28in wc = 1 psi

[wheeljack545]

If 28in. wc = 1 psi. That means to get 14.7 atmospheric pressure an engine sees. I would need to flow @411.6 in. wc. I know this does not account for piston draw,rpm, ring gap. But I just want to know if I am understanding this right. Thanks

[jfholm]

Goodluck! Consider the under taking to get to that point. First the pressure inside your bench. Lets say that the chamber side of your bench is 2 feet square by 4 feet tall. That means each wall would have 8 square feet or a total of 1152 square inches per wall. That means you would be putting a total of 411.6 X 1152 = 474163.2 pounds of pressure on each wall. Let me know when you are flowing so I can leave the neighborhood.

All seriousness though, you are on the right track though. You do want to flow as high as possible. You just need to check your pocket book and building skills. That is why most of us flow 28" to 36" wc. It is safer and easily attainable.

John

btw if I have not said so welcome aboard!

[wheeljack545]

Thanks John
Ive been a job shop machinist for 7yrs. I also worked at a cabinet shop for a year and can still go over there and use the machines. Yeah Im sure I would also not be able to be close to the head like we are on a sf 600's. I am going to see how high I can go. When I build this first one. Im going to leave room to add more blower. That way I can always upgrade when I have extra money. I plan on this one hitting 100 in. wc. Once its running ill sale my 600. to buy more stuff for it. Thanks again

[wheeljack545]

John I may have a good background. But that does not mean I know what Im doing. Im just trying to get farther down this road we r on. Just need more tools to do it. and thanks for the welcome.

[Tony]

John is quite right.
Not only the burst pressure of the bench, but the horsepower requirement of the blower starts to become frighteningly high.

Testing at 28" is entirely practical, and the electrical power consumption of all those blower motors running flat out can still be pretty fearsome as it is.

As soon as you start multiplying either the desired CFM, or the desired test pressure, you probably will not have enough mains electrical power available to run it.

That is what eventually stops most of us, not enough available Amps to build an even bigger bench.

[wheeljack545]

Tony thanks.
Yeah when I had the 220 outlet ran. I had them to put (2) 50 amp 220. So i could run at least double what I have now.sf 600. I have learned a lot with it. I just want to know more. I think I can build what I want for what I can sale my sf 600 for. The way I see I could up grade for free.

[Dan_DiM]

well even this is a gross over simplicity but if a cylinder of 50 cid has a head that for the sake of argument flows an average of 150cfm over the lift range @ 28in water it will fill the cylinder @28" depression in .01157 seconds which is about 2600 rpm. it's easy to see that an engine like this could produce much more depression as rpm goes up especially because flow doesn't go up in proportion to depression, i could see 60+ or maybe even 100 inches being useful but the cylinder doesn't start @ absolute vacuum so the 411.6 inch figure doesn't add up.

there are other factors like exhaust tuning which can give negative chamber pressures, valve event timing, velocity and inertia of the intake charge in the port which is effected by pressure a/f ratio and specific gravity of the fuel as well as humidity, plenum pressures, rod to stroke ratio, ect....

but like the others are saying you will most likely run out of available ampres before you hit 100" at 600cfm. that's not to say you cant flow small block heads making 350cfm+ at 50" with the right set of motors and proper planing which is more usefull than the 10-15inches i see heads flowed at then up-converted to appear as 28"..

[Heph]

I doubt you'll see naywhere close to 14.7 psi depression in an engine.
First because you still have some gaz in the chamber at TDC. Then as the pistons starts travelling down air is drawn in (even before it goes down with exhaust tunig/overlap).
I wonder exactly what is the maximum depression a race engine with high comp ratio would see ?


I'll be flowing small heads as per U.S. standards so I will likely see 300 cfm @ 28" (it's only a 2.0l engine after all ).

If I was to test at higher depression, what modification should be done to the stadnard PTS drawings?
I was thinking about adding some cross-brace in the settling chambers and the blower chamber.
Any other tought?