Plumbing OMP into Edelbrock Q&A

[Jeff20B]

As most of us know, RB has plumbed the OMP lines into their modified Holley carbs for decades now. It works. Why can't we do that with Edelbrocks?

I have a Camden supercharger project to get up and running and I have a perfectly functioning OMP. I've thought of three possible ways to plumb oil into the engine.

1. Directly into the carb like the RB Holley.
2. into the carb adaptor above the SC (equivilant to a carb spacer for you NA guys)
3. into the manifold - some Camden manifolds are already drilled and tapped for stock OMP injector fittings above the intermediate ports. My manifold is blank there.

PercentSevenC pointed out a potential flaw in #3. He said the runners possibly flow uphill there, and would result in oil pooling in the middle of the manifold, which would then dump into the engine under the right conditions leading to a batscreen effect. Having just examined my 5" manifold, that is not the case. It would seem #3 is possible.

There is a potential flaw in #2. Engine vacuum, or rather SC vacuum is high there and could potentially suck more oil into the intake than is necessary, leading to more oil consumption and smoke on startup and while idling; basically acting like a worn oil seal condition where none exists. Has anyone ever done this? I kinda sorta did on a weber lower manifold, which did smoke at idle.

Last but least is a partial flaw with #1 where it may be possbile to replace a percentage of fuel in the float bowl with oil, if idled for a long enough period of time. You've heard of Holley carbs 'loading up' on rotaries, haven't you? I fear this could happen with an Edelbrock similarly plumbed into the float bowl as the RB holleys are.

What is the best solution? #3? It's what Camden does.

[Rogue_Wulff]

Depending on the engine application, #3 might be the best way to go.
If the engine has the injector fitting holes, like an SE engine, I would plumb into those. Otherwise, install the stock oil injector fittings into the runners of the intake.
I don't like the idea of plumbing the OMP lines into the float bowls. While it resembles premixing, without the hassle of premixing, the extra oil would be slower getting into the engine. It would have to mix with the fuel before introduced into the engine.
Using the stock oil injectors would eliminate this delayed oil addition, and supply the added oil as needed.
I don't have the OMP on my SE engine fitted with the edelbrock. It was already removed when I got the car, so I have little choice but premix. I spose I could find an OMP and the oil injectors, then rig up an OMP rod. But, premixing is far simpler for now. FWIW, the car also came with a partial gallon jug of MMO, so I know it has been on premix for quite some time.

[Jeff20B]

So you think #3 into the manifold with stock injectors is the way to go? That sounds good. But why do I need stock injectors? Couldn't I get away with small barbed brass fittings? Is it a question of vacuum and boost pulling/pushing on the diaphrams inside the injectors, and controlling, partially, the rate at which oil enters the engine - which the simple brass fittings wouldn't have?

[Rogue_Wulff]

I would think the stock oil injectors are a better choice.
Generic brass fittings would have boost pressure trying to force the oil back down the OMP lines, where the oil injectors would keep this from happening. This theory seems to be supported by Mazda's use of the oil injectors in the intake/housings of factory turbo engines, rather than simply having a nipple to attach the OMP lines to the intake.
Since boost is part of the equation, another option that needs to be considered, would be makng OMP fittings at the top of the carb similar to the way they are situated on a 12A 1st gen Nikki. Of course, this will mean oil will be going thru the S/C, and who knows what that might cause.

[RotaryProphet]

Oil in the SC won't hurt anything; if anything it'll help it seal better, and there shouldn't be enough quantity there to make a difference anyway (not when compared to the quantity of fuel that'll be there). What you want is a way to put it into a non-pressurized place in the intake. I would recommend connecting them at the top of the carb (pre-throttle plates).

On a Weber setup on a first gen I ran the OMP lines through a pair of holes in the bottom of the filter box, looped around inside the box, and pointed face down into the middle of each carb barrel, held by a little metal bracket. It worked fine for an entire year or so, then I swapped to EFI and sold the webers.

[Jeff20B]

Thanks. My friend had an IDF Weber with a couple of small copper tubes someone added above the throttle plates. While idling oil would slowly drip.

The cheap triangle edelbrock filters use a flat metal bracket bent in the middle above the barrels; I could perhaps use this bracket to hold a set of OMP lines above the primaries.