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

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

Post by MASSIVE TYPE IV » Wed Jul 19, 2006 6:58 pm

And it did this afternoon!
I have a 2270 on the dyno and I'm playing with EFI plenums. The engine has stock cooling so I decieded that brent and I would try to see some traits about HP/TQ and RPM with various stock plenums on this size engine.

This was a quickie test so we didn't go crazy, after the results you can bet your ass that it will be getting replicated much more scientifically!

*Stock 45mm T/B used for all tests
*Stock 2.0 914 runners used for all tests

The first plenum we tried was the one that the math has always proven to be the best unit that could easily be outfitted to a 2270 engine, or for that matter even a 2056 and this is due primarily to it's volume. This plenum was factory on the 2.0 914 and it's vastly different volume and design wise than any other factory plenum.

We dialed in the EFI very well and then began power pulls. The power wasn't as good as we expected, but the engine does have a sidewinder header on it and I thought that may be a contributing factor (and it was, just not as big as we expected) here is the power run with the 2.0 914 plenum

RPM TQ HP
2000 113.9 43.4
2500 155.5 74.0
3000 162.2 92.6
3500 147.4 98.2
4000 157.5 119.9
4500 157.5 134.9
5000 147.4 140.4
5500 137.4 143.9
6000 107.2 122.5

This is an older engine combo that has been built for 1.5+ years awaiting an exhaust system, Tiger made this one for us especially for a Type III application, but it does still need work as you can see the HUGE DIP in the power at 3,500 RPM- this is the trait of the current sidewinder and why I do not like it much at all. These power numbers were about 10-12HP across the board lower than my acceptable limits for a 2270 "Daily driver" combo...The playing began-

The 2.0 914 T/B and plenum were going to cause more physical issues for installtion in the Type 3 anyway, so we decided to see what it would do with a smaller plenum and the same T/B. we used the next largest plenum, from a 2.0 Bus engine, it was physically optimum due to it's T/B location and low profile design.

We swapped the two out with no other changes made to the engine, the engine other than having to adapt the 2.0 914 runners to the more narrow plenum. This did add about 1" of runner length as we coupled the plenum to the runner with heavy walled Turbo hose...

As soon as the engine fired the only fuel values we changed was to get a better idle, a quick sweep through the RPM range told us the AFR was very close to that of the 2.0 plenum, all fuel values were left as is...

Immediately I noticed that the throttle response was up, way up and the engine wanted a bit more accelerator pump, so we did so and started pulling.. here are the results of the back to back test. weather did not change at all and 25 minutes separated the runs!

2000 119.3 45.4
2500 160.8 76.6
3000 164.2 93.8
3500 152.8 101.8
4000 160.8 122.5
4500 164.2 140.7
5000 160.8 153.1
5500 147.4 154.4
6000 124.0 141.6

The smaller plenum, with no other changes made more power at EVERY RPM than the larger plenum! The crazy part is the fact that this plenum should be too small for this engine, atleast according to the math!

Note that the pesky 3,500 RPM dip is still present in the RPM band of this test as well. At that RPM the AFR always ran rich and no matter what it could not be gotten rid of.. That is until we swapped the muffler for the original A-1 style that is a straight through design.. We did that and made no other changes and here are the results of that test that was done 5 minutes after the last one!

2000 107.2 40.8
2500 154.1 73.4
3000 170.9 97.6
3500 167.5 111.6
4000 164.2 125.0
4500 162.2 138.9
5000 164.2 156.3
5500 150.8 157.9
6000 127.3 145.5


Voila! The dip is gone!!!!

But the torque curve when graphed with this muffler shows the negative effects of the 44" long primaries of the Sidewinder, even with the better muffler. With this current design of the sidewinder as well as most any other arrangement that keeps the collector in the current location this amount of primary length seems to be the LEAST that could be ran. :-)

Basically this data as well as the other data I have gathered with the sidewinder is indicative of the fact that it will not compliment an engine making it's power at higher RPM. Trying to build a HI RPM combo(or even one that would make power to6K) based on the sidewinder would be a total loss of power at all levels and I believe we will find this even after we tweak the system to an acceptable level- just because of the 44" primaries.

