I have a number of engines and i would like to start all, if not most, of the engines to make sure they run properly then maybe sell or keep them. so if possible, I would want to run them on the same bottle of fuel so keep costs down

most have overlapping fuel requirements anyway

I have a FAI fuel, 0% nitro and 18% oil so i was hoping to run them all on the same fuel but most of the engines I have require 5-15% nitro or 20-25% oil.


here's the list of engines and fuel requirements (source from manuals, forum replies, etc)

I realised there are some errors so I re-checked them, those in bold have yet to be re-checked.

All of the engines would run off of FAI fuel. But the Supertigre G4500 would likely have some mid range issues. But it would work too. The Gilbert engine would likely prefer more nitromethane though, 15% to 20% nitro, but it would run using FAI fuel. The GMark radial and the Wankels, ought to work using FAI fuel, but I am not sure about them.

I normally use 5% nitromethane glow fuel and it serves me well. but I have run engines off of FAI fuel before and all of the engines I tried worked. But some had idle issues as the engines preferred more nitro to run better.

Originally Posted by earlwb

All of the engines would run off of FAI fuel. But the Supertigre G4500 would likely have some mid range issues. But it would work too. The Gilbert engine would likely prefer more nitromethane though, 15% to 20% nitro, but it would run using FAI fuel. The GMark radial and the Wankels, ought to work using FAI fuel, but I am not sure about them.

I normally use 5% nitromethane glow fuel and it serves me well. but I have run engines off of FAI fuel before and all of the engines I tried worked. But some had idle issues as the engines preferred more nitro to run better.

thanks earl.

speaking of which, i had a number of issues with the G4500 i ran yesterday. i think i'll start another thread on this.

I buy 10% nitromethane fuel for everything, including helis. It maybe increases the power a little, but mainly it improves the idle.

More nitro than that is good for helis if you can be bothered to carry two sorts of fuel (I can't). High nitro makes you open the needle more as it burns with a higher fuel/air ratio than methanol. Thus more fuel goes through the engine so it carries away more heat. And heli engines tend to get hot.

An engine is just a means to an end, it serves no purpose without a plane attached. If your planes/helis fly ok don't bother messing with the fuel.

The big SuperTigre engines tend to like lower oil percentages and the carbs tend to be sensitive to it more. Here in the USA, they sell or used to sell special big Supertigre engine glow fuel, with about 10% nitromethane and around 10% oil content. Using less oil allows for more methanol in the fuel and the Supertigre engines seem to like that.

Now I am currently flying a big 30cc ASP (1.80) two stroke engine using 5% nitromethane an 16% oil and it is working well. But it may behave even better through the mid range with less oil in the fuel though, as it is a little on the rich side through the mid-range. But in the summer when it is hot outside the engine runs well with the 5% nitro and 16% oil even if it is a little rich in the mid-range.

what about props ?

if an engine manufacturer recommends 8x3, 8x4 and 9x5, can I use 9x6?

anyway here's the list of engines and recommended prop sizes




I've shortlisted the few props to
8x3 for the gilbert thunderhead
9x5 or 10x4 for the OS wankel rotary gen 1 and 2, g mark radial,
11x7 for saito fa-45, merco 61, merco 49, os fs-20, os fs-90, ross twin 60
14x8 for enya r120-4c



I have problems deciding the prop for the torpedo greenhead because mine is a custom-made version. it's an in-line twin of 2 x 0.19 greenheads



the recommended prop for a single 0.19 is 9x4, 9x5 and 10x4, does this mean I can use the same prop?

The engines can have some overlap for propeller sizes. But you want to prop a engine for its specific power band requirements. Yes you can run a larger prop than suggested in some cases, it is just that the engine may not run that well with it.

Your twin would used a 10x6 thru 11x5 size prop as it is really a .40 size engine. Maybe even a 11x6 or 11x7 as it may not like to rev up but develops good torque instead.

most should do just fine with 10% nitro and 20% oil with a few exceptions: the wankels might really need the recommended 25% and the G-mark would probably be happier with it as well.....so if this is just for testing the engines you may as well go with 25% as it shouldn't hurt any of the other engines other than being a bit messier than needed. also keep in mind that the engines with lapped iron/steel construction are better off with all castor and not a synthetic.

and then there is the big ST, i imagine test running it with too much oil shouldn't be a problem but for flying the best would be 10% oil with 0% nitro and a modern CDI ignition system... fuel would be extremely cheap to mix yourself and the low cost of ignition today makes it a very economical way to add reliability and user friendliness.

