outssider

My Feedback: (23)

I'll throw in a little tid bit here...

has anyone noticed that the saito 100 has a much longer stroke than any 91....more even than the saito 120

going back to my hot rod days...I recall that an engine with a long stroke produces more low end torque...everything else being equal....

any comments ??

P51D-Paul

Hmmmmm. In warbird racing, the YS .91 AC/FZ would absolutely DESTROY any other similar sized engine. Mine loved the APC 13X8 pattern prop and easily turned it over 12k on the ground. These planes on 35% nitro pattern fuel would run well over 150mph with no modification. As a side benefit, not over-propping it made the bearings last much longer than others who used the "recommended" 14x10 to keep the RPMs low. One other thing I loved about that engine was it was pretty much set and forget. Not much fiddling for weather changes.

P51D-Paul

And, yes, I own both the YS .91 FZ and a Saito 100.

Hobbsy

My Feedback: (102)

Out, I used be in that camp too where I automatically assumed that a long stroke engine would be a slugger and short stroke engine would be a rever, however after many years of reading HotRod, MotorTrend, articles by Kevin Cameron in Cycle World et al I learned that it works out about even. Consider that when talking about two engines of equal displacement the shorter stroke engine will have a larger piston meaning more surface area for combustion pressure to, "push on" canceling out the advantage of the longer stroke engine with it's smaller diameter piston. It boils down to valve/port timing having the greatest effect on where in the rpm band the max torque or horsepower appears. The same can be said of the short stroke engine having a great number of power pulses per minute advantage being offset by the longer stroke engines stronger yet less per minute power pulses. You mentioned the Saito 1.00 should be a torquer and it is but the much shorter stroke .82 is also a torquer. Fun stuff to talk about.

P51D-Paul

The main reason for a shorter stroke and larger piston was to get more valve area in the combustion chamber. Stroke and piston area pretty much cancel each other out. Better breathing is the difference. And it still comes down to horsepower (the work actually being done). Having larger valve area means good breathing can be maintained at a higher RPM, which means the torque curve can be extended. HP=Torque*RPMS/33000 (I believe that is number).

Hobbsy

My Feedback: (102)

When you can get a YS to run reliably they are roughly 30% more powerful than an equal displacement naturally aspirated engine. So the .91 would be equivalent to a 1.20 and turn a 15x8 or a 14x10. The Saito 1.00 is a 14x8 engine. At one time I owned 4 YS engines, all FZ's, never again.

P51D-Paul

Most people we saw who had problems with reliability didn't know how to set the pump, or had someone who "thought" they knew how do it. Everyone I know who raced them had absolutely no issues with reliability. In fact, we had far fewer problems than people running other brands. Once set, they were beasts. The pump should be set with the screw on the bottom flush with the housing. Also, the higher the nitro, the more reliable they ran. 20/20 was the desired fuel for easy sport flying and 35/20 was good for a lot of power. We normally raced with 40/20 or 60/20.

speedracerntrixie

My Feedback: (29)

I can second that, anyone who has reliability issues with YS simply do not know how to set the engine up. Once you take the time to learn the engine while keeping an open mind and follow the directions from other successful YS users you would love the engine. I have heard many times when someone has difficulties that they simply were not setting up with appropriate filters, fuel, plug, regulator adjustments ect. If your not willing to go through the learning curve then by all means stick with OS and Saito.

Hobbsy

My Feedback: (102)

The problem wasn't the knowledge or the lack of it., you could get one to run fine for bout 90 days, go check out the YS forum in the Engine Manufacturers Support Forum. The competition guys carry 5 spares so they can have one that will run.

kmeyers

14 years later... the world has changed, but, this post roars back to life. I wonder if the op is still flying and which engine he put in his .40 sized plane?

speedracerntrixie

My Feedback: (29)

Comete BS! Who carries 5 engines at an average of 600.00 a pop? I have been racing a 115 WS or two seasons and just about to start the third with the same engine. I have failed to start only one and that was my fault for crossing the fuel lines. Again, the engine's require you to be a detail oriented type of guy, if your not then yes the engine may not be for you. Power per cc there is nothing that touches YS. That doesn't come for free, in this case it means the engine requires you listen and learn how to operate it. All the info is out there.

Hobbsy

My Feedback: (102)

Simply said, our experiences are different, I didn't say yours was BS. The best of my four YS' was a .53 that did not have a Low Speed needle, I asked Dave Shadel about that and he said to not waste my $35.00 for the conversion kit. He said to set the idle with the regulator and it worked perfectly, so much for not knowing how to set regulator.

speedracerntrixie

My Feedback: (29)

So explain why your engines would only run for 90 days or so and then would act up. What changed? The really only thing that could have changed is the cleanliness of the regulator which happens from poor fuel filtering or the regulator diaphragm gets damaged by either dirty fuel or the introduction of a chemical that damages the diaphragm. All being user error.

airraptor

My Feedback: (66)

whoa 14 years ago....
I agree with speed the YS engine is simple yet different than normal sport engines. more than anything guy that havent learned to run them will run them lean and mess them up. I switched to YS engines about 3 years ago and man I was surprised how easy they are to run and the power. I wish i had know about them long ago. I own 7 YS 70s, one 80, one 91, 11 115WSs, a 140 and a 170. I plan to have a YS in every airplane I can that can use the power. I was thinking the other day about putting a YS 115DZ in a 96" wing span custom built Lanier Laser 200.

Hobbsy

My Feedback: (102)

The YS FZ's I had would run reliably for a few flights and then would suddenly go rich in the midrange and then dead stick, they would land with fuel pouring out of the carb. I fly Diesels so a third adjustment is not beyond my abilities.

speedracerntrixie

My Feedback: (29)

Dave, that is a sure sign that there were debris in your fuel. What happened is that debris got into the regulator and was holding in the open position. Obviously not really the fault of the engine. That being said the filters that you could easily have run on a different engine may not have filtered well enough for a YS. This is one of the things one picks up along the way of the learning curve. The other is that you need to start up and allow 30 seconds for the regulator to establish a stable pressure in the tank. What we do is run the engine up to 3/4 power and then come back to idle then transition to full throttle and adjust the high speed fro m there is needed. YS engines tend to unload more in the air then other engines. This is a byproduct of the supercharging. They need to be set slightly richer on the ground then what most guys are accustomed to. These are things that you pick up along the way or hopefully someone comes forward and shares.

Hobbsy

My Feedback: (102)

Speed, I don't know if you've ever seen one of these, this is a Webra .87 that is crankcase supercharged like the YS', the tank is exhaust pressurized and not regulated. My .87 had plates over the holes where the one way valves were on the SC. Woops, picture #1 is mine.