Inducing swirl in a 4 valve head

[twimcam]

Yes, at high speed the intake valves have equal timing. There is only one high speed lobe. Instead of swirl flow, it will now have tumble flow.

[oldeskewltoy]

There was/is a 4AGE camshaft design for this... They are often called "Tri-Flow".

The thought was to help induce swirl in the big port 4AG head. The problem... (as I saw it), was they just cut the 2nd lobe (or was it the first) as you went down the camshaft... NOT taking into account the original 4AGE used TVIS. For those who don't know TVIS, it was an internal set of butterflies that opened a 2nd manifold passage @ about 4500 rpm



In a TVIS, engine, I'd think you'd want to match the earlier lobe to the non-butterflied valve, and not just machine a lobe without thinking about airflow



Note valves 1, 4, 5 and 8 don't have butterflies. I'd have cut the cams to favor the open passage... partly to improve tumble, but also because the TVIS 4AG head also has offset injectors favoring the butterfly closed ports. By opening the straight shot valve first, you get some air swirling when the 2nd valve opens "dumping" most the fuel into the chamber... Oh... did I mention this is batch injection so the fuel just sits on the back side of the valve.....

[Notchback]

Many OEMS do it - all of the Honda K series low speed lobes are staggered for swirl, even the high performance variants.

Thanks for sharing this. I will keep an eye out in the future. The ones I built in the past were stockers and I never had a reason to degree the cams so it went largely unnoticed.

[Notchback]

Look at Honda's Vtec system. They've been doing it since the early 90's. Two different cam profiles for each intake valve to induce swirl for low rpm fuel economy running. For full power, tumble flow is preferred.

Really? I wasn't aware of that. This was on earlier models from the 90's? I have built many K20Z3 engines from the '08 and newer and they operate on this principle: https://www.youtube.com/watch?v=stJM9EvZRgQ - A non-staggered design with high or low lift/duration only.

For full power it seems low tumble has been preferred when looking at this picture of a 2 cylinder research engine modeled after a Formula one design from the early 2000's. You can clearly see that flame front travel is faster on the low tumble head. I believe the tumble figures were .7 for the HT head and .3 for the LT head. I know that efficiency was better on the HT head but BMEP was higher on the LT head all else being equal. Also, note the flame front travel is more even in all directions from a horizontal point of view on the LT head. The degrees in the pic are crank angle using 180 degrees to describe TDC. It takes energy to make swirl and tumble, energy that could otherwise be used for flow if you don't need the added swirl or tumble for your particular app.

tumble.jpg

Very interesting diagram. Are you at liberty to say where is it from? I would like to read more.

The SAE paper is number: 2002-01-0244