Some of you may recognize the topic, I brought this up about a year ago and am just now getting a chance to work on the project. Here's the current setup:

'85 Ranger shortbed 2wd
289 cid, 5-speed transmission
Comp 282S solid lifter cam
all the other goodies that go with a decent engine build
estimated 350ish HP, Best of 12.9 at 110MPH in the quarter

The current induction is a Weiand Xcelerator low rise single plane with a Holley 750dp carb. Fun to drive, runs great, but there's always room for improvement.

I've always loved tunnel rams, the design and runners are perfect for maximum performance and good torque. But they don't fit under the hood, and I don't want to mess with my hood. So I had the idea to replace the dual-quad tunnel ram top with a custom built top and use side-draft carbs to feed the plenum; a tunnel ram without all the height of the carbs and air cleaner on top. Typical side drafts like Webers are expensive, I'm cheap, so surfing eBay I finally came across some CBR900RR (900cc 4cyl street bike) carburetors.

So here's where I'm at today, most all the necessary parts, some aluminum to build the plenum, and about to begin welding it all together. Will post updates as the project progresses, but here's some pics of the test fit.

All the parts on the bench (plus an extra ATV carb happened to be in the shot, not part of this project)


Test fit on the 289. Nothing welded, just all propped up with wood blocks.






Hood about 1/2" from closing, so I can peek through the gap, still have miles of hood clearance to the carbs.


Threw the dual-quad top on along with my Holley carb, just to see how tall it was. Call this plan B, if the CBR carbs don't like running on a V8. Hood is about 3" from closing when it hits the carb. If I cut the hood the carb would com about flush with the hood, just right for a bug catcher or shaker scoop I suppose.







Hope to post an update in a couple weeks!

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It has been many years (around 25 or so) but I had a tunnel ram with what looked like a crossram top. It dropped down and took the carbs across from each other instead of one behind the other. Dealing with a Ranger I imagine your space is limited so even that may not have worked. I bet if one went to looking they could find that top again. I had it on a 318 in a '37 Chevy PU with a couple small 4bbl carbs. I think I totalled out around 650 or 700 CFM.

awsome vision man! Good to see something different for a change.

That looks cool!.....curious if it will be to much cfm??

The carbs are 38mm CV (constant velocity), so they throttle actuates a butterfly valve (like a normal carb), but in front of the butterfly is a flat-slide that is vacuum (air velocity) actuated... the more air drawn through, the further the slide moves up and so fuel is metered appropriately at any flow rate within the carb's capability. I targeted this type of carb for this very reason, part throttle driving should be awesome with these. I don't think too much carb will be a problem due to the CV design, I just hope it's enough carb. Best I can tell, four 38mm carbs of this type should be similar flow to a 700-800cfm 4bbl, I think... Also based on the bike these came off of, a 900cc, 12,000rpm, 150ish HP engine... on the bike each carb is only feeding 1/4 of the time (four stroke, one carb per cylinder), so in theory with the carbs feeding 100% of the time they will be good for 600ish HP. One other way to look at it, 900cc x 4 (for 100% duty cycle) = 3600cc, at 12000RPM. That would be a lot more air than my 4.7 liter at 7500RPM. They're all really rough calculations, the proof will be in the pudding.

I'm a little concerned about idle, since all four are linked together, all four feed at idle, so I hope I can back the idle screw off far enough to get a good idle speed and still be mixing fuel. The other slight concern is fuel pressure, since these are meant to be gravity fed. I've read you can get away with as much as 5psi of fuel pressure, so maybe an adjustable regulator is all it will take to fix that problem. And also one person has mentioned that the float valve might be a tad small for this type of application, so if it starves for fuel at WOT I may have to look at enlarging that, which could be a whole nother can of worms.

my only thought is that on the motorcycle it is feeding each individual cylinder and you can get by with alot more cfm but when feeding into a common plenum might act to big.i was just looking at the size of the trumpet and by that it looks like they are about as big as a dominator venturi but i could be wrong.neat to see what happens.

cool idea!
i hope it works, i will definatly follow this one.

Ah yeah I see what you're saying about the trumpets. They actually have a pretty good taper to them, they go down into the body of the carb about 3/4 inch more than you can see. As mentioned they're 38mm, or about exactly 1.5 inch, throttle blade size, which is the diameter of the venturi of an 850cfm Holley, but the throttle blade diameter of a 450cfm Holley. I'm thinking since the restriction is the venturi (and Holleys have the booster in the middle of the venturi which chokes it even more) that it will be closer to the big end, around 700+cfm performance level.

I think it would look even cooler with a rack on both sides of the plenum! Are these Mikuni carbs? There will be lots of tuning parts available, so you should be able to jet them down if you need supply less fuel. Do they use rubber intake flanges to bolt to the engine? I don't think the fuel pump situation should be too much of an issue. Yamaha used the CV style carbs on their 4S snowmobiles before moving to EFI, so those were definitely not gravity fed.

You should be fine all-around. The idle is not a problem - remember, it used to idle an engine 1/5 the displacement. Acceleration enrichment should not be a problem with the CV feature to prevent a huge bog on tip-in. The fuel flow through the valve is good for 150hp stock with gravity, so 3-5 psi will flow far more through the same valve. Yeah, that will be fun! Although many 'cycle carb conversions have been done before, they're usually ITB-style without the plenum and runners. Props for creativity.

