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Old 01-11-2011, 04:16 PM   #1
Crazy_pilot
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Default Help me design a carbon fiber EG33 intake manifold

Background: I'm taking a manufacturing/design program at school and am in my final year. Part of this year is a design/manufacturing project that encompasses the principles taught in the course. This can be anything from CNC machining, welding, tool design, composites, plant layout.... Very wide open.

My project is a carbon fiber intake manifold for the SVX. I may accompany this with a new cold air intake (also CF, of course). I've been doing some research, but by no means am I an expert in engine design, so I'm looking for advice and help with this project. I've got the basic dimensions down and am currently working on my design in CATIA.

In case anyone's wondering why carbon fiber? Lightweight for one, the OEM manifold is quite hefty. I should be able to trim it down to just a handful of pounds. Heat transfer is the second big thing though. I'll have to see what happens once it's installed, but I'm hoping that the CF will keep intake temperatures lower. It may heat soak faster due to the low mass, but once air is moving through it it should cool rapidly.

My questions at the moment:

1. The SVX has a dual throttle body with two 60mm valves. In the stock manifold the plenum is divided but has a large valve that opens at certain RPM ranges, but it's going to be too complicated for me to incorporate into my design given my time and ability constraints. So, do I want a fully divided plenum, with each side of the throttle body feeding half the engine, or do I want a larger combined plenum?

My throttle body:



2. Plenum volume? Most of the articles I've found relate to forced induction manifolds and suggest plenum volume be 1.5-2 times the engine displacement, but not many have anything to suggest volume for N/A engines. 0.75 times displacement?

3. Runner length? I'll be keeping the diameter to ~45mm I.D. and will be using raised velocity stacks/trumpets inside the plenum. I'd like to target ~6000 RPM for peak power to combat the EG33's tendency to fall off in the upper rev range. From what I've found so far I should be aiming for ~10" runners above the injector stacks.

Any other thoughts or comments are welcomed, this is going to be a challenging project but also a lot of fun.

Some of the references I've been reading:

http://www.amsperformance.com/pdfs/intakemani.pdf
http://www.velocity-of-sound.com/vel...alculator2.htm
http://horsepowercalculators.net/int...anifold-design
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Old 01-11-2011, 04:35 PM   #2
vision.dynamix
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I would do a U shaped plenum, connecting at the back.
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Old 01-11-2011, 04:53 PM   #3
Crazy_pilot
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Interesting idea, it would give balanced airflow between the two banks (especially at idle with slow moving air) while still giving a good reflecting surface. Thanks!
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Old 01-13-2011, 02:15 AM   #4
Back Road Runner
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Well, for starters make sure that the epoxy you use with the CF handles heat. Some exhaust gas does end up back into the intake, and the IM needs to handle some heat. Subaru is of course using some plastic IMs, and the right thermoset does do the job. Epoxy is a form of thermoset, so it's a matter of using the right one. It may be that you will need an oven to cure the epoxy if it's a high temp variant. The carbon itself doesn't care about the heat, but the plastic does. Some used for high temp applications don't set at room temp. This may affect your part design if it needs to fit in some oven.

You might want to start off looking at some data that doesn't revolve around a random, turbocharged car. There are some basic calculations you can work with. I've found some useful information in the past over on Team Integra's forum:
http://www.team-integra.net/sections...?ArticleID=466

I will also point you to some engine modeling software, Engine Analyzer Pro 3.9:
http://performancetrends.com/program...0Installer.exe
It has a 10 day full trial. The program auto-locks after the 10th day though, and the lock is permanent and stored somewhere else on the harddrive. There are work arounds that are a hassle. Frankly, your school should have Engine Analyzer Pro and possibly Dynomation too, at least mine does. If your school has an automotive program, it should have a lab with it.

You'll need to get a lot of the main specs for the motor to model it up, and finding all of the info can be a chore. The more accurate you are with the info, the better the numbers you'll get. Then you can have the program run through length, diameter, plenum size, etc for you and show you what works best. I will note that other factors do influence the results including cams, head flow, exhaust, etc. You may have to think about what you are designing this IM to do. From what I've seen with teh 2.5L, stock is pretty close to ideal for a stock geared motor. Changes aren't necessary until you modify the flow requirements sufficiently.
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Old 01-13-2011, 08:59 AM   #5
Patrick Olsen
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There's some discussion of IM design (and some ideas that people have executed for EJ25s) in this thread. There's also some info in this thread.

Neither of those has a whole lot of technical discussion, they're mostly just show-and-tell threads, but you might get some ideas.
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Old 01-14-2011, 01:18 AM   #6
Crazy_pilot
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Back Road Runner:

That Engine Analyzer is pretty cool stuff, I'll have to play around with it. My program is aerospace manufacturing, no automotive engineering, so we're not equipped for much engine simulation.

As for the epoxy, we have a FLIR infrared camera that I used to take shots of the engine running and watch the temperature. Maximum that the intake hits (even after heat soak) is 92* C, so I'll base my epoxy choice around that plus a bit of safety margin. What I may end up doing is simply pouring thin layers of different epoxy, letting them cure, and then testing their characteristics. We also have several hundred pounds of pre-preg carbon in different weaves and weights (surplus from the company building the horizontal tail of the F-35, so it's pretty good stuff) and an autoclave large enough for anything I want to do.


Quote:
Originally Posted by Patrick Olsen View Post
There's some discussion of IM design (and some ideas that people have executed for EJ25s) in this thread. There's also some info in this thread.

Neither of those has a whole lot of technical discussion, they're mostly just show-and-tell threads, but you might get some ideas.
I actually have the first thread in my subscriptions, I've read it right through. Good info there. I also keep a keen eye on the whole custom fab forum, so I've seen the custom manifolds there too. It's great to see the ideas and work-arounds people come up with.
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