Engine technology thread.

[Palmy]

Hey tech-heads I have a question about direct injection.
Why do motors with direct injection still have port injection?

[Dimman]

Originally Posted by Palmy

Hey tech-heads I have a question about direct injection.
Why do motors with direct injection still have port injection?

Um, there's a whole stickied thread on it: http://www.ft86club.com/forums/showthread.php?t=3172

[arghx7]

Originally Posted by Palmy

Hey tech-heads I have a question about direct injection.
Why do motors with direct injection still have port injection?

Here's a two sentence explanation. It allows more flexibility in design of the intake port, combustion chamber, and piston to meet targets for emissions, fuel economy, and torque band. As a side effect, port injectors spraying on the back of the intake valves help keep valve deposits down.

[Dimman]

Le bump...

Question about flat-plane cranks that were mentioned in the exhaust thread. On V8's, I understand how it works exhaust scavenging-wise (firing order is so each bank acts like an independent inline-4). But what happens with the balance?

Also, on an inline-4 what is the benefit? (Yamaha has a flat-plane crank on their R1.)

[bambbrose]

I was always under the impression that they had less balance than a traditional crank. I'm eagerly awaiting someone with experience in this to chime in.

[old greg]

Originally Posted by Dimman

Le bump...

Question about flat-plane cranks that were mentioned in the exhaust thread. On V8's, I understand how it works exhaust scavenging-wise (firing order is so each bank acts like an independent inline-4). But what happens with the balance?

Also, on an inline-4 what is the benefit? (Yamaha has a flat-plane crank on their R1.)

There is a larger secondary imbalance than with a 90 degree crank.

Inline fours are almost exclusively flat-cranked. The M1 motogp bike uses (used?) a cross plane crank for improved throttle response and improved power delivery in transient throttle situations at very high rpm. Something to do with crankshaft inertia. On anything with a redline lower than ~12000 rpm it's totally pointless. On the R1, it's mostly just a marketing stunt IMO.

[Homemade WRX]

Originally Posted by old greg

There is a larger secondary imbalance than with a 90 degree crank.

Inline fours are almost exclusively flat-cranked. The M1 motogp bike uses (used?) a cross plane crank for improved throttle response and improved power delivery in transient throttle situations at very high rpm. Something to do with crankshaft inertia. On anything with a redline lower than ~12000 rpm it's totally pointless. On the R1, it's mostly just a marketing stunt IMO.

from what I recall, the R1 also used the split/cross plane crank as a means of traction control and thus increasing off corner acceleration. It's been a long time since I read the technical write up on the purpose behind its development.

[Dimman]

Originally Posted by old greg

There is a larger secondary imbalance than with a 90 degree crank.

Inline fours are almost exclusively flat-cranked. The M1 motogp bike uses (used?) a cross plane crank for improved throttle response and improved power delivery in transient throttle situations at very high rpm. Something to do with crankshaft inertia. On anything with a redline lower than ~12000 rpm it's totally pointless. On the R1, it's mostly just a marketing stunt IMO.

Thank god. I'm not crazy... Just mixed up the facts about the crank being 'not normal'. And from automotive perspective, the only 'not-normal' is flat on a V8...

On the cross-plane L4, do you think having the mass more 'even' rotation-wise would allow less counterweight? Something like that for the inertia part?

And Yamaha does seem to like being different for the sake of it (gave up on the 5 valve R1 only fairly recently...).

[Bristecom]

I really like this engine. The only thing I wish it had was Valvematic technology for better response/efficiency/power. I wonder if they actually had it on the table at some point during the design phase but chose against it or couldn't use it in this application for some reason. Of course, they would need two sets for a boxer instead of just one in an inline-4 so it probably would have added a lot more cost. But who knows, maybe we'll see it in a mid-life update.

[illmatic]

I believe the fa20 has avcs on both intake and exhaust.

[serialk11r]

There was a discussion on this a lot of pages back. For a naturally aspirated, direct injected engine with modest aspirations (haha see what I did there?), they probably kept it simple. One of the things about direct injection that isn't immediately obvious appears to be the amount of flexibility you have when it comes to phasing cams. With a cam intended for high speed operation, at low rpm it has quite low volumetric efficiency and thus reduces pumping loss. Direct injection helps combustion stability in this case.

While the low end torque looks crappy, it's actually not bad considering how long the cam duration probably is. In the 2GR-FSE technical pdf, they describe how they can increase "internal EGR" (I think this means EGR that happens by virtue of valve timing trapping exhaust gas in the cylinder) quite a bit before things go bad with the direct injection system. The low end torque would probably be much worse without it (and it would probably fail emissions without some sort of variable intake lift or something).

Variable intake duration would really help on a turbo though, as it wouldn't waste compressed air when you're at part throttle, and help transient response. But seeing how electrically assisted superchargers, mild hybrid systems, (and logically, electric exhaust turbines would follow) are going to replace traditional FI eventually, it might be a pretty long way off before continuously variable intake duration would find its way to all engines. Not to mention, it works best with variable compression ratio.

[Bristecom]

Yeah, good point. I'm glad they at least went with dual variable valve timing (AVCS). The Valvematic system would obviously increase complexity and may not be suitable or worthwhile for some engines.

[Homemade WRX]

well AVLS or valvematic would have been nice. AVLS is more crude, like vtec but very simple. You simply have two lobe profiles.

Valvematic just seems like another means of accomplishing the same type of motion that Ferrari uses for variable lift/duration.

[serialk11r]

Well apparently for the 1LR-GUE at least they said a variable lift system would pose issues at high rpm...I suppose that extra rocker isn't always suitable.

I also heard that Ferrari's moving cams have issues of their own though...I'd like to see the Japanese companies take a stab at Ferrari style cams.