Cam regrind... for efficiency?

[Turbinepowered]

odd that the Mazda2 "Miller-Cycle" engine has no supercharger, making it an Atkinson-Cycle engine, but they're still calling it a Miller-Cycle.

and that the Ford/Mazda and Toyota Hybrids use an Atkinson-Cycle gas engine in their hybrid drivetrains.

knowing that, kinda makes you think the hybrids should be getting even better mileage than they do.

Yeah, I'm not really sure how they're accomplishing that without a supercharger, since Miller Cycle specifically requires forced induction compensation for the decreased effective swept volume. Maybe they're doing something with resonance in the intake? I don't know much about stuff like that.

[ezekiel]

have you thought about, or tried to calculate, the amount of force the engine would have pushing back in that 15-20% of leaving the intake valve open?

like, to figure out what kind of boost pressure you'd need to keep the air in there?

would help with calculating, cause I'm sure I remember VNT turbos making about half a psi at idle,

[jtanguay]

wow 54 mpg with a 1.3L engine...  :roll:  why not just get a 1.0L geo and enjoy 70 mpg???  :lol: or splurge and go with a nice 1.9TDI and enjoy 50 some odd mpg with the ability to pass other vehicles...

i think a VNT turbo would be a must for this type of mod on a diesel.

[xud9te]

Great idea, but what I have never had cleared up to me is what is the difference between a miller (or atkinson) cycle engine and one with a lairy intake cam?  

I mean the miller cycle engines use a cam of around, or over 275 degrees, but there are plenty of NA race engines using a longer duration...

Of course the exhaust is open as well for longer giving a through flow as opposed to reverse, but where is the actual borderline? Is it just numbers or is there a mechanical (or thermodynamic) difference that I am missing?

In my mind would you not need to first calculate the pressure of the manifold exactly for the supercharging effect of leaving the intake open to make sure you have enough boost pressure to combat?

Also I have never heard of the miller cycle being applied to diesels ever, I assume for the reason already mentioned regarding drop in compression which would seriously hinder starting despite what kind of ane way system is used...

[Turbinepowered]

Great idea, but what I have never had cleared up to me is what is the difference between a miller (or atkinson) cycle engine and one with a lairy intake cam?

Don't know if I'm familiar with the lairy intake cam terminology; clarify please?

I mean the miller cycle engines use a cam of around, or over 275 degrees, but there are plenty of NA race engines using a longer duration...

Of course the exhaust is open as well for longer giving a through flow as opposed to reverse, but where is the actual borderline? Is it just numbers or is there a mechanical (or thermodynamic) difference that I am missing?

I believe the difference is that Miller/Atkinson doesn't do anything for the exhaust valve timing or duration; they are purely intake-valve oriented changes, with a typical exhaust duration and timing. And a naturally aspirated engine would be Atkinson; Miller requires some kind of forced induction (Unless you're Mazda, apparently, with a forced induction-less Miller... somehow...).

In my mind would you not need to first calculate the pressure of the manifold exactly for the supercharging effect of leaving the intake open to make sure you have enough boost pressure to combat?

I'm a little slow today perhaps, but what do you mean by the "supercharging effect of leaving the intake valve open," precisely? I am under the impression that the purpose of leaving the valve open is to reduce the effective volume of the air charge within the cylinder, thereby lowering the compression ratio while keeping a taller expansion ratio. And that any forced induction is simply there to restore the lost power of the smaller charge-air volume by increasing its pressure and density.

I'm also not sure what you mean by combatting boost pressure; do you mean calculating your manifold pressure so you know how much boost pressure you need to compensate for the loss of volume?

Also I have never heard of the miller cycle being applied to diesels ever, I assume for the reason already mentioned regarding drop in compression which would seriously hinder starting despite what kind of ane way system is used...

I think really that the advances in direct injection technology have helped any problems that would arise from the lower compression in starting. Intake air heaters, pilot injections, and better placement of in-cylinder glowplugs could all be applied to in indirect injection engine, or a direct injection engine with a high compression ratio.

I think that Miller, and even Atkinson, can be applied to a diesel by bringing its compression/expansion ratio back up into the twenties, but using the Miller or Atkinson cam to drop the compression back down into the 18.x range while leaving the expansion ratio the full 20.x or whatever it is designed to be.

[xud9te]

Sorry, by 'lairy' i mean long duration (not high lift), i.e. miller cycle engines have an intake cam of larger than 275 degrees duration.

Yes, i think i answered my own question in that the miller cycle engine relies on only intake cam changes in duration.

Mazdas miller cylce always uses a supercharger, in fact i know of only one production car engine, as fitted to the mazda xedos, that uses this cycle and is definately supercharged (although at a guess check out the mazda 626 supercharged diesel in case it uses the miller cycle of a form).

