Why the low torque?

[Quentin]

Sent from Tandy 400

[Quentin]

And here is the 2GR-FE. Basically, I think the double hump is a tradeoff that comes along with pushing the hp/L and maintaining high torque at lower RPM for drivability.



A Sienna, Camry, or RX driver is less likely to push a car to redline, so a strong mid range makes more sense. IS350 or FR-S driver would be different.


Sent from Tandy 400

[Ubersuber]

Continuous valve timing systems are primarily beneficial for fuel economy and emissions purposes. The difference in performance between continuous and stepped valve timing systems is not significant from a peak torque perspective.

Gas flow is the key.

Two aspects are controllable with the current systems commonly used: overlap and specific timing events. Porsche also adds variable lift but this is nowhere near as important as you might think and a review of specific torque outputs of Porsche engines will reveal the minimal effect variable lift has.

The limiting factors are always intake and exhaust tract lengths which, subject to some clever two stage intake systems not on our BRZ, are fixed.

The harmonics are limited by physics to one or two optimum harmonics in the normal rpm range of a street engine. Space limitations prevent optimizing these tract lengths for road cars and for competition cars the rpm ranges are well above the rpm ranges relevant for road cars.

So, at full throttle there will be at most two relatively narrow rpm ranges for which valve timing and overlap can beneficially be varied. This is a physical limitation that can only be altered by variable tract length. No exhaust system fitted to a road car uses variable header length and the most I've seen for intakes is a two stage system.

A "tune" whatever that means and different headers cannot improve this engine. They can change it but cannot improve it.

The importance of variable valve timing for maximizing torque at any given rpm is a function of the inertia of gas flow and harmonic amplification of the compression and rarefaction waves induced by valve opening events (regardless of timing) and closing events passing up or down the intake or exhaust tracts and reflecting from the opening or change in cross sectional area as the case may be. You can vary the valve timing to your heart's content but the physical length of the intake and exhaust tracts limits the rpm of the peak effect. You're lucky to get two peaks in a street engine.

The current limiting factor for variable valve timing (and lift for that matter) is the fixed cam profile. Porsche has one solution that is limited but along the same lines as FIAT Group's very clever multi air system. Ideally one does away with the cam ramp effect altogether and adjusts the timing and lift purely according to the engine's requirements by adjusting the valve lifter itself directly.

Given the systems in use by Subaru the specific torque output of this engine is class leading. The peak torque at whatever it is, 5,800 rpm or something like that, is only very slightly higher than the peak torque at 3,000 rpm or so. Very, very few street engines deliver this level of specific torque over a good range of rpm. Do the math yourself on any current naturally aspirated street engine and you'll see the Subaru is a stellar performer. Not a dip but two peaks and very cleverly arranged.

[Ubersuber]

Originally Posted by blackhawkdown

all i have gotten out of this thread is that there is no replacement for displacement, except FI but then you are going into another thread.

Correct with current economically reasonable technology. But FI is just an equivalent to increasing displacement but with the added advantage of variable displacement. An actual variable displacement engine was designed and tested by SAAB before GM drove them under.

However, FIAT multi air is a pioneer in the free lunch engineering club when it comes to unlocking more torque with conventional engine architecture. Instead of varying valve timing by twisting the cam or by switching from one set of cam profiles to a second set multi air replaces the cam profile (supplements more accurately) with infinitely variable valve clearance lifters. The resulting system limits pumping losses by removing the throttle plate and using valve lift and timing to control torque output. The cam profile becomes secondary to the lifter actuation. Very clever.

[rice_classic]

Originally Posted by Ubersuber

However, FIAT multi air is a pioneer in the free lunch engineering club when it comes to unlocking more torque with conventional engine architecture. Instead of varying valve timing by twisting the cam or by switching from one set of cam profiles to a second set multi air replaces the cam profile (supplements more accurately) with infinitely variable valve clearance lifters. The resulting system limits pumping losses by removing the throttle plate and using valve lift and timing to control torque output. The cam profile becomes secondary to the lifter actuation. Very clever.