So whats the moral of this story? (and so many others)

Bigger is not better- Not even with plenums, at least on this engine!

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Post by raygreenwood » Wed Jul 19, 2006 7:25 pm

Just from what I have seen factories doing....and some of the "correlations" therin.....I would think that the best sized plenum just in volumetrics for the 2270 is about 1.4 to 1.7L max.
The stock 914 2.0 plenum has plusses and minusses. The vertical inlet makes for a short path to the runner ports. But...without an iternal splitter...or a simple pyramid under the the TB inlet.....at some point...or some rpm.....there will be an ugly fight (turbulence) as the air tries to go roughly 2.5 to 3.0 directions at once.

Add to that....the turbulence from the throttle plate on the 2.0 914 plenum has almost no time and distance available to it to "straighten" the airflow before it tries to enter the runners

The one interesting thing about the side inlet 1.7/1.8 style.....which I always had thought was inferior to the 2.0 914 vertical inlet style.....is that the turbulence from the throttle plate...."swales"....out wide against the wall where the MPS nipple is...and the inlet air temp sensor is. That is why they are put there. It then bounces....and almost centers in the plenum before splitting to the runner ports. It could use a splitter or air straightener of some type too.

All of the mapped characteristics of any given plenum that you use...will change if the runner diameters or volumes are changed.
Beng that the 914 2.0 runners are the largest in dameter and length (and therefore volume as well).....it would be interesting to see the same engine...same plenums.....with smaller or larger runner diameters. All of that affects the replenishment rate of the plenums....through a given TB size. Cool stuff!

To date...one of teh best sizings I have seen from the VW factory....is the 1.7L engine...with the 1.7L plenum and runner set-up. When going to larger valves (42 x36)....simply going to the bus 2.0 TB is enough to retune the 1.7 set-up. When going to a better cam and better compression....just an addition of 2.0 914 runners is enough.

As you note.....all changes again with exhaust. Ray

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Post by Tom Notch » Wed Jul 19, 2006 7:45 pm

I may just slow down my plans on a new intake...... My modified bus one has been done and running pretty good for a few years, and its hooked to the same 914 runners.

and maybe I guessed close enough on the 37" primaries.
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Post by MASSIVE TYPE IV » Wed Jul 19, 2006 7:46 pm

Yep, I'm with you...
The only thing I could attribute it to was flow characteristics of the plenum shape and the T/B location. The turbulance is exactly what we figured was playing a key role with this engine..

So this clearly illustrates that plenum design can supercede volume in it's performance gains. Too many times I feel that guys get caught up with plenum size and end up with weird shapes and T/B locations trying to get the optimum capacity..

The engine idles much smoother without the "choppy" exhaust note that it had with the 2.0 plenum!

On the subject of the muffler differences:
I just noted the oil temps with the last run were 20 degrees lower than they were with the sidewinder muffler and head temps were averaging 10F less as well... :-)

I do believe there is no end with intake and exhaust science, there are literally thousands of combinations of plenum, T/B, runners, primaries, collectors, secondaries and mufflers... After all the playing around we do we haven't even scratched the surface..

I feel sorry for those guys working their asses off to build huge engines just to slap on some generic intake and exhaust system only to kill the entire engine... They are like lost souls that will die thinking "there is no replacement for displacement"

BTW- I have a 2.6L engine in the queue to dyno within the next month. It has the same runners but we have made a one off aluminum plenum for it to house a 60mm Mustang throttle body with shortened 2.0/914 runners. I will most certainly be swapping all of the different plenums and other runners and measuring the differences on an engine over 200HP and over 2.6L... This one has a Tangerine header, so the exhaust will compliment the tests way better than the sidewinder complimented this one... This test will deserve the full logger set up to get all the info possible.. (damn thats a lot of wiring!)

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Post by regis101 » Wed Jul 19, 2006 9:16 pm

What plenum/runner set-up are you using for the shop bus? I want to think you use 2.0 runners with a bus plenum.

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Post by MASSIVE TYPE IV » Wed Jul 19, 2006 9:25 pm

regis101 wrote:What plenum/runner set-up are you using for the shop bus? I want to think you use 2.0 runners with a bus plenum.
Yep, you got it.... I had to do it for packaging, but have been thinking about swapping up to the 2.0/914 plenum...

