Inliners International Forums General Discussion Engines Tri Power plenum progress

OK guys, use your imigination and you can see the final intake! I was satisfied with the last cardboard mockup so I cut the aluminum to its dimensions. Once I measure everything again for the umph teenth time, I can lay out all the hole centers, drill/tap holes for studs, then have it welded up. Just for good measure, I'll add three nitrous bungs, centered inboard on the side under each plemun opening. I will also use water heat at the bottom. I hope it works.

Nice That should Work Fine. }[oooooo]

Nice work for sure. I might think of adding a 1/4 inch pipe thread bung someplace to use for an accessory vacuum source or at least for convenience if I ever wanted to use a vac gauge for diagnostics.

Mike G

I agree 'totally'.

Stand-by for orders from all the 'slant 6 gang'. I think the only intake made for them was a 4bbl that had the carb next to the wheelhouse. That was circa 1962 or 63.

John M....

Hey John,
"4bbl that had the carb next to the wheelhouse. That was circa 1962 or 63."
Look close John. I think there is one of those long ram intakes in the picture. Is it El Plymino ?

Jim

Jim; you may be right.

I thought it was a set of painted headers.

JM.....

Here's the Clifford Hyper Pak intake. The motor is going into El Plymino. For now, I will stay with the 6 pak with short runners. The Clifford long runner is really for high rpm use and my cam is more low/mid range.

51 P;

That set-up will work really well on the dry lake, you should try it.

Before you put on the 3 carb, that is.

JM.....

What is your plenum volume? Your engine displacement? The plenum volume looks too large for a typical slant six engine.

Frenchtown. Thanks for the input. The motor is a .40 over 225 ci with head work, larger valves and a MoPar cam (460/268). I'm limited on length and carb baseplate width for the plenum.

I kept the width on top to just 3" which is a tad more than the width of the carb bases. The length was kept as short as possible for clearance reasons. Its 19". The runners are 1.75" dia. and 8" long.

The only variable left is the height, which I set at 2.5". My original plan had it at 2", but I increased that to make room for water heat at the bottom of the plenum. Its a street motor.

However, the height is easily changed at this stage. Are you thinking about the Helmholtz Theory and volumetric efficiency?

So your plenum volume is about 119 ci right? That sounds about right for a 230 inch motor.

Nice workmanship.

Well, I don't know of a formula for figuring plenum air volume! What is it?

If your question is about plenum volume sizing, a good rule of thumb is 50-70% of the displacement of the engine, higher % as your rpm range climbs.

If your question is how to calculate the size of your plenum, for yours it is: (area of trapezoid (side)) times depth.

Area of trapezoid is found as follows:

[(Long side + short side) / 2]* height
or (3" + 2")/2 * 2.5 = 6.25 in2

6.25 * 19 = 118.75 or ~ 119 in3, which is about right.

Thanks Rick. That's interesting. It appears theres a wide range of what plenum volume sizes can be and still be effective.

I've seen V-8 plenum size quoted at 40 to 50 percent around 5k to 6k rpm. 4 cyls's at 50-60 percent and 6's with 2 plenums feeding 3 cyl's each at 65-80 percent, with higher rpms using 10-15 percent smaller volumes.

My tri-power Offy intake plenum for a 218-230ci 6 cyl flathead is about 1 " deep.

I'm way out of my field, so I'm happy to know from the feedback here that I'm in the ball park with the size. I guess it remains to be seen what end of the rpm scale I will be in.