2.5L with lower revs/more torque, or 2.0L with higher revs?

[killerkid08]

If honda is any indication of the possibilities, the FR-S will receive a displacement increase, and a slight decrease in the redline or none at all. The s2000 (AP1)did rev to 8900 rpms though, so an increase can't be ruled out either (AP2 retained 8k of those rpms after the displacement bump).

[Suberman]

Originally Posted by Deslock

Not to be argumentative/condescending, but you're wrong.

Good point and well made. Nothing works like brevity if you're going to say something dumb.

I remind everyone that a = F/m where "a" is the acceleration you are trying to calculate, F is the force you have applied (and torque is force, not power or work) and "m" is the mass you are trying to accelerate. Conventionally, the formula is written to derive the required force: F = ma but that doesn't tell you what you all need to know.

Acceleration is an instantaneous phenomenon in that acceleration is the rate at which velocity changes (in speed or direction). Strictly speaking, 0-60 times don't measure acceleration but work, which is where the confusion no doubt arises. The fact remains that it is the engine crankshaft which must accelerate and it is torque that induces that.

If someone can show me where in that formula you see power go for it.

Yes, you can move the peak bmep up or down the rpm range but as you try to move it up you reach a point where acceleration is diminished because of the characteristics of piston engines and fixed ratio stepped gearboxes. For an illustration of that you could try to find the acceleration curve for an F1 car, just for example. Getting one of those off the line is very tricky as Mark Webber consistently demonstrates.

What you all forget is that the gearbox is what allows the engine delivering a given torque to deliver power, ie the rate at which the work can be done. Without a gearbox the acceleration curve would follow the torque curve exactly. If you can find a Road & Track graph you will see this pattern in every car, most notably in a car that achieves 60 in first gear.

[ZDan]

Originally Posted by Suberman

I remind everyone that a = F/m where "a" is the acceleration you are trying to calculate, F is the force you have applied (and torque is force, not power or work) and "m" is the mass you are trying to accelerate.

Yes, force is mass times acceleration, and of course acceleration is force divided by mass.

But there's a shortcut to getting this force by using the relationship between power and force and velocity.
POWER is FORCE multiplied by VELOCITY
P = F*V

You can calculate the force accelerating the car if you know how much power you are making at a given speed (which you can easily get from knowing speeds in gears and power vs. rpm).

If you want the accelerating FORCE being applied at the rear tire contact patches, you can calculate it just as I've shown in my previous post above:

F = power/velocity

Force in pounds equals power in ft-lb/second divided by velocity in feet/second

1 horsepower is 550 ft-lb/s, so:

F = (hp*550)/V

If you're making 173rwhp at 55mph (7000rpm in 2nd gear in the FR-S), the force F acting to accelerate the car is easily found.

173hp * 550 ft-lb/sec/hp = 95,150 ft-lb/sec
55mph * (88ft/s/60mph) = 81ft/s

F = (95,150 ft-lb/sec)/(81 ft/s) = 1180 lb

THIS FULLY TAKES INTO ACCOUNT GEARING AND TIRE DIAMETER!

acceleration a = F/m
If we use lb-mass instead of slugs for the mass, we get acceleration in g's for a car weighing 3000 lb:

a = 1180 lb/3000 lbm = .393 g

.393 g * 32.2 ft/s^2 = 12.7 ft/s^2

(note: this doesn't take into account rolling resistance and aero drag, which should be subtracted from the accelerating force F, but that is not pertinent to this discussion at the moment)

Acceleration is an instantaneous phenomenon in that acceleration is the rate at which velocity changes (in speed or direction).

And it is POWER that tells you what your INSTANTANEOUS acceleration will be from a given speed with a given mass.

I think the MISTAKEN idea that power is "torque over time" gives people the MISTAKEN impression that power can't happen "instantaneously". Totally incorrect, power DOES tell you what your instantaneous acceleration is.

POWER isn't "torque over time", it is the INSTANTANEOUS rate of doing work.

Strictly speaking, 0-60 times don't measure acceleration but work, which is where the confusion no doubt arises.

Acceleration is BY DEFINITION the rate of change of velocity.
0-60 time gives you precisely the average acceleration going from 0-60!

