custom plenum for Ford V8

[IaTR6]

Seeing the custom plenum work for the Rover urges me to present what I have done for my ford engine.
You can see that the manifold is a two part system, and the top half is 6" tall,
 which I cannot tolerate under my TR6 hood.
This is the adapter plate that attaches to the lower manifold, and has radiused entry into the runners. I would like to have velocity stacks that could be accessed for tuning, but I don't have the headroom.
A machinist said I shouldn't try this at home, but I got away with it.
This is the beginning of a plenum that will cross over the valve cover and place the throttle body on the drivers side. It is 1/8" alum and a little over 2" shorter than the original manifold top. I hope the volume isn't too large, and wind up killing all throttle response. The new plenum will be welded all around, and bolted to the lower manifold in the same way as the original. I will have alum. tubes for the bolts to act as crush spacers. When I have more progress on the plenum, I will pass it on.
Dennis

[rficalora]

Looks like great progress so far.

You did the radius with a router?  How slow can you dial down the RPM's?  I hope you did it in a bunch of passes & had some way to hold the aluminum other than your hands.  I had a piece of aluminum catch once on a table saw (geared slower but not slow enough).  It kicked the piece & about took my finger off.  Be careful.

[flyinlow]

That looks good
here is another option that I plan on replicating since it fits under a stock GT6 bonnet
that pic is from Matt Kline's build pics

[IaTR6]

Rob,
That is exactly what the machinist warned me about. My PC router doesn't have variable speed, so I started with a very light cut and increased the depth by 1/64" at a time. I did get a little more aggressive with the last cut and luckily still have my digits! I fatened the plate to a 2X12 with double stick tape to hold it. I am not recommending this, just showing what I did. I also think the D-handled router helped steady the cuts. I would suspect a machine shop could do this without risk for a reasonable sum, but I'm just nuts.
Dennis

[roverman]

Dennis, is this top plenum to have IR's included, like oem. piece ? Picture of top, oem. manifold, showing interior detail ? roverman.

[IaTR6]

Roverman,
I don't have enough room for individual runners, as I am trying to limit the overall height to ~3.5". I would have liked to have trhe runners, and perhaps if there is a second iteration I will. I could see each runner bending over the valve cover to a common plenum on the one side, like the factory, only unfolded. I worry about total plenum volume, and the effect on throttle response. There may be an advantage with fuel injection, as it doesn't rely entirely on a change in manifold pressure for fueling changes, where a carburettor might not react as well. I am definitely covering new ground for myself here, and may wind up with a train wreck. I should have the beginning of the upper plenum in hand soon, and will post pictures (if the welder comes through-he is two weeks past the promise date now.)
Dennis

[MGB-FV8]

Dennis, good luck figuring out the proper upper intake resonance tune.  Most of the Ford 5.0 Liter intakes are reversible but if the height is the problem try one off a '94-'95 Mustang 5.0 H.O.; it has a much shorter height than the '87-'93 intake.  BTW, I've also tried to shape aluminum with a speed controlled router but it still got away while having to free hand the material, and yes, I did screamed "OUCH @#*%!

Jacques

[roverman]

In plastic and aluminum, using a "piloted cutter", with a drill press is ok. IE., use a drop-in plug in the port, with proper size hole, for pilot. I made a monoflute cutter,(piloted), with an interchangable part-off blade/profiled, as the cutting tool. Keep the rpm down to prevent chatter. Your results may vary. Safety Glasses ! Good Luck, roverman.

[IaTR6]

Well, I have finished my custom plenum that goes on the lower half of the original Explorer intake. I achieved the goal of shortening the height by 2", but I have lost the effect of tuned runners that the original design had. I know that the necessary calculations, etc are beyond my skill level, and the room to fit such a design without changing the profile of the hood (bonnet) is just not there. I hope that proper selection of cam timing, along with the light weight of the car will help aleviate some of the lost torque at lower rpm.


This view shows the plenum crossing over the fuel rail, and the allowed clearance for taller valve covers to go over roller rockers. (2")


I tried polishing the aluminum, and got "good enough". I didn't enjoy it particularly.


This is the view from the throttle body mount to the inside of the plenum. The ramp on the bottom is not ideal I'm sure, but I needed the plenum extension to clear other items as I mentioned. The actual opening area at the ramp is larger than the area for the throttle
by more than 1 square inch, so we will see. The tube you see through the throttle opening is one of the structural compression tubes that transfer the mounting bolt clamping force to the lower manifold half, and prevent crushing of the 1/8" plenum.
The mounting bolts are 5/16" flange bolts with o-ring sealing under the heads. I only found the exact ones I wanted at ARP, and they are a work of art-and a little more costly than I would have liked, but what the heck.
I didn't do any of the welding on the plenum, I found a small shop to do it. They took 2 months to do the first two welds, but picked up the pace for the next two trips. Some of the welds could have been eliminated if the design had not evolved as I went, but this is a prototype design, not a production piece. (That's my excuse, and I have it written on a piece of paper in my wallet for reference!)

Dennis

[BlownMGB-V8]

You know Dennis, you could use internal dividers to get back at least some of the runner length. Something to consider anyway as it would be pretty easy to add them in.

Jim

[IaTR6]

Jim,
Since the plenum is completely welded all around, I'd have to saw it open to add the dividers. I had thought about whether I should have added some corners into the plenum to reduce its volume, but didn't. At this point, I will finish the car and engine and see what happens. I will post the results, but this project has a long way to go.
Dennis