2 cm hole - Small, cheap flowbench for restriction

[Thomas Vaught]

Most of the ones I have seen in my past Formula SAE work were a single throttle body deal before the restrictor.

I have seen winners who had an adjustable length runner manifold that helped on the torque in the lower rpm and dropped down to a shorter runner length at high rpm.

The team did this with a pneumatic cylinder and a stand alone processor that knew the manifold runner position and sensed rpm.

Pretty cool but I think it is outlawed today.

Tom V.

[DaveMcLain]

I don't think a 2cm diameter hole is a terribly small restrictor for a 600cc engine, not at all esspecially if you can do what you want on both sides of the restriction. I would say that playing around with a flow bench even a home made one with an sensitive inclined manometer would help you a bunch.

I have some restrictor plates that various customers have given to me over the years. One is a 1.5 inch two hole plate that was run under a 4412 Holley (500cfm @ 3inches of mercury). It's a pretty tight restriction on a 355 cubic inch engine but they still managed to make around 375 horsepower and turn it to 7200rpm!

It can be fun to take some clay and play around with the plate on the flow bench, it's amazing how much you can improve the flow by experimenting. It's pretty easy to make it flow about 15% better.

[larrycavan]

[DaveMcLain]

Yes, two 1.5 inch holes. I do believe that they also had to run 2 1-1/4 inch holes at some tracks. I know that's a lot more area than what we're talking about here with this 600cc engine but it was also under the 2 barrel carb and running on a 5.7 liter engine so it was quite a restriction.

From the research we did later when the customer had to run a 350cfm 7448 carburetor on the same size engine the smaller carburetor was MORE of a restriction than the larger carb and the 1.5 inch 2 hole restrictor plate!

350cfm at 40.6 inches of water isn't a lot of airflow for a 355 inch engine. What was very interesting was what worked best at the track rpm wise vs what the engine would do on the dyno.

When dyno testing the engine would power peak at around 5200rpm yet on the track they never ran it below 5200rpm when racing, leaving the corners at about 5500rpm and going into the next turn at about 6800rpm most of the time proved to be the best.

[larrycavan]

[Thomas Vaught]

Keith Wilson of Wilson Manifolds told me at one time the way they beat the "Restrictor Hole" rule
was they modified an intake manifold so that there was a wall covering every port except at the bottom of each port. The total area of all of the openings at the bottom (8) was the same as the area of the (2) 1.5" holes. Each port basically had about a .375 tall by 1.25 wide port
opening at the bottom.

Worked great until it was outlawed. Big volume before the port and big volume after the port.

Tom V.

[larrycavan]

[DaveMcLain]

The real trick to beating the restrictor plate is that once the velocity is high in the intake tract it needs to stay high. In other words, keeping the area small after the restrictor at least for a while will really help flow remembering that when the velocity drops the pressure increases. Good info.

[taphonomist]

After looking around a bit, I think a real simple pitot setup will be the most effective way to do this. This will be a pretty much single purpose setup, used only for optimizing the restrictor/throttlebody, and I like the simplicity (aka cheapness) of the pitot setup. Mount for the parts, long pipe with some drinking straws in it, a pitot, and some sensors.

I'd like to get the FP-1, but may go the roll your own digital route (cheapness again, and I know some electronics). Has anyone successfully used a Dataq setup for this?

thanks,
taphonomist

[Nick]

I am working on a Dataq setup right now. Still waiting for the parts. I will say this, after looking over the sensors capabilities and accuracy, I don't think you can beat a simple water gauge. It is completely repeatable and works every time. Just don't get bubbles on the water. And make sure there is not water in the tube where it should not be. Yes it is a bit of a pain, but so are electronics. I have to give credit to John for developing the FP1. I don't think I will ever give up my water gauges.

JMO


Nick

[Nick]

I am working on a Dataq setup right now. Still waiting for the parts. I will say this, after looking over the sensors capabilities and accuracy, I don't think you can beat a simple water gauge. It is completely repeatable and works every time. Just don't get bubbles on the water. And make sure there is not water in the tube where it should not be. Yes it is a bit of a pain, but so are electronics. I have to give credit to John for developing the FP1. I don't think I will ever give up my water gauges.

JMO


Nick