Ever think about, wonder why, manufacturers of TurboCharged engines make such a BIG issue of/about how soon/quickly the turbo begins producing BOOST.

Hint: It's not JUST about the need to provide increased HP/torque from the QUICK, QUICKER, onset of BOOST.

Back when I test drove an early model of the RDX I came away puzzled about why I could not easily drive the RDX without getting into the turbo boost mode.

Now I know why.

TurboCharged engines, as in the RDX, operate in DERATED mode, low relative(***) engine performance ~98% of the time.

That, derated mode, results in the need to run at higher than normal(***) engine RPM for simply cruising along (light engine load, loading) at freeway speeds. And that, in turn, results in relatively(***) poor FE due to the higher engine friction component.

*** Modern day non-turbocharged engines have a cylinder compression ratio on the order of 10:1, as much as 12:1 with the new DFI capability. The RDX doesn't reach this level of engine efficiency until FULL boost is available to compensate for the low "native" cylinder compression ratio.

Thus, RDX = POOR FE 98% of the time.

The FIX...Simple.

Operate the RDX engine in the Atkinson Cycle "mode" when lightly loaded, just simply cruising along. But then convert gradually into the Miller Cycle as the the throttle is opened farther and farther.

Design and use a variable "hesitation" intake camshaft. Basically, have the camshaft "hesitate" from say 0-30 degrees, at each high point of an intake valve opening according to the current turbo boost level. No boost, no delay.

Like a true Atkinson cycle engine, the "native" cylinder compression ratio would be ~13:1, but then effectively reduced to 10:1 via late intake valve closing, a portion of the cylinder's initial A/F "charge" being forced back into the intake manifold.

Then as turbo BOOST begins to climb the intake valves would remain open during the compression stroke for a longer and longer period, reaching an effective cylinder compression ratio of 8:1 with the boost pressure making up the difference, increasing the levelof A/F charge left in each cylinder after the intake valve closes.

So as you depress the gas pedal to attain more HP/torque of acceleration, QUICK acceleration, the engine would quickly transition from the Atkinson cycle into Miller cycle mode...

The Atkinson/Miller/West cycle engine...??

 

Do you read a bit of technical info, then make up bogus theories in your mind?

Derated mode? Please. 10:1 has never been considered low native compression on a pump gas engine either and the RDX doesn't run at higher than normal RPM's on the highway either.

 

I see you use the term "atkinson cycle" in many of your posts. Is it something you just learned about a few months ago and decided to start spewing throughout this forum to try and fool people into thinking you know what you're talking about?

Because seriously, even with all your big words, you sound like an idiot.

 

So you think the RDX engine wouldn't, couldn't, run at a lower RPM when cruising at a constant speed on a flat highway section if the compression ratio was more like 10:1 vs the 8:1 it is now.

And just where did you get this schooling...??

Did nobody ever tell you of the advantages of a flat, FLATTER torque curve..??

 

I really appreciate the good, kindly words, I'll be sure and take them to heart.

NOT...!!!!

 

Hmmm...

Anuone know..??

Is 8.8:1 the combined compression ratio, cylinder + turbo...??

 

You don't know that compression ratio in engines is static? Nevermind throwing a turbo on an engine doesn't change the compression ration simply by adding a turbo . It's a simply ratio calculation. V BDC/VTDC.

Please stop posting.

 

The RDX's cylinder compression ratio is STATIC, the RDX's overall "engine" compression ratio is NOT.

In the RDX the compression of the charge in the cylinder has two components, the actual cylinder compression ratio and the compression of the air volume before it enters the cylinder. The two "compressions" combined determine the engine output performance.

Except before the turbo spools up we only have the raw cylinder compression.

I don't know which number Acura would publish or even which definition they might use.

Do you..??

Manufacturers of Atkinson cycle engines publish the "raw", actual/"native", cylinder compression ratio, typically 13:1, while the effective overall, engine, compression ratio is much lower, typically 10:1.

To me, 8.8:1 seems a bit high for a turbo engine for the cylinder compression ratio alone. But 8.8:1 seems about right for a combined compression ratio, accounting for full boost pressure, especially if you cannot somehow prevent the owner from EVER fueling with regular octane gas.

That would also account for the relatively POOR FE of the RDX's otherwise smallish I4

 

8.8:1 is the static compression ratio of the K23-A1.

This however only occurs during the "Bongo-cycle".

 

Thanks much..

But now to show more of my ignorance.

"Bongo-cycle"....means...??

How is the boost reduction accomplished, intake pressure bypass or exhaust flow bypass..??

