Thief_of_Hearts

obviously more mods but which ones exactly? want to go as fast as I can NA while staying full basic bolt ons and street tires.I see that there are people hitting mid 12s but their traps are around 105-107.I am trying to trap somewhere along the lines of 110-112 to give me more of an edge on the street as well but still keeping it daily driver.I know a a basic stage 3 srts trap those times I think..not sure but it traps pretty good.I think they actually trap those numbers while hitting something 13.1-13.2 stock turbo full bolt ons.

I know it's apples to oranges but since I am switching from a skittle to a GT and all I want to make sure the GT will be quicker then my old car .

baha

Strange.. I trap about 105 with mid 13s , how come they hit mid 12s with trap speeds between 105-107 only?

with full bolt-ons you should be able to trap 110 IMO

howarmat

Good read from another forum:


1) Trap Speed will tell you about your HP to weight.
2) ET will tell you more about traction and your launch.

Of course ET is important to true drag racers, because the winner is the one that gets there first. However, we're not necessarily true drag racers in our attempt to get a power estimate. Honestly, ask 10 guys at the track "What kind of trap speed are you running?" and 8 out of 10 will answer with their ET - to one or two decimal places even. When you say, "No, no, I meant trap speed", they will fumble with a broad estimate with NO decimal places and might even have to pull a time slip out of their pocket to check. Try this question when you're at the track; it's almost funny.

THE DYNAMICS OF TRAP SPEED VS. ET

After running lots of quarter miles, it becomes clear that how well you do in the first 100 feet of the track is KEY to a good time. The last half of the track is KEY to a good speed.

Let's use an example of a stick-shift mini-pickup that on a perfect run, gets a timeslip of 19.50 seconds at 70.00 mph in the quarter.

Imagine that the light turns green, the truck moves two feet and the engine dies for three seconds. After restarting the engine, the driver proceeds to then complete a perfect pass. His time slip would show 22.50 seconds at 69.97 mph. The ET was 3.00 seconds high but the speed was almost unaffected.. why?? It's because his racetrack was 1318 feet long instead of 1320, and in those last two feet this truck usually gains an additional 0.03 mph. However, the clocks recorded the long time. My point? Much of a great ET is made by a great launch.

Now take this truck again, and the driver leaves right on the green light. However, he misses the 3-4 shift when he's at 1250 feet. He coasts for the last 70 feet while trying to find fourth gear. Now instead of accelerating another few mph in this final 70 feet of the track, he decelerates over this distance. His timeslip; 19.51 at 67.83 mph. Note how the et is almost perfect (only off by 0.01 second) but the trap speed is way off (over 2 mph slow)! On a good run, traveling that last 70 feet at an average of 69 mph, would have taken .692 seconds. At a 68 mph avg., that 70 feet takes .682 seconds. That's why his ET only varied by .01 seconds, yet the trap speed was 'way off'. My point here: the end of the track is critical to trap speed; shift rpm, missing a gear... these are the big players.

Hopefully these examples are clear. Neither of these runs are 'perfect' runs, it's just that one has an error at the start, one at the finish and the results are obvious. The start of the track is a big player in the ET, but a small player in the mph. The end of the track is a big player in the mph, but a small player the ET.

So for the casual T-Bricks member who wants to get a HP value, you don't have to buy slicks, or wish you had a limited slip differential. You don't really need to heat the tires in the waterbox, or launch with huge power braking. As long as people get their shift rpm right and don't miss a gear, even a rookie will get the appropriate trap speed for their vehicle.. but honing the perfect ET. requires being rude to a clutch, buying steeper gears or slicks.... hey, we're trying to make this recreational.

OPTIMIZING SPEED

If your goal is to get a good trap speed, what are your options? More power, of course - and less weight is obvious (but it will come out in the power calculations as no increase in power). Shift rpm chosen (auto or manual) and the time it takes you to shift (with a manual) are probably the most important tools you've got. Try different shift points to maximize your trap speed. Reduce rolling resistance by pumping up all tires to their rated pressure. Some people think that running lower pressure might help the traction in the rear, though. Of course more traction will help et, but with most street tires, running street tires within 5 psi of rated pressure will provide you with maximum traction in the first place.