0-60 in 6.5 seconds => 60mph/6.5 seconds = (88ft/s)/6.5s = 13.5 ft/s^2
If you go from 0-60mph in 6.5 seconds, your average acceleration was 13.5 feet per second squared. PERIOD!

You cannot calculate WORK directly from a 0-60 time! You'd have to integrate the actual force applied over the distance covered.

The fact remains that it is the engine crankshaft which must accelerate and it is torque that induces that.

Yes.

If someone can show me where in that formula you see power go for it.

Which formula, F=ma?
You can get the force F by taking engine torque in lb-ft, multiplying by trans ratio and diff ratio to get torque at the rear wheels, then divide that by tire loaded radius in feet, to get the force applied at the contact patches.

Or you can use F = P/V (force = power divided by velocity). Either way, it's the *same thing*.

For the case above, 173hp at 7000rpm in 2nd gear:
Torque is 173hp*5252/7000 = 130 lb-ft
2nd gear ratio is 2.188, diff is 4.1
tire spins 844 revs per mile
effective circumference in feet is (5280ft/mile)/844 = 6.256 ft
diameter is (6.256 ft/pi) = 1.99ft
radius is 1.99ft/2 = .995ft

F = 130 lb-ft * 2.188 * 4.1 / .995ft = 1172 lb

The same (within less than 1% due to roundoff and using 55mph instead of the more correct 55.5mph) force calculated by F = P/V above.

[Anaxilus]

Ugh, back to Physics 101. Not to be punny but 'A' is relative. You are talking about 'Proper' acceleration relative to 'G' (gravity).

[ame="http://en.wikipedia.org/wiki/Proper_acceleration"]Proper acceleration - Wikipedia, the free encyclopedia[/ame]

Which is ironic as the function of your premise revolves around speed @ 100mph which makes 'A' become a function of 'T' (time) not 'G' (gravity). Acceleration relative to speed and coordinates is something different. A= delta V/delta T. That form of acceleration is very much relative to the amount of work performed.

[ame="http://en.wikipedia.org/wiki/Acceleration"]Acceleration - Wikipedia, the free encyclopedia[/ame]

This is why you can have tractor motors and diesels w/ tons of flat torque all over but they are usually slower compared to gas motors because they don't perform enough work. If you have a motor/engine that does 550lb/ft but only 110hp, you have a very slow car.

You also don't need to complicate the scenario w/ added complexity of gear ratios to understand this premise. No matter what gear ratio you have, if your engine doesn't perform enough work, you're car goes nowhere fast. Plus the whole Mark Webber thing flubbing launches is hardly incidental and random chance.

Edit - I see ZDan offered a more thorough breakdown than my Barney explanation.

[Dimman]

Originally Posted by ZDan

You should be able to get a bit more up top by tuning the exhaust for higher rpm. But you won't move the peak upward in the rpm range by any appreciable amount, if at all. The cam lift/timing/overlap is still going to be optimized around ~7000rpm. Say you tune the exhaust for 7400rpm. You might get a bigger hp bump at 7400rpm, but you'd still make peak power closer to 7000rpm.

In any case, if you tune for specific rpm, without trying to balance things out at the negative points, you'd still get a dip, it would just be centered on a different rpm range.

Well, that's the problem with tuning for specific rpm ranges, you get ANTI-tuning elsewhere, giving you dips in torque. Tune the exhaust for 7000rpm and you might exacerbate the dip at ~4000rpm. Then if you compensate by tuning the intake for 4000rpm, you might hurt peak power again.

Need variable-length intake tracts. And exhaust primaries, too

I'm aware of the 'anti-tuning', which is what I was referring to with the high rpm positive return. Positive pressure return, not positive 'good'.

The thing with the low rpm torque peak of the FA20 is that it is a 'gift' of sorts to tuners. It's a ton of low end grunt for a 2.0L NA car, and generated by strong scavenging on the primary acoustic negative pressure return, which you don't see done on performance because it will cause the 'anti-tuning' at the upper range. So by shifting the acoustic returns further up the rpm band we can get almost a free lunch: fill in the 'dip', and push the 'anti-tuning' positive return to an rpm range beyond the motors operating range.

But we lose the low rpm hump. This isn't a huge deal when you look at how much more the FRZ motor makes vs the K20 in the old Si, but it is an inevitable trade off.

