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69937 Views 402 Replies 52 Participants Last post by  mukle
Do we really need them?
This is the question that I am researching right now.

Turbo or Supercharged piston engines typically use many cylinders arranged in-line and one or two superchargers. Superchargers deliver air at a relatively constant rate, while cylinders demand it in a varying manner, as the valves open and as piston speed varies through the stroke. Simple direct ducting would give problems where the nearest cylinders received more airflow. The pulsating demand from the cylinders would also show problems of either pressure waves in the duct, or a shortage of inlet air towards the end of the inlet phase.

The solution is to provide a large-volume plenum chamber between the inlet and the cylinders. This has two benefits: it evens out the difference in path restriction between cylinders (distribution across space), secondly it provides a large-volume buffer against pressure changes (distribution over time
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Finally you ***** guys have started to think about the plenum capacity issue.
Have you ever logged Your boost separately from front and rear cylinders?
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.
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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

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.
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I think there would be markets for a billet CNC plenum flange.
- 15-20 mm thick flange tovards a throtle body
- internal channels for IAC air in the flange
- 80mm long own pipes, dia 60mm
- a place for IAT
- a tube connector for a waste gate etc

Everybody could continue to build up a plenum how ever they want, Y-shape, a box, a barrel, left hand, right hand etc.

Normally aspirated guys could use the flange with special air filters or a scoop.
a reservation for NOS/meth/water injectors is good point RSC.

btw. I know a good CAD desiger for the plenum flange project. He is the member "mukle" here:D
About the cooler.
There is no sense to place an "air to air inter cooler" under an airbox cover.

But an "air to water cooler" connected to plenum, a small pump and a "water to air radiator" in some unnoticeable place would be a clever solution. Yes, some extra weight again.

It is another story, like a good turbo exhaust manifold.
But let's stay in a plenum.
Would someone supply all the dimensions of the most popular NOS injector in V-Rod.
NOS is illeagal here...like a turbo :cupcake
This project will be an open code.
I have an idea about the "multi purpose plenum flange" in my head. We try to meet with Mukle at next weekend and then he hopely can visualize the first idea by CAD. It will be a starting point for the further forum discussion. The flange will be CNC machined one piece aluminium part, for sure.

Does someone have "99499-04 Electrical Diagnostic Manual", is there some IAT resistance vs. temperature test values available?
We would need a 1/8 NPT threaded IAT sender to place it to the flange.
I got the measured plenum flange drawings done.
Muckle will do a 3D CAD model and then we can start to talk.
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"?
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Would these be sealed with bottom o rings?

Also wouldn't it be neater more functional and easier to just build it as 1 piece including the throttle bodies?
for sure, but I think it would be too expensive way.
What would happen, if a lenght of separate runners would be 10" istead of usual 2-3"?
Would there be a lot of turbulent pumping from a runner to an other?
Thanks Doug.
More arguments please?

Btw, IAT issue is solved. I found a very suitable sensor from KMS. .
Have to plan how to place it to the flange

Delphi or GM do not have correct resistance vs. temp curve for V-Rod.
Can you elaborate on the temperature curve part? I would have thought it sent the temperature to the ECU & it did the correction to AFR based upon temperature ?
I'm not sure what do You mean.
Look the picture in the post #97.
KMS has about the same temp vs. resistance (and volt) values.
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:D?

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Will this fix the unfiltered air problem at the TB?
Yes...and a boost leak via open IAC as well.
(IAC does not park to 0 step while throttle is added. It stays where it was on idle or goes to defined XX steps parking position)

a)Why the rear intake and not the front?
b)Have you come up with a base plate to fit over the runners?
c)Are you intending to weld onto the runners with the Y set up?
d)If a person is spraying Meth or Nos, how is this going to affect the IAT sensor. You will be spraying right on the sensor.
a) In the rear intake there is more space around and all screws are not on IAT's way.
b) no, You can design it. At the moment I'm stucked to the Y-idea.
c) I will start with 90deg 60mm silicone elbows from the flange, then 90deg 60mm aluminium elbows welded to 30deg 60mm aluminium elbow and the last a silicone elbow to IC.
d) yes, it could effect by increasing fuel. NTC part of IAT appears very little in a port and airflow takes meth/NOS mostly downwards. Better ideas for the IAT location with extra injectors?
Yep, my idea is similar plus some additional options.
We will produce 10pcs of them.
what do you think the cost will be karzza
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