Race Engine Forum UK

Guy,
I remember a few months ago that you had posted some information on the flow characteristics of the Volumex intake manifold (the one between the head and the supercharger). You were experimenting with modifications to the manifold in order to even out the distribution of the fuel/air mixture across all of the cylinders. As I recall, you were attempting to improve the flow to ports 3 and 4 in order to bring them up to the flow levels of ports 1 and 2, which are directly across from output ports of the supercharger. IE ports 1 and 2 are unobstructed while 3 and 4 have a 90 degree corners to deal with. Can you supply any information on the modifications that you tried and if any made improvements.
Thanks,
Tom McGaffigan

Hello Tom

This took a long time to fathom out. The final mod I tried certainly appeared to equalise the airflow between ports in the Vx inboard manifold, however that is a long way from saying it works on the engine because I don't know what final effect it would have on gasoline/air distribution.

I do have concerns regarding the robustness of the device it needs in there, hence at this time I have not pursued it further. Welded-in tabs and blades and crude things like that are a complete waste of time.

In fact, having determined the necessary modification I rather thought that it would be better to extend the shaft drive to the blower and produce an new inlet with matched lengths and of course never took it that far.

The photos show the difference before and after in airflow to the ports, I do not unfortunately wish to display a photo of the device, as someone with more money than I have will immediately copy it!

Guy,
Thanks for the reply and the pictures. Your comment:

…œThe final mod I tried certainly appeared to equalize the airflow between ports in the VX inboard manifold, however that is a long way from saying it works on the engine because I don't know what final effect it would have on gasoline/air distribution. " GC

is a good one. A flowing fuel / air mixture, as would be obtained from a supercharger sucking through a carb, may be a different story. While the fuel / air mixture passing though the Volumex is pretty well homogenized by the time it enters the manifold there might be a separation effect when this mixture encounters flow directors inside the manifold. Another factor that I would think needs to be considered is: Would the total flow through the manifold into the engine be increased or is the flow to cylinder number 1 just decreased thus lowering the overall flow into the engine? From the second photo it does appear that the flow through ports 2, 3 and 4 increased at the expense of the flow through number 1.
I would be interested in any additional information should you do any more research in this area. I have a few ideas of my own Ill have to give a try.
Thanks,
Tom McGaffigan

Well done Tom,

you are quite right to be cautious about what I have said.

GC

Hullo One and ALL.
Excuse me if I've done this wrong . I'm a first timer.
Just a thought about even flow rates through 1-4 ports. I agree entirely that they should be even, but is it a possibility for example ,that although No.1 is higher at the manifold,when fitted to the head if the valves are shut at No.1 wouldn't the flow at No.4 increase dramatically and so on and so on. Again I agree it would be better if they were all the same ,but it might be another advantage of having a supercharger.

Thank's David Bienvenu.

Good point David,

mind you, don't forget the air doesn't stop flowing thru no.1 inlet manifold port just because no.1 valve is closed.

Still a good point, and I'm not at all sure what will happen, which is why I have not taken this one step further!

GC

David has an interesting point in that only one cylinder at a time is getting flow from the supercharger / manifold. Never the less, the number 1 cylinder is directly in line with the output of the supercharger, thus the flow into this cylinder has a much higher dynamic velocity component than any other. Cylinder number 4 on the other hand, has to deal with a 90 degree turn and an adjacent manifold wall. Because of this, any dynamic velocity component for cylinder number 4 is severely diminished. It would be easy enough (for Guy anyway, hint, hint) to test the various cylinder flows by blocking off three ports, measuring the flow though the open one port and repeating this process for all the ports. I do recall reading in an old supercharger book that for manifolds flowing a mixture of fuel and air, 90 degree corners are not a bad thing. I think the theory was that the fuel will not separate out of the fuel air mixture due to the turbulent flow created by the sharp turns. I am not sure I buy this theory though.
Tom McGaffigan

Hint taken Tom,

but to be more valid I think it will need to be done on a head with manifold and valves fitted, one valve open at a time and 3 shut. It needs to be blow through as well, a bit of a handful to rig up and I don't unfortunately have any clean stuff here that I can test at present.

Now, if I had a run of Vx motors to do....

GC

Guy,
Good point about adding all the downstream hardware, in order to have as accurate of a test as possible. I would think that due to the similarity of all the ports and valves, the influence of the head may be minimal. On the other hand, the valves and ports represent a restriction so that restriction may tend to make the individual manifold runner and port assembly flow more uniformly. The assembly may flow uniformly poorly though. You make another good point about having a blow through (i.e. pressurized, dense air) input rather than a suck through (less dense air) setup. Add in the fact that a Volumex supercharger moves a fuel / air mixture and you have yet another variable. I have some spare VX engine bits and a high capacity electric centrifugal air blower. I'll have to run a couple tests. Any thoughts on building up a cheap airflow meter? I have a wind velocity meter that would be simple and give some direct velocity measurements. I can add a down stream restriction in order to dial in the pressure (boost). I will be using air, not a fuel / air mixture for my measurements though!
Tom McGaffigan

Hullo Guy and Tom.
It's been a while since this topic was discussed. But as a slight diversion. Once I figure out how to reverse the drive , do you have any thoughts on a VX blower working okay in a reverse direction. ie fitted on 16v Thema head. I have never had one to pieces to know whether things are exactly the same in both directions. I did see a picture of an old 6 in line engine with a vx mounted on the other side, which was something I had been thinking about for a while. I don't know whether this possible project is necessary, or should I stick to the 8v engines.
Thanks David Bienvenu

I cannot think of any reason why it cannot be run counter-clockwise.

Can anyone else?

G

I can not think of a reason a VX can not be run "backwards" in fact, it can be run "upside down" also. IE drive rotor on the top, not the bottom. Running it upside down will reverse the flow left or right compared with the same before fliping it over. One thing about reversing the rotation is the wear pattern on the rotors will begin on the other side of the phasing gear teeth, possibly increasing backlash faster than if it was run the same direction all the time. In addition, if the blower has been set up, with the rotors timed for a given rotation direction (as Guy sometimes does to compensate for gear wear) then the rotors may hit slightly when rotated in the opposite direction.
Tom

Some good points of detail there Tom, well done,

G

Thanks people.
I'm a little embarrassed by your reply Tom. I've been dreaming up complicated belt drive systems to reverse the flow. Never thought about the upside down thing . But the bit about increased backlash on the teeth,if run backwards. Wouldn't the backlash remain the same at least until there is noticeable wear on the new side, with the benefits of having new tooth faces on the reverse side. Setting the clearances on the rotors to allow for wear is a different matter. I have several blowers, with one being new old stock ,the rest seem reasonable, so I hope to have something okay to use. I'll keep thinking thankyou.
David Bienvenu

David,
Glad my post helps sort out your drive belt / flow issues. Yes, the backlash will initially be the same but reversing the rotation will cause the other side of the phasing gear teeth to be "run in" which will increase the backlash slightly.
Tom