I understand the miller cycle in a different way perhaps: the forced air from the late intake cylinder provides a pressurised charge to the plenum for the next cylinder to open, helping the worst part of cylinder filling, and the supercharger offsets this in order that no air flow passes a certain point in the intake tract.  

Of course this offest of positive manifold pressure must be constant, hence why all miller cycles use a supercharger that provides constant boost (not an exhaust driven one).  Other wise you would have very little effective compression ratio at low turbocharger speeds (and no power).

Maybe the main reason this technology has not been applied to diesels yet (or has it?) is that mechanical supercharging and diesel torque production are just two ways of skinning a cat??

[Turbinepowered]

Sorry, by 'lairy' i mean long duration (not high lift), i.e. miller cycle engines have an intake cam of larger than 275 degrees duration.

Yes, i think i answered my own question in that the miller cycle engine relies on only intake cam changes in duration.

Mazdas miller cylce always uses a supercharger, in fact i know of only one production car engine, as fitted to the mazda xedos, that uses this cycle and is definately supercharged (although at a guess check out the mazda 626 supercharged diesel in case it uses the miller cycle of a form).

Apparently the new Mazda engine, linked to earlier, doesn have a supercharger. According to the article, at least.

I understand the miller cycle in a different way perhaps: the forced air from the late intake cylinder provides a pressurised charge to the plenum for the next cylinder to open, helping the worst part of cylinder filling, and the supercharger offsets this in order that no air flow passes a certain point in the intake tract.

Of course this offest of positive manifold pressure must be constant, hence why all miller cycles use a supercharger that provides constant boost (not an exhaust driven one).  Other wise you would have very little effective compression ratio at low turbocharger speeds (and no power).

I'll be perfectly honest with you, I have never heard it explained that way. And at least to my way of thinking, if that were the case then an Atkinson cycle engine with no such forced induction would barely run.

I also haven't heard that all Miller cams have to run 275 crank degrees of duration. I'm assuming you're referring to crank degrees, because 275 cam degrees would nearly two complete rotations of the crank... I would imagine that the extra duration would depend on how much air you wanted to force back out. Close it a little late for a little air out, a lot late for a lot.

A quick peruse around the web... and most of the Miller cycle engines I could find were running about 240-250 degrees of intake duration.

Maybe the main reason this technology has not been applied to diesels yet (or has it?) is that mechanical supercharging and diesel torque production are just two ways of skinning a cat??

Miller Cycle isn't mean to produce more torque, it's meant to reduce fuel economy. Not really sure what you mean by comparing mechanical supercharging and a diesel's torque advantage from longer strokes and constant pressure combustion.

[lyeinyoureye]

After posting something similar on another board, the exhaust valve timing was brought to my attention. I'm not sure what you consider to be an acceptable level of peak power, or if the cam's profile would even benefit, but insuring the exhaust valves don't open too soon may allow the engine to extract more from the power stroke at lower loads/speeds. Even though the IDI diesel is fairly efficient at anything above about half load, it's efficiency below that really bites.

In terms of startups, I'm not sure if a grid heater would help all that much, since they tend to be used in applications with lower CR that don't need glow plugs persay. I mean, it'd help, but imo a block heater would also be a good addition.

[Turbinepowered]

After posting something similar on another board, the exhaust valve timing was brought to my attention. I'm not sure what you consider to be an acceptable level of peak power, or if the cam's profile would even benefit, but insuring the exhaust valves don't open too soon may allow the engine to extract more from the power stroke at lower loads/speeds. Even though the IDI diesel is fairly efficient at anything above about half load, it's efficiency below that really bites.

In terms of startups, I'm not sure if a grid heater would help all that much, since they tend to be used in applications with lower CR that don't need glow plugs persay. I mean, it'd help, but imo a block heater would also be a good addition.

My goal for this is only a mere hundred horsepower, though I'd live just fine with ninety or so. I could probably even live with seventy five, but isn't that below stock TD power anyway?

Only application I'm familiar with grid heaters in is on the Cummins bus engines, and I think they run at 18:1 and ditched the glow plugs in favor of a four-valve head and centralized common rail injection. I figure it can't hurt, especially if I put it in a special "cold start" bypass air intake.

[jtanguay]

would be nice if you could get a propane heater and send the fumes downstream to heat things up.  electric heat is okay, but propane would give you the BTU's to start relatively quickly.  now making it safe is a whole different story!

[Turbinepowered]

would be nice if you could get a propane heater and send the fumes downstream to heat things up.  electric heat is okay, but propane would give you the BTU's to start relatively quickly.  now making it safe is a whole different story!

Indeed, and plus that would just add a fuel to worry about topping off.

I've toyed with having an insulated coolant reservoir like the Prius does, but I don't think I want that added complexity either. So block heater, intake grid/intercooler bypass, and really, really good compression will be my starting aids, I think.