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