I've seen people ask this before and finally saw someone posted some information to see how well in performance a 1/4 mile run can be.

1/4 mile is 1320 feet. You take X amount of time to travel 1320 feet and you cross the finish line at X MPH. Since both are a measurement of time, combined they can produce some interesting results.

ET x MPH = feet. If your MPH and ET are good for a 1/4 mile, that number should be very close to 1320. If the number is higher, you probably don't have enough traction and were spinning somewhere on the track. If the number is lower, you're very quick but the HP is low which could be any number of factors such as head wind etc.

For NA cars, another conversion number to use is 1.57 which will give you a 1/4 mile time from an 1/8 mile run for those who don't have a 1/4 mile track to run at. My car is set up to run 1/4 mile and that conversion number works out very close for me.

After finding the first conversion, I decided to put in my timeslip numbers from a few weeks ago where I ran my personal best.

1/8 mile = 5.751
1/4 mile = 9.029
MPH = 148.78

OK, 5.751 x 1.57 = 9.02907. Wow, can't get much closer that that.

9.029 x 148.78 = 1343. Just slightly high. Probably lost a tiny bit because I was carrying the front wheels in the air for 80-90 feet.

A week later when I blew my engine, I was on a poorly prepped track. I could barely carry the front end 20-30 feet and felt the car spinning after the 330 mark. I only managed a 9.415 because of all the wheel spin but ran 150.45 MPH so the engine was making more HP. You'll never get 100% traction so the number will probably always be high.

Working backwards, take 1320 feet divided by the MPH to see what the potentially best ET would be and I get 1320/150.45 = 8.77. If I had traction and the car is set up for optimal performance in the 1/4 mile, I "could" have run 8.77 which I highly doubt I would have done but numerically it's possible. Be conservative for wheel spin and use a higher number like 1380-1400 and your ET will probably be closer. It the ET number is way off then the car isn't set up to it's best performance to 1/4 mile race.

Adjusting the car to max out in high gear at or just before the finish line will produce the best results. If gearing is too low like having 2.73 gears then you'll cross the finish in a lower gear or at a lower rpm. The car will be slow off the line but you could do 120 mph down the highway at an idle. If gearing is too high such as taking a stock engine car and putting 5.13 gears in the diff, it will be a fun car to drive around on the street but you'll run out of rpm or gears before you cross the finish line.

Interesting stuff, never heard of it.

I got 1366 for my et and mph, interesting I guess

mine's 1366 as well. ideally, i'd be running 10.6's in this heat with the 124mph....but not in actuallity...can't get it to 60'. i'd like to try more gear, but am afraid i might go slower.

1564.77 with my street car , 10.23 If i actually hooked .

1312. lol

^^^how do i get like you?!

10.49 pass = 1321.74
11.81 pass = 1352.24

I get 1448. 10.23 with traction, doubtful...

This is specious.

I know my current setup hasnt been close to being optimal for 1/4 mile but it sure is fun.... i've been 10.38 at 138 and 10.17 at 140 before on worse case side... thats 1432 and 1423

best has been 9.73 at 142 so thats 1382...not bad.

BUT I have been 10.05 or so at 115 on the brakes!! 1156 there!! OPTIMIZED

383 motor on motor was 1359 or so. On spray it was 1346.

Bolt on L98 was 1344.

Previous setups ran well, not all the way there yet but ran well. New setup is allll mph

put nitrous on the car, make it leave hard, and detune the crap out of it.

To show a bad combination, many many years ago when I was still running a 383, the car had a lot of power however I was still using 3.27 gears. The car would run 12.0 at 118 mph. The engine would start to get into it's power band as I was approaching the 1000 foot mark and really start to pull from there where most cars are starting to top out. It made bumper racing with a car that was dialed in at the same ET difficult and I won a few races because of it. Approaching the finish line and I was behind them so they would brake to keep from breaking out and I would zoom by for the win. They got off the line quicker than me and I was playing catch up all the way down the track but could make a top end charge at the end to make up the ET.

