Smaller plenum = more power?? It can!(sidewinder test too)

Post by **Piledriver** » Fri Jul 28, 2006 4:51 pm

Back to the original topic, try adding ~8-10 inches of TB sized steel tubing between the TB and plenum (side intake plenum, not the 2.0 Porsche one)

This should work to effectively eliminate the turbulence off the butterfly...
And allow some tunability (change the length should have various effects)

Ray and I have discussed this ages ago...
http://shoptalkforums.com/viewtopic.php ... sc&start=0
We start beating it to death at the bottom of page 1.

IIRC, theory says ~16-19 inches should be ideal, the 40mm diameter is about right and not quite as critical.
(Ram tube, the other part of a Heimholtz resonator setup everyone forgets, but is practical in this application)

(Yes, put the TB at the END of the tube)

Perhaps it's time to try a collector from Headers By Ed as a Plenum?

BTW, I need some different runners.
The 2.0 Bus ones are necked down ~1/4", all same size at ends IIRC.
(Plan on keeping the 2.0 bus plenum)

Racer Chris · Post by **Racer Chris** » Sat Jul 29, 2006 4:41 am

You're suggesting using a collector in reverse to split the air into the runners as it comes down a long tube from the TB - ie. an intake header. Very interesting. The splayed 2-1 collectors I use might be beneficial to keep the profile and the runner length down.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Sat Jul 29, 2006 9:35 am

Very interesting. The splayed 2-1 collectors I use might be beneficial to keep the profile and the runner length down.

I had the exact same idea....

Chris, can I borrow some stuff to try this with???

Post by **Piledriver** » Sat Jul 29, 2006 12:27 pm

Added some info/edited previous post.

IIRC somewhere it was discussed using 2 smaller plenums (180 degree timed) and 2 smaller TBs as being an optimal solution.

Each 2 cylinder plenum would have to be a larger percentage of the cylinder volume, but this setup has potential packaging advantages on an upright converted ACVW, as 1/3 and 2/4 are connected. (F&R of the shroud, no crossover) A pair of stock TBs should be great, even on a huge engine.

Yes, Chris, the original concept was exactly an intake header.4>1, with a slide-fit dual tube (collector)//plenum to allow easy plenum volume changes for testing.

Jake---You should still try the ram tube setup on the 2.0 bus TB, with the relocated TB. There is no reason that shouldn't work almost as well, and it's easy-peasy as Don says, as well as the length being an easy tuning knob.

raygreenwood · Post by **raygreenwood** » Sat Jul 29, 2006 2:53 pm

Its worth a try. But some things to consider. The volumes of plenums need to be sized to do several things all at once for each cylinder they are feeding. And....they need the volume to do those several things.....in an overlapping manner. Therin...lies the difficulty of getting your head around the problem. It is multidimensional.

In the singular form...for each cylinder....the plenum must provide enough air (thinking in very slow motion right now) to fill the volume of the cylinder as it is drawn in through the open valve with the cylinder on the intake stroke .
If the cylinder were just drawing from a perfectly sized runner tube....that tube would then have "0" atmosphere...and be under vacuum. So....the plenum volume must be large enough to replenish that runner. Now...all four runners are not trying to replenish at the same time. But due to the amount of time it takes for that air to travel the length of the runner (small amount of time that it is), be drawn into the cylinder and for the valve to slam shut ....you effectually get some overlap of air movement. This is time compression due to RPM.

Wether it is fair to say that you get the equivalent of 2 or 2.5 or 3 ...full or partial runners worth of air volume movement at a time...will be mainly a function of cam duration and stroke. Of course at some point.....runner volume vs cylinder volume vs plenum volume has effect on that also. But when that starts affecting time...its actually a restriction you have.

For example...if due to space constraints...your runners were of too short of a length....and therfore their volumes were too small for your application......then the cylinder is going to take the air it needs anyway. It does this by increasing the velocity....by drawing the same amount of air through a smaller volume of space.
In turn...to replenish what was taken...it draws more air faster from the plenum. The TB is then forced to flow more air faster to replenish the plenum. Yes....velocities are up...but the whole pelnum system will be under "tension" so to speak.
With that higher velocity of air movement......comes higher velocity stoppage of air movement when the valve slams shut. That creates higher velocity reversion to the plenum.
Some of that can be alleviated by a subtle diameter increase elsewhere in the system. For instance....a slight diameter increase in the runners would alleviate a bit of velocity/peakiness because the runner volume would increase. But then....you have to have the volume in the plenum to replenish the higher volume of the runners.......or......a slightly larger TB to make sure that the plenum is simply more easily replenished.

