Project Miatabusa Part 4.3 Intake Manifold

This week's half step toward 11,000 rpm Miata madness is a good solid head start toward making a workable intake manifold. Starting from virtually nothing, the fertile mind and ghettofabrication skills of Miatabusa braindaddy (that's the technical term for someone who father's an idea) Alex Vendler produced a believable plan and a compelling prototype using the tools and supplies scrounged from the hardware store, a costume shop, my garage, the local sex shop, and the sidewalk in front of my house. It was an entertaining weekend...

One of the trickier bits of converting a motorcycle engine to car duty is coming up with an intake manifold that will fit under the hood. In its 2-wheeled home, the Hayabusa's air box (which serves triple duty as a cold-air intake, air filter housing and intake manifold plenum) sits on top of the engine. The intake port is beautifully straight and hits the intake valve at a nice, high angle that promotes good high-rpm breathing, but even with the air box removed, this layout puts the air horns perilously close to the hood.

hayabusa miata miatabusa throttle body hose

Our first simple attempt at hood clearance was simply to turn the two center trumpets around so they bent down instead of up. It actually looked like this might work, since the shorter outer horns give a bit more hood room.

hayabusa miata miatabusa throttle body hose

Using the volume of the stock air box as a guide, Alex roughed out a cardboard mockup of a plenum to check clearance.

hayabusa miata miatabusa intake manifold cardboard plenum

It was close, but not only did the hood object by about an inch, the outer horns were getting their breathing restricted by the roof of the plenum. This idea simply wouldn't do.

hayabusa miata miatabusa cardboard intake manifold plenum

We aren't the first to do something silly like this with a Hayabusa, so we checked out some prior art for inspiration. The Hayabusa-powered rally Starlet I spotted in New Zealand last year simply used 4 silicone elbow hoses in place of the factory air horns. This is temptingly simple, and it negates some of the hood clearance concerns because the silicone can rub on the hood without really damaging anything. Ferdinand Suzuki carefully engineered those staggered air horns, though, and we're pretty sure we don't want to mess with the runner length that much. The Kiwi Toybusa technique will be kept as a last resort.

hayabusa miata miatabusa intake manifold


hayabusa miata miatabusa engine bay with cardboard fiber intake plenum

Another possibility was spotted on this Hayabusa-powered go kart dressed in Honda Z600 skin. Sadly, I didn't really photograph this car in much detail, as I spotted it years before this project came along. It appears that the builder added some aluminum elbows between the head and the throttle bodies. This lengthens the intake runners just as the silicone hose idea did, but it also moves the injectors away from the ports. The Hayabusa's injectors are tucked under the throttle bodies, aimed down the ports. WIth this layout, they're now pointed at the outside of the bend, spraying on the runner wall. At full wail, this probably won't matter at all, but at part throttle, this wall wetting will lead to inaccurate and inconsistent fuel mixtures. Might as well have carburetors at that point.

hayabusa miata miatabusa intake manifold


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Thursday, October 07, 2010 7:05 PM
That is amazing work.
Thursday, October 07, 2010 7:19 PM
Ghetto Fab at its finest!
Thursday, October 07, 2010 7:56 PM
Where can we buy the carbon fiber fabric material and resins to attempt some of this awesomeness?
Thursday, October 07, 2010 10:33 PM
Carbon fiber sheets and materials are available thru TAP Plastic. (along with Epoxy/ Resin, hardening). Pretty much everything you need to make whatever piece you want.
Scott Helmer
Scott Helmerlink
Friday, October 08, 2010 3:20 AM
Okay, so where might one find a source for quality pre-impregnated carbon fiber and honeycomb? I've seen ACP Composites as well, but as far as I can tell they seem to offer everything (including standard aramid honeycomb core material, resin, vacuum bags/bag-related accessories, etc.) BUT pre-impregnated carbon fiber. Standard, non resin-infused carbon fiber is fine and all for air horns and other non-structural/small items, but if I'm going to go to the length of honestly making my own carbon fiber parts for strength/light weight, I'd like to have the option of having proper "dry" carbon parts (assuming I can find an autoclave that I can use, of course :P) when I'm done.
Friday, October 08, 2010 5:08 AM
Amazing work again! But just one question would it no hav been easier to just add a speed lump to the hood aka Turbo bump like on the Talon's? Because if it was me I would have even gone to the lengths of buying a cheap plastic fake hood intake expoyied it on then cut the hood to clear the box. But maybe I am crazy lol.... Plus I dont have those mad skills to pull of a job like that! Tried to make a fibreglass box once and its now a really big paper weight somewhere and havent ventured much into its since.
Friday, October 08, 2010 5:51 AM
I read this whole thing slack jawed. Who says small business doesn't work? You guys hiring for a summer internship? All I need is a floor and some decent pay and I can be there in June.
Alex Vendler
Alex Vendlerlink
Friday, October 08, 2010 6:18 AM
@ Scott Helmer

