Torque Quiz...

[johnc]

Assume a couple mythical engines...

 

Engine A makes 292 ft. lbs. of torque from 6,000 to its 9,000 rpm redline.

Engine B makes 339 ft. lbs. of torque from 3,000 to its 6,000 rpm redline.

 

Engine A runs a 4.11 rear gear.

Engine B runs a 3.54 rear gear.

 

Both are in identical chassis and both have identical trans gearing with a top of 1:1. Both cars have an identical rpm limited top speed of 150 mph. Both have have identical traction limits, both vehicles are absolutely identical including having Schuey as the driver.

 

Using the information presented here, what are your answers to the following questions:

 

1. Which one puts the most torque to the ground?

2. Which one would be faster around a racetrack?

 

Hint: Latest issue of Circle Track Magazine, page 56.

[Brad-ManQ45]

I'd say it's a wash from the standpoint of torque applied in the rev range. That is assuming a 'flat' torque curve within the given rpm range.

 

Which one for the street? - the 339 would do it for me - better low end torque (below the 3000 rpm point).

 

Back when NASCAR had both small blocks and big block engines (about the same hp)- the small blocks ruled the small tracks 'cause they got the jump on the big blocks out of the corners. The big blocks ruled on the longer tracks (longer straightaways).

 

Apply this logic to the questions above.

 

And no, I don't have a way of viewing Circle Track magazine.

[blueovalz]

If there were a lot of gear changes throughout the course, I'd go with the high rev'r. A fairly constant speed oval track would make me reconsider using the low rev'r. And the answer is?

[Guest Cusp]

Well, I did the math on top speeds, and if the top gear is 1:1, I wonder if the car with the 3.54 gears CAN go to 150mph. With a 6000rpm redline, topped out in top gear gives ya some pretty tall tires to go 150mph. So, I'm not sure if it's the answer, but car A can probably go faster on top.

 

As for the torque question, I will guess engine A makes more torque based on the relationship between HP and TQ throughout the powerband.

[blueovalz]

If I've got the concept correct, they are equal in "torque to pavement" because of the added leverage or torque from the rear gears, but at peak RPM, the high rev'r turns the tires faster than the low rev'r even with the 4.11 gears. So I'd say same torque, but faster around the track with the high rev'r. I don't have the issue of Circle Track, so the answer is ??????

[Bob_H]

I'll take more RPM any day.

Ok, there are some missing assumptions. First, it is unclear if by saying both cars have an identical rpm limited top speed of 150 mph that you mean both have the same xx rpm limit, or one reaches 150 at 9k and one at 6k.

So I checked out both. I plugged it into a standard 83 zx tranny with the two ratios and the 6k and 9k redline. well, for the 9k motor to redline at 150 it took 205/50/15's. for the 6k motor to redline at 150, it took 325/50/17's. ironically, this negagted any gearing advantage of the 4.11's vs the 3.54's, making the two identical.

So lets assume they both are rpm limited to 6k at 150 mph. However, with the same tranny, to reach a 6k 150mph on the 9k engine combo,(read 4.11 diff), you need an unrealistic size tire of 345/60/18 vs. the 325/50/17's of the 6k combo,(3.54 rear), and that is close to 150 and 6k, but not quite.

Now for the interesting part.

Redline speeds in each gear for the 6k motor combo is: 49/81/115/150

Redline speeds for the 9k motor combo with the "imaginary" tire size is: 73/120/171/150(6k)

So, for Motor A, second gear is good for 120 vs. 81 in the other car. Now the fun stuff, torque to the ground in each gear.

Motor A:

1st-3674.767

2nd-2229.82296

3rd-1569.5

4th-1200.12

Motor B:

1-3674.59

2-2229.603

3-1569.678

4-1200.06

Basicly identical if you round.

So with Motor A, you can apply 2230 lb-ft of torque till 120 mph. In motor B, you can apply the same amount of torque till 81 mph, where you then drop to 1570 lb-ft of torque,(I am obviously using 2nd gear for this example).

So Motor A will clearly outrun Motor B due to RPM capability. But both put the same torque to the ground in each gear(answers #2). Shuey wins by a landslide in the Motor A combo(answers #1).

[KiD-ViD]

the one that revs higher is going to be faster....it makes alot more HP because HP is just a calculation of TQ. http://www.vettenet.org/torquehp.html

[johnc]

Although I left out some details that Bob added, in essence both cars should have identical performance on a race track. A higher crank rpm allows a race vehicle to run a lower (higher numerical) rear end gear giving a better torque multiplication at the tire contact patch. Ideally a race car is geared to be rpm limited in top gear at the end of the longest straight.

 

That's one of the big reasons NASCAR Winston Cup motors are turning 9,000+ rpms. I started thinking about this after watching the Pocono race where the 12 car ran the entire track in 4th gear with an incredibly low rear and the engine hit 9,400 rpms entering turn 3. That pushrod motor lasted 500 miles and they almost won the race.

 

It also helps explain why a low crank-torque engine like the Honda S2K engine can do so well on a race track. BTW... a WC engine has a power and torque curve very close in shape to the Honda S2K engine. The WC engine just hits higher peak numbers because of its greater displacement.

[Phantom]

So I would folllow the time honored racers tradition and cheat - put the 4.11 gears on the 339 lb-ft torque engine and use an overdrive transmission. It's all in the gears.

[Bob_H]

wait, i'm still unclear on the max rpm at 150 issue. so do they both hit 6k at 150 or both hit their max rpm at 150. if the second is true, then their performance is identical as you said,(that is what I interpret your comments to be). However, I still think that if the first case was true, then car A is faster, unless you prove otherwise.

-Bob

[Pop N Wood]

Engine A has significantly more horsepower than B.

 

And if you have ever read any of Grumpyvette's posting you know you need to build for max HP so you can put more torque to the rear wheels through the appropriate GEARING.

 

Engine A equals engine B's peak HP at something like 7000 RPM. Thus engine A will be producing more HP from 7000 to 9000 RPM than engine B is capable of at any RPM. I would think you could gear a transmission to let you run the entire race in this 2-3 thousand RPM band.

 

So I vote Engine A the hands down winner.

[johnc]

The top speed issue is not important. I was just trying to provide a little insight into what torque really is.

 

My little scenario has never and will never exist in the real world. Vehicles A and B would most likely have some driveline and chassis optimizations done to make best use of their particular engine.

 

Or, vehicle B would protest vehicle A's engine...

[Guest Anonymous]

Just my 2-cents. This points out the fallacy of NASCAR's outlawing the big-block V8's in the early '70s in a effort to bring speeds down (and improve safety). The engine builders simply took the small-blocks and developed them to produce the same amount of horsepower (which demands the 9000+ rpm levels).