Don't think I'll be doing that anytime soon 8)

I haven't touched the Bus engine in 5 years..

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Post by regis101 » Wed Jul 19, 2006 11:02 pm

So what is the length of the 72-74 bus headpipes with an off the shelf 4-1 header. Typical set up for the bay bus.

A sidenote is the "Headers by Ed" can design the diameter and length if given ALL the info. I used him alot for the V8 world, back in the day. May be worth a try at least for his input. Hell, I prolly dabble on his website. It's been a while.

That little pyramid piece that Ray was speaking of that needs to be in a 2.0 plenum is known as a "turtle".

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Post by raygreenwood » Thu Jul 20, 2006 6:25 am

Nice part name Regis! Somewhere....with all of the "old" information that is being unearthed these days.....I'm wondering when someone is going to find some of the original research VW/Bosch....did on the original plenum systems for D-jet and L-jet.
We look at those early plenum shapes...and think....Jeeeez....how odd is that? Those had to be very "educated" and studied designs at some level. As I began finding a while ago....they really are not that bad at all.

The ability to keep plenum turbulence down.....and "maybe".... only during the rpm/throttle position phases that correspond to the best peak HP and torque ranges of the engine the system is on.....I have been thinking ...would be a key attribute of any good plenum design.

If the turbulence gets too high......inside of the plenum.....it can keep the air from smoothly entering the plenum through the TB. It lowers the flow rate. If the TB cannot refill itself fast enough......it cannot refill the runners fast enough. Just logic will tell you that turbulence "could" increase at that point exponentially......due to the fact that the incoming air from the TB....would have to split and change directions many times per second....to get to the different runner openings....from the single directional angle it is travelling when it enters the plenum from the TB.

I have been wondering....and playing/experimenting........if a "plateless" butterfly system could alleviate enough of the initial throttle plate turbulence....to make runner port entry.....smoother and less turbulent. All of this would equal...less air friction and more velocity. It would be more like a tapered bullet shaped "plug" that moves in and out of the TB....instead of a butterfly plate. In this way....even the throttle shaft would not be a turbulence inducer. With something like this.....it would be possible to get larger or smaller throttle plate sizes with the same TB...simply by adjusting the rate of pull or lift of the "bullet" in or out of the TB.

I have also been thinking of a "splitter" for the inside of the 1.7L....more of a set of vanes...that pre-apportion the incoming air plume......into "quadrants" ...possibly just left side and right side. This way volume for the 1 and 2 cylinder side....doesn't have to be pulled across the inside of the plenum from the incoming air plume.
Any criss-crossing of air across the plenum to reach a runner port....from the incoming air plume....is turbulence. These would be just vanes....not actual baffels that bisect the plenum. Seperating the plenum into two "seperate" volumes....I feel would negate the ability of the overal volume of the plenum to smoothly act as a resonant buffer for harmonic pulses.

There is also some evidence I am seeing....that having the runner inlet ports one behind the other......in the same plane....with reference to the incoming air plume (ie: this means for instance...that runner inlets 3/4 and 1/2 are in the same horizontal plane)....may cause turbulence at certain rpms......as each runner port fights for the incoming air. The # 1 and 3 runner ports can effectively starve teh 2 and 4 runner ports when rpm....creates a certain amount of overlap of flow into each runner. Perhaps having slight...."scoops"..or runner extensions into the plenum.....say #2 and #4 going upward...and #1 and #3 going downward.....would give each runner port....more frontal access to the incoming air plume.


Some of this "thinking" on my part....is simply from measuring what the factories produced and tuning a lot on it.
Either way....its a 3-dimensional problem......that is time/rpm sensitive. It cannot be thought about in a "static" way. Just a handful of thoughts to get people thinking of the possibilities.

Thanks for the thoughtful testing Jake! Ray

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Post by dstar » Thu Jul 20, 2006 7:20 am

IF by plateless, you mean a slider type, it would STILL create turbulence, just LESS turbulence.

