boost on twin screw chargers

[5000gt]

Quick question.... is the boost on a twin screw lysholm charger dictated by rpm or is it internal design of the rotors?

Secondly, are there any ways of electronically controlling boost?

I was thinking... twin screw charger, electronic clutch pulley, and wastegate plumbed in to control overboost.... water to air coolers for easier (shorter) plumbing....

Engine.... unsure, maybe 2jzge, maybe the v12.... was thinking maybe using an IHI unit from the 2.3 mazda miller cycle, or 2 on the v12....

At the moment, just daydreaming possible paths to take.

Thoughts? comments?

[JustenGT8]

Hey Tan,
Twin screws are positive displacement just like roots blowers so theoretically full boost at any revs....real world isn't quite the same but near enough. The Miller cycle will be way too small but plenty of good brands out there.....be aware, they are waaaay more pricey than say a roots Eaton

[JustCallMeOrlando]

Justen is right with all of that. You need to work out what you want from the engine, how much power and size from there. Personally, I think it would be hot with 12 throttles, but hey, that's just me. Also personally, I think one blower is enough of a headache than trying to mount two.

[Norbie]

I think the main advantage of a positive-displacement blower will be lost on a big engine like the 1GZ. Even if you have a laggy turbo setup you'll never be lacking for torque! Full boost from idle probably isn't something you want, it will only torch the tyres.

[Siri]

yeah i was more interested in possibly using it on something smaller like a 2L or 3L max... the miller cycle units should be alright for that.... thing is though, those chargers run a bar on the mc engines.. does that equate to more or less on an otto cycle where the inlet doesnt stay open on compression??

I have some info on litres per rev at home somewhere also, and iirc, it was around the 2l mark...

EDIT: forgot i was using a workmate's laptop... cheers. Tan

[rms]

the miller cycle units should be alright for that.... thing is though, those chargers run a bar on the mc engines.. does that equate to more or less on an otto cycle where the inlet doesnt stay open on compression??

'Miller' cycle is purely advertising hype !

All current production engines have the inlet valve open (to a greater or lesser degree) on the compression stroke.
I don't know of any engine that closes the inlet valve at BDC.

So if you then add a supercharger, does that make them 'Miller' cycle ?
I also have an N/A engine that closes the inlet valve 90 deg ABDC, half way up on the compression stroke ! Is that 'Miller' cycle ?

[Norbie]

I suggest you do a bit of research. Certainly most (if not all) engines have the inlet valve open for a small part of the compression stroke, but nowhere near as much as a Miller Cycle engine.

[5000gt]

was that directed at me or rms?

n/a engines where the inlet stays open as long as an mc is an atkinson cycle isn't it? Then again, those 2 terms have been thrown around quite loosely....

[rms]

No, Atkinson cycle has the four strokes happening in one revolution of the crankshaft.
Atkinson has power stroke longer than intake stroke.

Miller cycle attempts to emulate this by delaying inlet closure.

At what timing angle do you draw the line regarding inlet closure ?

[oldcorollas]

at some percentage between length of intake stroke and power stroke?

what does the patent say?

edit:
this is the ozawa patent for the mazda "Semi miller" engine
http://www.patentstorm.us/patents/5682854-fulltext.html

[Norbie]

I believe a Miller Cycle engine normally keeps the inlet valve open for approx 20% of the compression stroke. I don't know where you'd draw the line but this is clearly a lot more than you'd see on a "normal" Otto Cycle engine.

[rms]

'Miller' engine - 20% - 36 deg ABDC
Stock engine - 30% - 50 deg ABDC
Sport engine - 40% - 70 deg ABDC
Race engine - 50% - 90 deg ABDC

[oldcorollas]

which miller cycle engine is the 36deg from? if it is the mazda, what was the retardation of the VVT at that time?
ahh


how much overlap difference is there between the engine i bet the "race engine" has more than 7deg?

and the length of power stroke for each of those motors?

it is the ratio of compression stroke length compared to the power stroke that makes it miller cycle, and a feature of the miller cycle is that it needs higher intake pressure (by artificial means) to return the engine back to the specific output of a "normal" engine of that capacity...

does a race engine with 90deg ABDC cam idle at less than 1000rpm? what would it's efficiency, from blowby, be at normal road revs.. 1500-3000?

edit: http://www.autozine.org/technical_sc...ne/petrol2.htm

[5000gt]

ummm, sorry for opening the can of worms.... feel free to discuss further, BUT, any recommendations on using the twin screw off the mazda mc on say, a 2jzge???

air intake - throttle body - wastegate - w2a cooler - plenum.

A larger electronically clutched pulley to drop boost off to prevent damage to stock 2jzge would be in order also....

Reason i'm stuck on the mc charger is how cheap they are....cheaper than most eaton roots even (obviously from the states). That and because it's a twin screw.

[rms]

it is the ratio of compression stroke length compared to the power stroke that makes it miller cycle, and a feature of the miller cycle is that it needs higher intake pressure (by artificial means) to return the engine back to the specific output of a "normal" engine of that capacity...

All I am saying is that I believe the spin doctors have been at work with 'Atkinson' and 'Miller'. In theory it may have advantages but in practice it is dubious. Manufacturers like to be seen as 'green'. The 'goal posts' can be moved around to suit the marketing/sales pitch.

If I take our race engine with 90 deg ABDC inlet close, change the exhaust cam timing to Ex open 70 deg BBDC and add a supercharger, does that change it from an 'Otto cycle' to a 'Miller cycle' ? Or a 'greener' engine ?
Compression stroke 90 deg. Power stroke 110 deg.

Apologies for being so far off topic, I will leave this alone now

To answer a couple of your questions.
Overlap 120 deg
Idle 1400 rpm, slides leak too much air and flywheel/clutch assy only weighs 5 kg
1500 - 3000 rpm, won't win any fuel economy runs.


Re 5000gt's question.
Boost is relative to blower capacity/revolution- v- engine demand/revolution, drive ratio and camshaft timing.