ORIGINAL: DR NITRO
For the past few years I have been paid to test run engines for a model fuel company. Since I have my own private flying field and am out in the middle of nowhere and retired, I can do this till my heart's content and not bother anybody. Mostly I run them on the several engine test fixtures, then a few of them I will actually fly on one of my planes or heli's. I even have a set of load beams to mount on car engines and a ducting system to cool the head when I test run them. I have gone through lots of engines, some were good , some were junk.
I use as a baseline, the average 40 size two stroke will run 15 minutes (at varying throttle positions) on 8 ounces of fuel. My goal is to get 400 hours on an engine or 100 gallons, whichever comes first. I have had numerous engines make it past this mark and a few that did not. To be be fair, I do a few things that the less experienced modeler does like shut them down for the day and do nothing to them until they are run the next day, I also run them a bit lean but only to the point where the rpm's are peaked, not past peak and generally use a prop that is on the small end of the scale for the given engine. I do run them on a fuel type that is intended for that design or recommended in the instructions. and always two identical engines are run identically at the same time, one with a competitors brand fuel and one with the company I'm contraced by, just for comparison.
Anyway, to make a long story short, I have run the engines you mention above and a bunch more of the OS line, this is what I got before the engines just simply wore out:
25FX- got to about 6 gallons
32SX- got to about 20 gallons after the first set of sleeves
40FX- got to about 20 gallons
46FX- (early ones) about 6 tanks
46FX- (later ones) about 40 gallons
OS 50- (airplaneversion and heli versions)- could not get past 10 gallons without it puking the bearings, longevity testing suspended on the modern OS 50
61FX- got to about 65 gallons
OS70 Heli-got to about 3 tanks on both engines, rods gave out. replacement engines made it to about 15 gallons
91FX- got to about 35 gallons
160FX- (after several tries and replacement motors, testing was abandoned)
OS 120 Surpass III- bearings failed around the 15 gallon mark, heads warped around the 50 gallon mark
OS 91 Surpass- got about 80 gallons before it was just plain worn out
OS 70 FL- after about two gallons of frustration, testing was abandoned.
As a comparison, heres some of my test engines that are in either the 400 hour club or 100 gallon club
Fox 35 CL, 40 bushing, 40BB, 45, 46, 50 and 74
Enya- 25, 40's (all the 40's), 50SS, 50CX, 60 (all versions) and 4-strokes: 46, 53, 90, 120 (old and new) and the 155 (everything tested)
Irvine- 46, 53
Super Tigre (italian)- 34, 40, 45, 51, 75, 90, 2300, 4500 (no chineese ones tested yet)
K&B (Pre Mecoa)- 40 (4011), 48, 61
Thunder Tiger- 25, 40, 42 bushing, 46, 61, 65 bushing, 120 and 4 strokes: 91 and 120 (everything tested)
Magnum- 46 (the only model tested)
Webra- 50
YS- 45, 53, 91AC
Saito- 56, 65, 72, 80, 91, 100, 120, 180 (everything tested)
Moki 135, 180 (everything tested)
MVVS 40, 49, 77, 91 (everything tested)
Rossi 45, 53 (everything tested)
Now heres some that did not make it to the club:
Anything Mecoa
Anything Leo
Anything MDS
Anything OS (modern)
Don't flame me guys, these are just the results experienced. In all cases, fuel should not have been an issue since failures in the OS line on one fuel were very soon repeated on the other, which indicates design problems.
Dr Nitro