Low Torque @ High RPM VS High Torque @ Low RPM
 

The FRS has


151 ft/lb @ 6400 RPM






How would you compare this if we had a 200 ft/lb @ 3000 RPM


In other words, Low Torque @ High RPM VS High Torque @ Low RPM

HP = (Tq * RPM) / 5252

You'd have 114HP there.

Then BMW has 241hp
The frs has 200 hp


BMW has 200 Ft-lb @ 3500 rpm
Whereas frs has 151 @ 7000 rpm


I'm confused

Those are peak values.

The BMW doesn't produce 241hp at 3500, it produces 133 hp when you hit peak torque at 3500

High torque at all rpm, thanks.

and high RPM range

Your FRS only has 200 HP at around 7000 RPM, it has less anywhere else.

Torque is how much rotational force the engine is outputting.

This changes drastically along the RPM range of any engine. Mainly because of how quickly the air can enter the engine and how quick the combustion burns.

If you want to have an engine with high RPM power, you want to try to keep the torque output good near the redline, if you want the engine to have "low end torque", you try to make the torque curve fat in the low RPM (long stroke specs. gives good torque, but limits the high RPM potential due to piston speeds). If you want good torque in the low and the high RPM, that's where you start needing variable cam timing, ignition timing, and everything else that is "variable".

Or you can do it the american way, and just make a very big displacement engine, then you have gobs of torque everywhere even with 2 valves per cylinder.

Take a look at this stock FR-S dyno:

http://www.tune86.com/sites/default/...n-frs-dyno.jpg

The solid red line is torque (in lbs-ft) and the dotted line is horsepower to the wheels.

Let's take it in 1000 RPM increments.

At 3000 RPM, you have 140 tq. Using the formula LuisGT posted [HP = (Tq * RPM) / 5252], you have: 140 lbs-ft x 3000 rpm / 5252 = 80 hp.

RPM - TQ - HP
3000 - 140 - 80
4000 - 122 - 93
5000 - 139 - 132
6000 - 140 - 160
7000 - 130 - 173

You can see that peak hp is 173 hp (to the wheels) at 7000 rpm. Assume 13.5% drivetrain loss and you have the manufacturer's rating of 200 hp to the crank (200 hp - [.135 x 200] = 173 whp)

High torque at low rpm is for trucks and drag cars.

High revving cars are for twisties.

To each their own.

:burnrubber:

Drag cars spend little time at low RPM. You've got to rev them pretty high to get the most out of those big lift, big overlap cams they put in them.

:threadjacked:
What's the point in having high end torque? Would'nt you rather have low end torque for quicker starts?

Why would one say high revving engines be better for twisties?

Sorry for the noob questions

fcuking Newtonian physics, how does it work?

Drag racing engines are revvers optimized for max power up top, even more so than roadracing engines which have to be tractable over a broader rpm range.

High end torque means more max power lol.

I don't think there's a really good reason for high revving engines in twisties, they tend to have higher power density but for most people I think it's the fact that an engine that can spin faster than the engines in most cars on the road is cooler, and makes it have better noises.

POWER is what is important. Power is torque x rpm. Making torque at elevated rpm is key to making maximum power. That's why a 2.0 S2000 accelerates faster than the FR-S/BRZ. The s2000 makes peak power at 8300 and keeps making usable power up to 9000rpm whereas the FR-S/BRZ peaks at 7000 and signs off at 7400. Same weight, same torque, but S2000 revs much higher, so it makes more power, and as a result is 5mph faster in the 1/4.

Think of it this way: engine power, not torque, tells you how quickly you can accelerate from a given speed. If you make 200hp by spinning a 1.0 75 lb-ft engine up to 14,000 rpm or by spinning a 2.0 150 lb-ft engine up to 7000rpm, they'll give you the same acceleration (each geared appropriately of course).

1 horsepower is 550 ft-lb/sec. This is NOT "torque over time", it is rather the *rate of doing work*. The "ft-lb" term isn't torque, but work. Push something with 1lb of force a distance of 1ft in the same direction as the applied force and you've done 1lb x 1ft = 1ft-lb of work. Motion is required. As opposed to 1 lb-ft of torque. Hang a 1lb weight off the free end of a 1ft horizontal cantilever beam and you have 1 lb-ft of torque at the fixed end. No motion required, and the force and distance terms (lb and ft) are not in the same direction but perpendicular to each other.

