I would guess there has only been two versions, the current version is designated FA-40A and looks like the one you have may be an early engine.

Google found this thread on an RC forum with a few links but only thing I could find following the links was the 40 was produced between 1980 and 1989. Didn't see anything that said when the 40A was introduced.
http://www.rcgroups.com/forums/showthread.php?t=2360061

This post shows a photo of an early 40 next to a later 40, big difference in size but not exactly sure if the 40 you have is the larger engine.
http://www.rcuniverse.com/forum/glow-engines-114/9315616-saito-history-2.html

Doubt anyone has any first hand CL experience with the early 40, my first Saito was a 40A.

Just from the pictures it looks like the early 40's are close to the same size and probably weight of a modern 56 but with less power than a 40A. Doubt it would be worth the effort to try and fly with it but would look nice for a display engine.

I had an FA series 40 that looked like that. Not super power, but very strong and dependable. I flew it in a 72" rc piper cub.
I had an FA series 65 also. Ara D. ended up with that in a big buzz bomber. Great engines. Heavier than the newer counter parts, but really reliable

Terry - I had three of these and I believe I still have a new one left.
Regarding "HEMI", as far as I know, all the SAITOs have hemi heads.

This particular SAITO was my first 4S engine and it was a very user-friendly and smooth powerplant.
I had it on my Euclid which is a very slightly enlarged Sig Chipmunk.
Throttle wired wide open, no modifications (it would probably have benefitted a bit from Bob Reeves excellent intake modification)
Total weight was around 50 ounces and it would do the entire pattern with no problems.
I did win a few firsts in intermediate and advanced.
The fuel that worked best was 20% nitro, 50/50 castor/synthetic, 11-8 Master Airscrew prop.

If you use it, make sure it has plenty of cooling air as it tends to run a bit hot. Also, make sure it breathes outside air - it likes cool intake air.

It met its demise when I belled it in in the bottom of the hourglass. When the engine hit, it tore the lugs off the case!

It's a good engine - give it a try.

Bob Z.

Terry - the SAITO 40 should work well on the Cardinal or Pathfinder.
I also had mine on a Brodak P-40  and it was a great combination. It's a bit heavy so I pushed it back around 1 1/4 inches.

When I used the castor/synthetic blend, that was around fifteen years ago.

I have never had a 4S engine gum up but I have heard from numerous sources that it's better to use a higher synthetic content (maybe 18/2) as the small amount of castor will proved good long-term corrosion protection.

Bob Z.

With a bit more searching I found these, so I have the information I wanted.
The FA-40 MK III and FA-45 MK II are the same except for displacement.
Thanks to all for your interest and input.

Terry