If I had the V6 heads milled to get a 13:1 compression ratio on my '01 AWD RX300 and then restricted the intake manifold pressure via the DBW system such that the effective compression was never greater than 10:1 would I have a "virtual" Atkinson Cycle engine?

 

Probably not without your valves destroying the pistons on the first few revolutions. Domed pistons with valve recesses probably the only way for this radical an increase in compression. How are your metallurgy, casting, and machining skills?

For a primer on self experimentation with piston design and manufacture, rent "The world's Fastest Indian (motorcycle)" - true story about how an old geezer in Australia (played by Anthony Hopkins) breaks the world's motorcycle speed record at over 200 mph at Bonneville 30 or so years ago. The shelf with blown pistons and other sundry parts says it all! "Next time", he says after the latest disaster, "I'll try three parts Chevy, two parts Ford." (for the new piston castings). Great story!

Of course you would also need a CVT to take advantage of the enormously expensive Atkinson mods, on the extremely unlikely and costly chance that it would do anything but self destruct unless done by anyone less than Toyota's R & D stable!

And of course the HiHy's engine is not an Atkinson design, so you would be breaking new ground as well as the bank. There may be a good reason beyond the R&D expense for a projected limited volumn model that Toyota left it as a basicaly conventional higher compression design.

Good luck, great dreams!

Pete

 

I thought the HiHy was an atkinson cycle engine, and I was certain I read it from a reliable source. Ends up Wikipedia's entry on atkinson used to list the HiHy...incorrectly.

Does anyone know what are the differences (if any) between the hybrid & non-hybrid version of the highlander engine which help provide better ICE mileage (if any)?

 

The hybrid 3.3L V6 is a somewhat de-tuned version of the standard's V6, with max. power and torque at significantly lower RPM's, increasing efficiency and flexibility. I am convinced that the CVT of the hybrid is a large contributer to FE, in that it is always in the "right" gear with its continually variable gear ratio, keeping the engine at max efficiency under low or high demand conditions, and without the power loss (heat generation) of an oil-filled torque converter.

Pete

 

If I don't open the throttle valve enough to put a full charge, say only 70%, in the cylinder then the effective compression ratio should be 10:1...

Right?

 

The Prius and FEH/MMH derate the I4 and increase FE by implementing the atkinson cycle via leaving the intake valve open for a portion of the compression stroke, thereby forcing some of the intake stroke charge back into the intake manifold.

It seems to me the same thing could be done by regulating the atmospheric pressure in the intake manifold via DBW, E-throttle, intake flow control.

Do you suppose that's how the RXh and the HH derate the V6..??

 

At first I was going to rely to this thread with my own questions like... of COURSE it wouldn't work (because the HiHy is not designed to take advantage of such technicques) but then one of my research links SPECIFICALLY listed the Prius as an Atkinson engine so I decided that I had no clue so abstained. Who's to say that Toyota didn't ALREADY design the HiHy's engine in this manner. In other words, maybe your already too late...

 

The Atkinson cycle engines in use all have high compression ratios of 12.4-13:1 - the Prius the highest. The HiHy's CR is pretty high at 10.8:1, which it can tolerate without detonation/pre-ignition, even with reg. gas with ignition timing retardation, because it is never subjected to a lower RPM load: with load, the CVT immediately adjusts to a lower gear ratio for higher RPM's where detonation is inhibited.

We feel that with the slight lag when full throttle is applied at slow speeds - the response time for the CVT to adjust to a higher ratio, the engine to reach it's max power RPM, and the electric motors to engage. Not too different from the slight turbo lag in my Volvo.

The detuning of the HiHy's engine seems to be by electronically limiting the peak RPM's to 5400 instead of 6400, and optimizing torque torque at lower RPM's (3600 vs 4400, I believe) for partial throttle flexibility and efficiency. They have limited the max RPM, I think, because this number is sustained at max throttle with the CVT, rather than varying as with a "normal" transmission with fixed gear ratios, where with each gear shift, the engine is at peak power, then max RPM's only briefly with each gear shift at full throttle.

Since power is the product of torque X RPM's, that's how very high reving small racing engines can produce massive HP, but are useless at lower revs, with valve timing and lift optimized for torque at the top end, say 8000-10000 RPM's. This requires huge valve and manifold cross sections for the air flow needed, and/or forced induction by turbo or supercharger.

Pete

 

In addition on the Prius, they actually tweaked the engine block. The crankshaft is offset from the center of the cylinders.

I'm quite sure that they didn't go that far with the TCH or HiHy/RX400. As far as I know their engine blocks are identical with the "gas" versions.

 

Below is a list describing the major difference between the 3MZ-FE engine on the ’06 Highlander Hybrid and the 3MZ-FE engine on the ’06 Non-Hybrid Highlander:

Engine Proper

•

•

•

•

•

•

•

•

•

•

•

(ISO9141) to CAN communication