BRZ vs. Prelude Si vs. S2000. . . Initial Thoughts

[Symmetrical]

[ZDan]

Originally Posted by Jawnathin

MT got 98.1mph in an AP1 and 95.5mph in a BRZ. I don't doubt that others have gone faster though.

http://www.motortrend.com/roadtests/...0/viewall.html

MT getting 100.5 in a stock AP1.
94/95 for the FR-S/BRZ and 100/101 for the AP1 are pretty representative of what these cars can do bone stock.
98 for the AP1 is an outlier on the low side, 95.5 for the brz is an outlier on the high side.

[ZDan]

Originally Posted by Jawnathin

Power under the curve represents of the engine output over the entirety of its operating range.

F20C average from 2500-9000rpm = 135rwhp (using the 202 peak rwhp curve above). FA20 average from 2500-7400rpm = 121rwhp (using the 173 peak rwhp curve above).

y your definition the engine with less peak power is inferior despite romping on the other everywhere else in the power band because only peak power matters.

I have never said or implied that.

Of course the power curve matters. But the FA20 and F20C power curves are *similar enough* that peak power does a good job of indicating performance.

Ancient equation for peak hp from 1/4-mile trap speed (aka "ricer math" in recent decades...):
hp = (trap speed/234)^3 * weight
FRS/BRZ: (95/234)^3 * (2750 lb. +200 lb.) = 197 hp
AP1 S2k: (100/234)^3 * (2800 lb. +200 lb.) = 234hp

Is your car always at a MPH/RPM where it makes peak power? No?

Of course not. But my S2000 *is* always at a much higher rpm range toodling around town than the LS2 car. I drive in the rpm range that gives me the oomph I need for what I'm doing. In the S2000, that rpm range would be a bit higher than in the FR-S/BRZ. I don't see the big deal here.

A broader power band gives the engine and driver flexibility.

FA20 powerband is not broader than F20C's. F20C engine is supremely flexible, btw. Totally happy ~2000-6000rpm around town, totally happy 6000-9000rpm at the track.

The fact the F20C needs to be revved out to get anywhere is why it has such poor fuel economy.

It is geared lower overall, and they kept 6th low as well. It could have handled taller gearing, but that didn't fit with its mission. FRZ twins get better mileage primarily due to DI and far better aero, though.

There is no way an F20C is as driveable around the street as a 545hp LS2.

It is MORE driveable, but that's partly due to a tuning issue. Cam surge makes it lurch at low rpm low load, total PITA. Also, the clutch is much heavier and shifting is more of a chore. The S2000 is a much easier car to drive around town.

I've got a 560~whp C6Z and even with its crazy tall gearing, it can pull strongly from nearly any rpm in every gear. You can do something silly and try to go WOT at 800rpm in 6th, but anything reasonable and it pulls quite well. Even if I never taking it above 3k RPM I can accelerate quicker than most traffic.

I know the feeling But still, when I know I need to accelerate in the S2000, I keep the revs up. No biggie. I am practically never in a situation where I go from just cruising to WOT randomly, and in any case downshifting the s2k trans is more of a snick-snick joy than a CHUNK-CHUNK chore.

And because of that torque, the car can be geared super tall and have excellent fuel economy. I get close to 30mpg on the highway vs 24mpg for the AP1 S2000. under the same conditions in the S2000. Hell, its even better in the city too. Who would have guessed that a 7.0L V8 would be more fuel efficient than a 2.0L 4 cylinder?

I've gotten 29mpg max highway in the LS2 RX-7. Usually more like 25. And in town, 15 or less. With vastly inferior aero, I've gotten 31-32mpg max hwy in the S2k, usually more like 27, and easily get 20-22 in town. I don't know how or why some people manage to get crappy mileage in the S2000...

So you never exit a corner at an RPM less than peak power?

Where'd I ever say/imply that?

I find that interesting, I hear S2000s fall in and out of VTEC all the time at the local autocrosses. Clearly they're doing it wrong and you should come teach them how its done.

Must be stock AP2s. Big difference between 6000-8000rpm powerband vs. 6000-9000. Anyway, autoX bores me, never done one in the s2000.

For the 10th time, my position is about power under the curve in general, a 'misused concept'. Not specific to FA20 vs F20C. And even then, that is not true. There are certain speeds that despite the shorter gearing and higher revs, the F20C doesn't make as much torque to the wheels as an FA20. Look at 25~mph @ 2nd gear for both cars as an example. BRZ should be around 3000rpm and the AP1 @ 3200rpm.

And by the time you reach 30, they're even again as the FA20 goes into its midrange hole.

This pretty much happens in any gear/mph with the FA20 @ 3k rpm, which is where the car likes to sit and cruise around in. Pretty much where the car sits 90% of the time.

