Plenums

Good and equal WOT air flow in plenum is important to get maximum power.

There exists another point in a asymmetrinc V2 (one crank pin).
Stock camming and stock timing

Front cyl in TDC.............0 deg
Front intake opens........342 deg
Front intake closes........590 deg

Time for fill plenum.........52 deg

Rear intake opens.........642 deg
Rear intake closes........890 deg

Time for fill plenum........172 deg

Front intake opens.......1062 deg

What I have been trying to say, in case of asymmetric V2 engine a turbo has much more time to generate boost for a front cylinder than for a rear cylinder. That's why a relative high plenium volume is needed, to reduce difference of conditions for cylinders. All volume between compressor wheel and butterfly is countable.
This is raising up while more boost, rpms or cubics.

There is a little bit same situation on exhaust side.


While you have VRFI or T-max, autotune is taking care of different need of fuel to maintain a target AFR individually (trim) for both of cylinders.

I do not have fact, how much more power a front cylinder is producing in your case, 10hp I guess.

I would like to share my PERSONAL thoughts about a plenum capacity.

As a general "thumb rule" for equal firing interval engines:
4cyl engine, plenum volume 1x engine displacement
1cyl engine, plenum volume 4x engine displacement

so
2cyl engine, plenum volume 2x engine displacement

Our engines are 120deg/720deg = 17% asymmetric, from 2cyl towards to 1cyl.
By taking it into the consideration our plenum would be 2.4x engine displacement.

Too small plenum volume causes unbalanced VE between F and R.
Too large plenum causes lag when spooling up. The difference of spooling lag is unnoticeable, while you are in correct area of plenum volume.

If I would make a new plenum, I would choose
plenum volume 2,5...2,8x engine displacement.

An airflow in a plenum and intake ports is better to be linear.
A good turbulence in a cylinder guarantees smooth and equal mix.

-


RSC was asking about my current setup,
I'm a fan of fluent Y-idea instead of a box.
There is a 5 years old picture of plenum I did at that time. (some more pictures in my gallery)
At the moment I would do something else. For example the tight curve in the down pipe, just after compressor, is bad.


A pipe diameter is generelly 50mm, except separate sections for F and R are made of dia 60mm.
Volume of the pipe mess, including a cooler, is around 3500cc.

For 1130cc it was 3.1x engine displacement.
At the moment for 1487cc it is 2.4x engine displacement.

I have logged F and R port pressures till 12Psi (no more scale in my tool) and around 8000 rpm. They stayed equal.
At the moment I do not excatly know, how is the balance of F and R VE when 9000rpm/14Psi.

here is a draft of the "multi purpose flange"



open questions:
- IAT, any idea where to find a suitable threated sender
- how to seal a plate/box bolted on the flange
- possible BOV connector(s)
- breather connectors for normally aspirated solutions. (in every case connection via an oil catch can)
- can NOS injectors be fitted (90deg) like they are in the picture
- how much it can cost

What else should be included to the "multi purpose flange"?

Met member Mukle tonight...here is an output couple of hours later:notworth:.

Now the IAT is palced.

Is there still something to improve, or shall we start production?