YS or OS for Raptor 90?

[creightoncarr]

OK, I've decided to give up on my Raptor 60 and convert to a 90. I'm trying to decide on the engine and am having a tough time deciding between the YS 91 ST4 and the OS 91 SZ-H. I have not flown either. I see a lot of guys using the YS engine but I can't seem to find the specs for it. I would appreciate some opinions on these engines in the Raptor. I've never used YS and have always had good experiences with OS engines. Will the OS fit into the converted Raptor without having to modify the head?

[bgjames111]

For one, don't modify the head, if the front fan casing isn't big enough, just buy the new one for the 90.

anyway, both are good engines, I have the ys and it runs great. I'm pretty happy with it. I wish it had a little more power though.

[Laurens]

The new YS longstroke is out, Ronlund has them.

[creightoncarr]

The new YS longstroke is out, Ronlund has them.

I saw that. Will the longstroke fit in the Raptor with the new air duct? I can't seem to find any power specs for the YS engines.

[Laurens]

I think so, and otherwise my friend MR Dremel will help me out :mrgreen:

[creightoncarr]

How come I can find no power output specs for the YS 91ST? Is there is significant power difference between the 91ST and say the OS 9SZ-H? I know the YS is likely to run smoother, which I like, but not at the sacrifice of a lot of power. I have a 91ST NIB, but I'm wondering if I should go with the OS instead. Can anyone whose flown both comment on whether the OS feels significantly more powerful?

Also, is there is difference between the 91ST and the ST4 or are they the same thing? I see some vendors advertise the ST4 and others the ST. On the YS web page I only find the ST, no mention of ST4.

[BigVanVader]

For raw power I think the OS has the upper hand,at least until the arrival of the YS91SR which is the long stroke version and is supposed to be on par power wise with the OS......for set it and forget it tuning the YS wins hands down....since the new YS is here I think that will be my next choice for a 90 size engine.

[creightoncarr]

To put an end to this thread, I ended up going with the OX .91SZ-H. I put it in yesterday and flew a couple of tanks to tune an break it in. It seems to have tons of power, but I was having problems with overspeeding on fast descents in idle ups. I think that once I install a rev limiter I'm going to be extremely happy with this engine.

[Kinger]

IMHO the SZ wins hands down in the power department over the YS91ST. It's not really as noticeable in wide open flying, but when you start loading the motors up the additional torque of the SZ really starts to show. However, when it comes to motors being smooth and relatively easy to tune, I think the YS wins. I've flown a friends R90SE on 8.27 with the YS91ST and it was one smoooooooooooooth machine. My 90SE with the SZ on 8.27 defintely had more grunt, but it certainly doesn't seem as smooth as the YS and in order to have a decent pump you really need to go with the Cline mod which increases the cost of the motor.

I'm waiting to see reports on the new YS91SR. If folks who have flown both the OS and YS start coming back indicating that the YS is comparable or has just a smidge less power than the OS, I'll probably end up with one. Of course, that's also going to be somewhat dependent on how well you can get parts for the new SR's in time. At least with OS, you can usually get parts relatively easily. (Except for carb barrels for the SZ :roll: )