Don't take too much notice of me--just talking to myself reminiscing--bring back the "70's!!. Talking Girlings that we sold. Editing so might be mucked up.
The gas immersion i'm talking of--ie gas girlings, [we were the importers for nz in the day] must be run inverted as there's always a gap above the oil for rod displacement.
They were designed so the piston tops out above the oil so 'had' to be inverted so piston is always 'in the oil'.   
Gas & oil gets mixed of course, but the rod displacement gap remains, so the neutral inch or so remains if mounted normally.
Decent ones have a gas piston of course to separate & keep oil under compression.
Man the Girlings were primitive but think Huskies had then from new when long travel arrived. We were the importer for Huskies back then too.
Even more primitive but good solid shocks were Mulholland's with two gas insert bags to put down each side of the damper internals when changing oil, Gas bags were there from new. First one i saw i though what the hell is this haha.
No real gas rebound tension as such or very little, but kept the oil under pressure so it was always where it should be & could fill it right to the top & not have to take rod displacement into account.
Ok all from about 45 years ago memory--but!!, not sure why i wrote all that lol. But wait there's more!!.
Gas Girlings came in soft-medium-& hard. Hard damped you could mount well forward on the S/arm [more travel] with modifies subframe.. They didn't last if mounted on a severe angle & just wore out. Were good at the time though. 
Wish i'd ended up with boxes of them when the shop changed hands but--never mind. I even drill some of mine in the base to change the oil & fitted yamaha gas valves in to recharge.
Also i ran out of long travel ones at home after i retired but had short ones so 'Arc Welded' them into Suzuki PE bodies to get the length [& survived to tell the tale]--no gas explosion.

I never had one of the early Girlings apart...  I raced with them in the 1970's on my Husky and have them on one of my Husky's today...  I don't know how they work internally and there could have been a reason to only mount them shaft down.  That is normally the best way and shock manufacturers recommendations should always be followed.

Here we called them "emulsion" when there was no piston or bladder to separate the gas from the oil. 

I did a LOT of suspension tuning when I raced small single seat buggies off-road in the 1980's and 1990's...  first with Works Performance shocks and later with Fox Shocks...  I had virtually no money and the emulsion shocks were considerably cheaper.  I was sponsored by both companies and they gave me technical advice and eventually parts. 

On both the Fox and Works emulsion shocks you had to carefully measure the oil level to leave room for the shaft when fully compressed.  Body in the vise shaft up, cycling the shock resulted in a "dead spot" when nearing full extension because of this air gap.  That all changed when adding 250 psi or so of nitrogen.  Compressing the shock would "mix" or emulsify the nitrogen into the oil...  no more dead spot as the shock extended all the way.  You still had the same amount of "free space" for the shaft inside the body...  but instead of a large gap of gas at the top, the gas is now dispersed as little bubbles throughout the oil. 

On a gas pressurized shock with a piston or bladder to keep the oil separate from the nitrogen, you can just release the pressure and take the shock apart to change the valving.  Easy peasy. 

On an emulsion shock, not so easy.  Unless the shock has been sitting motionless for an extended period with the valve up, releasing the pressure results in what seems like an endless shower of oily foam...  Even after pressure is released and shock opened up, the oil left in the shock body looks like it's gently boiling as the nitrogen bubbles escape.  Slow and very messy process and if I wanted to reassemble right away I would have to dump the "gassy" oil into a jug for later use and fill with fresh. 

On one of my off road cars I had emulsion Fox shocks on the rear mounted shaft up to protect the shafts from getting sandblasted by the debris thrown up by the front tires... you could feel the "dead spot" if the car had been sitting a long time.  But it went away right away and was never an issue or felt in a race.