Where this is rambling going?....is that in a plenum system.....subdividing into two plenums would take away a very important factor.
The volume of the plenum is drawn from by several cylinders at one time in an overlapping fashion. In direct opposite timing....but simultaneously.....that same volume is used a ....damper.....for the reversion pulses of the cylinders whose intake valves are slamming shut. Seperating the volume among two banks....negates some of that damping ability.
I would think that it would only operate (the split plenum).....if both of the plenums were made a bit oversized. Therin......you would lose some velocity that way...and then would have to go to a smaller TB on each side...much smaller than you might think...to keep vacuum and thus velocity up where it needs to be.

Short of actually splitting a plenum.....I think it could be "fenced" a little and have great effect...much like a dual plane carburettor manifold.

For example.....on a 1.7L type 4 plenum....using what Piledriver was speaking of with just a plain throttle plate type TB.
By adding 10-12" of tube between the TB and plenum would, allow the TB plate plume of turbulence to dissipate. From what others with more experience have told me....it takes roughly 10 times the TB diameter...in distance...to dissipate the plume of turbulence.
Of course...now your plenum volume is artificially too large by a good amount.

But....lets think of several things that we might do inside of the plenum to get rid of some excess internal volume. (1) I would extend the runners into the plenum. Then cut out the side of teh tube....where it faces the incoming air from the TB. You are making directional scoops. Then......angle each one either up or down slightly so none of the runners are masking each other from direct access to incoming air. From the point of view of looking from the TB back...the runner pairs would look like "donkey ears"....with me so far?
(2) In order to keep excessive high velocity air from wanting to pass over or under the donkey ears and proceed toward the rear of teh plenum where the cold start valve is......you need a hump...or smooth ramp....on the floor of the plenum and the rood of thr plenum. This would be a horizontal wedge running from side to side. It would reduce some of the excess volume you now have...and force the air into teh center area of teh plenum without changing its direction....so it is more easily accessed by the donkey eared runner extensions.(3) Since you have a firing order of 1-4-3-2....it would we be an assumption that the cylinders would draw in this order.....all overlapping turbulence aside for the moment. To keep side to side, plenum crisscrossing pulling of air down to a minimum......I would tilt the extended runner openings (donkey ears) of say...1and 3 upward and 4 and 2 downward. Then run a horizontal bisector plate between them. This is not a full bisector...end to end on teh plenum. It is more of a "splitter" or air guide. It apportions the incoming air into two groups . The plate would start right before the runner openings of 1 and 3...and end right behind the runner openings of 2 and 4. This allows teh whole volume of the plenum to be reacted with....by reversion....but helps to guide the incoming air to where it needs to be.

To do this kind of experimenting....you need to take stock plenums and sperate the weld cleanly with a band saw.....so you can re-seal them back together after you have made internal shape modes with hand shaped epoxy....and then test them. Sorry for the length. Ray

Bleyseng · Post by **Bleyseng** » Sun Jul 30, 2006 7:43 am

Good post Ray!

Have you ever figured out the % of the metal in the diaphrams?

Racer Chris · Post by **Racer Chris** » Sun Jul 30, 2006 9:02 am

What I am wondering is, can a plenum-less 4-2-1 intake header be made to enhance a broad range of engine performance in a similar way that it can work on the exhaust side? Or perhaps it would help to add a plenum immediately after the TB and before the primary runner, similar to the way a 4-2-1 exhaust likes a "resonance chamber" at the end.
If so it would make design of a single TB intake for use on DTM cooled engines much simpler. It would also simplify turbo installations.

farmer · Post by **farmer** » Sun Jul 30, 2006 9:22 am

I doubt that Chris. Because none of the factory cars, that I know of is using this setup. Not even Subaru. To my knowledge, everybody uses a plenum, or runs straight port on port.
but it is relatively simple to try and see if there is a gain in it.

T

Post by **Piledriver** » Sun Jul 30, 2006 10:11 am

There aren't any factory cars (other than the Subaru) that CAN have 20+ inch runners, and none have engine compartment room as a 914 does.

I'ts a worthy experiment, but mind you, the collector IS the plenum.

