Landracing Forum
Tech Information => Technical Discussion => Topic started by: donpearsall on March 02, 2011, 01:06:32 AM
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Has anyone successfully made a turbo plenum from fiberglass or carbon fiber? I have a ZX-10 that I need to build a custom plenum for and think using fiberglass would be much easier to fabricate to the right shape. I have never seen a fiberglass plenum before and maybe there is a reason. The advantages are ease of making a complex rounded shape. The cons may be failure due to flexing and heat.
Any comments about this?
Thanks
Don
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Don for a low boost system I am sure it wold be fine however after seeing Aluminum plenums that were made with .100" thick material bulge after a back fire I would not want to see what fiberglass would do in the same situation.
Not to mention many of us riders "lay over the plenum" while making a very fast pass... :-o
Use the force...don't let the force use you.
John
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Don, I'm sure you have seen carbon fiber high pressure bottles. So it is possible, shape may affect the max pressure, but I don't think you will get there. Fiberglass.... I would say probably not, Carbon done right, should work great.
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The composite construction of fiberglass or carbon fiber will withstand pressure pulses better than malleable aluminum.
Fiberglass will work as well as carbon fiber. You need more layers to achieve the same strength.
How thick? As with any pressure vessel you need to look at the total square inches, the pounds per square inch, and the load path through the structure, ie. square shapes don't hold pressure as well as round shapes.
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Don for a low boost system I am sure it wold be fine however after seeing Aluminum plenums that were made with .100" thick material bulge after a back fire I would not want to see what fiberglass would do in the same situation.
Not to mention many of us riders "lay over the plenum" while making a very fast pass... :-o
Use the force...don't let the force use you.
John
Just don't have a back fire. :-D
What about the intake charge temp causing a problem?
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The high pressure bottles that I've worked with have been aluminum wrapped with carbon fibre.
Pete
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Stainless - those high pressure bottles have aluminum inner shell which is wrapped with CF. I wonder if current aluminum plenums could be CF wrapped then vacuum bagged and cured to help support the weld joints though, hummm...
Don - I believe this is possible but with significant learning curve that's probably why its not common practice. There are resins out there which can easily handle the heat but most of these require post curing, which can also make the mold more exotic too. Geometry of the finish part is also key to handling pressure.
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Consider this:
A plenum wall measuring 10"X10" with 10 PSI will have 10 pounds for ever inch....meaning really high internal forces trying to separate the plenum (1000 psi per wall however shape will also have a factor).
http://www.about-air-compressors.com/force-on-a-compressed-air-tank.html
Ransom T also was correct, the polymers used to make CF are affected by high temps.
Basically I would suggest not even considering it.
~JH
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Thanks for the comments everyone. John I know very well your point about leaning over the bare plenum for 5 miles and wondering if it will go bang. I already experienced that once. I keep seeing images of that Harley drag racer video who got his arm blown off from an exploding engine. Messy.
Just looking for an easy way to build a plenum, but will probably go with Al or SS with my minimal welding skills.
Don
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There is some reasoning regarding using low strength and "softer" metals for pressure vessels, which is what a plenum is. The thinking is to use a material that has a yeild strength a good percentage below its ultimate strength this allows the material to yield (stretch) when over pressured and then when it fails it will typically just stretch until a crack or small hole is formed which relieves the pressure. If you use a high strength material such as 4130 which has a yield strength close to its ultimate strength, especially if you heat treat it, then it just blows up "BANG!" and can generate shrapnel at the same time. I would think that both fiber glass and carbon fiber would act like this. So Don if you are going to build it from stainless be sure to use something in the low 300 area, like 302 or 304. If you do aluminum I highly recommend designing the plenum so that you can back weld most of the joints.
Rex
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Use 304 or 316 SS, 302-303 SS welds poorly.
416 SS is another option, welds nicely with TIG and then can be heattreated/annealed to a consistant condition.
Gun barrels are made from 416, depending on application pressures up to 45k psi.
A comment on fiberglass and CF, use multiple layers and directions of fibers for strength. Add layers of Kevlar.
