I found a formula for 1/4-mile speed:

speed = 234.742 multiplied by cube root of (horsepower/weight)

Anybody have a similar formula to calc 1/4-mile time?

Especially I'd like a formula that calcs 1/4-mile time but includes a parameter for torque, as I think that will make a difference. For example, my 300 I6 F150 (4200 lbs) and my wife's 3.0 L Aerostar (3400 lbs??) both have 145 hp (rated), but my 300 I6 has about 100 more foot pounds torque. Surely that would make a difference on the calculated 1/4-mile time. Without the torque factor, wife's van is 1 second quicker because of weight advantage. I don't think this is right.

I know this is all academic, but the best I can do as the wife won't race me.

 

I used my Drag 2000 program to predict my 1/4 speed and ET. The speed is 110 MPH and ET is 12.55 seconds. I am sure that these numbers would be ideal conditions. Using your formula my speed comes out to 118 MPH. I also used Dyno 2000 to figure my engine specs it comes out to 443 HP at 5500 RPM's and 459 Ft-lbs torque at 4500 RPM's. My engine is a 400 +.030 with 351C-4V heads, Crane cam, Edelbrock intake, 750 CFM Carter carb, Sanderson headers, Mallory dist, Holley Annilhilator ignition. According to Drag 2000, I would be at 5200 RPM going through the traps. It takes into account the gear ratios and shift points. With different ratios the results may be better or worse. Your simple formula doesn't account for any variables.

Dan Lee
'53 F100
400C-4V

 

You're right. My formula (actually derrived from a horsepower formula found in Hot Rod Magazine) leaves out most variables. I believe I read (not sure if was in same Hot Rod article) that gear ratio is not highly significant so long as the engine is run in the power band. To a degree this is true, though shift points are important. Anyway, I believe torque would be a significant factor especially as I described above where two vehicles are similar in horsepower. Does your program account for torque? I suspect that none do, at least directly. Since your program deals with gear ratios, it may be indirectly accounting for torque based on RPM.

 

Tall, Your right about torque, it does make a difference. Most formulas and programs don't include a bunch of stuff but are still useful for looking at things like cams, carbs, head flow...
They also completely ignore the design of the car, most trucks are as smooth as a brick in the air.

Dan's 400C makes the same torque as a stock 428 4v but the 428 does it almost 1500~2000 rpm lower. The point is that the torque curve has more to do with an engine that any HP number most of all peak HP numbers. Your 300 6 has a ton of torque at a VERY low rpm and is considered a great tow engine. That why you can move that truck with the same HP as the car.

Also, I bet her car makes it's peak HP a LOT higher than yours. I looked up a friends Mazda RX7 with a rotery engine and it's peak HP was over 7000rpm! it really sucked getting it going, but was ok after that. I have a 24volt electric winch motor for my truck that puts out more than TWICE the torque of most big block (850#), but it only spins at 55rpm.

Carrol Shelby once said: "torque wins races and HP sells cars"
Also, engines don't actually produce HP, HP is a calculated number based on torque.

What I've been interested in is figuring out the HP based on 1/4 mile and 1/8 mile times rather than just 1/4 times, I think that would give a better picture of the torque.

 

karljay: Thanks, 300 I6 makes peak hp at 3400. Aerostar 3.0 's peak hp is somewhere like 4600. I'll try to look up the formula from Hot Rod. I believe it was hp from trap speed and they thought that was better indicator of hp than 1/4 mile time.

 

Speed through the traps is an indication of HP. A drag racer needs to select his gears so that his RPM through the traps is at peak HP. That is true for an 1/8 mi or 1/4 mi. All the torque in the world won't help if the peak is at 42 MPH at 10 feet from the start. The 300 I6 may pull a heavy vehicle of the starting line quickly, but when it peaks the Aerostar will start to gain. Whether the Aerostar passes or not in a 1/14 mile, or a 1/8 mile depends on variables, such as gear ratios, aerodynamic drag etc.

If I get some time soon, I will try to simulate the truck with the 300 I6 and the 3.0 litre Aerostar. Then we can compare the ET's.

Dan Lee
'53 F100
400-4V

 

Thanks, I try to post the hp data I have. But it will be on Monday. I kinda thought the Aerostar might take me off the line because it has a slush box and my first is so low (3.90 on a 3.08 rear) that I have to shift around 30 mph. Once I am in second above 2000 rpm, if the Aerostar is near me, I think I will leave it far behind. I drive both a lot and notice the Aerostar really has a lot of work to accelerate from freeway speeds but the 300 I6 moves out pretty good. Anyway it would be interesting to see what your program does.

 

I need some info for my simulator.

1 Truck weight = 4200 lbs

2 Truck HP = 145 @ 3400 RPM

3 Truck torque = ? @ ?

4 Gear Ratios 1 = 3.90, 2 = , 3 = , 4 = ?

5 Rear Ratio = 3.08

6 Tire Tread width = 6?

7 Tire diameter in inches = 27?


1 Aerostar weight = 3400 lbs

2 Aerostar HP = 145 @ 4600 RPM

3 Aerostar torque = ? @ ?

4 Gear Ratios 1 = , 2 = , 3 = , 4 = ?

5 Rear Ratio = ?

6 Tire Tread width = 6?

7 Tire diameter in inches = 27?

You can email this to danlee_58(No Email Addresses In Posts!)

