Thanks for the pics John! Are you using a carbide bit in the plenum as well as in the ports? Finishing with a sanding roll in both areas also?

When I am totally done with an intake I will hit it with 40-60 grit sanding rolls. Pretty on an intake is not the way to go if you know what I mean. When you look down your number 3 port from the plenum take a real good look at what would be considered the short side. Now turn it so you are looking from the port side and look at the short side again. The curvature of that wall needs more rounding, curvature to it. When it is bolted to the head I had to look down #5 to see how well the port was lined up on the flowbench. Stop and think about what the air-flow has to do and why that sharp angle needs attention. air is coming down the plenum toward what would be the front of the engine. Now it not only has to go around the peak in the runner but it has to now change direction in the pushrod pinch and go the opposite direction toward the rear of the engine. Its hard enough with just the head to keep the air attached to that wall. When I put my velocity probe in the plenum and checked air-speed at the pinch it maxed out my gauge at 401 ft per second so its actually higher than that. (WAY TO HIGH)The runners on the Indy intake have a lot more volume and that's why the rounding of the runner helped it more. I wish I could play around some more right now but it will have to wait till next week. Gotta pay the bills.

Sorry I forgot to add, Yes I have 6" carbide burrs that you can get from Summit if you need them fast. I rarely use the aluminum cutters as they are really aggressive. I buy WD40 by the gallon and pure some in a small dish so I can dip the cutter often to keep it clean and cool. Tranny fluid works too but is messier.

Interesting read all the way through.

I run a 2" HVH which is a cnc tapered 4 hole for the top and an open for the bottom inch, I like the way you blended the open spacer into the plenum but with 4150's I never found much power there, there IS power working the roofs of all the runners into the plenum, I just never layed one all the way back that far unless we were running a 4500.

The interesting thing is with intakes and intake ports is it's pretty much (general rule of thumb) a 3:1 ratio, you look for roughly 3 times the CFM than the port is actually flowing in the running motor....that of course is because any intake valve is completely SHUT roughly ~2/3'rds of the time....X cubic feet per minute/ 3 = a NET of 1/3 X cubic feet in 20-23 seconds. It's good to apply the @.050 duration and divide it into 720 degrees, take that product and multiply by 60, that's the number of seconds per minute the valve is off it's seat. And by varying the @ .050 degrees you get some perspective of how much additional time you get to fill the hole. doesn't sound like much but apparently it is

good stuff! Thanks!!

When I started playing with my Friends Indy intake the first words out of my mouth were "no way would I buy one". Well now I am eating my words because except for a few runners, with a little work when the heads flowing 301 it still flowing 301 with the intake on. Its a shame this combo is going in a street car. If you are interested in seeing the work done on the Indy intake let me know. I am finding out thru lots of testing that number 3 and 6 runners on a small block mopar manifold need the most work. I want to set the beside a Chevy Victor Jr. and see why it isn't an issue on that manifold. I didn't really sit down and figure out how much he has in this intake but I think Ryan charged him 300-400 for the intake from Indy. Relocated and drilled new mounting holes for Edelbrock heads and gasket match as close as he could without the heads and blend in about 1 inch (150 dollars) plus what I charge him.

I would like to see the indy I also have some pics of mine to compare.

That will be interesting to see.

One thing I've found is the Vic 340 needs to get the fuel columns 'down in the plenum' to get the inside (3-5, 2-6) runners to work, there are those ridges along the top sides of the manifold that handicaps those runners until the runner velocity seems to even them up. The HVH cloverleaf combined with a big cfm carb with downleg boosters seems to be the best combo I've found. So the outside runners seem to have an 'easier time of it' until the motor is really loaded and all the runners are 'pumping', those inner runners (like an M1 Big block) tend to draw harder of the sides of the plenum. Lighter loads and the outside runners temd to hog the flow and look better on the bench.

I understand about blocking the port but with an intake manifold dry airflow doesn't really give an accurate account of what's really going on with Wet (fuel suspended in air at various densities) columns of air shifting back and forth against valves slamming open and shut.

Dry flow is awesome in terms of measuring IMPROVEMENTS but (as I said in previous posts) it doesn't really tell the whole story since you're measuring DRY CFM in one direction and air/fual mix is only cycling in the right direction (toward the piston) for 20+ seconds of that minute.

What I was saying about the inner (3,4,5,6)runners of the Vic 340 is they seem (to me) to will be more reliant on the outside runner walls for maximum flow since the outer wall doesn't end at a runner divider like the outer (1,2, 7,8 cylinder) runners do. The outer cylinder runner port windows (which are the inners in the plenum) to the plenum are smaller when you consider you can include the actual sides of the plenum as part of the (3,4,5,6) runner port windows. Charging the plenum is the key to single plane manifolds IMO and that is harder to simulate in terms of flowing a manifold in terms of what's really getting past the valve in a running engine, that's all I'm really saying.


Tougher to explain but easier if your looking at the plenum/runner relationship. Air has to flow around the Vic's 'Ridge' between the 3-5 and 4-6 at low velocities but once the plenum is "charged" the flow (I think) improves more than you would see on a flowbench.

I agree. Its real nice that the piston stroke actually helps correct some of these little issues.

Have you guys played with putting a "turtle"(deflector)
in the bottom of the plenum to deflect the air flow
to the runners

Funny you bring that up Mike. I checked out the Brodix site and read up on them. I kinda made a small one with duct sill and did some crude testing. No change so I made up one of the ugliest balls of duct sill that you could image and stuck it on the bottom of the plenum. Flow was only down 5cfm on that test. There is a post on Yellowbullet right now and a guy was told his plenum volume was to big so he cut down a piece of 2 x 4 wood and put it in the bottom. The car ran the same.

I wonder if the reason little is noted with those turtle experiments is the plenum volume was reduced with the addition of the flow director. As I understand it the turtle simply helps with the "turn". So the trick is to find the optimum balance between the turtle's volume and the plenum's initial (pre-turtle) volume. IMO if there was no improvement with the turtle the plenum is already too small. Understandbly there is only "so big" one can go in terms of volume given packaging restrictions. I also think it's just as important to correlate any gains seen dry flowing on a bench with dyno testing ona running engine. Because there's a lot of physics that are not being accounted for in a dry flow test.