Custom Intake Manifold

[Schmleff]

I have been using early Aerovee intake manifolds since I built the plane. I have never really liked them as they did not have enough area to clamp the hose to. I always safety wired them to keep them from them from coming apart in flight.

Since my manifolds do not properly align with the ports on my new heads, I decided to build a new set of intake manifolds.

I got a set of intake flanges from GPAS for $6.95 and two 1.5" U-Bend exhaust tubes for $9 a piece.

I center punched and pilot drilled the U tubes and used a 1.5" hole saw to cut the tubes into sections. Pretty simple, I have about 10 min invested until this point.

More to come as I make progress...

 

[o2koold]

Thanks for posting this Jeff,
I have just finished reading "Speed with Economy". It has me really questioning the short cuts I have taken on my intake because it was easier/off the self. At this point, I have been contemplating doing just what you are doing. I look forward to seeing more.
Scott R

 

[maddogbrown]

Looks nice so far Jeff, just wanting to know how you will weld those pipes so close together?

Have you thought about a balancing tube between the left and right intakes?

Mike

 

[Schmleff]

I intend on wire feed welding them. They really are not that close together. They will have a balance tube.

 

[Schmleff]

After some thought, I am not sure about the balance tube. I will put the fittings in and try it with and without.

Anyone have any experience with running or not running one?

I have been reading here: http://www.thesamba.com/vw/forum/viewtopic.php?t=307376&postdays=0&postorder=asc&start=0

 

[JuergenA]

Hi Jeff,
many engines have the balance tube: Rotax912, parts of Limbach engines(VW), parts of Sauer engines (VW).
I don't know, if it is a must, I think, it is only, to make a compromise for factory tolerances. In my new setup, I will test, if I can compensate the tolerances with small rotating angles on the Posa carb. You know, the Posa is rotating position sensitive at full throttle.
with best regards
Juergen

 

[privatepilot03]

A balance tube will decrease the strength of the air charge on the side of the engine you're trying to feed. The engine oscilates from one side to the other so adding a balance tube will "pull" from the wrong side of the engine robbing you some of the suck torque (jeff will appreciate that term) that each side of the engine sees. We already have a giant balance tube in the form of a single intake manifold. We used balance tubes in the car world because the intake manifolds were 100% separate from each other and it seemed to help smooth out the idle.

Not a very elaborate answer, hopefully it makes sense though.

Chad

 

[Schmleff]

Thanks Chad. It does not look like GPAS, AeroVee or Revmaster use them. It was on my old Aerovee intakes so I just used it without question.

I think I will add the bungs and try it with and without.

 

[martinroy6100]

Good thread here, I built my intake from some stainless I had laying around and I was thinking I needed to add a cross over tube at some point. I don't believe I will do this after reading what is being said here. I know that when I went up to Ellision they had a cross over tube on their 1835 test engine. Their set up was on a single port and mirrors the Happy engine intake. I know that without the cross over idle in my 2276 is not as good as my 1835 of the past. A general question is what size is your intake? GP sais 1.5" but Arovee has theirs at 1.375, I read in some tuning books that higger intake speeds for the mixture would be better as it would not give time to sepperate the mixture out. Ellison indicated that with our long runners the mixture was more of a rain storm that a mist, any idears on whether 1.375 would be a better solution to intake sizing?

Martin Roy N61QC

 

[privatepilot03]

80% of the diameter of the intake valve is the general rule. That would put you at 1.25" if you have 40mm intake valves. The higher the operating RPM, the more port volume your engine can handle. In Jeff's case, he's winding his engine up a few hundred more RPM than most so he can handle the decreased port speed in exhange for the increase fuel delivery volume.

1-3/8" is probably an acceptable compromise for sport flying, but I'd err to the smaller size if I were you.

Chad

 

[thomefran]

I was just wondering why we don't use a real fuel injection system? Other than the expense. Wouldn't it be more efficient? I know that I have the cheapest system that is used on these vdubs. Zenith updraft. Works good so I haven't fixed it yet and I'm still learning. I have found several for around 1500 dollars that seem to be good.

 

[privatepilot03]

Cost and complexity. Fuel injection requires fuel pumps which require a fair amount of battery current. That means a charging system. A lot of folks aren't comfortable unless they have redundant systems so that means the potential for dual pumps, dual ECMs and on and on.

I'd very much like to work with a FI system on my next development but it's tough to justify when $400 will buy you a gravity fed fuel system that is dirt simple and reliable. Simply bolt it on and fly.

Chad

 

[maddogbrown]

Hey Jeff,

I am glad that you will try it both ways, with and without the balance tube. I have tried to find out more about it on the net (not much out there), and most of the time it is used with dual carbs to help at idle (any thing above that did not make a diff).
But I also have seen it on GA aircraft with single carbs. I would hope that the reasons for adding something that could fail/cause problems has more to do with balancing cht/egt rather than a smooth idle and low torque.

Just thinking about running at ~3/4 power and leaning out to the max...

Mike

 

[Schmleff]

Well, the first one is a paper weight. I have to keep to my saying "I build everything 3 times"...

 

[Hans]

as to using a balance tube or not: the Limbach & Sauer models that do, as well as Rotax 9xx engines are without exception fitted with dual carbs. Single carb engines don't use them, on these there is no need for it.

Hans

 

[mike1]

your manifold is the balance tube.

 

[Schmleff]

Finally making progress again. The exhaust is done and the intake is tacked.

 

[Schmleff]

All welded up. Just needs trimming sanding and paint. The bung is for the manifold pressure fitting.

With any luck, It will convert Avgas into noise this week still!

 

[eschrom]

Looks nice, Jeff. I wish I got things done as fast as you do.

The runner extends beyond the branch-offs that go to the ports. Is there a theory behind that?

Ed

 

[Schmleff]

Its just so that both pipes see the same thing as they are drawing from a common plenum. I am trying to get balance mixture to each port.