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

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Piledriver
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Post by Piledriver » Mon Sep 25, 2006 8:59 pm

The following info may be useful to someone making calculations based on the Helmholtz math.

2.0 runner length, valve face to 2.1 Vanagon plenum (Or bus 2.0, same width) is ~21 inches, measured with a huge ziptie inside.

The runner area is approximately 1.6 sq inches. (~37.5mm ID)

Peak torque (.6 Mach) for this runner area would be ~4200 RPM on a 2270. (Check Jakes posted dyno numbers... Good match)

Helmholtz tuned length depends greatly on cam timing, more cam=LOWER tuned RPM for a given runner length.

I propose that the Sidewinder would respond very well to LESS ex timing, as that makes the runners "shorter" tuning wise.
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Wally
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Post by Wally » Tue Sep 26, 2006 1:47 am

Stop theorizing, start practicing!
T4T: Type 4 Turbo engine, under construction

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Post by Piledriver » Tue Sep 26, 2006 2:31 am

Preparing to practice...

Jake is unavailable right now for good reason, I can wait.
Money's in the bank last I checked.

I'm starting to think the Wasser/Vanagon might be a better choice for the setup I have in mind, as it's exhaust ports don't suck, and it is less likely to have cooling issues, and a top of the line full custom SS exhaust can probably be had for a lot less than any decent T4 setup.

It could also really USE a fuel economy boost...

Would almost certainly require custom pistons tho.
(not sure how much dish I can carve out of AAs TF 94Bs)

A set of Euro spec (DGs? DJs...cant remember, 10.5:1 CR) would just about do, but they seem either unobtanium or ~ as expensive vs full customs, without the forged goodness...
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Post by Twystd1 » Tue Sep 26, 2006 4:47 am

Piledriver,

How much do you think a set of JE customs pistons will cost you?

Clayton

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Post by Piledriver » Tue Sep 26, 2006 10:50 am

Twystd1 wrote:Piledriver,

How much do you think a set of JE customs pistons will cost you?

Clayton
A set of ARIAS go for ~550, and they don't mind doing one set.

Gave up on JE, even their off the shelf stuff is hellishly expensive.

GoWestys WISECO 96mm WBX sets w/VW cylinders were $550 + core jugs last I checked, but only 9:1...
(9:1 is ~ stock on a MV WBX, and a good CR for serious boost on a WBX from all reports, with a "normal" cam.)
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Post by Plastermaster » Tue Sep 26, 2006 12:04 pm

Pile, Are you planning a H2O engine? I would assume so with H2O heads. Especially with less cooling issues. To step into water cooled engines there are many possibilities. Why this rather than subie or others?

Ron

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Post by Piledriver » Tue Sep 26, 2006 12:22 pm

Plastermaster wrote:Pile, Are you planning a H2O engine? I would assume so with H2O heads. Especially with less cooling issues. To step into water cooled engines there are many possibilities. Why this rather than subie or others?

Ron
1)have one in use, and a nice low mile core.
2) Very det resistant chamber
3)very nice exhaust ports for planned goals
4) Cheap compared to Subaru (anything)
5) Fits, Requires no engine adaptor.
6)"Experimental" cam will set me back <~200.
...the same on a Subaru would be ~$2K

The 914 is still getting a T4, cam TBD.
The Vanagon will get a replacement 2.1, with the mods.
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Post by Twystd1 » Tue Sep 26, 2006 10:56 pm

Pile,

Do you have the EXACT specs for the pistons you want?
(Including dome configuration?)

There might be a possibilty that I can help you get a custom set of JEs for less than a set of Arias. MAYBE...

Let me know if I can help. I know some folks. Let's just leave it at that.

Clayton

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Post by Piledriver » Wed Sep 27, 2006 1:07 am

Thanks, I may take you up on that.

I won't start that one until the T4 is in, so ~ a month.

I might play with dome (or in this case, dish) config.
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Post by Twystd1 » Wed Sep 27, 2006 4:06 am

Kewl.

Just trying to be helpful... And learn something at the same time.

Clayton

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Post by Piledriver » Fri Sep 29, 2006 2:51 am

OK, just to have it recorded, .6 Mach (peak torque) on a 36mm ID runner should be at 4,327.31 RPM, more or less.