 

now im just beginning to think somethins wrong with this dude

 

Please show me a modern car that reduces/controls boost by bleeding intake pressure. They all use exhaust treatments (often wastegates) usually controlled by a solenoid and actuator. Our turbos uses variable flow path, but I'm not sure if that also acts as the wastegate.

 

All, insofar as I am aware, Supercharged engines bypass manifold intake boost pressure into the "open" or back into the intake. Ford got into trouble with the SC T-bird bypassing into the intake because they didn't initially realize that multiple passes of the same air volume through the compressor would result in heat level climbing and climbing and climbing.

So they had to add an intercooler after the fact to cool the airflow being bypassed back into the intake.

But yes, it is my understanding that most, if not all, "turbocharged" engines use a wastegate to "dispose" of surplus exhaust gas pressure. But wastegates often, if not always, bypass those surplus exhaust gasses directly into the atmosphere, some with small mufflers to "quiet" them.

I doubt if CARB and/or the EPA would allow that for a US passenger car.

So, like you, I have no idea how the boost pressure gets reduced even though/when the exhaust gas volume is still rising.

Two function BOV, Blow-Off Valve, maybe..? BOV fully open to the atmosphere (or intake for quieting??) with throttle closure, but also with ECU controlled partial opening to moderate/limit/reduce boost pressure..??

 

OEM wastegates get routed back into the exhaust system as OEM turbos have internal wastegates.



See the trap door, that is a wastegate, controlled by an actuator and routed into the stock exhaust stream.

There is nothing wrong with trying to learn, but you are making technical posts and criticizing vendors without the knowledge to be doing so.

 

...

 

You don't even know how turbo's have their pressure controlled, yet you comment and speculate all over the map about bleeding intake pressure with BOV's and how wastegates almost always bleed to atmosphere which is quite simply wrong.

 

Sorry, my wastegate experience is mostly with Porsches and the "like", beginning, long ago, with a turbo 944. All of the wastegate implementations I have expereinced have "vented" to the atmosphere, sometimes with smallish mufflers to quiet their "BARK".

My immediate, first, thought when you were so kind as to educate me on the way the RDX used the wastegate was that "wait, isn't there oftentimes so much exhaust pressure downstream of the turbo that bypassing excess pressure there would have little effect". But "moderating" the level of turbo boost that way seems perfectly reasonable.

But here again I was unduly influenced with my Porsche background and experience overall and in the racing venue, dare I to bring that up.

But yes, given the primary passenger/public roadway use of the RDX, venting the "waste" gasses directly back into the downstream exhaust path seems very practical.

Especially if you have a BOV as "backup" to quickly vent the intake manifold excess pressure when the throttle is partially lifted/closed. Where, again, does the BOV vent that excess pressure too...?

 

Most, if not all OEM setups recirculate the excess pressure back into the intake, after the MAF.

I belive the BOV is right next to the I/C (down to the right) and tubes back into the intake. I can't be 100% sure without popping the hood.

 

Seems to me that there must be a method for the engine/transaxle ECU to "forget" about all the airflow that just previously flowed through/pass the MAF/IAT, got compressed, seriously compressed, within the intake manifold volume, and with BOV "pop-off" is now history.

 

Okay, I'm confused, REALLY confused (like you said..??)

Just googled for:

BOV recirc*

Bottom line of what I learned via the search is that if the BOV output is vented to the atmosphere then the engine/transaxle ECU gets "confused". On the other hand if the BOV output is re-inserted into the intake path everything seems to work.

That I much understand, the BOV output air volume has already been measured and "accounted" for, so if it just simply disappears into the wild blue yonder..

My confusion factor on this arises from my doubt that the intake pipe/duct volume, CSA, between the CLOSED throttle plate and the MAF/IAT sensors isn't sufficient to hold the BOV air volume without causing reverse airflow, "backwards" airflow, through the MAF/IAT.

Am I just simply over estimating the volume of airflow into the intake path, "recirc.", from the BOV opening that results from a sudden/quick full throttle plate closure during FULL boost...??

 

Administrator: Sorry, I inadvertently exceeded the edit time, would you be so kind as to delete my previous, to this, post...?

Okay, I'm confused, REALLY confused (like you said..??)

Just googled for:

BOV recirc*

Bottom line of what I learned via the search is that if the BOV output is vented to the atmosphere then the engine/transaxle ECU gets "confused". On the other hand if the BOV output is re-inserted into the intake path everything seems to work.

That I much understand, the BOV output air volume has already been measured and "accounted" for, so if it just simply disappears into the wild blue yonder..