Instead of : +1, 0, -1 (Low, Mid, High rpm) we get: 0, +1, 0

The advantage of the DOHC with cam phasing (which the ECU tunes can adjust) comes in with acoustic scavenging. We have a lot of control, LSA, overlap, advance and retard, with which to extend positive scavenging effects and slam the door on 'anti-tuning' giving stronger or broader effects than you may be used to (The S2000 and bike motors lack dual phasing, rotaries are fixed ports, GM can just advance/retard whole OHV cams at once...)

But few tuners and parts builders understand the effects of acoustics and just chase flow, so we may be waiting a looong time. Also, as you have pointed out people on here still believe you need back pressure so it will be an uphill battle.

[Suberman]

This thread is getting a bit distracted from the real topic but one howler really does need to be corrected: power is work over time, specifically energy consumed over time. It most definitely is NOT instantaneous.

Torque accelerates, not power. This is very easy to illustrate: take two cars with identical engines (same power) and fit one with a shorter final drive ratio. This car will accelerate more rapidly than the other car with the taller final drive. No increase in power but torque is multiplied by the gear ratio.

Acceleration is a rate of change of velocity. By definition it is an instantaneous unit: so many feet per second per second. Every point on the acceleration curve correlates to an instantaneous acceleration at that point in time and, not coincidentally, corresponds exactly to the torque available at that point in time.

Adding displacement adds bmep across the rpm range, assuming other factors equal and thereby increases torque and acceleration. It's that simple. Power has nothing to do with it.

[Suberman]

Originally Posted by Dimman

I'm aware of the 'anti-tuning', which is what I was referring to with the high rpm positive return. Positive pressure return, not positive 'good'.

The thing with the low rpm torque peak of the FA20 is that it is a 'gift' of sorts to tuners. It's a ton of low end grunt for a 2.0L NA car, and generated by strong scavenging on the primary acoustic negative pressure return, which you don't see done on performance because it will cause the 'anti-tuning' at the upper range. So by shifting the acoustic returns further up the rpm band we can get almost a free lunch: fill in the 'dip', and push the 'anti-tuning' positive return to an rpm range beyond the motors operating range.

But we lose the low rpm hump. This isn't a huge deal when you look at how much more the FRZ motor makes vs the K20 in the old Si, but it is an inevitable trade off.

Instead of : +1, 0, -1 (Low, Mid, High rpm) we get: 0, +1, 0

The advantage of the DOHC with cam phasing (which the ECU tunes can adjust) comes in with acoustic scavenging. We have a lot of control, LSA, overlap, advance and retard, with which to extend positive scavenging effects and slam the door on 'anti-tuning' giving stronger or broader effects than you may be used to (The S2000 and bike motors lack dual phasing, rotaries are fixed ports, GM can just advance/retard whole OHV cams at once...)

But few tuners and parts builders understand the effects of acoustics and just chase flow, so we may be waiting a looong time. Also, as you have pointed out people on here still believe you need back pressure so it will be an uphill battle.

This is very useful commentary.

The easiest way to fill in that dip is by low pressure supercharging. This should be a bolt on and I would be astonished if STI and TRD don't already have mules on test with exactly this configuration. Whether you use TRD favoured method of mechanical supercharging or STI favoured turbocharging makes little difference. For the modern world where fuel economy is so important even to sportscars low pressure supercharging is the simple way to get more torque for better acceleration. In fact, this engine could easily be supercharged so as to significantly boost acceleration without adding any power at the top end at all, though this won't be done in reality.

[Dimman]

Originally Posted by Suberman

This thread is getting a bit distracted from the real topic but one howler really does need to be corrected: power is work over time, specifically energy consumed over time. It most definitely is NOT instantaneous.

Torque accelerates, not power. This is very easy to illustrate: take two cars with identical engines (same power) and fit one with a shorter final drive ratio. This car will accelerate more rapidly than the other car with the taller final drive. No increase in power but torque is multiplied by the gear ratio.

Acceleration is a rate of change of velocity. By definition it is an instantaneous unit: so many feet per second per second. Every point on the acceleration curve correlates to an instantaneous acceleration at that point in time and, not coincidentally, corresponds exactly to the torque available at that point in time.