914fan · Post by **914fan** » Mon Jul 31, 2006 8:22 am

I thought that on turbo applications the intake was not as important due to being under pressure not vacume.
As far as a reversed header for an intake I think it would work. Think about it. That is what an intake is. you have the air cleaner (muffler), hose to throtle body (pipe from collector), Intake plenum (lenghtened collector), and runners (pipes to colector from head). The only diference is the throtle body, and that the colector should probable be larger / longer to increase volume. You could even use a 1-2-4 and pair the cylinders in the 2 section to reduce the reversion or dare I say take advantage of it. That would be just like exhaust scavanging. I would be willing to bet that your curent tangerine system would be a good starting point, as far as lengths and deminsions. You could place the throtle plate where you would place your first muffler.

Post by **Piledriver** » Mon Jul 31, 2006 9:09 am

Ideally, the NA "boost" from a perfectly tuned intake RUNNER would be ~10% at the first resonance freq of the primaries, and ~%5 at the second. Given a ram tube, a little more is possible.

A plenum sort of decreases the "Q"(quality) of the tuned peak, and increases the width of the boost peak, reducing the amplitude, and posibly allows some "crossover" effects where the reflected pulse from one intake event boosts the adjacent cylinder when its intake opens.

ON BOOST, that 10-12% is ... less important vs pressure, lost in the noise so to speak.

IIRC, the factory runners give ist tuned freq at ~3200 RPM... second at ~6400.
(10%/5%) and the first one is a real benefit, the second COULD be on a modded motor.
The ram tube tuning can provide an additional peak, or reinforce one of the existing ones.

OTOH, a properly made, tuned setup would surely help spool up and off boost drivability greatly, have perfect air distribution, and have less restriction, so more airflow for a given pressure, (Turbos are all about airflow, boost is a secondary effect, max airflow with the least boost possible is the better way to think about it, less pressure == less heat)

The nice thing about a ACVW is that the runner lengths are long enough that BOTH the first and possibly second tuned frequencies are at useful RPMS, at least for a street engine.

On most engines, the runner lengths are too short to have anything BUT the second/third frequency (~5%/2.5% boost, theoretical respectively) so it's even less of a big deal.
(Due to packaging issues)

914fan · Post by **914fan** » Mon Jul 31, 2006 9:33 am

I agree that the intake in important on turbo apps, and that a better intake design would allow for more airflow. Where I was going is that due to the fact that a turbo application in under pressure (just like an ehxaust system) you can overcome runner length/ plume volume issues. On a N/A system those are far more critical and not as easy to fudge. I could be wrong. I was trying to say that perhaps the first system could be made in comjunction with Jakes turbo developement. 2 birds, 1 stone. IF Jake sees potential with it then more R&D could be devoted. However if in a pressurised system it does not work, them it *may* never work. Atleast not without some serious time and effort (MONEY). However using the basic design lengths of a known good exhaust could give you a head start on the development. What goes in has to come out. If it is good enough to handle the exit, it may be good enought to handle the intake.

On a side note does anybody know that volume there is on exhaust. Say you intake 1 liter of air/ fuel at the proper mixture. After combustion does that increase. Heat increases air volume right? If there is a set amount of increase in volume, say 15% then you could reduce the intake track (based on a known good exhaust) by that amount and perhaps still be good.

Also if the throtle is inline with the colector would that decrease the turbulance. Or does bouncing off the intale plumn (1.7) help?

raygreenwood · Post by **raygreenwood** » Mon Jul 31, 2006 11:55 am

(14fan....you may be hitting on something that may help to answer the question of Racer Chris. The experiences of many people ...suggest that proper volumetric sizing may be of less relevance in a turbo application. Its quite possible they are 100% correct.
I have always contended....that poor volumetrics are poor volumetrics. I would think that the pressurizedd plenum of a turbo engine could negate "SOME" of teh poor volumetrics....but that it would work even better if it were properly sized and had proper geometry. After all.....even though teh plenum is pressurized with a turbo....a restriction is a restriction.

Racer Chris....I think the main dynamic difference...is that an exhaust is a pressurized environment versus....a vacuum/partial vacuum environment for teh plenum. One is pushed...the other pulled. If we can isolate what differences each dynamic really has to each other...and what similarities....you may be correct that applying exhaust principles to a plenum could solve problems. Its definately worth just trying out. Ray

914fan · Post by **914fan** » Mon Jul 31, 2006 12:21 pm

I agree. Its worth trying out.
Chris, I would love to test it for you. You could send a normal tangerine and an intake tangerine. I wouldn't mind the work of testing

Plastermaster · Post by **Plastermaster** » Sun Aug 27, 2006 3:18 pm

www.shoptalkforums.com/ merged intake header?

Here is another thread on the subject.
Ron

Edit-- I cant get it to turn up as a link.