My confusion factor on this arises from my doubt that the intake pipe/duct volume, CSA, between the CLOSED throttle plate and the MAF/IAT sensors isn't sufficient to hold the BOV air volume without causing reverse airflow, "backwards" airflow, through the MAF/IAT.

I acknowledge that the BEST the BOV can ever do is reduce the intake manifold pressure to 1 atmosphere. What remains will sustain a fairly high engine output for a brief period, a VERY brief period until the closed throttle plate takes effect...

But that's not at all unlike a nor-turbo engine quickly coming off WOT.

So am I just simply over estimating the volume of airflow into the intake path, "recirc.", from the BOV opening that results from a sudden/quick full throttle plate closure during FULL boost...??

 

Approximately 25 years have passed since the intro of the 944 Turbo (been there, drove the crap out of them), it's probably OK to assume that turbo technology has advanced somewhat, not even to mention different approaches to engine control and management, in whole or in part, by different manufacturers.

WildWest's reference to EFI dates back to when my ex-Marine roommate's spanking new Escort with (gasp) EFI would stop dead in the vicinity of automatic door openers, airport radar, or CB radio (remember them, good buddy?) base stations. Things Have Changed.

The Bongo cycle is an excellent example of current tech as explained by XLR8R. K23-A1 dynamics, short and sweet. Don't make it difficult by half or more by trying to apply partly-understood engineering dynamics from a quarter-century past. The knowledge gap is even more obvious when trying to grok the difference between a waste gate and blow-off valve.

Miller. Atkinson. Good way back when, but overwhelmed by current tech. Check out what's happening with throttle-less engine control. It's all in the valve action, and even then, those may be replaced...

BTW, my wasted $$ on a CP-E intake and Hondata reflash have netted an average 2.5 mpg increase overall taking into account occasional deep explorations of the GO pedal for pure gratification. Since this isn't supposed to be happening because other folks have said so, I can only assume that someone has circumvented all security measures and is adding gasoline to my tank. Please let it be Shell 93.

 

"Throttle-less.."

Have I neglected to post my idea regarding use of a variable speed positive displacement SC as a way to implement a Miller cycle and eliminate the need for a separate intake airflow metering throttle plate..??

Or the use of an oxygen generator to separate oxygen from nitrogen and only allow nitrogen, almost a FULL charge of same, to enter the engine at idle or low power settings.

Use PURE oxygen for WOT and a controlled reblending between the two depending on the power level required.

1 atmosphere in the intake manifold ALWAYS....

My bad.

Or is that too far "out of the box"

To many theories, assumptions, speculations involved....

Makes me wonder why the US seems to have had such a great surplus of those in the past.

But hey, let's keep the criticisms flowing, my "feathers" are quite throughly oiled, and just as long as a bit of knowledge is passed my way along "with" things will remain on the plus side for me.

 

Administrator: Sorry, I did it again, may I be forgiven..??


"Throttle-less.."

Have I neglected to post my idea regarding use of a variable speed positive displacement SC as a way to implement a Miller cycle and eliminate the need for a separate intake airflow metering throttle plate..??

Or the use of an oxygen "generator" to separate oxygen from nitrogen and only allow nitrogen, almost a FULL charge of same, to enter the engine at idle or low power settings.

Use PURE oxygen for WOT and a controlled reblending between the two depending on the power level required.

1 atmosphere in the intake manifold ALWAYS....

Sure, not even remotely feasible using technology of today, but look at the potential for return on investment, a 0.4L engine does the work of today's 2.0L engine with a dramatically lower frictional component.

Sorry, my bad.

Or is that too far "out of the box"

To many theories, assumptions, speculations involved....

Makes me wonder why the US seems to have had such a great surplus of those in the past.

But hey, let's keep the criticisms flowing, my "feathers" are quite throughly oiled, and just as long as a bit of knowledge is passed my way along "with" things will remain on the plus side for me.

 

Throttle-less...

I see an Acura RDX in my future, maybe...

I was initially attracted to the RDX because upon reading about the SH-AWD system in detail, viewing the on line videos, etc, I decided it had to be the absolute best F/AWD system in existance today.

F/AWD = Front torque biased AWD system, most with a sideways mounted engine or derived from a FWD "base".

I currently have a 2001 AWD RX300. The RX's F/AWD system is just barely adequate provided you have an early one with a VC, Viscous Coupling, mounted across the center diff'l. The VC will, on rare occassion, help to provide increased torque to the rear drive line, as much as 75/25 F/R vs the normal ~95/5.

