BRZ / FR-S Boxer Engine Dyno Powerband revealed

[WingsofWar]

Originally Posted by bambbrose

I'm actually quite impressed with the group of guys and our knowledge here at ft86. Great minds think alike?? :happy0180:

yeah, the fact that there are really smart gear heads in here gives this forum a big edge, interesting character, and more topics.

Even im pushed to learn more, and i haven't been this active on a forum since 02-04 when i had a s14 i was trying to build.

[SUB-FT86]

Originally Posted by val_lixembeau

Exactly the opposite. HP is a measure of how "quickly" the torque can be applied.

Think of it this way, torque is a measure of force, but instead of measuring how hard you can push, it measures how hard you can twist.

In a straight line, you've heard that work=force*distance right? What power measures is how fast you can do that work.

Now let's translate that to circular motion...

Work is now torque applied over a certain number of revolutions. So power is torque times revolutions over time. That's why we sometimes say that power is just a number derived from torque.

Imagine two engines with the same peak power, but one with low torque and one with high torque. We'll use perfectly flat torque curves for simplicity. That would mean that the low torque engine needs to rev at higher rpm to produce the same power as the high torque engine.

In theory, these engines placed into the same car could produce identical acceleration if they were geared appropriately. The low torque engine would just need to rev higher. The problem is, people don't like to rev their engines, and manufacturers don't like to gear that way because of cost, mileage and reliability.

And that's why most people think of torque numbers as being responsible for the acceleration that you feel. Because low torque engines aren't geared low enough to produce the same acceleration as high torque engines, and even if they were they might not be able to rev high enough to take advantage of that gearing.

I feel very much like this. I always feel when I high rev a 4banger that the car is in so much pain that something will break and I would be SOL. I hope the FR-S doesn't feel this way but I wonder if flat 4 engines feel buttery smooth like a V8 or I6?

[Homemade WRX]

Originally Posted by old greg

That's about how old I thought he was, because of how much he thinks he knows.

Originally Posted by 7thgear

and you're the smartest one here, right?

I think he simply meant that 'the more you know, the more you realize you don't know'...I'll be the first to admit this and I've been eating, breathing and sleeping engines for the last seven years...on the engineering level (two of which college/internships and the rest in the field).

[86'd]

The curve looks similar to this

(I know there are some big differences between the engines though...)

Yet the TQ on the BRZ engine doesn't seem to drop off, which makes me think there's some room up top.

[Dimman]

Originally Posted by Levi

Why join the right and left side of the headers together? Could not they be completely seperate?

So some of the exhaust energy can be transferred to other cylinders to assist in scavenging.

[serialk11r]

Originally Posted by old greg

That's about how old I thought he was, because of how much he thinks he knows.

:P I'll take that lightheartedly. I have reasonable proficiency with physics, but that's about it, and I think I make that pretty clear when I post about stuff? Everyone has lots to learn afterall, and discussing things is a good way to learn. I get bored a lot and rant on about stuff.

As a general disclaimer, everything I say is based on empirical evidence I have seen and extrapolated using basic mechanics/thermo, I have no actual experience with this stuff, but hopefully that'll change someday soon.

And SUB, 2010 would be the last time I was in a physics class, but not the last time I was in high school.

[Exage]

Originally Posted by SUB-FT86

I feel very much like this. I always feel when I high rev a 4banger that the car is in so much pain that something will break and I would be SOL. I hope the FR-S doesn't feel this way but I wonder if flat 4 engines feel buttery smooth like a V8 or I6?

Chicken $*** hahaha.

What engines really really hate is lugging. This is where the engine is very low on RPM and fuel delivery is high under load. The engine is trying to increase engine rpm to an acceptable level so there is actually power and or avoid stalling.

You find that after ignition the forces on the piston are extremely high because it's [the piston] not moving at the speed the engine is designed to run at. The 2ZZ makes a particular knocking noise when it's lugged, some but not all engines do.

