Beams velocity stack length tuning

[timbo]

That manifold would be great for the fact that you would clear the brake booster.

[LittleRedSpirit]

Curves in inlet ports I believe can help acceleration of the charge (torque) and also help mix the fuel into the air better I thought. I may be wrong but its what I've been told. Playing with where the butterfly and injectors are is also able to change the result. As I understand it, the closer the injectors and butterfly are to the head, the better (more efficiently) the engine will perform at low rps. Conversely, if you move the butterfly and squirter's farther away then you can have a better fuel mix at high rps and a smoother less turbulent air stream. I've tried to design my 2az manifold to give balanced performance but specifically to peak its efficiency at 6500rpm. The injectors in the head that shoot right at the valve will be good for efficiency, but I may look at introducing a different fuel or fuel source further up the inlet some day. The engine isn't designed for high rpm like a beams so this may prove unnecessary. I just have to see how it goes.

On the 2az, which I know is quite different to a Beams I ended up going with the butterfly 192mm from the valve top (as its about as close as you can practically make it), and a total average inlet length of 345mm from the back of the valve. I have about 5 degrees of tilt to bring the throttles down, but you can still clearly see the valves through the trumpet with the butterflies open.

Also, the length of inlet and butterfly position are related to inlet cam timing, and there are certain guidelines about the inlet length vs rpm and cam timing that you can follow. See the table below.

My engine with vvti all the way on advancing the inlet cam, it will close at 20 after BDC, which even though there is no line on the table, we can extrapolate as being suitable for around 2000rpm. Then with vvti off allowing the cam profile to shine through and close 60 after bdc, we can see that my length is suitable for around 5000rpm. By reducing the trumpet length I can Push this to a matched length for 6000 or even 7000rpm. I've been after a torque monster type set up with this, hence why my inlet is designed to be most efficient with standard cams and to highlight the peak torque range of the standard power delivery, which is listed as:

Thanks to Wiki: "Output is 117 to 120 kW at 5600 rpm with 162 lb·ft (220 N·m) of torque at 4000 rpm"

Since the 2azfe is a fairly long stroking motor to begin with, I don't intend on rotating it faster. I'm just increasing compression to 11:1 from 9.5 or so, adding itbs and keeping a fairly long inlet that is a little more focussed on the torque than hp output, but with room to tune and adjust.

My throttles have been spaced apart an extra 10mm over standard because that is the difference in port spacing between a 20v and a 2azfe. This allows me quite a big trumpet bell mouth and still 3-4mm in between each one. I wonder what effect this has. I can try my T3 trumpets as a comparison later I guess. The trumpets are just under 100mm long, maybe 94 or 95mm.

I found this table useful:

[LittleRedSpirit]

Something else which I've always had a theory on that Id love to see you guys test on the dyno, is a measure to enhance the reflection of pressure waves back down the inlet.

Remembering back to science class aa a boy, I recall that a parabola will gather or focus light to a point (like car headlights), giving it a directional focus. Could a parabola do this for any waved energy, eg air pressure waves. If so, Is there some benefit in having a parabolic cap above each trumpet built into your trumpet enclosure to enhance the reversion of these waves. I know some makers of ITB trumpet style airboxes, eg Jenvey, mention the advantages of having a flat face opposite the trumpet opening to reflect pressure waves, so I wonder if a parabola would do this more efficiently?

Thoughts?