Bodywork, Paint, Interior, Trim, & Wiring

This isn't a bodywork question, but the materials and processes...

I'm thinking about making a "plenum cover" for a Rover manifold based fuel injection system out of carbon fiber and epoxy resin. The original OEM part is sand-cast aluminum, and it has an integral throttle body which is pointed 90 degrees from the direction I'd strongly prefer.

This is the OEM plenum cover:


I'm imagining a simpler plenum cover with a flange that an off-the-shelf throttle body will bolt to. Of course I could fabricate something out of aluminum, but I'm thinking carbon fiber could be made to match my bonnet and look really cool. Very, very preliminary "brainstorming" stage...

Anyone have ideas or advice to share about this?

Do I need to worry much about heat or fuel vapors damaging the carbon fiber part?

I'll probably be be mating to metal parts at two flange surfaces - the "plenum base" and the "throttle body flange". Is that an issue? Can the plenum base and the throttle body flange be aluminum, or are there corrosion issues with that? Would plastic or stainless steel be preferable? Should I plan on using an adhesive at these joints, or are mechanical fasteners more suitable?

Rover plenum base with trumpets installed:

(Nothing says I have to use these parts or that I can't severely modify them!)

Curtis, I think that if it's just the carbon fiber look you're after I'd modify the existing plenum by TIG welding and then blast it and wrap it in carbon fiber cloth and cure it in a vacuum bag. You'd have the look, none of the modifications would show and you'd still have the security and maintanability of the mechanical fasteners and the alumimum threads. Just machine the fins off the top and it would really look slick under that carbon fiber bubble in the hood.

And give up the tremendous weight reduction?

;o)

Curtis, you would need some quality hi temp resin , you should vac bag the part and post cure up to 375 f or better
also you would need to use perforated peel ply when bagging, a shiny surface is very desirable to slow down the
deteriorization of the inside of the part, as hydrocarbons tend to attack the substrate, if you used standard peel ply which
is designed to promote secondary bonding it would provide a surface that would easily allow the hydrocarbons to
migrate into., race cars can get away with this trick stuff cause the are constantly apart and can be cleaned readily.
Dave

Check out some examples of firberglass & carb fiber intakes at:

[www.mez.co.uk]

All kinds of variations.

M.

Curtis, faux carbon fiber ? I've seen this at car shows. Maybe like "silk screening" ? We know your digging carbon fiber, but what is the reward , other than looks ? Tig modifying your existing plenum to integrate with your aluminum plenum feed,(firewall), and then faux the carbon appearance ? Cheers, roverman.

Matching the bonnet would be nice, but the big attraction of carbon/epoxy is that the process facilitates more elaborate shapes. I don't have a TIG welder or a milling machine... but I can sculpt a wooden plug, make a fiberglass mold, and lay-up a carbon part. I'm sure I could learn to vacuum bag. (Maybe even visit my good buddy in Michigan to borrow vacuum equipment, eh?) Fake carbon is definitely not going on my car. If real carbon/epoxy isn't feasible, my path forward is probably a thin gauge steel fabrication with a satin black finish. I just wanted to explore the carbon/epoxy option.

This thread needs more photos, doesn't it?

Here's my favorite photo from the page Martin linked to:

(I wonder if Westfield has a trick for keeping fuel fumes away from their carbon. Just because they made a part doesn't mean they made a durable part! I'm imagining lining the carbon part with high quality foil tape... Might you trust the adhesive? Or maybe some sort of super paint? Carbon parts are too expensive to be disposable.)

And here's where I'm starting from:

(note the new carbon/epoxy recirc shield, and that I have very little room to package a throttle body and air cleaner.)

Curtis, I used Epoxy resin to seal IHC Scout fuel tanks that were full of pin holes. Held up to gas just fine. Like Dave said, use high temp resin and go for it.

Huffakers' prototype 4 bbl, for the RV8 was fiberglass. They used clear, hi-temp resin and made dyno runs with it. They put phosphlorescent dye in the gas and watched the action "inside" the manifold, with a strobe blacklight. Stealthy ! Don't sniff too much resin/lol., roverman.

Curtis the Westfield plenum is from www.actproducts.co.uk/shop/induction I used their triple plenum in my old TVR Griffith 5L engine, it had great throttle response for engines over 300 hp. They also make a single and double plenum to replace the oe.
Tim the boss is very helpful and produces a quality product.

Julian

Consider forming some very thin sheet metal around your plug before laying up your carbon fiber. Dave can tell you which ones the resin will stick to the best, plus you can braze spacers or other inserts where you need them to add strength. Go thin for formability and light weight, as about all you need is a barrier. Then you have the best of both.

Jim

. . . and then you can market them to us to pay for your R & D! I'd like one please . . .

:-)
NCtim

Yes Tim, But he WILL have to pay for an add. Curtis, while your on a carbon binge, maybe an intake manifold to fit TA heads ? Cheers, roverman.

Something I think I can help out on finally(I'm usually getting advice from you fella's with way more experience than me)

I actually attempted to build a carbon fiber plenum for a graduate level elective class in M.E. - heres my experience.

I was limited by budget/time so I had to go with some donated carbon fiber weave and epoxy(used in structural building reinforcement). It was extremely hard to form around my mold, however much better materials are available.