As shipped the RX cannot have tire chains mounted on the rear wheels due to TOO TIGHT clearance between the tread and suspension. I added 1.5" wheel spacers all around so as to be able to use rear tire chains FIRST and ONLY, for reasons of safety. When the tire chains are fitted, rarely here on the Seattle eastside, the VC will tighten up the center diff'l a little quicker due to the F/R wheel circumference variation. An obvious additional plus from the spacers is a slightly wider stance and therefore more stability.

So I test drove one of the early RDX's. I was impressed overall but didn't have a chance to really try out the SH-AWD system. Two other aspects of the RDX kept me from following up. A minor one was the seeming to me, CLUTTER, of the center dash instrument (non-tech)area. But a more important one was the fact that the turbo would come on line with even the slighest additional pressure on the gas pedal.

I suspected that would result in rather poor gas mileage in comparison to my RX and as many of you now know that proved to be the case. Because of the turbo boost capability the RDX engine compression ratio is ~8:1. But that low 8:1 ratio results in a severe lack of early onset of torque until the turbo spools up.

So, let's dream a bit, just a bit.

Assume I have just won the lottery.

I would immediately buy a new RDX and turn it over to a group of students at Western Washington State college with the following instructions/goals.

Convert the engine to the Miller Cycle.

Discard the turbo and instead use a lightweight low inerta carbon fiber positive displacement SuperCharger. The SC would be engine belt driven, primarily, but via a Toyota HSD type CVT/diff'l. The opposite input to the CVT/diff'l would be a 2-3HP synchronous AC motor, the motor itself driven by a variable frequency inverter such as Toyota uses for the various HSD drives including the Prius' A/C compressor.

The engine would use a Porsche VarioCam-Plus intake valve lift system to vary the effective Miller Cycle compression ratio from 13:1 to ~8:1. 13:1 during idle or light load cruising, but as boost came on, rises, due to increased gas pedal depression or engine loading the compression ratio would rise linearly until at FULL BOOST the compression ratio would be ~8:1.

There would be no need for a throttle plate, the VARIABLE SPEED positive displacement SC would provide the engine throttling functionality.

Obviously there would be no turbo spool-up delay.

Probably yeild more HP/Torque than stock plus STELLAR FE, so much so that a smaller engine might be more appropreate.

Questions..??

 

Miller cycle....


http://www.autoblog.com/2007/05/31/m...-mazda2-demio/

http://www.themotorreport.com.au/821...lenge-hybrids/

 

Great, The more I think about it the more I find myself confused about the practicality of the "recirc" mode of a BOV. I'm not in any way disputing that the recirc method is in crrent use.

But.

When the BOV opens the area/volume of the intake duct/path between the throttle plate and the MAF is already under the pressure of 1 atmosphere. So it seems to me that venting the excess intake manifold pressure back into the intake duct/path would result in at least some level of reverse air flow BACKWARDS through the MAF.

Anyone know where I'm going wrong..??

 

Got it....

The throttle plate is downstream of the turbo compressor section.

That allows the turbo to remain somewhat spooled up via the BOV porting the pressure side into the intake side without having the "spool up" airflow come through the MAF/IAT.

 

Hmmmm...

Given the need, desire, to have the turbine remain "spun" up as long as possible and as high as possible, as evidenced somewhat by the BOV recirc function, wouldn't it be desireable, more desireable, to use the BOV to regulate, prevent overboost, as the engine RPM rises and then reaches the RPM point at which boost is reduced substantially...??

If the wastegate is used for this boost regulation and boost cutback then the turbine "idles" down, downward, and the future inertial effects are lost. On the other hand if the BOV is used to moderate boost pressure the turbine will remain under pressure, spooled up, ready, "more" ready, for the next, upcoming, downshift.

 

The BOV/BPV isn't to keep the turbine spinning, it's to stop pressure surges on the impeller from occuring when the throttle plate slams shut between shifts (more important with a manual trans).

Also, without a wastegate, the turbo would overspin. The wastegate is controlled impeller speed. Without bleeding that exhaust gas off, the turbo would keep spinning faster.

 

Overspeeding the turbo....

Isn't that something that can be addressed during the engine/turbo design phase..? If you know the maximum exhaust volume the engine will produce then simply size the turbine accordingly.

Not saying the RDX doesn't have a wastegate or doesn't use the wastegate, just questioning what, which functions the wastegate can/is/should be used for.

 

Stoichiometric......stoi-chio-met-ric.....stoichiometric.

It's such a great word -- it sounds so "learned" -- you've gotta work it in there.

 

Yes, if one could remember from time to time how it's spelled. Hard to sound 'learned" if the spelling is incorrect. I would use spellchecker if I could get the 'beginning" spelling somewhere close enough for spellchecker to recognize what I'm really trying to say, spell.