12 x 118 = 1416 so you can see the combination was really off. Better gears to allow the engine to use it's entire powerband down the 1/4 mile but still running the same MPH means the car should have run into the low 11's. There's a lot more than just gears involved. A properly matched torque converter will also change how the car performs. My 118 MPH was more common to a car running 11.4 than a car running 12.0.

It's more for those people who want to know if their ET or MPH is close to what it should be. A car that has a high MPH, may not have a low ET etc but in a normally aspirated situation the calculation should be close.

I dont understand the power band being hit by 1000 foot, if you get into the RPM it makes peak power, it would get into power in 1st gear and then stay in it in the shifts. That justifies a crappy short time, but by 330 feet i thought you would be rowing through gears where a motor wants to be.

Gears not deep enough and not enough stall speed in the converter. Engine started making power at 4000 rpm however because of the low stall converter and the long gears, it too time to get to that rpm after shifting into high gear. Even through the lower gears, the low stall speed converter takes time to get the engine into the powerband. That's why you always want a converter to match where the camshaft starts to make power. After that the rest of the car needs to be set up to utilize that.

Powerband is determined by the cam grind. If you can't get the engine to operate in that range then you're wasting power.

The cam in my current engine has an operating range of 4300-8000. I was launching at 5000, roughly where it makes peak torque. The converter stalls at 6200 on the transbrake so as soon as I launched, the rpms shoot up to the stall speed and stay there until the vehicle momentum and load on the engine start to allow the rpms to climb. I shift at 7500 and the rpms drop back to 6400. That keeps the engine at the high end of the power band the entire length of the track where it will make the most HP. If you have a lower stall converter, you would be farther down the track before the rpms reach the shift point because the converter isn't allowing the engine to get into it's powerband quicker. Deep gearing will also help this.

The camshaft I had in the car last year had an operating range of 5000-7500. It worked well but the heads wanted more at the top end and the cam grind was limiting performance. I was launching at full stall speed instead of off the 2-step.

If your entire is setup for maximum 1/4 mile performance then that 1320 number should be very close but there's always some other factors which could change that number. Any kind of power adder will usually do it. Turbo cars always have high MPH compared to their ET

Close, but not exactly. It's actually interesting how close it works out considering all the variables, like the fact that 1/4mile time and speed are measured in different locations (speed is up to time taken to cross a box at the end of the track...). It comes out slightly ambitious WRT to the ET, but close (over the range of most people's times here about .15-.4s off)

So to get real numbers, for
MPH = (hp/weight)^1/3 * 234
ET = (weight/hp)^1/3 * 5.825

the thing is that you really don't need to know hp or weight to compare your et to hp, you just get a hp/weight ratio or find it's inverse and you can compute both.

Real world, your mph tends to be pretty close to correct WRT to hp/weight, you won't typically run much faster an mph with a better launch, so if you take your mph and work backwards you should be able to calculate your theoretical best ET.

This is why both education and lotteries are run by the government.

ET is in seconds. Speed is miles/hour. ET x MPH = seconds times miles divided by hour; it is NOT equal to feet (although you could convert it to feet).

ET is measured from when your front tire clears the staged beam on the starting line until some part of your car hits the beam at the finish line. There are a bunch of variables right there - the start line beams and the finish line beams are not the same height off of the track, in case you didn't know that.

The speeds on your time slip are an average over 66 feet. Your actual speed at the 1/8 mile or 1/4 mile line is higher than what is on the time slip, since (theoretically) you are accelerating over those 66 feet. This introduces variables such as wind (already mentioned), aerodynamic efficiency, etc. To say nothing about some racers running on a rev limiter for the last few hundred feet.

A few years ago, NASA lost a multi-million dollar Mars probe because a contractor was doing course error calculations in English units; NASA was taking their numbers (without units), assuming they were in metric units, and giving course correction commands to the probe. When it got close to Mars, it was just enough off that it couldn't make a proper landing. The English unit numbers were close enough to the metric unit numbers than nobody caught the mistake until they lost contact with the probe and the investigation started.

That the ET x MPH number comes out as close as it does to the length of the track in feet is mathematically irrelevant.

(For the record, the first example, 9.029 seconds x 148.78 miles/hour, equals 1970.2 feet.)

Exactly... 1320 mile-seconds per hour isn't a particularly meaningful quantity.