The high pressure bottles mentioned are constructed with "tows", CF strands in a string and wound very carefully around the shape for strength.
There is always the option of putting in a burst panel.
John
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And on that note there would be nothing wrong with making an aluminum or SS plenum and then covering it with CF for a wow factor.
It would after all look sweet.
~JH
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If I had to ride it, the plenum would be titainium with an alum burst panel.
But then, I am not riding or paying for it either!!
John
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And when you weld up the plenum be sure you back purge to ensure the structural integrity. If you don't understand the terminology or procedure, don't do the welding.
Pete
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As with all pressure vessels, it would probably be a good idea to proof test the finished plenum but filling it with water, then pressurizing it with compressed air to some reasonable safety factor over its intended peak boost pressure.
By having most of the volume filled with water if it "pops" there is very little volume expansion and pieces parts will not fly as far as if the pressure was entirely compressed air.
Normal engineering practice is for 2x safety factor but given the personal risk for a rider laying on top of the plenum I would test to 3x or 4x design boost pressure.
This will also pre-set any bowing or oil canning of surfaces so that it is mounted in a manner that such flexing will not break the mounting brackets.
Larry
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You could make it out of mild steel. Cheap, easy to work and weld, and reasonably ductile for absorbing a backfire. Plate it for corrosion resistance (HPC, zinc, whatever) and it will also add some weight to the bike as well.
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An Aussie company makes CF plenums , mostly for Triumphs , but he can or has done others , i asked several yrs ago but the price scared me off
http://www.racecomp.com.au/turbo.htm
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You could tack everything together then have a welder finish it. :cheers:
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I built my plenum from 6063 aluminum extrusion with a 1/4" wall thickness. End plates are welded on both outside and inside. I'm very lucky to have an extremely skilled welder able to do that.
(http://i107.photobucket.com/albums/m290/hombre_1/DSC06149.jpg)
(http://i107.photobucket.com/albums/m290/hombre_1/DSC06216.jpg)
(http://i107.photobucket.com/albums/m290/hombre_1/DSC06189.jpg)
You can source a few different 6063 extrusion shapes here: http://www.rossmachineracing.com/plenumextrusions.html
You will notice they don't sell any thinner plenum material. :roll:
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Nice Hombre!
My first plenum let go after a wicked backfire, scared the hell out of me.
I suggest making it considerably stronger than necessary, it also helps if you need to tap into it for fittings or BOVs or what have you. Aluminum is light, cheap, corrosion resistant and strong if thick enough.
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How about a "pop-off valve"........they are adjustable to various boost pressures and prevent "blowing up" your plenum in case of a back fire..............................................................................................
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Nice Hombre!
My first plenum let go after a wicked backfire, scared the hell out of me.
Thanks, Dean... that might have hurt if you'd been laying directly on it!
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How about a "pop-off valve"........they are adjustable to various boost pressures and prevent "blowing up" your plenum in case of a back fire..............................................................................................
True. But once I figured out that the aftermarket "heavy duty" valve springs were actually weaker than stock, I corrected the backfiring issue. Great learning experience.
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Carbon fibre can do the job and there are resins that stand up very well to chemicals and high temperature. It's doable for sure but not for someone with little or no experience. Glassfibre comes in many different forms and the aero spec stuff is excellent but chopped strand mat is a no no in this case. It's a case of how deep your pockets are IMO.
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Excuse my ignorance, but is the air box on a naturally aspirated motor subject to the same vulnerability to backfire induced explosion as a turbo-charged one? And why would a turbo-charged air only system be subject to such an explosion?
Also, I see plenums attached with silicone hose and hose clamps. Is the plenum really the weak point?
Uh Oh! ......I think I should probably make a stronger blast panel over my motor than .030" aluminum, even if mine is naturally aspirated.
Tom
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Also, I see plenums attached with silicone hose and hose clamps. Is the plenum really the weak point?
And those routinely blow off if they are not properly restrained with straps across the hose to keep the joint from spreading.
To answer your direct question, the issue is more of shape than anything else.
A round tube is inherently strong at resisting internal pressure but square and angular shapes get a real workout from pressure changes "oil canning" the flat surfaces, and often fail at the corners.
