Millers Cycle

[unarmed_skyline]

Hey guys,

im in the process of turboing my n/a atm and am planning on running the engine on a Millers Cycle,

the problem is i know a bit about what the the millers cycle is and does but am not sure what sort ecu is

needed to run this effectiently. Pretty much the cycle holds the intake stroke for longer creating a different

store and effectivly lowering your compression ratio, so in a n/a engine with a high compression ratio this is very useful when running boost.

Does anyone know what computer i will need?? What kinda cam's i will need?

And i was wondering if anyone knows anyone is melbourne that will be able to tune the car in this configiration?

Thanks for your help

[ebola]

Wiki is your friend.

The miller cycle is an interesting concept, and one that will penalise you heavily in the low rpm region when you have a turbo.

does your engine have vvt? if not, don't worry. just set the cams, lose all low end power (sounds like my rb20), and you should have better on boost performance.

Aside from from vvt management, there should be no visible difference to the ecu. It doesn't know, and doesn't need to know about the inlet stroke - only how much air is in the piston(via the AFM)

If you have VVT, I can post some thoughts up.

just remember, this is theory. I hope its solid.

EDIT: Don't trust the 'lower the compression ratio' line of thought. The way it does this is to force air out of the piston. so, yes, the compression is lower - because you have less air in the piston. think about it. also, it makes the compression ratio vary (don't know how much) according to the amount of boost. It would be great for track cars, I suppose, they run at full boost as much as possible on the track.

I wonder how much difference 2 bar would make?...

Edited May 8, 2006 by ebola

[Big Rizza]

Hey guys,

im in the process of turboing my n/a atm and am planning on running the engine on a Millers Cycle,

the problem is i know a bit about what the the millers cycle is and does but am not sure what sort ecu is

needed to run this effectiently. Pretty much the cycle holds the intake stroke for longer creating a different

store and effectivly lowering your compression ratio, so in a n/a engine with a high compression ratio this is very useful when running boost.

Does anyone know what computer i will need?? What kinda cam's i will need?

And i was wondering if anyone knows anyone is melbourne that will be able to tune the car in this configiration?

Thanks for your help

Do you mean converting your engine to run on the Miller Cycle, or are you putting in a Mazda Miller Cycle engine out of a Eunos 800M and turbo'ing it? Either way, it sounds like a waste of time to me. Mazda abandoned their Miller Cycle development, so it can't have been that spectacular in the first place.

I could be wrong as I'm not a mechanic and have literally zero experience with the Miller Cycle, but surely the Miller Cycle engine would only work with a supercharger, as the off boost performance of a turbo would be absolutely horrendous and lag would be spectacular. Would work on boost, though... So I am lead to beleive.

I have seen nat atmo engines with as high as 11.5:1 running the conventional Otto cycle on pump fuel and stock internals. Boost is kept to only 6psi, though. I think you may even find that the cost of converting to Miller Cycle when testing, dyno time, development etc. would outweigh the cost of rebuilding the engine with lower compression and stronger pistons.

Like I said, I don't really have the experience with the Miller Cycle to give you a definitive answer, but I think you are wasting your time. On an aside, has anyone on this forum heard of a vehicle being changed to the Miller Cycle? I never have, am I just being oblivious?

Edited May 8, 2006 by Big Rizza

[Warpspeed]

I have done a bit of work with Miller cycle engines, both computer simulations, and in car.

Agree, that the benefits of the Miller cycle can only be gained with a positive displacement supercharger, it will definitely not work properly with a turbo.

The whole idea is to move most the work of the compression stroke away from the piston, and do it instead with a much more efficient rotating supercharger. You can then apply massive amounts of intercooling and end up with a far lower charge temperature at the end of the final compression stroke.

The secret of the Miller cycle is also in the very high expansion ratio that can be obtained with a relatively late exhaust valve opening point. But to get all that extra efficiency, the exhaust valve MUST open into a low exhaust back pressure.

With a turbo, that simply is not going to happen. If exhaust back pressure is say, twice boost pressure, it is just not going to work properly. I suspect it will be very gutless off boost, laggy, and the fuel savings you expect from this are just not going to happen.

An RB25DE would make a wonderful Miller engine, fit a screw supercharger, a large front mount intercooler, and a much longer duration inlet cam. I would expect it would go rather well, and maintain the original normally aspirated fuel economy with heaps more power. To get the best out of it, a power FC would be required and probably a set of DET injectors.

When fuel goes to $2.00+ per litre, low compression turbo engines are going to become fairly expensive to run. You could get similar performance from a Miller, with far better part throttle economy. No lag with a supercharger either !!

[unarmed_skyline]

thanks for the replys, i'll prob stay away from the millers cycle with the turbo, i orginaly came across it when i was looking at supercharging the car but that was ending up a bit to expencive, i wasnt sure on the effects of using it on a turbo but as it has been explained now i will stay away from it and just keep the boost low until i upgrade the internals.

[unarmed_skyline]

thanks for the replys, i'll prob stay away from the millers cycle with the turbo, i orginaly came across it when i was looking at supercharging the car but that was ending up a bit to expencive, i wasnt sure on the effects of using it on a turbo but as it has been explained now i will stay away from it and just keep the boost low until i upgrade the internals.