[Werner]

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I take the liberty to quote a post from 12.10.2017 from MikeK:

There is a HUGE DIFFERENCE in operation between the Original patented Marvel INVERSE oilers and the Ampco and other simple knockoffs that feed oil DIRECTLY proportional to engine vacuum. People often confuse the two as similar in function.

An inverse oiler (Only Marvel oilers) feed less oil when the manifold vacuum is high (cruising, idling) and more when the vacuum is less (accelerating, going uphill, etc.)

Ampco and the other wannabies are simple suction devices. At high engine load (low vacc) they feed nothing. At high vacc idle and cruising they feed the maximum.

I have several Marvel oilers (I collect them) and would only run an inverse oiler, never a direct proportional one like the Ampco's. If you are using it on an industrial engine with constant speed and load you may want the Ampco, but those, unlike the Marvel inverse oliers, must be mounted lower than the engine vacc connection.

Marvels were required original equipment with Judson supercharger kits in the 70's or no warranty on the rotor and housing. They were also popular on gasoline engine trucks. Ampcos were often added to industrial stationary engines.


The Original Inverse Oiler Patent.
Notice it was issued to Paxton, not "Marvel"


Now, this just begs the question: Why bother, just mix the stuff in your gas. That all comes down to droplet size and what happens to the stuff. In either case some of it will be burned as vaporized fuel and some deposited on valve stems and cylinder walls. Atomizing it through a carb will create extremely small droplets as the fuel vaporizes and leaves the MMO behind. When mixed in the gas you will get more burn and less product delivery to metal surfaces than with the coarser spattering that a direct droplet feed will provide.


40 years ago I built and ran quite a few SBC race engines, both strip and circle for myself and others. They all had the metal can (unbreakable) MMO inverse feeders. Never seized an exhaust stem or ripped up a cylinder. More than I could say for the competition. Since it was mostly low vac. & W.O.T. the inverse oiler worked best. An Ampco would not. However, for lots of idling and easy high-vac street driving with little or no W.O.T. the Ampco (which I do NOT collect) would probably deliver a better feed rate profile. So I guess you could say I like the overall concept of both of them.

Yes, the directions for the Marvel oilers, both initial setup and rebuilding, are online if you search.