Hello folks. I am in the process of conceiving a new modification for my truck. A hybrid camshaft comprised of otto and atkinson based cycles. You see my aim is to reduce pumping losses to improve efficiency while not inheriting the many cons of both combustion schemes. Based on the chart here the modification would be used on adjacent cylinders in the firing order to not upset the balance. By doing so using slightly longer intake duration not drastic the losses would be in fact minimal. I may lose 20 hp but my belief is that with the extra air hanging around in the manifold I may in fact gain a bit of power as the otto timed cylinders would ingest the extra air and gain a bit of power. Modern cars with variable valve timing, most notably hybrids use both schemes on one camshaft. So why not our pushrods. Exhaust valve timing is identical among all cylinders. All opinions welcome.

 

 

 

Nonsense.

 

Well how so? I believe with the right amount of finessing and design that Perhaps this may work. I wouldn't think balance would be an issue as it follows cylinders in the firing order. The perks of using this on my 4.0 would be decreased resistance in the for of pumping losses. At low speed this would, from my hypothesis best and even better at freeway speed as most cars only need 20 hp to even cruise. I forsee mpg on the highway increasing to 20 mpg maybe 23 if your coasting with a light foot. Think about it. when your cruising at 65-75 mph on the Highway in some spots, your throttle is nearly close. The engine has to fight just to breathe. With half the cylinders using the modified cycle, the engine has to work half as hard, so energy saved to go elsewhere.

 

Why thank you read my other reply below. Chime in folks. Anybody's welcome.

 

Longer duration intake timing causes the engine to breath better at high rpms, but also causes the intake air to move slower at lower rpms, which reduces power at lower rpms where most 4x4ing occurs.

Short duration intake valve opening causes the air in the intake system to go faster, which increases power at lower rpms... but chokes air flow when the air velocity reaches the speed of sound. The speed of sound is 767.58 mph (miles per hour) or 67547.4 fpm (feet per minute).



You can actually calculate when a cam will choke off the air at some higher RPM:
maximum rpm =
67547.4 x average open intake valve area x 12
0.327 x 4.6 liters x 61.02 x 2

 

If you have slightly longer intake valve openings on half of your V8 (e.g. a classic fixed cam), then those cylinders will breathe better at high RPMs and worse at lower RPMs.

In contrast, if you have a variable cam, then you can breathe better at both lower and higher RPMs.