What would be REALLY cool, is to use a multiplate setup that mimmics a camera's shutter. Airflow stays centered and just gets larger or smaller.
:twisted:

THAT would be a PITA to design though......
8)

Don

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Post by MASSIVE TYPE IV » Thu Jul 20, 2006 8:47 am

The plateless idea is something I have been thinking about for a long time.. It would not be that hard to make, but perfecting it would be difficult. I have a design for one that would allow the air charge to be cooled upon entry to the plenum and it is so simple that it could be waterjet cut....

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Post by Tom Notch » Thu Jul 20, 2006 9:15 am

inflatable donut of some sort
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Post by dstar » Thu Jul 20, 2006 9:27 am

Tom Notch wrote:inflatable donut of some sort
Like the shaft seal on our ship!

Excellent idea Tom!

Don

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Post by Tom Notch » Thu Jul 20, 2006 10:30 am

I wonder why our engineering dept. wants me around, I'm not a trained engineer. and I don't have their "box" bounds :wink:

dstar wrote:
Tom Notch wrote:inflatable donut of some sort
Like the shaft seal on our ship!

Excellent idea Tom!

Don
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Post by MASSIVE TYPE IV » Thu Jul 20, 2006 10:50 am

I wonder why our engineering dept. wants me around, I'm not a trained engineer. and I don't have their "box" bounds
If an engineer was here the 2 Liter 914 plenum would still be on the engine and he'd be scratching his head as to why it didn't work, instead of just swapping the damn thing to see what difference was made..

Remember that Bumblebees and Helicopters don't fly on paper, but mother nature puts one in the air and Igor Sikorsky made the other happen and did so against all odds with the VS300.

Paper is good for one thing and thats hanging on the holder in the bathroom!

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Post by raygreenwood » Thu Jul 20, 2006 11:07 am

The design I am playing with....is shaped like a simple double ended rifle bullet. It is tapered toward the rear (inside the plenum) as well.

The widest area.....say 42mm...is what plugs the TB at idle. From the outside looking in.....it looks like the spinner on a jet engine.

As the plug is pulled out of the TB...toward the outside into the intake boot....its cross section gets prgressively thinner.

The crank or arm on the throttle shaft on a stock type 4 TB.....has only so many degrees of turn. I have already made a chart of the available amount of throttle shaft rotation...in 1/2 degree increments....equals how many mm of true open area of the stock throttle plate.
If you are using the same number of degrees of the same throttle shaft rotation for the "bullet"....then it is quite simple to plan the rate of taper.

If you replace the stock throttle shaft arm....with say...an eccentric "capstan"....like that used on some WC TB's....and install a set screw....you can adjust to make any rate of lift...or pull for the "bullet".

You can even get wider TB opening faster than you could with a throttle plate. The "bullet" will probably need a boat-tail on teh plenum side after the taper to keep turbulence very low.

How to install and activate this? Its actually simple.

You need a "hoop" mounted on the outside end of the TB. It will look similar to the hoop on a lamp....that goes around a light bulb...and holds the lamp shade. With me so far? In the center of that two armed hoop is a rod (say 8mm.....hollow) with a compression spring on the outside.. That hollow rod is screwed into a hole drilled through the center of the bullet. The spring rests on a step in the bore through the center of the bullet. Its what keeps the bullet closed.....and is the return spring.

The bullet is moved....via a cable running through the top arm of the hoop. It is attached to the bullet. the cable is attached to a cable capstan that is mounted to the throttle shaft.

You step on the pedal...it pulls the original cable.....that turns the "disc" or capstan atached to the throttle shaft. The cable that moves the bullet....is mounted at 90* to the throttle pedal cable. The distance from center of the bullet pull cable......meters the eccentricty of the disc....and changes the rate of lift to fit any engine.

This means.......that even the throttle shaft will not need to protrude into teh bore any more. Just need a stub shaft up top.

And.....you move the TPS from the bottom of the TB.....leave it upside down to mount on that D-shaped stub shaft.....make a bracket for it.....voila....TPS still works too.

Been thinking about this one for a while. It would be very cheap to build.

The bullet can be made on a lathe...with just some simple spot drillings for idle bypass. It does not even have to be metal. It could be high temp plastic.

I can drop sketches to you (after I clean them up) in a couple days Jake. Ray

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