On the street, driving semi-speedily, I find myself around 4000, and cruise at 75mph on the highway is 4100rpm. If you drove an S2000 every day, you would be driving it at higher revs more of the time, and you'd do this without even thinking about it. Key difference: if I get on it from 4000, I basically never lose torque. If you get on it in the FR-S/BRZ from 3000, you get decent torque, then it drops off significantly, then comes back. Not ideal, possibly annoying, would either get used to it or hate it more and more over time, I think.

Uh, just look at the dyno plot? At what point under 6000rpm is the F20C making more power?

If we're limiting both engines to less than 6000rpm, yeah, the FA20 has "more power under the curve". But that's an odd stipulation to make when the real power from both engines is somewhat north of 6000rpm... Power under the curve: F20C has a TON more, but tie one hand behind its back, and yeah, it loses.

Both motors are peaky. The FA20 is just stronger down low and in RPMs suited for street driving.

"RPMs suited for street driving" is not a constant from car to car.

The point is that despite whatever bickering that goes on in this thread, is that they're not worlds apart. Neither car is slow but neither are quick.

OK, agreed

the end

[CSG Mike]

This is somewhat amusing... because I actually agree with both of you...
@ZDan: Have you purchased a FRS/BRZ yet? I have a pretty good amount of seat time in them

[WolfpackS2k]

Somehow in one issue of Road & Track they cranked out a 0-60 time for the AP1 S2000 of 4.9 seconds.

[iLuveKetchup]

Originally Posted by ayau

Is this your aero theory again?

Zing!

[dsmx17]

I'm pretty sure the point someone was trying to make was that in the case of the op, being constricted to break in revs ~4k and under the fa *should* feel peppier than a f20 (also under break in assuming ~4k)

either way I have enjoyed reading the banter, good to know some other people on here actually understand mechanical theory.

[Suberman]

Anybody noticed that the Honda engine doesn't produce significantly more torque than the Subaru?

Acceleration is a function of torque to weight ratios. Power to weight ratios are just shorthand for torque. Only torque accelerates. This is why supercharged engines punch so far above their weight if power to weight ratios are used. Of course poor low end torque can be compensated for by gear ratios but drivability suffers big time. Anybody look at the 50 and 100 cc TT motorcycle numbers? 14 spd gearboxes and a very narrow torque band.

Rpm makes more power for any given torque at that rom but generally speaking moves the torque curve up the rpm range.

Since volumetric efficiency for emission certified street engines is getting pretty uniform these days this is no surprise.

Bmep is the holy grail. Can you get high bmep at low rpm and at high rpm! Hello variable valve timing.

[ZDan]

Originally Posted by Suberman

Anybody noticed that the Honda engine doesn't produce significantly more torque than the Subaru?

The F20C makes *less* torque than the FA20. The difference is that it continues to make torque at higher rpm. POWER.

Acceleration is a function of torque to weight ratios. Power to weight ratios are just shorthand for torque. Only torque accelerates.

Power to weight is indeed the more important metric. Engine torque/weight is by itself meaningless, it doesn't give enough information to determine performance.
Torque at higher rpm is BETTER than torque at lower rpm, because at higher rpm it is making more POWER. This is why the heavier S2000 is quicker than the FR-S/BRZ despite making less engine torque.

Power is the ability to apply torque *at the rear wheels*, where it matters, at a given speed. Torque at higher rpm puts more torque *at the rear wheels* than torque at lower rpm, because at higher rpm it is getting more torque multiplication through gearing.

Power is the rate of doing work. It is force multiplied by velocity, or torque multiplied by rotational speed. This is what *accelerates* things.
Torque moves things, but it doesn't tell you how FAST you can move them.

With engine torque, you have to multiply by the gear ratios to get rear wheel torque and then thrust at the rear wheels (what pushes the car forward) from that.
Engine power, on the other hand, is directly related to thrust at the rear wheels.

Power is force * velocity. Engine power is rear wheel thrust multiplied by road speed. You can easily calculate thrust at the rear tires in pounds from engine rwhp and road speed without knowing gear ratios or tire diameters.
1 horsepower = 550 lb * ft/sec
Thrust = 550*rwhp / road speed in ft/s.

This is why supercharged engines punch so far above their weight if power to weight ratios are used.

Evidence? If you plot the 1/4-mile trap speeds of cars (preferably those that make either much lower or much higher numerical values for hp than lb-ft) versus power/weight and torque/weight, you'll find strong correlation for power/weight, not so much for torque/weight. Whether or they get their power and torque naturally aspirated, turboed or supercharged.

Rpm makes more power for any given torque at that rom but generally speaking moves the torque curve up the rpm range.

Of course if you tune for higher-rpm torque, you will generally sacrifice lower-rpm torque somewhere in the rev range, even with variable valve timing.

Since volumetric efficiency for emission certified street engines is getting pretty uniform these days this is no surprise.
Bmep is the holy grail. Can you get high bmep at low rpm and at high rpm! Hello variable valve timing.