For the visual learners:

[ame="https://www.youtube.com/watch?v=Td9Gz_h7Qpg"]How Fiat MultiAir Technology Works - YouTube[/ame]

[Dipstik-sportech]

Originally Posted by Ubersuber

Correct with current economically reasonable technology. But FI is just an equivalent to increasing displacement but with the added advantage of variable displacement. An actual variable displacement engine was designed and tested by SAAB before GM drove them under.

However, FIAT multi air is a pioneer in the free lunch engineering club when it comes to unlocking more torque with conventional engine architecture. Instead of varying valve timing by twisting the cam or by switching from one set of cam profiles to a second set multi air replaces the cam profile (supplements more accurately) with infinitely variable valve clearance lifters. The resulting system limits pumping losses by removing the throttle plate and using valve lift and timing to control torque output. The cam profile becomes secondary to the lifter actuation. Very clever.

Didn't BMW have that style of variable lifter throttle plate-less technology years and years ago?
Also I'm pretty sure Saab didn't attempt a variable displacement engine, but rather a variable compression ratio one with a tilting cylinder head.

[Mikem53]

Originally Posted by Ubersuber

An actual variable displacement engine was designed and tested by SAAB before GM drove them under.
(Other incorrect facts and opinions deleted cause of excessive misinformation)

LOL... Amazing.. Saab didn't need any help going under you moron.
They were on their way out cause nobody wanted their unreliable
and ugly cars. GM and subaru stepped in to try and make something of
What was left of a company that didn't have a future.

[Ubersuber]

SAAB's engine was variable compression ratio and supercharged (variable displacement).

BMW did indeed use variable valve timing to reduce pumping losses but only by moving the camshafts. FIAT uses variable lifters to allow the computer to create a different cam profile in effect.

[Mikem53]

Originally Posted by Dipstik-sportech

Didn't BMW have that style of variable lifter throttle plate-less technology years and years ago?
Also I'm pretty sure Saab didn't attempt a variable displacement engine, but rather a variable compression ratio one with a tilting cylinder head.

Don't confuse him with real facts..
Seems displacement on demand is being used in other simpler forms these days with good success..

[Ubersuber]

Originally Posted by Mikem53

Don't confuse him with real facts..
Seems displacement on demand is being used in other simpler forms these days with good success..

The variable compression ratio wasn't the feature that produced the power, it permitted high boost pressures. The secret to this engine was its variable effective displacement. The size of the combustion chamber was increased to allow much higher boost pressures than a fixed compression ratio could tolerate. This is the function of supercharging: increasing the effective displacement of the engine. The limiting factor has always been detonation which varying the combustion chamber size neatly extended. Power levels approaching 150 bhp/litre were readily achieved with this technology.

Varying the compression ratio only would simply reduce power. The "real facts" have to be properly understood in order to understand what the real facts actually are.

Displacement on demand is about as sophisticated as disconnecting a spark plug wire to save gas. Reduction of pumping losses is the objective. Very few manufacturers are bothering with this and all it does is reduce engine power to save a bit of gas.

FIAT's system is much more intelligent as is supercharging of some sort.

[Mikem53]

Originally Posted by Ubersuber

The variable compression ratio wasn't the feature that produced the power, it permitted high boost pressures. The secret to this engine was its variable effective displacement. The size of the combustion chamber was increased to allow much higher boost pressures than a fixed compression ratio could tolerate. This is the function of supercharging: increasing the effective displacement of the engine. The limiting factor has always been detonation which varying the combustion chamber size neatly extended. Power levels approaching 150 bhp/litre were readily achieved with this technology.

Varying the compression ratio only would simply reduce power. The "real facts" have to be properly understood in order to understand what the real facts actually are.