Adding displacement adds bmep across the rpm range, assuming other factors equal and thereby increases torque and acceleration. It's that simple. Power has nothing to do with it.

Adding displacement has nothing to do with bmep.

In layman's terms bmep=torque/L.

[ZDan]

Originally Posted by Suberman

This thread is getting a bit distracted from the real topic but one howler really does need to be corrected: power is work over time, specifically energy consumed over time. It most definitely is NOT instantaneous.

You are wrong. Power absolutely is the INSTANTANEOUS rate of doing work. In the same sense that SPEED is the INSTANTANEOUS rate of change in position.

To say that power *isn't* instantaneous is to make the same error as Zeno's Achilles and the Tortoise paradox (in which it is reasoned that given a head start, the tortoise can never be caught up with by Achilles).

Torque accelerates, not power.

Power DOES accelerate, and in fact engine TORQUE by itself doesn't tell you enough, whereas POWER DOES. Power tells you exactly how much force you have available to accelerate the car from a given speed.

This is very easy to illustrate: take two cars with identical engines (same power) and fit one with a shorter final drive ratio. This car will accelerate more rapidly than the other car with the taller final drive. No increase in power but torque is multiplied by the gear ratio.

Wrong again. You can run the exercise I gave above for ANY kind of gearing and you will get the same result, same F.

Ferinstance, with 4.88 gearing, 2nd gear at 7000rpm is 46.6mph or 68.3 ft/s
Power is 173rwhp, so force acting at the contact patches:

F = 173rwhp * 550 / 68.3ft/s = 1393 lb

Same power at lower speed => greater force acting to accelerate the car.

Taking rw torque through the gearing and tire radius:
engine torque = 130 rw lb-ft (173rwhp*5252/7000)
Torque at the wheels (2.188 2nd gear, 4.88 diff):
130 lb-ft * 2.188 * 4.88 = 1388 lb-ft
Force = torque/tire radius = 1388 lb-ft/.995ft = 1395 lb.

SAME (allowing for roundoff error accumulation)

And it's always worth pointing out that with shorter gearing you have to upshift sooner, and LOSE your mechanical advantage over some ranges of speed. Overall power/weight is not changed, so overall acceleration is not changed. Lower gearing will not generally improve 1/4-mile trap speeds, because that is a function of POWER/weight. If you don't change either power or weight, you aren't going to see major changes in trap speeds.

Acceleration is a rate of change of velocity.

Right, just as POWER is the rate of doing work.

By definition it is an instantaneous unit: so many feet per second per second. Every point on the acceleration curve correlates to an instantaneous acceleration at that point in time and, not coincidentally, corresponds exactly to the torque available at that point in time.

And the torque at the wheels (y'know, where it MATTERS) at a given speed is A DIRECT FUNCTION OF POWER.

Adding displacement adds bmep across the rpm range, assuming other factors equal and thereby increases torque and acceleration. It's that simple. Power has nothing to do with it.

Power has EVERYTHING to do with it.

Let's take a different engine, making the SAME 130 lb-ft of torque, but only making half the power as the examples above: 86.5 rwhp.

If the engine is making 86.5 hp out of 130 lb-ft, it is by definition spinning at (86.5/130)*5252 = 3500rpm. Keeping 4.88 diff gearing, this equates to 23.3mph or 34.15 ft/s

Keeping the same 4.88 gearing, actual torque at the rear wheels acting to accelerate the car is:
130 lb-ft * 2.188 * 4.88 = 1388 lb-ft at the wheels, same as above.
1388lb-ft/.995ft = 1395 lb. thrust, same as above

Using F = P/V:
F = 86.5hp * 550 / 34.15ft/s = 1393 lb.

Again, SAME RESULT. Accelerating at the same rate at half the speed takes half the power, but the same torque!

Acceleration is the DIRECT result of force applied at the rear tires' contact patches.

This force is a DIRECT function of POWER and SPEED.

This force is the SAME as what you get if you take engine torque through the trans/diff and rear tire radius.

Feel free to not understand, but do NOT discourage others from understanding!

TNX...