BMEP (torque) at higher rpm is more important than at lower rpm for making power. Variable valve timing is fine, but to REALLY be able to breathe at elevated rpm, you need greater valve lift and duration (which VTEC provided for the S2000).

[DarkSunrise]

^^

Agree. If only Subaru could have found a way to implement active valve lift on the FA20. Maybe with the STI version.

[Suberman]

F = ma. Power is not relevant. F means torque in the case of an engine.

Indeed, power is just torque x time and bhp is a derived figure. The horsepower curve is not measured but calculated. The torque curve is measured and converted into bhp (that's the origin of the b for brake)

It is a common misconception that power to weight ratio is a helpful number and comes from a time when horsepower was the only figure the engine manufacturer published.

Power is indeed the rate at which Work is done and Work is just not related to acceleration. Power is a constant speed factor and is a good indicator of top speed, but not acceleration.

With two vehicles compared and each has the correct gearing power to weight can be considered to be useful for comparing predictions about acceleration intervals but only as a stand in for torque. Look at the torque curves and the weights and you'll literally see the acceleration curve differences. This is especially true when comparing supercharged engines or diesel to gasoline for example.

[ZDan]

Originally Posted by Suberman

F = ma. Power is not relevant. F means torque in the case of an engine.

But what is important is the force F that is accelerating the car, NOT what torque the engine is making.

The force F that is accelerating the car is *directly* related to engine POWER.
F = 550*power/speed in ft/s

Indeed, power is just torque x time

No it is not. And it is not torque divided by time or "torque over time" either.

It is torque multiplied by rotational speed.
It is also force multiplied by linear speed (thrust * road speed).

and bhp is a derived figure. The horsepower curve is not measured but calculated. The torque curve is measured and converted into bhp (that's the origin of the b for brake)

Actually, disconnect the plug clip that senses engine rpm at the dyno, and you will get POWER only, and not engine torque. It is the engine torque that is derived from power, not the other way around. You know engine POWER because you know the dyno drum speed and torque, hence you know dyno drum power. You don't need to know engine rpm to know engine power because it is the *same* as dyno drum power. You *do* need to know engine rpm in order to derive engine torque from power.

It is a common misconception that power to weight ratio is a helpful number and comes from a time when horsepower was the only figure the engine manufacturer published.

NOt a misconception at all. Power is the relevant quantity.

Power is indeed the rate at which Work is done and Work is just not related to acceleration.

The RATE of doing work, which is what power *is*, is *absolutely* related to acceleration.

Power is a constant speed factor and is a good indicator of top speed, but not acceleration.

Of course it is the *only* way to estimate acceleration. Engine torque is not by itself useful.

Power is not a "constant speed factor", it determines acceleration potential.

With two vehicles compared and each has the correct gearing power to weight can be considered to be useful for comparing predictions about acceleration intervals but only as a stand in for torque. Look at the torque curves and the weights and you'll literally see the acceleration curve differences. This is especially true when comparing supercharged engines or diesel to gasoline for example.

If torque/weight is more important, why is the S2000 so much quicker than the FR-S/BRZ? Power/weight is what is important. Engine torque doesn't tell you enough.

[ZDan]

Originally Posted by CSG Mike

This is somewhat amusing... because I actually agree with both of you...

My disagreement is with what I inferred to be the idea that the S2000 has a narrow powerband relative to the FR-S/BRZ. This is objectively untrue.

If limiting to 6000rpm, of course the S2000 suffers!

@ZDan: Have you purchased a FRS/BRZ yet? I have a pretty good amount of seat time in them

Not yet. Still some life in the S2000 at ~155k miles
Maybe next year...

[CSG Mike]

Originally Posted by Suberman

Anybody noticed that the Honda engine doesn't produce significantly more torque than the Subaru?

Acceleration is a function of torque to weight ratios. Power to weight ratios are just shorthand for torque. Only torque accelerates. This is why supercharged engines punch so far above their weight if power to weight ratios are used. Of course poor low end torque can be compensated for by gear ratios but drivability suffers big time. Anybody look at the 50 and 100 cc TT motorcycle numbers? 14 spd gearboxes and a very narrow torque band.

Rpm makes more power for any given torque at that rom but generally speaking moves the torque curve up the rpm range.

Since volumetric efficiency for emission certified street engines is getting pretty uniform these days this is no surprise.

Bmep is the holy grail. Can you get high bmep at low rpm and at high rpm! Hello variable valve timing.

Torque (in a naturally aspirated application) is a function of displacement.

1 liter = 75lb/ft +-5, roughly

Power is work over time. Put it this way. If you give us weight, drivetrain configuration, and horsepower, we can accurately predict a 1/4 mile time. However, if you give us weight, drivetrain configuration, and torque, it could be anywhere.