Originally Posted by earlwb

The engines can have some overlap for propeller sizes. But you want to prop a engine for its specific power band requirements. Yes you can run a larger prop than suggested in some cases, it is just that the engine may not run that well with it.

Your twin would used a 10x6 thru 11x5 size prop as it is really a .40 size engine. Maybe even a 11x6 or 11x7 as it may not like to rev up but develops good torque instead.

fs-90 running at 11x6 prop? that way i can still use the same prop for 6 engines.

any clue on the torpedo greenhead?

Originally Posted by ZAGNUT

most should do just fine with 10% nitro and 20% oil with a few exceptions: the wankels might really need the recommended 25% and the G-mark would probably be happier with it as well.....so if this is just for testing the engines you may as well go with 25% as it shouldn't hurt any of the other engines other than being a bit messier than needed. also keep in mind that the engines with lapped iron/steel construction are better off with all castor and not a synthetic.

and then there is the big ST, i imagine test running it with too much oil shouldn't be a problem but for flying the best would be 10% oil with 0% nitro and a modern CDI ignition system... fuel would be extremely cheap to mix yourself and the low cost of ignition today makes it a very economical way to add reliability and user friendliness.

thanks for yr advice

G'day.

Your twin Torpedo has two different variations of the the engine (look at the venturi and head fins, even the plugs are different). Given that, it should swing a 9-10x6 nicely. What did the builder use to connect the front to the rear engine?

* Danny *

Originally Posted by danny mz

G'day.

Your twin Torpedo has two different variations of the the engine (look at the venturi and head fins, even the plugs are different). Given that, it should swing a 9-10x6 nicely. What did the builder use to connect the front to the rear engine?

* Danny *

the plugs are different because i used the head as a glow plug holder to make it easier for me to test all the glow plugs that i had.
i still have the original ones.




I have no idea what he used as i bought it sometime ago.

but what i can tell is that the pistons move in different timings, as in, they dont go up and down at the same time.

I have several sized engines. Mostly OS and Super Tigre. I run 10% Omega in all of them. Which fuel you decide on should be based on how quickly you use it up. Fuel content changes when it's stored. If not stored properly it can accumulate moisture, evaporate the methanol "making your 10% nitro go to 30%" and so on. IMO I'd use 10% across the board on all of them and store the fuel in a cool, dark, dry place. When storing fuel always mark the fuel level on the jug with a magic marker then if you notice the fuel is above your mark then it's accumulated moisture. If it's below the mark then it's evaporated methanol and your nitro content has went up. Nitro is paraffin based and it doesn't evaporate easily.

I just use straight fuel, with 13% synthetic oil in all my engines.

Like you, I have an Enya 120R, an OS 90, a Saito 45 and an Enya 40 (46). They all seem to be happy on this fuel.

The next fuel that I mix up will be 12% oil.

Originally Posted by ZAGNUT

most should do just fine with 10% nitro and 20% oil with a few exceptions: the wankels might really need the recommended 25% and the G-mark would probably be happier with it as well.....so if this is just for testing the engines you may as well go with 25% as it shouldn't hurt any of the other engines other than being a bit messier than needed. also keep in mind that the engines with lapped iron/steel construction are better off with all castor and not a synthetic.

and then there is the big ST, i imagine test running it with too much oil shouldn't be a problem but for flying the best would be 10% oil with 0% nitro and a modern CDI ignition system... fuel would be extremely cheap to mix yourself and the low cost of ignition today makes it a very economical way to add reliability and user friendliness.

i bought the wrong fuel

10% nitro 20% oil. might have to exchange it.

is it possible I get a small amount of FAI fuel evaporate then add it to the 10-20 to bring up the oil level?

or just run it a little rich?

just buy some castor and add it too your fuel. klotz benol would be a good choice and aside from a good hobby shop or online vendors it can be found anywhere that deals with dirt bikes and go-karts. straight medicinal castor from the pharmacy will also do but will cost more.