REACTION TIME

The ET clocks don't start until you've actually moved around 8 inches (this is called the rollout)... so don't worry about trying to leave right on the green light. You could wait 5 seconds after the light turned green, and still get a 19.50 timeslip in our truck example above. Your timeslip does show a separate calculated time, the "Reaction Time", which in this case would be 5 seconds. That is the time from the light turning green until you rolled out of the starting zone. It's not a big thing for our discussion here.

THE LAUNCH

For the most part, a decrease in ET is accompanied by an increase in trap speed, but don't go overboard on the launch in your zest to rule the world. Just try to get smartly underway without spinning the tires much at all. Traction levels usually drop a solid 0.10 g when the tires start spinning.

THE HP FORMULA

Here's the formula to use to calculate HP:

Net HP = Weight in pounds* (Speed in MPH/228.4)^3

As an example, Car & Driver tested the 744 Turbo in their June 1990 issue. The car weighed 3,081 lb. without the driver.. the 'race weight' was 3,231 lb. The car ran a 15.7 second quarter at 86 mph. Let's plug it in to the formula:

HP = 3231 * (86/228.4)^3
HP = 172 Net

Volvo rated this at 162 Net. We come out a little high. Or does Volvo underrate a little? I'll say this - I've used this formula for years and that's how the 228.4 was honed - actual experience from cars that had actual power curves - and when I use it on Volvos it tends to always come out a few percent higher than the factory rating. This could simply be that Volvo underrates just a little.

Still, for such a simple formula and such a simple test, it's surprising how accurate this can be. And the best thing is - there's no arguing the numbers on a timeslip. There are always differences between a DynoJet and an Eddy Current Dyno, or G-Tech numbers, but every setup is done by someone different and subject to error. The quarter mile is arguably the best comparison a diversely located group like Turbobricks will ever have. The only real difference to argue about is the altitude of the track! You can compare ET and mph all day and have a good discussion.

HANDY RULE OF THUMB

Once you have a baseline, you should probably use a rule of thumb that each additional 6 HP will give you another mph. That's for a 3200 lb car that runs 88 mph. If you want the real formula for different weights or speeds, here it is:

HP for another mph above "X" speed: = Wt * (((X+1)^3-X^3) / (228.4^3))

For instance a 89 mph quarter vs. an 88 mph quarter for a 3200 lb car:

HP delta = 3200 * ((89^3-88^3) / 228.4^3))

HP delta = 6.3 HP

Once you're going 110 in the quarter, it would take an additional 10 HP to go 111 mph in the 3200 lb car.

60 FOOT TIME

This is the standard measurement tool to evaluate your launch. It's the time that it took you to travel the first 60 feet of the track. Naturally, patterns emerge again after looking at lots of runs and of course these correlate best to time, not mph. Typically, most everyone's 60' time will be between 14% and 16% of their quarter mile time. If it's under 13% or over 17%, this was not your best pass.

1/8 MILE VS. 1/4 MILE

After monitoring tons of good passes, patterns emerge. Typically, the mph at the quarter is around 1.26 times of the mph at the eighth, and the time at the quarter is around 1.55 times the time at the eighth. You can use these values if you only have a 1/8 mile track and get a real good idea of the theoretical 1/4 mile.

IS MY ET TO SPEED RATIO REASONABLE?

One fact of the quarter mile is; no matter how slow or fast your car is, the mph multiplied by the ET will pretty much be the same number every ti

moosestang

There's only two ways to increase trap speed that I know of. Lose weight or increase horsepower.

moosestang

Howarmat, could you explain what this symbol means? ^3

Baddog

[quote]ORIGINAL: howarmat

Good read:


1) Trap Speed will tell you about your HP to weight.
2) ET will tell you more about traction and your launch.