Sorry to keep this [Oil Thread] going lol
Maybe we'll agree to partly disagree a little, [forgotten what i'm disagreeing about now] but to my way of thinking the only way running it 'normal way up' with gas imulsion & 'not' having a dead spot at the top would be if the manufacturer ran a spacer on the shaft to stop the piston coming above the oil & ran a body long enought to get the full travel. Talking Girling Gassies & if mounted shaft up they'd have to top out for the problem to show. But that happens whenever the wheel is off the ground.
If i try those Gassies on the floor shaft down as they should be wth no springs & if i try hard enough they go past the oil 'just before' getting into the bottoming out rubber. Take a hard landing or soft springs to get there but!!. Non dismantleable those.
I recon those YZ DT shocks with the reservoir would work great if a bladder was fitted to the reservoir cap. Probably room for one a bit like honda or whoever uses that system. I've seen clever people on here rebuilding those so--be interesting.
Your turn? haha. Think i'll give up, can't even say while i'm ahead--but before get lost. Can see you've had a lot more experience with different types & brands than i ever did.--working in a Yamaha shop.

Interesting page here for them that are--Interested.
racetech.com/page/title/G3S%20Shock%20Types 

Caution- long ramble follows... 

RT325, I agree that your test of slowly compressing a Girling without a spring could result an a loss of damping as it bottoms out.  However, I can't imagine Girling would have designed shocks that lose damping just before bottoming out?  That's where you'd want the compression damping to be the hardest and you really wouldn't want all that compressed spring and bump stop energy to extend the shock without rebound damping even a little bit after bottoming. 

In my experience, I'd bet Girling didn't design a shock with no damping at the end of travel.  Emulsion shocks absolutely "foam up" very quickly which is why in actual use that complete loss of damping won't happen.  The oil and gas quickly becomes a consistent "froth" inside the shock body.   

When I started racing I realized very quickly that the stock engine had more than enough power to go faster than the suspension could handle.  Plus they had a "box stock engine" class for quite a while...  stock class died after a while because almost everyone was modifying for more power...  and some threw on aftermarket shocks.  I really couldn't afford either but I got a good set of used Works Performance emulsion shocks from another racer who seemed to have an unlimited budget...  he had swapped to Works Performance reservoir shocks with the bladders after only a couple of races.  (Back then, Works Shocks builds were all over the place...  they would "custom build" and it seemed no two sets ever built were the same... even if the purchaser provided Works with the same application, use, and driver weight...)

Anyway, I had far more time than money and after several calls to Works the employee I was speaking with befriended me and asked his boss about sponsoring me.  He called me up and told me to drive out to their shop in Northridge to see him.  (It was a long drive for me, but I did).  He showed me how to take the shocks apart, a really basic overview of how they worked, and to my surprise gave me a whole bunch of pistons (most slightly used) and a box of the valving springs they used.  I found a nitrogen fill tool at an aircraft surplus store cheap and rented a small bottle of nitrogen from the welding supply.  Down the rabbit hole I went.  Works didn't share any real technical information (I'm not sure they had any?) So my efforts were 99% trial and error and 1% educated guesses.  It wasn't long and I could go just a little faster than others through the rough stuff and work my way near the front...  but then on the longer smooth straights, the guys with HP drove right back by. 

But I was in the stock class so I usually was fastest stock engine even if I finished middle of pack.

One of the most annoying things I learned after spending countless hours of swapping and drilling pistons and changing the little springs that control the little ball bearings in the valving of the Works Performance Shocks is that you can't swap to their reservoirs with bladders to keep the oil separated without starting all over!  Emulsion valving is WAY too stiff once you're using straight oil for damping that's not all frothed up with nitrogen bubbles.  I had to start all over with the valving. 

The Fox shocks were much easier to tune as they used a "shim stack"...  and if I remember correctly you swapped to different pistons when going from emulsion to non-emulsion.  (Fox uses a floating piston inside the reservoir or shock body to keep the gas and oil separated...  I like that and the shims better than bladders and springs/balls)

I have RaceTech's suspension bible...  The pictures are nice and make "logical" sense.  Note that they do not sell emulsion shocks and also say that emulsion shocks are not considered "high performance".  My guess is whoever wrote that has zero real world experience with emulsion shocks?  I have a lot of real world experience with both types and I can't say an emulsion shock is better or worse than a non-emulsion gas shock in terms of performance.  I won a lot of off road races with both types. 