I used one layer of carbon fiber/epoxy and was told it would 'never hold' by the 'experts'. In the end supported the required load but in the end wasn't up to my standards in looks to use.

From what I figured out your plenum needs to support roughly 10psi - this is to compensate for the outside atomospheric air pressure and your maximum vacuum. Something that should definitely not be overlooked! I was required to also model and simulate my plenum in a finite element analysis program - designed in solidsworks. Besides cost/time I chose to go with one layer because I found it extremely difficult to model multiple layers in solidworks/cosmos(FEA). There might be possible ways to simulate it in solidworks/cosmos, but if not I'm sure other programs are available. The plenum with one layer of CRFP that I designed passed stress test in the program - and also in real life; not only supporting a friend weighing 200lbs but also me at 275lbs - which came out to well over 10psi with the surface area.

I made two molds - started using foam for the positive mold -due to time/cost I layered it with clear scotch tape and a cheap release coating. Then I built up the layers of tape to compensate for thickness and made a negative mold. I used these two molds as a 'sandwich' mold to create the carbon fiber mold. It worked very well for my project/presentation. But I would have rather made something out of aluminum or wood like you intend to.

As you said - vacuum molding is a good way to go. You can even make your own setup. It doesn't so much increase strength, as much as it cuts down on weight by removing excess resin. It also provides a very aesthetically pleasing product, as long as both molds are very smooth.

Since I'm running a 4.9L rover - I designed my plenum to be 20% larger and have a surface with the ability to run a 4.6l modular mustang throttle body which I believe is 2x55mm. I was planning to use an aluminum backing plate for the TB and mounting point; just to make sure that it had some reinforcement to avoid cracking that may be caused by vibrations. I couldn't get my carbon fiber weave to shape in a way that allowed me to use the exisiting body that the trumpets are fitted to. So I figured if it worked I'd eventually have to create a new manifold and what not.

That was my experience - you seem to have more time than I did and on the right track. If I were you I'd go ahead and make your main mold - whether it be negative or positive and work from there. Since it can be difficult to model you could perhaps make a few models using several different layer amounts(for instance 4 layers, 6 layers, 8 layers). Then place a weight covering their area and see what the result is. I was told originally using the typical CF weave(that I should have used) it could take between 7-10 layers for a reliable plenum.

As far as forming the final product. I definitely recommend vacuum molding to reduce weight and to have a great looking piece. Either go to michigan or make a DIY setup. If you want to take it to the next layer of auto-clave(using pressure+heat) - you could make that yourself also relatively easy since its a smaller piece. The auto-clave method is whats used to make the strongest parts - you bake it at "X" temperature under "X" pressure for a certain amount of time.. very strong, very light, and the best of the best.

Your thoughts on lining the inside is a great consideration I never thought of - I'm sure a proper epoxy would hold very well. There's a shop nearby to me that specializes in making epoxies to mate "X" material to "Y" material for whatever the conditions may be. I have no doubt a proper epoxy would hold up.

As you know research is the most important part - wish I had more time! If you have any more questions let me know, I did the research just didn't have the time or resources to create the perfect plenum.
Also - my apologies for the unorganized post - in a rush but just had to respond since I have experience in this area. I have some other points to add later on but if you have any questions feel free to contact me.

Curtis and gang,

If you want me to make some molds I'd be happy to help with R & D. I can make plastic or wood molds on a cnc if you send me your cad models. Incorporating an MG logo would be cool.

Cheers,
NCtim

Unfortunately the paper I wrote covering the design is on my school computer which I don't have access to - but I have a few
a pictures and notes left over. I'll post up - complete different type of weave and epoxy but it might help.

*If using a similar design to the original design your 'weakest' area will be the top plane of the plenum - due
to its larger surface area.

So here are some pictures

The following two imagines inlude dimensions of the plenum I designed and
a quick render. The throttle body surface is flat to accomodate the twin tb setup.
It also does not have a flange surface - but was constrained during analysis to mimic a flange.


[i46.tinypic.com]

[i47.tinypic.com]

280lb male covering ~15-20sq" area
[i47.tinypic.com]

Deflection stresses - unsure if that was with the one or two layer design
[i48.tinypic.com]

Von mises stresses - again unsure if one or two layers
[i47.tinypic.com] von mises


If I recall correctly the overall volume was 20% to 30% larger to compensate for a stroker setup.
The model I made came out correctly besides the flange - but finish was not to my liking due to the
weave used. I believe HJ3 is the manufacturer. Solidworks is a great tool but in some instances it
didn't mimic physical test. Solidworks claimed final weight of 0.43lbs - final weight was closer to a pound,
which can be attributed to not using a vacuum method(you can see the terrible finish in physical pictures).

If you figure out which CF material you're using and how many layers I'd be happy to design and run a simulation for
you(if needed). After everything I did I still think the best method is to use "x" amount of layers, with the construction/cure method you choose,
and then use a X" x X" square of the finished CFRP and subject it to X weight to insure it can hold at least 15psi so you have
somewhat of a safety factor.

Anyways - sorry for the long post again, I can never seem to keep it short and sweet.

Curtis, you might want to look at "PFPT",(plastic faced plaster tooling). This allows male/female tooling to be built, that closely controls thickeness of build-up and resin content. Years past, I spoke with a Gurney Eagles employee, who claimed great success, with this method. We were also using similar tooling at Northrop, at the time. Cheers, roverman.