So, 200hp is 200*550 = 110,000 lb-ft/sec. Rate of doing work, but also ability to apply a force at a given speed. Say, 110 ft/sec, which is 75mph. 200hp can apply a force of 1000 lb at 75 mph (110,000lb-ft/sec divided by 110 ft/sec).
That's 0.333-g for a 3000 lb car.
240hp is 132,000 lb-ft/sec, that's 1200 lb for acceleration at 75 mph. 0.4-g acceleration for the same 3000lb car. Quicker.

this discussion is useless without gearing information

and relative weight

and relative usage

the fr-s also has the same tq at 2500 rpm whats your point?

before drive train losses we actually have like 165 ft/lb fyi with headers the dip is gone and its closer to 170ft/lb from 2500-7000 rpm

I've had both types of cars. Both have their moments. You really get addicted to the swell of torque as you roll into the throttle on low revving torque engine, but they die above 5000rpm (mine was supercharged so that didn't help). The power is always there, you just need to put some foot into it and you're gone.

High RPM engines are less rewarding around town, but much more rewarding when you're getting on it. The extra downshifts required to get anywhere are a bit annoying but you get used to it and learn to anticipate. The wail from the exhaust at 8000rpm is like nothing else. Definitely more work, but I would say the rewards are also greater.

That's a very usable explanation.

You compared the F20c and the FA20 in this explanation, would you revisit it comparing an engine that makes more HP than Torque to an engine that makes more Torque than HP?

The example I have is a friend who races an STI makes 300hp Awhp but makes 330ft/lbs of torque. If "work" is a relation of torque-in-motion does that suggest, within the realm of your explanation, that his engine is leaving "work on the table" or is failing to turn all of it's torque into work?

Finally, the class he races in has a 10:1 power to weight ratio but the rules say if your engine makes more torque than HP, you have to average the 2 and thus his car has to weigh 3150lbs instead of 3000lbs. I feel like because his engine makes more torque than HP, he's being handicapped by having to be heavier than a competitor who makes 300hp and 300ft/lbs and can weigh 3000lbs minimum weight.

Your thoughts?

Turbos sort of let you have the best of both worlds.

My evo: 276 hp @ 6500 rpm and 268 ftlbs @ 3000 rpm. Though the general consensus is Mitsubishi understated the hp due Japans gentlements agreement back then.

Power and torque are different things, so you can't really say you have "more torque than power". The relative values are quite different in different units systems for this reason.

But I know what you're getting at, an engine that makes peak power somewhat beyond 5252rpm vs. one that makes peak power below that rpm (roughly). A revvy higher-rpm engine vs. a torquey low-rpm engine.

It does mean that the engine isn't breathing well above 5000 or so rpm. If it was still making 330 lb-ft at 5000, that would be 314hp, so torque is falling off below that rpm.

I agree with you. They should go strictly by horsepower IMO.
My time trial club does something similar, they add 2/3*horsepower to 1/3*torque in lb-ft in what I think is a misguided attempt to come up with "real world" power. But you can't add or average values for two different things! Should just go by power. Torque by itself doesn't tell you anything about performance potential. Power does.

There is no argument here. Flat Torque Curve is the perfect one every-body want. Unless you can not have it, then it is depend. Torque is all relative to RPM and gear ratio.....when it is down to that, that is where people differ from each other, and that is why you need a test drive

It really doesn't mean much, since it's purely an artifact of the units. A relatively high horsepower with a relatively low torque means the engine has a powerband high in the rev range, while a low horsepower high torque engine has a powerband low in the rev range.

Not at all - it's turning all of its torque into work just fine. That just means that it is making its peak torque below 5252 rpm, and the torque falls off relatively quickly above that value.

He is being handicapped, without a doubt - an identical weight car making 315hp with a similarly broad powerband (geared appropriately) will definitely be faster, at least in acceleration. Horsepower, not torque, is what determines how fast a car accelerates (assuming it is geared correctly for the engine and desired usage).

That system will be very, very kind to a super revvy, low-torque motor that breathes well at high RPM then (and very unkind to a low-revving, large displacement or turbo engine).

However if he had 315HP, without reducing his TQ value, he'd have to add even more weight. Are you suggesting that since his car weighs 3150lbs that if it made 15 fewer TQ's and 15 more HP, it would be faster? To me that sounds exactly right.

For you and Zdan: So to meet he rule of 10:1 it's simply HP to Weight. But if your car makes more torque than HP (like the STI) you have to average the two in order to determine minimum weight. So if you were to submit a rule change so that the minimum weight was only based off of HP, how would you make that argument to win the votes of your fellow racers in that class?

