If I could find a correction factor for the speed of sound I would have to make the chart all by hand or make a correction or convertion for the n/a chart.

 

I just look around here but have been thru all of this. All of my research has ended up with the plenum volume/shape is most important. I made a intake for my 4.3 Typhoon and used a schedule 40 4" weld elbow on a 4bbl intake I welded bungs in.

I have a D-1 / 16lbs small block that i have had a couple of different intakes on and found the same thing, currently I am loosing the stealth ram and putting a victor efi on it with a custom plenum.
Remember the old 3.8 boosted indy engines? they used a stock designed lower with a huge plenum. (at least the same cubic inch as the engine).
If you plan on making a intake out of sheet metal (you must have a ton of time make sure you use at least .187 thick aluminum so it doesn't blow apart.
Oh yeah forget the prostocks they only work between 8000 and 10500 rpm.

Good luck.

 

So the plenum should have the same volume as the engine? Interesting...

As far as time... i have all winter first thing I am doung is milling the stock intake off. If you have seen the 84-85 buick GN intakes you know how bad they are designed. Inlet is in the back of the intake. It goes UNDER the intake manifold to the front, then comes up and dumps into the main plenum whe the air has to flow upward, hit the roof, then be bounced back down into the runners.

I milled off that roof, and put a false floor in the plenum at the base of the runners. I will make a new "upper plenum" where the air will now enter. This will allow the air to flow directly down the runners. I am debating on whether or not I should build in a traingular wall in the middle of the plenum to help more evenly split the air to each side of the motor. I could technically make them like runner extensions if I were that ambitious. Anyway, the old inlet is sompletely milled off and will be tig welded closed. Right now it looks a bit like a single plane carb intake on the inside.
If I need to get 231 cubic inches of plenum volume, I'll have to do a little design modification for the upper plenum, but it's not too late. Are you sure about that design aspect?
This is just a quick short term project utilizing the base form the stock intake. I have a guy water jet cutting flanges for me to build one from scratch. But that will be an over the winter project

 

One of the consern's for boost is the thickness of the materal it is made from.You don't want your intake to "balloon" every time it gets boost.That has a tendency to distort it's shape and lead to cracking and incorrect fit and flow.

 

I searched for months and that is what i found. Can you buy a carbed 3.8 manifold and go from there?

 

yep. I'm keeping an eye on this one. http://cgi.ebay.com/ws/eBayISAPI.dll...e=STRK:MEWA:IT

they run $230 new, plus it would have to be converted to efi, then I'd have to buy a dry throttle body, carb hat, etc. That's why I have kind of shyed away from this direction to some extent.

 

You sure you want to pay that much for a intake?
The shipping is going to be more!