Of course ET is important to true drag racers, because the winner is the one that gets there first. However, we're not necessarily true drag racers in our attempt to get a power estimate. Honestly, ask 10 guys at the track "What kind of trap speed are you running?" and 8 out of 10 will answer with their ET - to one or two decimal places even. When you say, "No, no, I meant trap speed", they will fumble with a broad estimate with NO decimal places and might even have to pull a time slip out of their pocket to check. Try this question when you're at the track; it's almost funny.

THE DYNAMICS OF TRAP SPEED VS. ET

After running lots of quarter miles, it becomes clear that how well you do in the first 100 feet of the track is KEY to a good time. The last half of the track is KEY to a good speed.

Let's use an example of a stick-shift mini-pickup that on a perfect run, gets a timeslip of 19.50 seconds at 70.00 mph in the quarter.

Imagine that the light turns green, the truck moves two feet and the engine dies for three seconds. After restarting the engine, the driver proceeds to then complete a perfect pass. His time slip would show 22.50 seconds at 69.97 mph. The ET was 3.00 seconds high but the speed was almost unaffected.. why?? It's because his racetrack was 1318 feet long instead of 1320, and in those last two feet this truck usually gains an additional 0.03 mph. However, the clocks recorded the long time. My point? Much of a great ET is made by a great launch.

Now take this truck again, and the driver leaves right on the green light. However, he misses the 3-4 shift when he's at 1250 feet. He coasts for the last 70 feet while trying to find fourth gear. Now instead of accelerating another few mph in this final 70 feet of the track, he decelerates over this distance. His timeslip; 19.51 at 67.83 mph. Note how the et is almost perfect (only off by 0.01 second) but the trap speed is way off (over 2 mph slow)! On a good run, traveling that last 70 feet at an average of 69 mph, would have taken .692 seconds. At a 68 mph avg., that 70 feet takes .682 seconds. That's why his ET only varied by .01 seconds, yet the trap speed was 'way off'. My point here: the end of the track is critical to trap speed; shift rpm, missing a gear... these are the big players.

Hopefully these examples are clear. Neither of these runs are 'perfect' runs, it's just that one has an error at the start, one at the finish and the results are obvious. The start of the track is a big player in the ET, but a small player in the mph. The end of the track is a big player in the mph, but a small player the ET.

So for the casual T-Bricks member who wants to get a HP value, you don't have to buy slicks, or wish you had a limited slip differential. You don't really need to heat the tires in the waterbox, or launch with huge power braking. As long as people get their shift rpm right and don't miss a gear, even a rookie will get the appropriate trap speed for their vehicle.. but honing the perfect ET. requires being rude to a clutch, buying steeper gears or slicks.... hey, we're trying to make this recreational.

OPTIMIZING SPEED

If your goal is to get a good trap speed, what are your options? More power, of course - and less weight is obvious (but it will come out in the power calculations as no increase in power). Shift rpm chosen (auto or manual) and the time it takes you to shift (with a manual) are probably the most important tools you've got. Try different shift points to maximize your trap speed. Reduce rolling resistance by pumping up all tires to their rated pressure. Some people think that running lower pressure might help the traction in the rear, though. Of course more traction will help et, but with most street tires, running street tires within 5 psi of rated pressure will provide you with maximum traction in the first place.


REACTION TIME

The ET clocks don't start until you've actually moved around 8 inches (this is called the rollout)... so don't worry about trying to leave right on the green light. You could wait 5 seconds after the light turned green, and still get a 19.50 timeslip in our truck example above. Your timeslip does show a separate calculated time, the "Reaction Time", which in this case would be 5 seconds. That is the time from the light turning green until you rolled out of the starting zone. It's not a big thing for our discussion here.

THE LAUNCH

For the most part, a decrease in ET is accompanied by an increase in trap speed, but don't go overboard on the launch in your zest to rule the world. Just try to get smartly underway without spinning the tires much at all. Traction levels usually drop a solid 0.10 g when the tires start spinning.

