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Author Topic: Turbo plenum  (Read 52371 times)
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fredvance
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« Reply #15 on: September 14, 2008, 01:24:33 PM »

Thanks JH I love you too man. grin
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« Reply #16 on: September 14, 2008, 02:20:33 PM »

Panic---I would guess that it has to do with force vectors and surface area---my UN-SWAG--
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Jonny Hotnuts
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« Reply #17 on: September 14, 2008, 02:36:21 PM »

I modeled the design to emulate this plenum.



Here is a pic of the bigcc plenum.....uses straight tubes....even their ultra plenum have only a slight radius.


Hopefully I wont loose too much with the way I did it. Most of the turbo hayabusa plenums I have seen use the straight pipes with 0 radiuses.

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and this is your idea of getting a few things done around the house? 

what spec alooominum did you use?  not my subject, but I know that some will be a disaster.

How does the clearance to the back face of the plenum compare to the diameter of the trumpet - looks a bit close to me.  Not that you have a back face yet.


Andy,
I am not sure of the spec....only that these were plates measuring 3'X4' that were used to bridge the span between a trailer and the loading dock, and intended to have enough support to hold constant foot traffic. I would say its somewhat harder than most aluminums I have worked with

The distance is 2.5" (64 MM). I am considering making an arched, bolt on top. I also intend that I will be able to swap tops for secondary injectors if I dont use the port fuelers

BTW:
Loved the pics of your car.

Also will toss you some ideas about using non standard application turbos for this project (holset) for instance.


Outside dimensions are 14.5X6X2.5
« Last Edit: September 14, 2008, 02:50:18 PM by Jonny Hotnuts » Logged

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Rex Schimmer
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« Reply #18 on: September 14, 2008, 06:16:45 PM »

Johnny,
I pulled out my old copy of Roark and Young "Formulas for Stress and Strain" and did a little "pie are square, three bags full" on you plenum and 20 psi should not be a problem if you used a weldable alloy of aluminum. That would typically be a 6061 (prefered) 6063, 5052 but if you did a 2024 or one of the 7000 series then your weld strength might be in question. It is possible to weld these alloys and actually make good looking welds, an I must say that I am impressed with your welds appeance for having done them with a "mud" gun, but the welds are typically very brittle and of low strength. I would highly suggest that you attempt to find out what the alloy is before you spend more time on this project. No need to build a great looking piece and then have it fail because of the alloy.

Rex
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« Reply #19 on: September 14, 2008, 10:20:43 PM »

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I don't understand why the shape affects mechanical strength, though.

It is due to the mechanics of the way the surface flexes. A large flat surface has very little stiffness to "oil canning" under pressure. It tends to concentrate most of the bending action near the edges and this frequently causes work hardening and fatigue cracks along the corners, especially if welded.

If you are running a large square box it helps to put stiffeners inside the panels to give them more resistance to bending up in the middle of the panel due to pressure build up, or to put pass through gussets that connect the middle of the large panels to each other so the bowing in the bottom panel tends to help resist bowing in the top panel for example. I have seen a couple folks drill a hole in the large top and bottom panels with a tight fit for a rod, and then weld the rod top and bottom to the panels to tie them together and prevent (more like limit) flexing under boost.

At 30 psi boost the forces are pretty large and each time you go on and off boost the surfaces will flex in response to that change in forces. Large rounded corners will distribute the panel edge bending over a much larger area and add some mechanical stiffness due to the geometry of the panel.

Imagine what the box would do if you made it out of thin rubber sheet and tried to blow it up like a balloon. It does the same thing under boost although on a smaller scale. Any feature in the design that  concentrates bending forces in one small area will set you up for a fatigue crack over time. Any sort of backfire (even a minor one) into the manifold of course will almost guarantee lifting the largest panel in the plenum box as momentary pressures might go over 100 psi.

http://forums.nasioc.com/forums/showthread.php?t=674571  <--- some of these manifolds cracked shortly after install
http://www.magnusmotorsports.com/intakemanifolds/index.htm   <---- see the subaru intake manifold picture

Larry
« Last Edit: September 14, 2008, 11:19:52 PM by hotrod » Logged

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« Reply #20 on: September 15, 2008, 08:43:52 AM »

Remember at 30 psi boost, if your plenum is 10" x 10" measurement on the top surface the total amount pf pressure is 3000 pounds, 10x10x30=3000, food for thought.
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« Reply #21 on: September 15, 2008, 09:00:40 AM »

Gee, thanks, why didn't I think of that???

[/sarcasm]
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« Reply #22 on: September 15, 2008, 11:18:24 AM »

Quote
I would highly suggest that you attempt to find out what the alloy is before you spend more time on this project. No need to build a great looking piece and then have it fail because of the alloy.

Rex

Because this plate was gifted is there any practical way to determine alloy type?

I did a few welds on some test pieces and "attempted" to beat them apart with an engineering hammer.

On what I did find is that the penetration was good and required more force to separate the sections than I was willing to exert at the time. On the section that I was able to fold over it did not break until it was at about 45 deg..
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« Reply #23 on: September 15, 2008, 12:19:21 PM »

Hey Jonny

Here is a pic of the spigot area of my plenums.  It is a billet CNC piece.  If something like this would help your project PM me.