Displacement on demand is about as sophisticated as disconnecting a spark plug wire to save gas. Reduction of pumping losses is the objective. Very few manufacturers are bothering with this and all it does is reduce engine power to save a bit of gas.

FIAT's system is much more intelligent as is supercharging of some sort.

Yawn... More misinformation from your basic lack of understanding.. DOD is more sophisticated than you make it out to be..
But let's not confuse you with facts and reality.. You go on simplifying things to make your incorrect ass-umptions seem plausible somehow.. Whatever..

[Dipstik-sportech]

saab svc engine concept promo 2000: [ame]http://youtu.be/oxR-3Un6WkU[/ame]
Show me one point in that video where they say increased effective displacement. You can throw around your theories all you want, in the end "effective displacement" is not a real thing. You're attempting to say that it makes the engine seem bigger due to the supercharger, that's nothing new bud. The only way to alter ACTUAL displacement it by increasing cylinder volume not combustion chamber volume. Also BMW did have the same free valve system in the works i just checked but it hasnt made it into production and that was back in 2001 i believe. Oh, FYI Saab did kill itself off GM cut them loose like other companies did before due to there no profitable design ideas.

[Ubersuber]

Originally Posted by Mikem53

Yawn... More misinformation from your basic lack of understanding.. DOD is more sophisticated than you make it out to be..
But let's not confuse you with facts and reality.. You go on simplifying things to make your incorrect ass-umptions seem plausible somehow.. Whatever..

It isn't actually, but I can see why someone of your obvious intellectual capabilities might think it is sophisticated.

[Ubersuber]

Originally Posted by Dipstik-sportech

saab svc engine concept promo 2000:

Show me one point in that video where they say increased effective displacement. You can throw around your theories all you want, in the end "effective displacement" is not a real thing. You're attempting to say that it makes the engine seem bigger due to the supercharger, that's nothing new bud. The only way to alter ACTUAL displacement it by increasing cylinder volume not combustion chamber volume. Also BMW did have the same free valve system in the works i just checked but it hasnt made it into production and that was back in 2001 i believe. Oh, FYI Saab did kill itself off GM cut them loose like other companies did before due to there no profitable design ideas.

It does seem pointless to continue this debate with you but what the hey.

I'm sure you have some theory or other explaining how a variable compression ratio can produce ANY extra power so please feel free to share it with us.

As for variable displacement only supercharging can achieve this so far, although the Atkinson cycle engines do create this effect and no doubt you can explain how that happens also. Hint, when is a calculated CR not the true CR?

It is quite clear to anyone who understands these things that the SAAB engine developed its power and torque by supercharging and not by varying the compression ratio. The combustion chamber size was varied precisely to maintain the effective compression ratio more or less constant. The Atkinson cycle engine pulls off much the same trick with a fixed CR and a fixed displacement. The Miller cycle version uses supercharging to better exploit the Atkinson cycle (Mazda's new skyactiv gasoline engines can run such nominally high CR because they use the Atkinson cycle as well as a carefully shaped combustion chamber in the piston head to allow lean burn. Mazda has a lot of experience with the Atkinson cycle and the Miller cycle).

To assist you in more fully understanding why the SAAB variable compression ratio engine worked only because it was a very highly pressurized supercharged engine and for no other reason it may help you to recall the F1 engine rules which stated an equivalency between 4.5 litre naturally aspirated engines and 1.5 litre supercharged engines (when running the same fuel) which was a 3:1 equivalency, which later was reduced to a 2:1 equivalency which allowed the 1.5 turbos to literally blow the very successful 3.0 litre normally aspirated engine into the history books. Even 3.5 litre normally aspirated engines could not compete with 1.5 litre blown engines.

Rest assured that you are alone in failing to understand that variable effective displacement is very real. The current CO2 emissions regulations in Europe are pretty much requiring that all powerful engines be supercharged in some form or other.

Displacement on demand won't cut it and everybody in the industry knows it.