What are you making? Prepreg is not necessarily stronger than vacuum bagging or even wet lay up. While it ensures the correct resin ratio that's not that key if you are not making an airplane wing part or something like that. I think you could make any carbon part one would want on a car with regular wet layup or vacuum bagging. Condom bagging has it's obvious limitations but with the advent of the "Magnum" and "RoughRider" that technique has room for growth too.
Friday, October 08, 2010 7:00 AM
@scott helmer
you also have to realize that pre-preg carbon has to be kept at around 2 degrees Fahrenheit and also has to be baked at (i believe) around 400f, but i could be wrong on the exact temperature. aside from those 2 things, prepreg is much easier to work with. it doesnt fray as much, you donthave to work with sticky liquids that get everywhere, etc. for just a few DIY things though, dont look at pre-preg as the "right" way to do it. the grams of weight you'll save isnt worth the extra cost.
Friday, October 08, 2010 12:02 PM
Like SteelbluesleepR said, pre-preg is kept in cold-cells at about 2 degree celsious (prior the usage).
Pre-preg is stronger than vacuuming. Vacuuming process just makes sure there are no bubbles/ voids in between the fibers, whereas pre-preg has the exact amount of hardening in it, evenly distributed.
For little carbon fiber projects I generally use Baltek core. It's cheap, easily attainable and strong.
Friday, October 08, 2010 1:50 PM
what a tease!! how can you just stop in the middle like that?!
Friday, October 08, 2010 2:14 PM
If you want to look at it in realistic terms, on a part like the intake manifold, the resin add up to only a couple of ounces, so the weight savings is negligible, but the cost is high. And making your own honeycombed parts is just asking for trouble. Get an air gap between the honeycomb and the carbon sheeting and the part will just tear itself to bits as it becomes stressed.
Scott Helmer
Scott Helmerlink
Friday, October 08, 2010 2:37 PM
Whoah, whoah, whoah. Nobody ever said anything about using pre-preg with the vacuum process. I know exactly how one creates carbon fiber parts, and like I said, I wouldn't even dream of making a dry carbon part without access to an autoclave (I guess I should have also mentioned access to a cold/dry enough area to store it in). Either way, who ever said that I was intending to make a part any time soon? Being recently unemployed, I barely have the money to buy aftermarket parts, much less pay the tooling costs, rent an autoclave, and likely redo the entire process at least once due to an unforeseen manufacturing error. I was just asking as at some point (probably within the next 5 years, after I hopefully get the lucrative position of being a Journeyman worker for my local utilities company), I will most likely be doing a few things involving carbon fiber. The areas in which I intend to use carbon fiber are primarily structural, and as such it is imperative that I use as little as possible (s@#$'s expensive), while maintaining an ideal ratio of resin to fiber, for strength's sake (more/less resin than is ideal results in a weaker part, end of story). On top of that, for the cars that I have right now, I'd like to at least look into making body panels that fit my needs without having to go fiberglass, or have them custom made, or buy either Seibon or VIS or whatever parts. I don't know about you, but I don't know that many people with 1UZ-powered AE86's or EZ30R-powered first generation Impreza's. Those are the two cars I have, and I'd like to have all my ducks in a row before I go ahead and spend thousands of dollars building them (the Impreza, a 2.5RS coupe, is currently bone stock. The AE86 is non-running), all right?

