up on the clutch and break things. It slows down the engagement just a bit. On the 2002's you'll have to do that yourself.

One of the top WRX drag racers in the country describes the technique where you stage, and then let the clutch out a bit until you can tell it is just ready to engage (the friction point) is just a fraction of an inch away.

Hold at a moderate fast rpm (everyone picks a slightly different number) I use about 3000 3500 rpm.

Now comes the key to launching under boost.

You can only build boost under no load conditions when the engine is accelerating at WOT .

Just as the second yellow comes on, stomp the throttle to the floor from your stage rpm, the engine will take about a second to rev to red line. There is only .500 seconds between each of the yellow lights.

Watch the tach and as the rpm swings by 5000-5500 rpm let up on the clutch quickly.
(you can't wait for the green light you have to start leaving on the last yellow)

Since you prepositioned the clutch right at the friction point there will be very little clutch motion, or shock, your engine will be very close to 5500 rpm when the clutch engages and under some boost because you floored the throttle a fraction of a second earlier. If you get all that coordinated you should have enough torque and energy stored in the flywheel so the engine does not bog.

Hang on !!! you will be accelerating at over 1 G and hit red line in low in about 1.5 seconds.
Be ready to shift !!!!!
The biggest time loss that keeps folks at 2.x seconds is a slow shift, you have to shift quickly to get back under power in second gear before you complete the first 60'.

Shift quickly and firmly but NOT VIOLENTLY !!! your not trying to break anything just be quick.


I tell folks to hold the shifter in their fingers not to grab it like a club, this gives you more feel and makes you less inclined to try to rip the shift knob off the console.
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