* Plenum_spigot_detail.JPG (57.75 KB, 613x554 - viewed 242 times.)

* plenum_floor.JPG (39.05 KB, 609x380 - viewed 229 times.)
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« Reply #24 on: September 15, 2008, 01:15:17 PM »

I went to see a friends turbo installation, he had a sexy looking rounded plenum reminiscent of early porsche race stuff.  I asked him how he made it, as it looked like a couple of weeks work.  He looked a bit embarrassed and admitted that he'd made it square and the boost had done the rest.  Don't worry, it was a lot thinner than 1/4".
Andy

He wasn't the first....

Quote from: JackD

The last water tank that Nolan built was measured to fit the frame in the nose just as tight as could be made.
IT was a beautiful job of fitted and welded aluminum.
It was all straight cut pieces with some folded corners and the rest was welded and fit pretty good.
That evening ,I came over to check on the progress and found the tank was all radius in the panels and really fit the space available.
 I had no idea who and how all that extra work happened , but now it was better than ever.
As we were locking up that night he said "I saw you looking at the tank and you never actually asked about it." What happened, was during the day he fired it up and chuffed a head gasket into the water jacket and the squeeze from 1 jug " PILLOW POOFED" the tank to fit.
It was an unintentional result ,but he silently enjoyed the credit for all the extra work.
 If you were brave enough to ask , he was brave enough to share the truth.
That is really the important part for both sides that needs more work.
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John Romero
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« Reply #25 on: September 15, 2008, 01:28:25 PM »

...Any sort of backfire (even a minor one) into the manifold of course will almost guarantee lifting the largest panel in the plenum box as momentary pressures might go over 100 psi....

Larry

It can go a hell of allot higher than that...  grin



My favorite part of the picture is the thread inserts that were pulled out and now look like little springs poking up in the air. Apart from the obvious plenum damage and a few sensors missing the engine was fine.
« Last Edit: September 15, 2008, 01:31:29 PM by John Romero » Logged
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« Reply #26 on: September 15, 2008, 02:09:04 PM »

Let's see... when did they start using pop-offs on GMC blowers, was it 1955...?
A simple cover plate, loaded in place with a calculated valve spring and installed with gasket sealer (after all, it's a safety device not a regulator) will cost, what - $10.00?
Since this is EFI, only hot air is vented and shouldn't disturb anything, so no duct is needed.
Safe vent = 4 1.5" holes (7.1 sq." area) with a hole saw, with a 6" 6" 1/4" thick rectangular plate across the top.
A 3/8" hole (valve stem size) centered between vents, 3/8" bolt inserted through the roof (or your choice) of the plenum from below with thick big diameter washer under the head (pin the bolt in place, or make sure you can reach it from inside). Bolt goes up through cover plate by 2", secured by lock-nut and valve spring collar. 7.1" area your boost + 5 psi. E.g., 20 psi expected, 25 psi 7.1" area: the plate will pick up against 176 lbs. of spring tension, but just barely.
Remember, just cracked may not vent excess boost as fast as the compressor is supplying it, so don't assume a pressure drop is a done deal.
1 big triple valve spring should do it, test with a compressor for cracking pressure. It may need to lift 1/2" to vent everything, so a big spring is needed.
More vent area? Bigger holes, more holes, 2 springs etc.
Carbureted? Must exhaust only into a safe duct, and pass outside the vehicle without going near exhaust, electric, rider, etc.
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John Romero
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« Reply #27 on: September 15, 2008, 02:16:58 PM »

The pic above had a 3" diameter pop off valve on the top. It wasn't enough  grin  It continued until we installed dual blow off plates about 1"x6" each in addition to the pop off valve.

The real problem was that the entire plenum was wet with a combustible mixture of methanol & air so basically we had a 26 liter pipe bomb. Ahhh good times, good times ...  tongue
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« Reply #28 on: September 15, 2008, 05:17:17 PM »

After calling my friend who gave me the plates he was able to find the original purchase voucher from about 6 year ago.

The plate is 1/4" 5052.

http://www.ez.org/aluminum.htm

Quote
5052 This is the highest strength alloy of the more common non heat-treatable grades. Fatigue strength is higher than most aluminum alloys. In addition, this grade has particularly good resistance to marine atmosphere and salt water corrosion. It has excellent workability. It may be drawn or formed into intricate shapes and its slightly greater strength in the annealed condition minimizes tearing that occurs in 1100 and 3003. Applications: Used in a wide variety of applications from aircraft components to home appliances, marine and transportation industry parts, heavy duty cooking utensils and equipment for bulk processing of food.


Good, bad or other?

-JH
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Peter Jack
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« Reply #29 on: September 15, 2008, 05:52:50 PM »

Good Jonny. We usually weld it with 5356 wire which feeds much better than 4043 in the machine. A little preheat definitely helps the quality of the weld and a thorough degreasing and wire brushing with a stainless brush will add to the quality of the weld. Save the brush for aluminum welding only.

Pete
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