Jesus Christ, is it so hard to answer a question without assuming that the person asking has no idea what they're talking about?

JDMized: I'll look into the Baltek core when I get a little closer to actually making parts. I suspect that it'll come in quite handy in creating a clean, usable dash for the AE86 (my interior is f'ed, and I'd rather just make a simple, usable dash out of wet layup CF than try to find another one) without necessarily killing my wallet. I won't be needing to do so with the Impreza, as I intend to use an '06 STi dash/center console for it, as it will spend most of its life as a street car.

Either way, anything else on this subject should probably be put in the forums. I'm sure somebody on this site would appreciate a good write-up on the different weaves, weights, processes and materials involved in making carbon fiber parts. I still have to study up on which direction the standard 2x2 weave is meant to impart strength, for example. Hell, I wouldn't mind a set of parameters to put into AutoDesk Inventor for FEA analysis, as I'll probably go that route for a certain other project that I have in mind :P
Dave Coleman
Dave Colemanlink
Friday, October 08, 2010 5:18 PM
Jesus Christ? When did he post?
Scott Helmer
Scott Helmerlink
Friday, October 08, 2010 6:28 PM
Eh, last Christmas or so I think. Something about how he was having troubles with his girlfriend. Couldn't bring her to climax more than once, or something like that.

At least that's what I thought he was talking about?

By the way, I can't believe I forgot to mention this: keep up the great work Dave! I can't wait to see the Miatabusa finished.
Saturday, October 09, 2010 8:48 AM
Is there going to be any more on this? I would really like to see how the runners are bonded with the plenum and the intake pipe/filter.
Alex Vendler
Alex Vendlerlink
Saturday, October 09, 2010 8:58 AM
Oh there will be more. I am filling and sanding the foam plug as we speak. The runners will be bonded into the box with resin and cloth. They will be part of the box and it all should be very sturdy. I am using 400 deg. F safe resin too.
Saturday, October 09, 2010 11:54 PM
Awesome! I can't wait!
Sunday, October 17, 2010 5:49 PM
To the guy that said you have to autoclave pre-preg. That's not true at all, there are literally tons of dry carbon that is made for oven applications. Also, cure temps and times vary for different resins. Most of the time the temp varies for the part as it is cooked.
Tuesday, October 19, 2010 10:40 AM
Nice work, Dave. Pragmatic, common sense, and smart. Looking forward to seeing more of this.
Wednesday, October 20, 2010 5:28 PM
Just as a comment from a Hayabusa guy, it is a very common mod for us to replace those longer center "velocity stacks" from within the airbox with another set of the outers (the shorter) runners. This from most dyno estimates seems to move the torque and horsepower curves up the rev range, which may be counter productive for your purposes and desires for torque, but would be an ultimately even more simplistic solution to your issue. Just my $.02.
Saturday, January 15, 2011 7:27 PM
Just have to say this was a great article- a welcome departure from much of this site's other content that could better be titled "How to Buy Parts From Our Sponsors and Bolt Them Onto Your Car." That's probably a bit harsh, but it seems like tech discussion in most automotive media today more closely resembles those full page "articles" in newspapers that have the tiny print at the bottom stating that it's actually an advertisement being passed off as an article. Unless you're trying to sell condoms. Then forget everything I just said.

Actually, the condom idea was especially genius. I've had to make silicone couplers for weird bends before using FG tape and the condom idea would have made them come out much prettier and been much easier to work with. I may have to do a 'rough rider' coupler one day in honor of this.
Saturday, January 15, 2011 11:44 PM
Good point kgx I agree, maybe not in the same words, but all in all a good point. It is nice to see some more advanced mods than bolt ons. There are all kinds of grades of readers I would imagine. These guys have to try and keep them all coming back and pay the bills that is just good business.

Where is the ending to this? There is a part six about wires already :/
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