A Fathers day what is it.....Ok, it's another Fox, but?

Based on what I have seen, the engine appears to me to be a Fox .45. I'm quite familiar with the .40's. I have bushed Fox .40's, Fox .40 ball bearings, cast iron versions, ABC versions and one Quickie version and one Aldrich large case .40. The Quickie was a .40 event which used a .50 sized case. It most closely resembles what you show in the picture. However, the knurled front on your engine at the drive washer is something I have only come across on the .45. In addition, the 2 bolt carb similar to the same setups on the .15's, .19 and .25 engines. After the .40 size displacement, I get a bit lost with the Fox's, I know they're Fox, I just don't know the ins and outs.

Everything i have seen with that back plate says Racing engine https://www.ebay.com/itm/Fox-Quickie-500-Racing-Special-Model-Airplane-Engine/254265054378?hash=item3b3360d4aa:g:UyEAAOSwFMRc6ZHp and some here https://www.google.com/search?rlz=1C1SQJL_enUS817US817&biw=1493&bih=776&tbm=isch&sa=1&ei=iKAHXcG-C8HAsQXOirWIDg&q=fox+model+airplane+engines&oq=fox+model+airplane+engine&gs_l=img.1.1.35i39j0i24l2.23479.24306..28972...0.0..0.86.463.6......0....1..gws-wiz-img.8hh_hvMxcsY#imgrc=8K8uC_BICOgnBM: i know there RC but could have been changed over ?!

Bob, I have a NIP Fox needle for that if you want it.

No charge, I’ll never use it.

Sorry I cannot be of any help in the ID of this engine, but I have to ask. What is the 'bump' near the top on the right side for?

It is a first generation B case Fox 40.  It is definitely not a racing engine or an Eagle!  This case was used for the 40 and 45.  All 40s were stamped 40 as is yours.  45s had no markings.  Many variations were made from this case.  Besides the displacement, there were twp basic styles, bushing main bearing and ball bearing mains.  There were RC and CL versions of both.  The BB version had a large front housing, see the picture.  CL versions came with sport venturies suitable for suction running.  There was also a large bore carb with a combat special needle valve assembly.  Any of the aforementioned were available in lapped or ringed versions.  Most of the bushed engines had the knurled prop driver, while the BB engines used a steel prop driver.  These were Duke's first large bore designs.  They used a one piece head, not a button and clamp design as on later versions.

The wart on the bypass allowed fuel to flow into the schnuerle boost port.  This design was improved and was still made when Fox shut down.

It was used for 40, 45, 46, and 50 displacements.  The 46 was an ABC design.  The 50 was a 45 with a 60 piston.  The Quickee 500 was an ABC version in this case.

All of this information and more is in Tim Dannels American Model Engine Encyclopedia,

i tried the Fox Q500 engine back in the racing days, it was as strong as a Rossi, but not even close to the Nelson or Jett engines. Also, had a .50 lots of power but could never get carb dialed in, always had a slight hesitation.