I have been running 30% nitro 18% oil fuel in my Saito 100 on a Pulse 60. The price of 30% over 15% makes me consider changing to 15% nitro fuel. How much differance is there? Will I notice a huge differance? The Pulse has plenty of power with the Saito 100 running 30% and runs great but it would be nice to save some money on fuel.

Yes, you'll notice a difference.
Having said that, he engine will still run OK.
Try it and see.

As was said the engine will still run pretty good but just not as much power.

Blazer,


The RPM difference from changing from 15% to 30% nitro fuel is typically ~200-300 RPM.

The fuel consumption is ~30% higher with the 30%, so your overall fuel costs will skyrocket.


Changing from down 30%; you'd be surprised how frugal your engine has become...

You would have to close both the high-speed and the low-speed needles, by a significant amount.

if you have a tach, buy a gallon of 15%, and see what your difference is, like someone said above youll have to readjust your engine a bit though. Because of cost, i use15%($17 locally) in all my 4 strokes, and club fuel 10 %($12 a gal.) in all my other 2 strokes. I bought a gallon of heli fuel(30%) a while back and was somewhat impressed, but immediately switched back to regular to save

Typically you have the lean the needle a little when you go to less nitro.

My experiance is that it is more than that. That is more like the increase without going to a cooler plug. If you do it is more like 600 to 800. Of course if the compression ratio is too high you won't see that or you may even have a performance decrease.

You may also need a hotter plug.

Quote:

ORIGINAL: Sport_Pilot

My experiance is that it is more than that. That is more like the increase without going to a cooler plug. If you do it is more like 600 to 800. Of course if the compression ratio is too high you won't see that or you may even have a performance decrease.

Hugh,


You say this as if various heat-range plugs ARE available for four-stroke engines...

Most modelers are only aware of the OS F...

They say the Fox Miracleâ„¢ is a bit colder, but its lower price is the only reason people buy it.


All other four-stroke plugs (K&B, GlowBee, Novarossi, Etc.) are not even rated as to heat range...

Really you probably wont notice any power difference when dropping down from 30% to say 15 % nitro content with this large Saito 100. if it was a small 21 sized engine this would be a totally different story as the small engines love a higher nitro content compared to the larger sizes. i went through this stage with many r/c power boat engines and picked up australian speed records in the process , even some of the best U.S. racers commented on the not so good effects with high nitro on larger engines . most model aircraft engines are not designed to run high nitro especially the 4 strokes as head clearance and dome sizes are there to stay stock. when going to a higher nitro content its not just a matter of richening up the main needle and fitting a different heat range plug , you must raise the head dome by fitting correct sized shims which means the engine will have less compression compared to stock but will handle the nitro plus plugs wont get destroyed .

They are but only by shopping from differant manufactures. From my experiance from hottest at the top to coldest at the bottom.

Thunderbolt 4C Hottest plug
OS F
Fox Miricle Plug
K&B 4C Coldest.

I haven't tried it but there has been a race club out West that has a class where they race four cycle engines with very high nitro fuel. I understand they add extra head gaskets and use two stroke plugs. I do not know how well they idle, but that may not be a factor for their competition.

Also, there are other plugs I have tried but I cannot remember how hot or cold they are. The Miricle plug is only slightly cooler than the OS but there is a fairly wide margin between the others especially the K&B 4C. I picked up and extra 300 RPM or 600 total by switching from 15% to 25% fuel with the K&B 4C over the Fox Miricle Plug. I got 300 RPM from the fuel and the same Fox plug I was using after retuning. I then put in the K&B plug and found I needed to lean it and the RPM was 10,500 over the original 9,900 or so from a TT .91 FS and APC 14-6 prop. It was a big help with the fun fly competition and I won the climb and glide event and the entire event.

I buy it because it is a better plug than the OS F for moderate high nitro fuel such as 15%. The OS F is only better with 5% fuel, but that may be different on other brands of engines. I assume it is only lower in price because Fox doesn't chrome plate it, that has nothing to do with its performance.

If you are using the ubiquitous OS F plug then it may be a 300 to 500 RPM drop depending on the prop you are using. But that should be adequate for sport flying and the fuel will last much longer.

The newer Saito's, at least the ones sold in the US are made for high nitro, in fact the distributor recommend 30%, that seems to be what the present compression ratio is set up for. The high nitro for smaller engines is a rule of thumb because of the smaller distance the flame front has to cover, but there are a few, especialy those made for overseas market which will not run well on high nitro.

My experience with the Miracle plug is somewhat different to that.

I threw one in a TT46Pro when the OS#8 failed.

It was obvious that the Miracle was a *lot* colder than an OS #8 because the engine really burbled in the mid-range and if you tried to lean it out it would just quit. Put another OS#8 in and it was good as gold.

In my 4-strokes, the Miracles don't give anywhere near the same idle as an OS-F. Once again, I expect it's the colder design of the Miracle that is responsible for this.

I did find that the Miracle worked as good as anything in my ST90 but it only lasted about two months before it was starting to act "cold" in that engine too which I suspect is due to a reduction in catalytic effect.

I'm wondering of the Miracle is cheaper because there's less platinum in the filament which also makes it a cooler plug.

FWIW, today a friend and I tested a Saito .90 twin on 15% Powermaster, then 30% Cool Power (with 4oz. Castor added ) and noticed a gain of 400 r.p.m. when peaked.

It went from 9,900 max on 15% to 10,300 on 30% with an APC 13X7

It may be you got some bad plugs. I have had that happen from time to time, even with OS plugs. I don't know if its shipping or nicks in the filiments or what, but evey once in a while a plug doesn't last as long as it should, or doesn't tune as others of the same brand and type do. I haven't seen a correlation of this happening in one brand or another, it has happened that I can recall to OS, Fox, and K&B. Not yet to Enya plugs, but because of expense I don't use those as often.

What plug or plugs did you use?

SP...first we used K&B 4 stroke plugs and then O.S. type F's just as an experiment.
Both types provided a good idle and transition, and both cyls. stayed lit [8D] during all of the testing.
I couldn't tell any difference.

Proptop,
It was a differant engine and todays plugs may not be the same but I got more Revs on the K&B 4C plug over OS-F and Fox miracle plugs on high nitro (25%), but you had to lean it down from the hotter plugs becase the extra fuel was quenching the hot plug. Picked up another 300 RPM for a total of 600 RPM from 15% nitro.