David

70XL: Yeah a bank on each side would definitely look awesome, but I think it would be way overkill unless I get up well over 400-500hp which isn't gonna happen. Also if they run well the long-term plan is to build an intake duct/box to duct air from my ram-air box/filter to the carbs, which would be a little more work with two banks of carbs (would need two air boxes I suppose). And yes they have a rubber coupling to connect to the engine so my plenum will have four 1.5" diameter 1" long aluminum tubes to mount them.

They are actually Keihin carbs, but still I think parts are pretty easy to get (can get anything from the servicehonda web site) and I think the jets are pretty easy to find.

PSIG: Thanks that gives me a little more confidence that I won't have too many problems. The fuel pump pressure is a very good point, really rough math tells me 12" of fuel (rough height of the fuel level above the carbs on the CBR900RR) would amount to around 0.25PSI, so with 3 PSI the same restriction should flow about 3.5x more (kind of a square-root relationship) so it should be enough fuel to make 3.5x the 150hp of the CBR900RR, which is over 500hp. Even with some wide margin for error in the math, as long as I can get the carbs to hold a couple PSI I should be OK for fuel flow.

Quick update, gotta make progress in a Makin' Progress thread after all!

Project has been going pretty slowly thanks to the holidays and all the family stuff, but have had some time to sneak out in the shop a couple hours here and there. I'm at the stage where I'm ready to start welding it together, and since I have next to no experience welding aluminum, and only have an oxy-acetylene torch to do it with, I'll be doing some practicing before putting the torch to my hard work!

On the bottom plate, since it is 1/4 inch aluminum the saber-saw just didn't like chewing through it, so I started by making an outline of the cut, then used the drill press to punch a couple dozen holes just inside the line to remove the center portion. Then I bolted the plate to the tunnel ram bottom and used the die grinder to cut to size. Note, when die grinding aluminum, if you don't have the bits made for aluminum, it helps dramatically to dip the bit in some sort of lube every 15-20 seconds. I used so me cheam 10w-30 motor oil and it worked pretty good keeping the bit from getting clogged with aluminum.





I precisely measured the carbs center-to-center, marked locations on the top piece, and used the drill press and hole saw to make the holes. These are a little under-sized, so I can grind to exact fit the carb rings (sitting on top of the plate). The rings are 1.5" aluminum tube cut to 5/8" long. The carbs are about 1/16" larger diameter, and since I can't find 1-9/16" aluminum pipe I had to cut these, expand them slightly, and weld the gap shut. Turned out pretty decent. They are a little marked up looking because I ground a slight notch near one end to help the carb's rubber boots latch on when they are installed. These will be the first welding, followed by welding this assembly to the bottom plate pictured above.



I've been doing a little practice welding. My original plan was to weld the rings to the top around the exterior inside corner (as shown below), then from the back side grind the plate to perfect match the rings. I'm finding it hard to get the base 1/8" metal hot enough to weld without overheating the 1/16" ring, and in general just getting the heat focused in the weld area since it's an inside corner. So my new strategy is to grind the holes so the rings just fit inside perfect, then from the "inside" of the plenum weld the tube to the plate. That should make it easier, heating an outside corner, and also will hide my ugly welds (they don't gotta be pretty, they just gotta be air tight).





I hope to get some work done over the new year weekend, wish me luck!

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Nice. I'm curious how your fuel distribution will be. Not too concerned, as the CV nature should prevent much dropout or lean-out. I never could get OA aluminum welding down with reliability, but I did get a chance to have an old-timer aircraft weldor show me Oxy-Hydrogen. Awesome. I did a couple sound (not the prettiest, but sound) 6" butt welds on my first try. By the time I was half-way through the second one, the bead was looking pretty sexy. Like welding ice blocks with a hair dryer, but fast.

Easy to set-up with an Oxy regulator for the hydrogen, and the pink didymium glass-blower's glasses. I loved seeing everything clearly while working, as it appears through the didymium to be waving a nearly dead torch over the metal, and suddenly bloop - there it goes and you're off and running. Without the special pink glasses it looks like solar flare in your garage. LOL Just a thought if you have too many issues with OA, or plan to do much aluminum.

David

Pink didymium glasses for OH welding, also used in glass blowing:

I tried to design the carb placement with mixture and flow distribution in mind (not knowing a thing about them of course lol). The carbs are designed to sit at about a 30 degree downturn from horizontal (probably close to the angle the bike's cylinders are layed over towards the front), so I designed the plenum with that in mind. The air/fuel coming out of the carb bore intersects the base of the plenum at pretty close to the mid-line of the plenum bottom, so that way each cylinder should have a pretty straight shot from at least the nearest carb. Not sure how much that matters, and ultimately I don't have any way of testing the distribution, so will just cross my fingers and hope it's good.

I've read a little about oxy-hydrogen, didn't know if it would be any easier or not. Being able to see is definitely important though, I had to set up my 1000 watt halogen light over my shoulder to get a much light as possible to see while I'm welding. Was there anything about the OH flame that made it easier than OA, or was it just the fact that you could see better? I thought a smaller, hotter flame would be beneficial, but I dunno I'm a newb when it comes to any kind of welding.

Sure would be nice if F/M would add a Ranger section, there are quite a few of us with Rangers in our Ford collections.