30% and head shims

[moyesboy]

Who runs a 50 hyper on 30% with one std head shim?
Who fits a second head shim to lower the compression for 30% nitro fuel?

[smokingtommy]

never had to shim a os 50 at all ,its already a low compression engine as it is

[Cuppa]

I run an OS91HZ-R with both shimms, you will get the motor to tune much better with the correct shimms for the fuel you want to use(higher comp ratio= advanced ignition runs hotter)

cheers
Cuppa

[smokingtommy]

as far as i am awere all os 91 engines are ready to use with 15% nitro so yes a 91 will need to have the exstra shim for use with a 30%
unlike the 50 which can be run on 30%
i have always stuck by running 20% with a good oil content and have always had a good life out of all my engines
the qestion to ask ya self is do i really need to run on 30%

[Eckchaz]

I'm with smokingtommy on this.. think its with 91's... its straight run up to 20% (already has 0.1 shim fitted) and that is to be exchanged for the 0.2 for higher nitro (30%) content. The reason why you would fit both shims is to make tuning easier but its not a given you have to fit both shims because your running 30%. My 55 only has the normal "gasket" fitted afaia.. it is run what you want with no need for seperate shim, otherwise wouldnt OS sell the incretment shim like a 91? Again a good question.. I dont know your flying skill but do you realy need to run 30%?

[smokingtommy]

have had this bookmarked for years and has some very good info
http://www.jupiter-venlo.nl/Algemeen...0EN%20v3.1.pdf

[del19_82]

I'm with Tommy here, I personally think 30% is too much for a 50 size engine, I tried it once and never noticed any real difference in power. I did notice the engine ran slightly cooler but that was all really.


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[moyesboy]

I like the 30%, 20% holds me back - but not as much as blown motors. I'm flying quite hard I reckon.

I'm not going to shell out the insane price for an OS 55, might be more tempted by the redline.
Or maybe just a .53 with an OS hyper carb...

I just rebuilt my motor with a new piston an ring and stuck an extra shim in there for a laugh. I can easy take it out if the power is down.

[smokingtommy]

if you fly quite hard the tt53 would be a bit of a let down as it dose not really have much grunt ,and the 53 dose come with extra shims ,never tryed one with the os carb but it dose need a bit of modding to fit i think and im sure it dose give the 53 a bit more get up and go due to better air in take, but this problem with the carb was on the first batch some 3 years ago now , and its all been sorted,
if you not wanting to change down to 20% them maybe look at some other fuel as to what you have been using and see if that helps.
But to be honest i would say give the 55 a shot when you can stretch that little bit extra or the YS56 both have been proven very good engines just like the os 50 and that little bit extra power could mean you could drop to 20% and give the engine a longer life with out blowing the engines brains out

edit / agree the os and the ys are over priced for a 50 size engine !!! when you can get a 50 size plank engine for half the price