(1.57 sq in)

There are ~3 threads on this same subject, not sure if this is the right one...
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Post by raygreenwood » Tue Oct 03, 2006 5:31 pm

Been out of town for a week.
Arlo...the issue of turbulence from the butterfly is HUGE.
For instance on the stock plenums.....not only are you getting turbulence trying to make the incoming air turn 90* right after the butterfly....you get turbulence trying to make the air stream turn yet another 90 to get into the runners. This is also why the factory made the plenum wall curved right behind the TB on the 1.7/1.8 plenums. The incoming air has a tendency to move in a straight line as it moves through a restriction and gains density through compression. In this case....the compression is from velocity and restriction (the TB). Some of the incoming air deflects off the back wall right behind the TB, and starts to roll as it moves toward center of plenum. Add to this.....the plate in the TB....makes a huge plume of turbulence. More precisely....it is cavitation....or near cavitation in the airstream.
Add on top of this that a single airstream coming in is being pulled rapidly in roughly two directions...left side or right side to enter one of four ports.
You have to remember that the volume of the runner is just barely enough to fill one cylinder. If it were not for the plenum volume being there....a vacuum would be pulled on the runner. A complete vacuum.

As it is...in a few millisecond at speed.....the cylinder will empty that runner. Almost instantly....that runner will empty perhaps 1/3 to 1/2 of the volume of the plenum to refill itself.
This causes a huge quantity of directional changes in the incoming air that is already highly turbulent due to the throttle butterfly.

Put simply...turbulence is energy. Turbulence is drag. Drag is restriction in air velocity.
Air velocity is GOD with fuel injection. This is precisely what a lot of people are not understanding. Fuel injection is NOT simply about the act of precisely injecting fuel. It is....roughly 50%...about the act of injecting fuel. The other 50% is about creating hugely better atomization by injecting that fuel at the right location......to take advantage of a high velocity airstream.

If you have large turbulence in the plenum...it will take most of the length of the runners to get that straightened out....and lose velocity and therefore potential density ...all the way down the runner.

Numbers I have seen from reliable sources......mostly v-8 carburettor tuning people...tell me that it requires 8-10 times teh diameter of the TB...in length of intake tract...to calm the turbulence of the TB plate. In carbs...this turbulence is actually helpful in many cases to keep the fuel suspended....but can actuall ybe a detriment to getting the incoming air mixture into the right "plane" and runner of a carburetted plenum.

Yes..the turbulence at WOT is much less.....but unless you are on the drag strip....exactly how much of the time are you at WOT?
Airflow may sometimes act fluid....but it is not a fluid.
Pile is right that if you had the ROOM to get teh airflow generally directed....an air straightening honeycomb could take care of a lot of it.

But...the usefulness of an air straightener is directly proportional to how long it is. In other words...if it is a sheet of honeycomb only 1/4" thick....its affect may be not enough. Bear in min...that the long the honeycomb tube gets....the more drag it has. The more velocity lost.

Just some things to think about Ray

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Post by Piledriver » Tue Oct 03, 2006 6:47 pm

Picture this if you will...

Nice tapered collector//plenum, appropriate volume for the motor.

End of the plenum resides the TB or possible ram tube with TB at other end. (Still feel this might work)

Inside "plenum" reside a set of radial dividers/dampers running long ways.

They do not go all the way to the center---Their purpose is to suppress turbulence and keep the motion in-and-out only on the right axis.
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Post by raygreenwood » Wed Oct 04, 2006 10:50 am

Now you are thinking 3-dimensionally! :D
You have to be able to picture in your mind what the airflow looks like. I can only do that...because a few years back I did a smoke and camera test with a tuboscope and a strobe. The pictures were crap only because you get only a backlit segment. That shows you nothing except what is happening in a 1/2000 of a second of better instant. But what I saw through the viewfinder had motion...was peculiar...and not what I expected to find.
Once you get an idea of what things are obstructions to incoming air....you can start to think. By obstructions...I do not only mean restrictions and actual physical barriers. I mean anything that makes turbulence. That could be a directional change due to influence or reversion from any runner, a bounce off of a wall etc.

Picture this if you will: In teh stock system...we are trying to make the air turn corners easier with less velocity loss and turbulence.
Does everyone here know how an airplane wing works? Curved top...flat bottom. The straight line forward motion air has velcoity and pressure and takes longer to transit the top curve of the wing than the bottom. This cause a differential in pressure than is lower on the top of the wing than the bottom. Put as crudely as I just did...the wing is pushed upward. Conversersly the higher pressure at the bottom escapes downward...again put crudely.

So think of a ...."vane"......curved on one side and flat at the bottom. Flex than vane in an "arc" with the curve and flat bottom toward the runner opening....just before the runner opening and an inch or so out toward the miuddle of the plenum.
This vane presents little frontal drag to the incoming air...but through laminar flow "might" direct air off its flat side into a vortex (parly due to teh curve of the vane)...into the plenum. A change in direction made simpler....maybe. Just some thoughts. Ray

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Post by Piledriver » Wed Oct 04, 2006 4:12 pm

But...I _ALWAYS_ think in 4 dimensions! ;-)
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