Second question..

How would you go about getting a turbo engine to reduce torque and increase more HP up top? Change in turbo size, tuning, boost pressure?

Precisely. Note that when I refer to a broad powerband, it doesn't mean that it has to be in the same place, it just has to be broad. So, for a revvier, lower-torque motor, a broad powerband could mean that it's making within 5% of peak power from 5500-7400rpm, while for a high torque, lower rpm motor, it could mean that it is making within 5% of peak power from 4000-5800rpm (note that I'm not mentioning torque here). Either one will work just as well (assuming similar peak power) for racing.

(The broad powerband is important because it allows you to be making near peak power at all time, by shifting appropriately. A very peaky motor, especially with a wide ratio gearbox, will not be as fast as the peak horsepower number might imply)

Good recap on the basics. I am aware of the relationship of TQ and HP but in the context of higher TQ than HP especially in a ruleset with a 10:1 power cap I hadn't given it much thought. I never thought of a torque value actually being a "penalty" on a race car. It's interesting how that plays out.

330TQ, 300HP car is required to weigh 3150lbs.

Take the same car, remove 30 ft/lbs so it's 300/300 and now, according to the rules, it can weigh 3000lbs and should be noticeably quicker because the engine still does the same amount of "work" but now the car weighs 150lbs less.

This is what happens when we have "rules". :)

http://pickledduck.com/wp-content/up...e_you_know.gif

Would be good to see a dyno plot. If the 330 peak is down low enough, he could conceivably pull timing down there and not really hurt performance. But if its in the meat of the powerband, could be a bad move.

It can do the same *maximum* rate of work at peak power rpm, but it depends on where the 330 peak is whether you could get away with lopping that 30 lb-ft off the top and not have it hurt performance. Depending on the gear ratios, the engine will have to perform over a ~2500-3000rpm range. If the 330 lb-ft torque peak is in that range, then knocking it down will have a negative effect on performance, which would be partially offset by the weight reduction.

I'd rather have a flat power curve (which means torque that decays as 1/rpm). That's not very common though...

To inter change Torque and HP, you have to do it from the sheet metal. It involves a lot of stuff

Compression, displacement, AFR, Cams profiles, Engine RPM.......gear boxes...

take S2000 for example, 2.0, AP1 = 9k RPM engine redline vs 2.4 , AP2 = 8,300 RPM redline, and AP2 have the same HP, just with more Torque

Not so much on Petrol engines alone

So far, Flat torque curve can be obtained easier by using Electric motors. Either Full Electric Vehicle, or Hybrid.

Having a flat power curve (with torque decaying) isn't fun. As soon as the turbo spools up it feels like it sort of falls flat on its face. Something like this with the Jettas. Typically its a result of a small turbo being pushed beyond its efficiency range and not flowing enough at higher rpms.

http://www.dragtimes.com/images_dyno...Jetta-Dyno.jpg

Well....that is BECAUSE TURBO. But basically every manufacturer want to achieve that flat.

A flat power curve will be the fastest though (for a given peak power), since it lets you stay in the powerband more of the time.

Flat power curve at 300hp will be faster than 300 PEAK hp, yes. But if the power curve is flat over a broad range, it's because torque is falling off rapidly which means you're not breathing well at higher rpm. Open up high-end breathing and you could have a powerband that starts at 300hp and ends up at 330hp, which would of course be faster.

If your buddy's power curve looks like this one:
http://www.dragtimes.com/images_dyno...Jetta-Dyno.jpg
Scaled up to ~330 lb-ft/300hp, I'd say yeah, lop off the top of the torque curve below ~4500rpm by pulling timing or something. Wouldn't hurt track performance much if at all, and he could lose that ballast!

This is true for events that limit you to X hp and I full agree. But for street driving, I'd much rather keep torque and gain peak hp.

I'd rather a slightly larger turbo that can pull right to redline than a small turbo that spoolers quicker but starts to struggle beyond 5k

I had a conversation with him last night. His TQ peaks at 4.1k and then drops like a typical STI dyno graph. The big clue is that he's boosting up to 21-22 PSI earlier and as the revs climb the boost falls to 16-17 PSI. That would explain it. He could run boost at 17 or 18PSI max and run it all the way through the rev range, as well as playing with timing. Either he removes the weight with this exercise or he stays at his current minimum weight and finds a way to reduce the the TQ spike, broaden the band and bump up the HP by 15WHP and boogy down the straight a little better.