If you get a good healthy backfire in a NA engine you can get high enough pressures to split a plenum, especially if the situation causes fuel mist to get blown into the intake plenum then that fuel air mixture gets ignited by a second backfire.
Even at relatively low over pressures like 3-4 psi, if you add up the surface area of the flat surfaces and multiply by that small over pressure the resulting numbers are pretty impressive if the plenum is any size at all.
Suppose the top of a square plenum is 6 inches wide by 8 inches long, that is 48 square inches. If your backfire pressure is 4 psi, than there is 180 pounds of force trying to rip the top off the plenum. Is your plenum strong enough for a good sized man to jump up and down on it with no failure?
If a pre-existing crack is developing it can unzip the corners and launch that flat plate with surprising force (and velocity).
If a spin or some other situation causes fuel air mixture to get pushed back into the intake plenum for some reason and then it ignites you have a small fuel air bomb.
Larry
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Just to add my 2c worth into this discussion;
When I was running my turbo funny bike, with 30 PSI boost and 3 stages of nitrous we usitilsed 2 burst plates, one on each end of a long tubular plenum chamber. Theses were made from plastic milk cartons, and would burst at approx 45 psi if they were 2" in diameter.
Plastic allowed flexing to take account of any turbo pulsing due to the nitrous, but would still burst nicely if needed. The burst panels were held on with bolt on rings and we never had any failures.
HTH
Neil
PS
The plenum was 4" OD .125" wall
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I tried the carbon fibre idea a few years back... It was costly and kept cracking. We switched to mild steel painted it inside and out... Works well was cheaper to make or alter at will... The bov is a good idea... Get the pressure in front of the turbo out during shifts if you close the throttle slightly, shuts the waste gate for quicker spooling between shifts, prevents some surging issues as well
Bak189 knows a lot about turbo 4's... I try to watch what he says in discussions...
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We found that over 24 PSI boost requires V-band clamps rather than slip joints.
(http://i107.photobucket.com/albums/m290/hombre_1/IMG_1035.jpg)
(http://i107.photobucket.com/albums/m290/hombre_1/IMG_1027.jpg)
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We found that over 24 PSI boost requires V-band clamps rather than slip joints.
(http://i107.photobucket.com/albums/m290/hombre_1/IMG_1035.jpg)
(http://i107.photobucket.com/albums/m290/hombre_1/IMG_1027.jpg)
Can more than understand why... That's a ton a boost...
Is there any good way to weld a flange into the compressor housing?
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Is there any good way to weld a flange into the compressor housing?
Machine the "lip" off the impeller housing outlet, machine coupler to fit over outlet and V-band half... then weld together. Make sure you measure 3 times, because there will be no free play with welded V-band clamps. :-)
(http://i107.photobucket.com/albums/m290/hombre_1/C38-92.jpg)(http://i107.photobucket.com/albums/m290/hombre_1/IMG_0863.jpg)
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Are you seeing any issues with exhaust movement from heat expansion when you hard couple the inlet ?
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Are you seeing any issues with exhaust movement from heat expansion when you hard couple the inlet ?
I believe you mean hard couple the outlet. :?
I don't have an exhaust heat problem with the Rotrex because it's crankshaft driven, a blower not a turbo, with dedicated oil coolant/lube system.
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:-D yeah that end
Ok ,Rotrex is a different thing to turbo
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The modern Triumph Bonnevilles are NA engines and they have a peculiar habit of blowing their air boxes apart when the engine backfires. The air box has an inlet. What we learned is a small hole like an inlet or a pop off valve is not large enough to relieve explosive pressure quickly enough. A burst panel is needed.
There might be some link between fuel collecting in the bottom of the air box and them blowing apart when the engine backfires. I like to have a drain at the lowest point in the air box and I would put one on a plenum if I used one. The drain would be opened if I suspected that unburned fuel was inside.
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when i use water injection upstream of the plenum i always drill a 1/16 hole in the base of the plenum , on the low side when on the side stand
makes sure there is never a collection of water , same could apply for fuel