[gt8613]

Cant say I know much about engines...BUT...if you were going to drop a sc in the car and other mods for MAX hp output....wouldnt tge 2.0 be better because it could sustain more pressure? Assuming the 2.5 is made by boring yhe cylinders...

Sent from my SAMSUNG-SGH-I537 using Tapatalk 2

[CSG Mike]

How about a better flowing head?

The flow on the FA20 is abysmal.

[kramrle]

Originally Posted by Anaxilus

1zz comparison to 2zz has nothing to do w/ the FA20 or a potential 25. Toyota was married to VVTLi long before they developed direct injection. The FA20 gets 100hp/L w/o VVTLi and so could a 2.5L. I'm pretty sure you could rework a stock FA20 head along w/ the intake manifold, intake and exhaust to flow enough air to hit 250bhp w/o making the head itself 'bigger'.

While the 4.8 V10 is AMAZING as an engine unto itself. It's actually quite a poor match to a 3500-3600lb car due to the lack of relative torque. This is one reason the 8.0 Viper ACR was able to outdo the LFA Nurburgring using essentially a tractor motor. If only the LFA was lighter. Still, the 4.8 is awesome and the best sounding engine you could have bought recently. Unless you have a thing for cross plane cranks for some reason....

Now, if someone wants to put 5 valves/cylinder on a 2.5L H-6 with ITBs, I'd go for that. Drop another 200lbs and I'll give Toyota a $40K starting bid.

As a daily driver of a Celica with a 2zzGE engine, and an occasional driver of GT86 at Toyota track days in France, there is one thing I noticed.
a) The 2zz has imho a better low end torque (drop it to below 1500rpm in 6th and it will still accelerate even uphill. The F20 needs higher revs to deliver low end torque and to run smooth.
b) The 2zz has more pull between 6k up to the redline at 8.2 k rpm. It's the livelier engine. The FA20 is just boring. It falls asleep way before the redline.
Bottom line - i don't care if it's a 2L or 2.5L as long as it is well made and deliver progressively power right to the red line.

[Anaxilus]

Originally Posted by gt8613

Cant say I know much about engines...BUT...if you were going to drop a sc in the car and other mods for MAX hp output....wouldnt tge 2.0 be better because it could sustain more pressure? Assuming the 2.5 is made by boring yhe cylinders...

Sent from my SAMSUNG-SGH-I537 using Tapatalk 2

Assuming it is just a bored block and Toyota/Subaru do nothing more then yes. However, you have sleeves, sleeve coatings, and other add-ons a manu can add or improve upon. The irony is a weak NA block could end up re-engineered to be an inherently superior one due to the inherent weakness inspiring improvements that were seen as unnecessary cost additions in the original application.

Plus following your same argument you'd also want to drop the 12.5:1 CR of the stock engine, so either way pure OE stock is not ideal. MAX power also necessitates a replacement of pretty much most of the internals. This would also help alleviate concerns about changes in rod/stroke ratio whose significance is debatable and relative to the specifics of the engine in question.

But with proper engineering or modification, the larger displacement will always provide for more power potential assuming no fatal design flaw exists.

I think people underappreciate the importance of torque for this car and overappreciate the perceived relative 'lightweight' of the 86. It's really not 'lightweight' in stock form and neither was the S2000. People have gotten used to their fat cars I guess.

[Anaxilus]

Originally Posted by CSG Mike

How about a better flowing head?

The flow on the FA20 is abysmal.

Originally Posted by kramrle

As a daily driver of a Celica with a 2zzGE engine, and an occasional driver of GT86 at Toyota track days in France, there is one thing I noticed.
a) The 2zz has imho a better low end torque (drop it to below 1500rpm in 6th and it will still accelerate even uphill. The F20 needs higher revs to deliver low end torque and to run smooth.
b) The 2zz has more pull between 6k up to the redline at 8.2 k rpm. It's the livelier engine. The FA20 is just boring. It falls asleep way before the redline.
Bottom line - i don't care if it's a 2L or 2.5L as long as it is well made and deliver progressively power right to the red line.

Exactly. I think there is a lot of circumstantial evidence to suggest the base FA20 was gimped intentionally for various reasons. Remember too, this is the base engine which basically slots in where the 1ZZ would have been w/ the Celica. Celica was also 300 lbs lighter than the 86.