A guy at the club gave me this engine. I can't seem to find any info on it even from the O.S. web site. It's like they never made it.

What I'm really interested in is finding a pitts muffler for it. The spacing of the muffler mounting bolts is 53 mm (2 1/16").

Any info is greatly appreciated.

Kerry

Kerry,


It is an OS.90FSR.

This is a beast, power-wise, compared to current .90-.91 engines, with larger intake bypasses.
The current OS.91FX engine is a bored and stroked OS.61FX, with narrow intake bypasses, which limit its high end power.

This engine is, however, significantly heavier as well.


The strange thing is that the ASP (Sanye China) clone of the OS .91 engine uses a 20 mm diameter crankshaft, like the even larger displacement sibling of your engine, instead of the 17 mm crankshaft of your engine... giving it even more power potential through its much larger crankshaft gas passage.

Hi Dar,

How much more is the power of this OS.90FSR versus the power of the current .91FX ?
As well, if you compare with the current line of OS Heli Engines, which have 3.0 to even
the 3.3 bhp, is it all in the intake "magic" or it has to do a lot with the Exhaust too ?

Or the same questions in another way, is it possible to improve the current .91FX
by drilling/polishing the intake to make it as close as possible to the Heli engines,
of course if you have had time to look at and compare them ?

And one more Question (maybe we can copy this into the MVVS page; please
advice how to do that, or just move this to that page if you can): - On the 15cc
MVVS it is stated possible to rotate the sleeve so the Exhaust could take side or
rear position. OK, that is really great and one more reasons for me to "migrate"
from OS to MVVS. Could we compare the Power of the MVVS versus
those .91 (FSR, FX, SZ, etc OS-types) in the different position of the
MVVS's exhaust, i.e. as you guessed I am expecting MVVS to have different
output power at high-end in all of the four(4) different positions of the exhaust,
is that the practically possible and what is the outcome ?

Regards,
Nick

Nick,


Comparative engine tests performed by someone that can be considered biased toward one of the competitors, are not regarded as objective...
...So, I will not buy any OS engine to compare to the MVVS...

It is true; before you operate the MVVS .91/15 cc engine, you can undo the bolts that connect the cylinder casing to the crankcase, carefully release the bond between the two parts (taking care not to bend the con-rod) and reinstall it in a rear-exhaust configuration, or with the exhaust on the other side.


Even more so than the OS.91FX, which has a 17 mm crankshaft, the MVVS has a 15 mm crankshaft, which is even more biased toward lower RPM torque and spinning large propellers. This is through harnessing high flow speed, which increases low RPM cylinder charging, rather than high flow, which increases high RPM power.

The target is retaining flying fields, in this day and era, where high RPM will do more harm than good, by making a noise than non-R/C people consider more offensive.


...And even then, the HP claims that you stated are more nonsensical then ever...

Go to [link=http://www.jettengineering.com]Jett Engineering[/link] and use the PropPower to calculate the horsepower from their guaranteed RPM data for their very high performance .91 engines. ...And Jett engines are more powerful than OS...

I have one of these engines as well as the .91 FX. What Dar says is true. The Older FSR is heavier and but produces more power and IMO throttles better.

This is the Pitts Muffler you are looking for. The 1.08 shares the same exhaust.

Regards,
Jeff

http://www2.towerhobbies.com/cgi-bin...&I=LX8682&P=ML

Thanks. Looks like that adapter part is the key.

Kerry

I should have mentioned that I'm thinking about putting this in a GP Skybolt kit that I'm building. I've read that they come out tail heavy, so a lead sled up front should be okay.

Kerry

The 90FSR is 127grams (~4.5oz) heavier than the 91FX.

I have a .25 FSR that is well above and beyond any other OS .25 that they ever built! Lots of power but tractable; easy to handle to boot. I wish they hadn't discontinued the FSRs.

CR

I put an APC 14x6 prop on the engine last night. There is NOT enough shaft length to put a spinner backplate on.

Have prop hubs increased in thickness in recent years? Does anybody make 'thin' props? Is there a certain brand that is thinner than others? Is wood thinner?

Help!!!!

Thanks
Kerry

Check Graupner-G-sonic and also the wooden one of Maro at:
www.lindinger.at
or
www.der-schweighofer.at

I have the following ones with thickness:
APC 14x6 has 18mm and it is a bit heavy for OS.91 anyway,
Graupner-G-Sonic 13x7 has 12.5mm
Maro 13x7 has 13.5mm.

Both versions of the old 90/91FSR had the same crank with a short propshaft. A sleeve style prop nut should allow enough length for any prop and spinner.

A sleeve style prop nut??? Could you give me an example?

Thanks

Kerry

Also, I should have asked, what prop size would be appropriate?

Thanks
Kerry

A sleeve style prop nut:
http://shop.lindinger.at/product_inf...ducts_id=15942
That makes APC 14x6 to be OK for OS.91.

And you might not needed if use propellers MARO (wood):
http://shop.lindinger.at/advanced_se...sort=5a&page=2

or Graupner-G-Sonic(composite):
http://translate.google.com/translat...006-35,GGLR:en

Well, not every good thing is located outside of Europe.

Thanks for the info, but it's not much help here in the States.

Kerry