THE HP FORMULA

Here's the formula to use to calculate HP:

Net HP = Weight in pounds* (Speed in MPH/228.4)^3

As an example, Car & Driver tested the 744 Turbo in their June 1990 issue. The car weighed 3,081 lb. without the driver.. the 'race weight' was 3,231 lb. The car ran a 15.7 second quarter at 86 mph. Let's plug it in to the formula:

HP = 3231 * (86/228.4)^3
HP = 172 Net

Volvo rated this at 162 Net. We come out a little high. Or does Volvo underrate a little? I'll say this - I've used this formula for years and that's how the 228.4 was honed - actual experience from cars that had actual power curves - and when I use it on Volvos it tends to always come out a few percent higher than the factory rating. This could simply be that Volvo underrates just a little.

Still, for such a simple formula and such a simple test, it's surprising how accurate this can be. And the best thing is - there's no arguing the numbers on a timeslip. There are always differences between a DynoJet and an Eddy Current Dyno, or G-Tech numbers, but every setup is done by someone different and subject to error. The quarter mile is arguably the best comparison a diversely located group like Turbobricks will ever have. The only real difference to argue about is the altitude of the track! You can compare ET and mph all day and have a good discussion.

HANDY RULE OF THUMB

Once you have a baseline, you should probably use a rule of thumb that each additional 6 HP will give you another mph. That's for a 3200 lb car that runs 88 mph. If you want the real formula for different weights or speeds, here it is:

HP for another mph above "X" speed: = Wt * (((X+1)^3-X^3) / (228.4^3))

For instance a 89 mph quarter vs. an 88 mph quarter for a 3200 lb car:

HP delta = 3200 * ((89^3-88^3) / 228.4^3))

HP delta = 6.3 HP

Once you're going 110 in the quarter, it would take an additional 10 HP to go 111 mph in the 3200 lb car.

60 FOOT TIME

This is the standard measurement tool to evaluate your launch. It's the time that it took you to travel the first 60 feet of the track. Naturally, patterns emerge again after looking at lots of runs and of course these correlate best to time, not mph. Typically, most everyone's 60' time will be between 14% and 16% of their quarter mile time. If it's under 13% or over 17%, this was not your best pass.

1/8 MILE VS. 1/4 MILE

After monitoring tons of good passes, patterns emerge. Typically, the mph at the quarter is around 1.26 times of the mph at the eighth, and the time at the quarter is around 1.55 times the time at the eighth. You can use these values if you only have a 1/8 mile track and get a real good idea of the theoretical 1/4 mile.

IS MY ET TO SPEED RATIO REASONABLE?

One fact of the quarter mile is; no matter how slow or fast your car is, the mph multiplied by the ET will pretty much be the same number every time. Before the NHRA changed the way that speed is measured

howarmat

Thats not my work, its from another post on another forum.....sorry, not a track guru by any means

jawsgt

well i figure my car to be around 285 hp according to the forumla...of course i had to use a scientific calculator. and at sea level im making 299 hp. this sound rite for a 106 mph trap speed?

Thief_of_Hearts

thanks for that great post Howarmat..

I am concerned about trap times because I not only want a good ET at the track but
I want to have a fast street highway car as well.I don't to be pulled on by a car that runs
a slower time but traps higher and ends up pulling me ,sometimes by alot lol.

say,for instance I would trap anywhere from 100-103 at the track (stage 2 turbo srt-4 open dump) but the best time I ran sofar was a 13.8 though the car is fully capable of high 12s on slicks with a good driver.There were a few stis and some wrxs that run great times but trap either around the same or a little bit higher..say,mid to high 12s but on the freeway from a roll I would often pull them by a few cars at first and then by like 3-4 up top past 120 or so.But then again I have a little bit more power to the wheels and less drivetrain loss because of the fwd.Big difference though between a mid 12 car and a nearly 14 second one eh? then again if I
sit and spin the tires hard enough I can get better traps say 103-105 lol.


Just thinking how bad it would suck to have a descentET with the GT but with traps in the 105s-107s even,on the street..against some equally modded and lighter cars..it's gonna loose,
it'll hold itself off on it's own pretty good from a DIG but not too confident with the traps/top end etc.But then again,this is all NA without the supercharger kit,with it and running mid 11s or
better I don't think it would be such a problem..either way lol.

street nor strip.