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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?

Pretty poor design from what my research is showing. The flow is reaching 0 by the time it hits the back wall on the plenum. The flow then also has to go around a piece of angle iron welded into the bottom.

I would like to add small flutes in the bottom and cut the top off and angle toward the front. This way the flow would come in and angle down to the flute. Thus giving a nice smooth flow.

Now to measure the flow to both cylinders I suppose I could use the inspection ports to mount 2 different gauges to measure the boost of the front and rear.

I am up to hear as what you think about this matter Karzza.

karzza you are way further in this then we are.

I accept any and all wisdom on the matter of the plenum.

I understand that the bigger plenum will allow for the more upper end of the HP range.
A smaller plenum will allow for the lower end and torque help.

Then the how to find the happy middle and correct flow is what we strive for.

This is one big learning process.

Tying to figure to Cubic Displacement to use 1/2 to 2 time the displacement.

I am going for 3/4's of the Displacement.

Learning the intake runner length for flow and cooling of the flow of air.

My head hurts already!!lol
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Correct about the bigger plenum will increase the lag.

I feel that Trask went with the smaller turbo so as not to have a lag.

Yes it is there but not as much as the bigger turbo.

There are other turbos out there with true ceramic bearings in a bigger turbo and will spool up trwice as fast as the 25.

Well the second option would be a Y set up. I was thinking about this before I saw Karzza's intake.
I think we could do this pretty easy. I would like to put a spike in the center of the inner Y to devert the flow of air.

If we was to go with they Y set up then there would be no need to change the air box cover.

I am hoping that Karzza can post up some pics and give some more insight to this.

The timing of the valves openiong and closing are just creating all kinds of problems.
How many time have we heard of the front cylinder going out. This whole time thinking the boost was being pushed in the front cylinder when in reality it was not.

This is just my opion. When looking at the flow of the air it takes the least amount of resistance. The rear cylinder was taking it all in and leaving the front to be lean.

This is going to lead to some people viewing this.

I do not by any means permit the use of my ideals and thoughts.
This is to protect my future projects.
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Hmmmmm. Interesting. Why could'nt the stock airbox be used? Might leak, but, so what? My SC just uses rubber elbows. No seal around the bolt heads. Hmmmmmmmm. Joe
Joe it is not tht easy.
Pressure is pressure yes.
But the flow of air to the intake is another matter.

Take a look at this site and scrool down a bit and look at the flow pics.


The Y set-up is a way of providing a chamber for each cylinder.
Thus allowing the turbo to fill the chamber above the TB's.

I understand what you are saying.

The more volume over the rear is better. Just trying to minimize the difference.

I suppose if you where to tune the runners at different length you could greatly minize the difference. But this is not good. Long runners do nothing but hurt the intake of boost.

So to find the sweet spot that takes care of both the front and rear would be seperate chambers period.

Since we only have one turbo we have what we have.

Do you have any pics of your plenum?
Did you reduce the front inner diameter of the chamber over the TB?
Is your Y set-up offset any at all?
Is the inner diameter tapered to a smaller diameter?
I can see that the diameter is quit larger then the Tb openings.

My head hurts!
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Total novice here so please excuse, but why not a single TB with a y and then tune the length and shape according to each cylinders needs?
If you had one single TB you would not need a Y!

So now the Y would be below the the TB's. Correct.
You would still have the same timing of opening and closing of the valves.
Just talking out loud here...

have enough volume not to hurt the engine as it daws it in.
to have a limited amout above this so there is always enough there
if to big it will hurt on the engine response (slow)
if to small it will increase velocity of the incoming air.
high velocity will lower the boost...Not good.(faster response)

as the engine is boosted it rotates the crank faster allowing the engine to pump more air and faster.

this is where you need to have a plenum to store more air then what the engine cd is.
but how much more...
more then the amount of air passing through the engine at WOT!
so at this speed of transfer the runners are not going to big deal.

but to have a turbo that can fill the plenum as fast as it is removed.

air has to flow smooth.
so any air moving across a wall will have restriction
restriction slows the air down.
no restriction means smoother flow.
Y set-up straight into TB's

air turbulence...
No turbulence means less atomization of the fuel and mixing the air
More turbulence means more atomization and mixing of fuel
once the valves open the force of air is moving into cylinder bouncing off the piston, mixing up in the chamber. very nice...