Emulsion shocks take a whole lot more effort and are a ton messier to tune.  And you have to be very consistent and precise with the oil level.  Not just so there is enough space to prevent hydrolock when shock is compressed...  but if you change the oil level, you also change the effective "viscosity" of the oil/gas mix.  I learned that the hard way too.  One time I was trying to increase damping slightly and had run low on "unemulsified" oil after a couple of valving changes. (I used to buy shock oil by the gallon). Long story short was the valving change results were opposite of expected.  Done for the day, I let the shocks sit for a few days (and depressurized slowly over that time) and found the oil level to be a little low upon disassembly.  I filled them to the exact level I had been using and retested.  Now the results of the testing were as expected...  but it was too much damping.  So more changes.  It seemed to never end.  I think it was about a 3/8" difference in oil level that noticeably reduced the damping.  You don't have that problem with non-emulsion shocks.

I was usually winning the stock engine class but the class was shrinking quick and sometimes there wasn't the 3 stock entries required for a class so I had to beat the modified engines to win.  Due to my health, I had to take a break from racing every week and used the time to research and design my porting.  The engine had an oval exhaust port with a bridge. I carefully measured and using Jennings "Two Stroke Tuner's Handbook" guidelines I determined that the bridge could be removed if the port was carefully shaped...  it would end up just below what Jennings stated was maximum width.  With a hacksaw blade taped up to make a handle and hand files I went to work.  I didn't have the money or skills to build a custom pipe so I carefully measured the stock pipe and "reverse engineered" to determine my exhaust port height that would hopefully work with the stock pipe.  I had to raise port quite a bit.  Transfers were untouched because I didn't have the skills/tools and because the "time-area" according to my measurements was actually perfect for a racing engine at the new higher target RPM according to Jennings.  Last was using a plate of glass and sandpaper to "mill down" the top of the cylinder and head for proper squish.  (That took forever!)  I didn't use a head gasket. 

These little Hondas used a CVT belt drive like a snowmobile.  I carefully modified the clutches to raise the engagement and operating RPM. 

First race out I got the holeshot at the start.  Now the fast guys couldn't easily pass on the smoother long straights.  I continued to focus primarily on my suspension because it seemed to me that was the limiting factor since the courses were usually pretty rough and I had power to drive faster than the suspension would allow..  It became easy to win... and I did...  a lot. 

And yes, later on with a different car I used emulsion shocks with shafts up.  Worked great.  I think I had that setup during the 24 hour off-road endurance race where John and I set a world record for both our class and the overall car record.  Many gas emulsion shocks are sold today for trucks and Jeeps and are mounted shaft up.  Maybe I'm wrong, but in my experience it doesn't really matter which end is up on a gas emulsion shock...  though shaft down is definitely better for unsprung weight in most mounting arrangements and especially on a lightweight vehicle... 

And again, if the manufacturer says to only mount a certain way, I'd follow their advice. 






 

Very interesting MarkT I read it a few times eager to read and learn more from you.  
 Ps what year were you racing sounds awesome 

Wow haha, i'll read it all tonight & thanks for such a long story. Interesting i saw you say they must foam up so damping is always there in racing use [words to that affect anyway] & that makes sense which i'd not thought of.--Till Later.

Very interesting! By the way, Works Performance is still around. (at least they were 2 yrs ago) I contacted them about my 78 PE 250 shocks bought in 1987 and got re-build parts. They work great now. Were very helpful with info. Contact was This email address is being protected from spambots. You need JavaScript enabled to view it.
alnarv

When Gil passed away, the original "Works Performance" company floundered a little while and then closed. 

A couple of years later his daughter took up the torch and opened a new company she called Worx Shocks...They still have the same 30 day performance guarantee and they still seem to cobble together new shocks from whatever parts they have around when an order is placed (going by what a member from the forum I know got from them a few years ago).   So that much hasn't changed.  Getting into providing parts and rebuilding other shocks is great...  they didn't do that a long time ago.

Works Performance (and likely Worx) used very dated design...  copies of an early Charlie Curnutt shock design according to another member here.  One of their graces is that the design works really well even if they aren't perfect.  Curnutt shock designs are pure genius. 

Ok stop mucking around you guys & just put front forks on the back--problem sorted.