 

The Formulae for the Quarter mile on anything I own, is the time it takes to eat a samwich and down a short beer!

 

I simulated the F150 using a '69 Ch**y truck for aerodynamics.

1 Truck weight = 4200 lbs

2 Truck HP = 145 @ 3400 RPM

3 Truck torque = 265 @ 2000 RPM

4 Gear Ratios 1 = 3.90, 2 = 2.25, 3 = 1.50, 4 = 1.00, 5 = 0.80

5 Rear Ratio = 3.08

6 Tire Tread width = 9.165

7 Tire diameter in inches = 28.750

I got the following results:

1/8 mile 12.757 secs @ 60.0 MPH
1/4 mile 19.404 secs @ 73.8 MPH

It never got into 5th gear.

I simulated the Aerostar using a '69 Ch**y Nova, since there are no mini-vans in my database.

1 Aerostar weight = 3400 lbs

2 Aerostar HP = 145 @ 4800 RPM

3 Aerostar torque = 165 @ 3600

4 Gear Ratios 1 = 2.47, 2 = 1.47, 3 = 1.00, 4 = 0.74

5 Rear Ratio = 3.73

6 Tire Tread width = 8.385

7 Tire diameter in inches = 25.740

I got the following results:

1/8 mile 13.207 secs @ 63.0 MPH
1/4 mile 19.643 secs @ 76.3 MPH

It never got into 4th gear.


THE RESULTS ARE IN:

The F150 with the 300 I6 wins by 0.239 seconds over the 3.0L Aerostar.

Recap:

Although it was nose to tailpipe at the finish, it was the early lead by the high torque 300 I6 which could not be overcome by the higher revving 3.0L V6 that led to this victory.

Dan Lee

 

The speed of neither vehicle agrees with the formula.

The reason is that neither is at peak HP at the traps.
The F150 is 2770 RPM vs 3400 RPM for peak HP.
The Aerostar is 3987 RPM vs 4800 for peak HP.
I think a gear change is needed!

 

Looks like I need the Aerostar's 3.73s. Then 2nd would be low enouth to use as a first gear and I probably could go a lot quicker. That semi-creeper first is a detriment to drag racing. It would be interesting to see what happens if we optimized the gears in both vehicles and, if you are willing to run it again (I don't know how long it takes), run the F150 without first gear, that is, use ratios of 2.25, 1.50, 1.0 and 0.80 (as if it were a 4 speed) with the 3.73 rear end.

 

I have been away a couple of days. I just got back and ran some variations of the runs.

The first was to give the aerostar the same aerodynamics as the truck. That is a drag coefficient of 0.5 vs 0.42 as in the original case.


1/8 mile 13.270 secs @ 62.0 MPH
1/4 mile 19.834 secs @ 74.1 MPH 3874 RPM

So we can see what effect the shape has at this speed.

Then I modified the truck so it started in 2nd gear and went through third and forth. I also changed the rear ratio to maximize the RPM at the traps. I tried 3.73 like the Aerostar, but it shifted into high just before the traps. I wound up with 3.67:1 ratio.

1/8 mile 12.487 secs @ 60.0 MPH
1/4 mile 19.034 secs @ 75.5 MPH 3472 RPM

Next, I used the aerostar with the 0.50 drag coefficent and maximized the RPM at the traps. I got a 4.45:1 ratio.

1/8 mile 12.617 secs @ 61.0 MPH
1/4 mile 19.069 secs @ 76.6 MPH 4779 RPM

Now things are nearly equal. The drag is the same and they are both at peak HP. The truck is heavier, but the Aerostar AOD has some slippage.
The speed is still less than your formula predicts, but that is probably based on something a lot more slippery than 0.50 drag coefficient.

 

Thanks again Danlee: The lower rear end gear shaved off a few tenths of a second, but I thought it would do better than that--maybe shouldn't have chucked first gear. Also your program probably assumes a Hurst shifter. But it appears that the Aerostar may be quicker because in reality it should have a lower drag coefficent than the F150. As I recall reading somewhere, the Aerostar was designed with a very low drag coefficient, which had something to do with it being called the Aero-Star. It may very well be below 0.40. The F150 also was aerodynamically designed, but I would expect nowhere below about the mid 0.40s. Now if we could slip the 300 I6 and the 5 speed into the Aerostar we'd have one tough towing machine and probably knock it down into the low 18s on the quarter.

 

I`ve come accrost a calculator that seems to be accurate.

>>>http://www.carnuts.com/on-line_dyno.htm <<<

with the info i put in it came to within .02 to my time slips and it told me the horespower at the rear wheels to get there....
It may be of use to some one else !!



__JOHN__Õ¿ö
FTE Club #7
Member-
http://www.cruisin-north.com/
Santa Rosa, Calif.
72 F-250
ICQ#6030753
http://www.ford-trucks.net/users/jbhf250/
https://www.ford-trucks.com/pictorial/big/1972_f250_2.html