Miller-Cycle V8 conversion?

This is an interesting idea: http://me.a-spec.ca:6001/Room/MillerCycle.html
and here: http://autozine.kyul.net/technical_school/engine/petrol2.htm

Essientally you take a standard N/A Otto-cycle engine like an LT1, then slap on a supercharger (include an intercooler for temps) and use a custom cam that pushes the intake valve closing point to nearly 50* past BDC.

Why bother? well, the result is that of a massive exhaust cam, with an intake cam designed to reduce the dynamic compression ratio a LOT. The idea is that the supercharger (if it's a positive-displacement design) will make up for the loss of dynamic compression with boost, getting you back to and past a NA engine in power output.

So where's the advantage? The whole idea though is to reduce pumping losses a normal compression stroke would see... but you're stuck with a lame intake cam and reduced hp that you normally would have had on an otto-cycle at WOT. The tradeoffs though result in an idle/cruise you have a much more efficient design and mpg.

So the question is... how is this any different than a supercharged engine with a lame intake lobe? Why the unique name of "Miller-cycle" I mean really... what's the patent for? :confused:

Is there something else (besides a DCR-retarded/boost-compensated design) that I'm missing here? is the intake valve timing adjustable for high-rpm use?

Just curious if anyone's worked with this design... seems like a normal blower engine with a green-peace label?


(on a side note, I never really considered the EGR system as "pressurizing" the intake to reduce pumping losses... but I guess it makes a little sense in hind sight... anyone know what kind of psi we're talking about in EGR operation?).

Yes, closing the intake valve later will reduce pumping losses, but strapping a belt driven supercharger to the engine will increase frictional losses by a rather large amount. Is the Miller engine really ahead when you consider this? I wonder.

I have been trying to find info about the miller cycle engine, and I'm not coming up with a whole lot.

I get the basic concept, about keeping the intake valve open past BDC, until the piston is about 30% up the cylinder and using the supercharger to prevent backflow.


What I'm trying to figure out is, if you're starting with an Otto cycle engine, such as the LT1, is converting to a Miller cycle engine really just about getting a special camshaft?

Yes, I know, you obviously need a supercharger.


But other than that, what goes into it? What would you want in the way of a head? Can a centrifugal supercharger work? I know it would be down on power in the lower RPM range, but other than that, would it work at all?


I'd appreciate any info you have, and any material you can point me to.

That's weird...

I would swear that I started my own thread on this after searching and not finding anything. (although, my search didn't include a hyphen)


Did some moderator move my post onto this thread?

I hope so... if not, I'm losing what little mind I have left.

Originally posted by LameRandomName
That's weird...

I would swear that I started my own thread on this after searching and not finding anything. (although, my search didn't include a hyphen)


Did some moderator move my post onto this thread?

I hope so... if not, I'm losing what little mind I have left.

Try these:

http://www.mazda.com.au/articleZone.asp?articleZoneID=92

http://www.gizmohighway.com/autos/miller_engine.htm

A friend had a Millenia S. Yep it drove like a 210 hp sedan. Any engine problems required an engine swap. Dealers were not trained to fix it. After warranty that would cost over $8K. My friend traded it before the warranty ran out. Got an M3. Now has a G35 coupe. That's a nice car!

"Of all the things I've ever lost, I miss my mind the most."...Anon.

Yeah, I found those articles yesterday. They're interesting, good read, but not enough technical info.

Thanks anyway though... I do appreciate the effort.

I think there's a reason Mazda stopped using that kind of engine.

That reason, in my opinion, is that they have enough trouble convincing people that their first wacky engine (the rotary engine) is a good thing.

Somewhere I can almost hear Mazda execs having a stern sit-down meeting with the engineering teams and saying something like: "Look, would you stop it with all these wacky engines, please? We took on enough problems when we committed to this damned rotary engine, we aren't going to fight the good fight for a second engine design that nobody else in the industry is using."

I also can't imagine how you could gain much efficiency in reducing pumping losses when you shove 30% of the air back out the intake valve after the rest of the engine worked so hard to get it in the cylinder in the first place.

If there is nobody here who is fairly knowledgeable about Miller Cycle Engines, could someone at least point me to a good source that IS?

Perhaps a particular book, or maybe a performance related company?

has anybody done the opposite of this? Convert a Miller cycle engine to an Otto cycle engine?

To have some real fun, convert from 4-cycle to 2-cycle. Just overdrive the cam and bolt on a supercharger.

If electric valves ever get practical, I bet we will see engines that can go from 4-cycle to 2-cycle at will for incresed power.

To have some real fun, convert from 4-cycle to 2-cycle. Just overdrive the cam and bolt on a supercharger.

If electric valves ever get practical, I bet we will see engines that can go from 4-cycle to 2-cycle at will for incresed power.
I was thinking about that also :D

Interesting... you'd need an aweful lot of headroom in rod strength, rod bolt strength, and the cooling system to ever consider a 2-stroke operation on a V8. Doing so would probably penalize you in weight a fair bit at "low" power otto-cycle mode. 4-strokes are more efficient (VE) anyway... I really doubt you'd ever see this in a race engine or likewise any OEM (think emmissisons controls :-O... no chance of this being a EPA-approved engine).

Would be cool to kick around if built to handle the very different modes... but I'm not sure what application it would apply to.

I've got a 305 that I have been considering doing this with...