In addition it's harder on engine and drivetrain components on (lets say) a SUV with a trailer heading up a steeply (20%) graded hill highway on a high cruising gear. If the engine does manage (by some miracle) to keep a stable low rpm then you may face cooling issues with a long enough hill because the water-pump isn't going to be rotating at an acceptable rate to provide the quantity of coolant that will needed to be circulated (same with the automatic transmission fluid). So in this circumstance it's actually advisable to drop down a gear or two and make some noise because it will cause less wear on the drivetrain. Most people are too scared of destroying their engines to do this, instead the auto tranny will overheat and possibly pop... their loss.

In addition you have something designed like the 2ZZ that makes it's maximum 131 lb-ft torque at 6700rpm (127@4400 is stated), it's "not happy" below 4000rpm (especially at WOT) under load. It's funny because it's an NA engine which means it responds instantly but is lazy in the low rpm range.

[serialk11r]

I hear this "lugging" thing a lot, but I can't decide whether it actually makes sense or not. The friction in an engine doesn't start going up until well below idle speed, and at higher speeds the components are definitely under a lot of stress. Efficiency does go down near 1000-1500rpm typically but I think this is probably because the burning charge has too much time to cool down. The only thing I can see is that the rods are under max compression for a longer period of time but I don't think this is much of an issue especially for naturally aspirated engines.

old greg do you mind sharing your wisdom? :P

[Calum]

It has more to do with oil delivery to the journal bearings. As engine speed lowers it's harder for the hot oil to develop a hydrodynamic wedge. This leads to metal on metal contact which as Im sure you know is bad. There are some things that can be done to extend the low rpm performance of the bearing but all to my knowledge negatively effect the high rpm performance, in one case even causing the bearing to pump oil against the oil pump.

[Kostamojen]

Originally Posted by WingsofWar

oOo you and Dim might be right. Im looking at other dyno comparisons of the EJ251 with different headers. Never really paid attention to acoustics until now.

FYI, that dyno chart I posted is comparing stock headers to some JDM equal length headers that I installed between runs.

The headers/exhaust don't get rid of the dip.

[Exage]

Originally Posted by Calum

It has more to do with oil delivery to the journal bearings. As engine speed lowers it's harder for the hot oil to develop a hydrodynamic wedge. This leads to metal on metal contact which as Im sure you know is bad. There are some things that can be done to extend the low rpm performance of the bearing but all to my knowledge negatively effect the high rpm performance, in one case even causing the bearing to pump oil against the oil pump.

That's a good point, usually oil pressures are decent at idle rotation. I'm a little skeptical on the metal on metal contact point. It could be possible with the exerted force, especially with the oil viscosity at temperature.

I've never seen a document on any engine lug tests. So this will interest me.

[ZDan]

At low engine speeds, the hydrodynamic wedge that supports the conrod bearings isn't as strong. Consider the film strength of the oil in the bearing gap with no relative motion. Weak. Applying full torque is a bad idea at low engine rpm...

At high rpm when inertial loads dominate, the high speed gives a MUCH stronger hydrodynamic wedge to support the conrod.

[serialk11r]

How relevant is this? If BMW feels safe giving their engines full boost at like 1200 rpm or something then it's probably safe to say these effects only exist around 1000 or below right?

I guess it makes sense that the oil would get squished out of the bearings more easily at low speeds, thanks for the info. Didn't think of that.

[Exage]

Originally Posted by ZDan

At low engine speeds, the hydrodynamic wedge that supports the conrod bearings isn't as strong. Consider the film strength of the oil in the bearing gap with no relative motion. Weak. Applying full torque is a bad idea at low engine rpm...

At high rpm when inertial loads dominate, the high speed gives a MUCH stronger hydrodynamic wedge to support the conrod.

I understand what he is saying. However you used "isn't as strong". This begs the following question: At which RPM point is the hydrodynamic wedge not able to support the forces?

Obviously this depends on many factors of the engine during lugging (including the engine itself). RPM conversely affects both oil pressure and forces on the bearings and respective journals.

I would be interested to see at what rpm and parameters the hydrodynamic film breaks down, throw in some different oils, different temperatures...