Y set-up vs trasks

better overall flow of air.
less dead space inside.
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Hmmm, then would the distance from the head to the single TB give you a tuneable chamber, or does it have to be before the TB ?
air flowing at the speed of sound...:D

wish the rod went that fast.
This is an interesting thread, surprised it hasn't really been discussed up till now. I know we talked about it at Lanes that weekend will be interesting to see what comes from it.:popcorn
A new plenum design!!!!

I hope :deal:
You guys are killing me!!!!

I should have known all the BB guys would be all over this.lmao

At least I know someone is undserstanding what I am saying.

So now you all put your heads together and solve the issue with one turbo hahaha.

Jan yes I do agree with you on this.

I was thinking about putting a expansion chamber before the split in the Y set-up.
split the expansion chamber in half and drill holes in the part that splits the chamber.
Finally you ***** guys have started to think about the plenum capacity issue.
Have you ever logged Your boost separately from front and rear cylinders?



ding ding ding....
Yeah I know...

:rofl: Great the next thing is gonna be be twin turbo supercharge it!

Actually I was wondering if a center feed plenum with a splitter built in wouldn't work as well.

see if I ever help you...:D
PM sent Greg
pi × r 2 × h
pi × r 2 × h
just the formula for volume.

I have been amazed by turbos - when I was maybe 20ish I put a turbo off a vette on my VW bug. It was fun for about 6 months!
The turbos on 911 Porsches back in about 76 would come on like an animal.
My Audi's were amazing with the 5 cylinders.
Watching truck and tractor pulleys using every combination of turbos.
And my truck new from 1997 has been tweaked and still out performs any new truck AND it's still together!
Makes me know I know nothing! I have tried to understand all these different applications and plumbing.
Probably not adding much to this but, the plenum and getting to it seems to be the area for improvement. Space and aesthetics seem to be a challenge, adding a better intercooler with all the designs out there sure makes me think we could change up the direction of everything.
I am looking into it Jeff...

Stay tune!! :D

EDIT: To make this really work you need a really big one like karzza!!!!!

trust me...
pi × r 2 × h
just the formula for volume.

Total Volume = 160.072 cubic in.

Plenum = 113.142 cubic in.
Charge tube = 35.343 cubic in.
Hose = 5.303 cubic in.
Risers x2 = 6.284 cubic in.

1130 cc = 69 cubic in. x 2 = 138 cubic in.
1250 cc = 76 cubic in. x 2 = 152 cubic in.

So if the rule of thumb is 1-2 the engine displacement I would say we have plenty!

So then with the the timing of the v-rod how much do we need for the front and the rear?
Assuming you are redesigning!

Are we learning anything!!!! lol
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I see what you are doing.
FYI...You are not at a 8 psi until you are at WOT and the turbo has enough time to pressurize the hole cylinder as the valves open.

Thus 8psi in plenum and 5 psi under the TB's...

The hole purpose of the plenum is to crate a reserve of air for the engine.

With all the research I have done, There is not formula or set amount of volume for a plenum.

Old school was to do 1.5 to 2 times the volume.

my nopi tunner guys say .5 to 1 for our motorcycles

I really think with this engine it is the nature of the beast.
The timing does not help at all and just make thing even more complicated.

So let me go one step further.

1130 = 69 /2 = 34.5 cubic in per cylinder...
Now come up with a way to fill each cylinder with 34.5 cubic in.
It is now easyier to create a reservior for both intakes.
The charge tube alone has almost the same amount of volume.

The ideal is to creat a runner a smooth as you can and without restrictions.
Even a straight pipe has restrictions along its sides.
There is no way of getting around this.

But you can use designed air flow to get the most efficient way of getting the air to the intake.
This is why you see different shapes and sizes of the plenums.

There is nothing wrong with the TRASK plenum design.
I am 100% sure they did pressure testing to verify cylinder pressures at WOT.
I have been told this by Nick himself.

I am want to change the Plenum shape and size to make it more efficient. I also would like to add a Cooling method at the same time.
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I need to add alittle more.

So now that you have a smooth runner to the intake.
How do you get the air to mix with the fuel.

The more you can create turbulence in the cyliner the more atomization = more power you can have.

This is very important to do.

The more you create turbulence the more heat is being made.

The more you can cool the intake of air the better the power.

Question is how can you do all this at the same time.

Swamp keep in mind this is forced induction.

I have a design ideal in my head.

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