Finally bought some high nitro fuel after 35 years running nitro. Would appreciate suggestions.

I finally ordered 65 percent nitro from technology hobbies for a treat for my son and I. My whole life 35 years of running boats I have wanted some and just want to try it before I get out of boats eventually. I hope I can learn to make the engines right to handle it.

If its too much I might blend it with lower nitro fuels I have to have 43 percent or so nitro. But I have little engines like the nova 12 and a .19 in my zip rigger and all these 21 engines I just had to see what its all about and finally be able to pull some props I was not able to before.

Glow plugs I just received some p3 os hot from Grim but I might have to run a colder value . I have a bunch of different heat ranges to try just wanted a heads up on which to go with that you all would recommend.

Do I need to now increase the head squish?
Most of most of my engines are set at 6 to 8 thou and the os xm 21s are no shim so 2 thou or whatever they say it comes out to. actually forgot to check the 21xm or cant remember.

Also head Bowl volume looks like it might be ok but might need to be smaller or shallower squish angle I might be opening a can of worms but I really want to try it on these smaller engines.

I am reading through search on IW now before I melt a piston or something but anything off the top of your heads I would really appreciate any input. It might be too much to ask on a post. I will continue searching learning as much as I can as well.

Generally,keep squish tight like you have it,less fuel trapped in the squish area,less detonation.Don't run it lean ,wind that needle out or 3rd channel dial lol,Then you have to hope the bowl volume isn't too small,you'l find out if the glow plug coils distort,also depends on exhaust port timing/height which determines dynamic compression,also,there is a ratio between the area of squish band to the area of bowl dia which determines/sets squish velocity,I can't remember if its 50% or 70,that is the magic number,I think 50%,One of the big boys here can correct me lol,,A slight taper on squish band should be ok,keep bowl edge sharp,,hot to medium glo plug should be ok,don't overcool the engine as the more nitro the more cooling and you need more heat to burn more of it going through the engine,I'm no engine guru,but I think I'm close lol

Rod Fonda said:

Generally,keep squish tight like you have it,less fuel trapped in the squish area,less detonation.Don't run it lean ,wind that needle out or 3rd channel dial lol,Then you have to hope the bowl volume isn't too small,you'l find out if the glow plug coils distort,also depends on exhaust port timing/height which determines dynamic compression,also,there is a ratio between the area of squish band to the area of bowl dia which determines/sets squish velocity,I can't remember if its 50% or 70,that is the magic number,I think 50%,One of the big boys here can correct me lol,,A slight taper on squish band should be ok,keep bowl edge sharp,,hot to medium glo plug should be ok,don't overcool the engine as the more nitro the more cooling and you need more heat to burn more of it going through the engine,I'm no engine guru,but I think I'm close lol

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I checked one of my heads and the bowl to squish ratio was around 45%,so up to 50% should be ok,most racing engines seem to be in that range..A poor man's trick, if compression is too high, and you have a spare head or 2 is to slightly/evenly widen the bowl on one side with a dremel and put that side facing opposite the exh port,The scientific method is to calculate the dynamic compression,measure bowl/squish volume and aim for around 9:1 comp,cheers David,,Hope it works out well.

Rod Fonda said:

I checked one of my heads and the bowl to squish ratio was around 45%,so up to 50% should be ok,most racing engines seem to be in that range..A poor man's trick, if compression is too high, and you have a spare head or 2 is to slightly/evenly widen the bowl on one side with a dremel and put that side facing opposite the exh port,The scientific method is to calculate the dynamic compression,measure bowl/squish volume and aim for around 9:1 comp,cheers David,,Hope it works out well.

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Thanks Rod I appreciate you telling me about that.that's a good tip there for sure.
I received a call today It might be a bit before I get to try some fuel I have 20 percent and it works pretty well for most days running.
I am trying to pick up extra head buttons for the os style 21s and a friend has a lathe that we might give turning one a go soon. I know most of my engines are 19cc or so head volume and I will try to monitor that plug and try to keep them on the rich happy side as long as it doesnt get away from me . Sometimes it still does. I told my son this would be a good time to put to use all the remote needles I have laying around and get them installed. I would like to try also one with a almost flat squish 1 degree I have read and see what that does as well.. again appreciate your time on this.

Davidkrienke said:

Thanks Rod I appreciate you telling me about that.that's a good tip there for sure.
I received a call today It might be a bit before I get to try some fuel I have 20 percent and it works pretty well for most days running.
I am trying to pick up extra head buttons for the os style 21s and a friend has a lathe that we might give turning one a go soon. I know most of my engines are 19cc or so head volume and I will try to monitor that plug and try to keep them on the rich happy side as long as it doesnt get away from me . Sometimes it still does. I told my son this would be a good time to put to use all the remote needles I have laying around and get them installed. I would like to try also one with a almost flat squish 1 degree I have read and see what that does as well.. again appreciate your time on this.

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I'm happy to help.It's good for brain exercise to think and write at my age lol..I'm hoping one of the engine gurus here will correct me and give more accurate info,but I think I'm close,,any questions,just ask,,let me know how it goes.

Davidkrienke said:

Glow plugs I just received some p3 os hot from Grim but I might have to run a colder value . I have a bunch of different heat ranges to try just wanted a heads up on which to go with that you all would recommend.

Do I need to now increase the head squish?
Most of most of my engines are set at 6 to 8 thou and the os xm 21s are no shim so 2 thou or whatever they say it comes out to. actually forgot to check the 21xm or cant remember.

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Increasing your nitro content will cool your operating temp, a hotter plug to offset this change may help. Something else to note, pulling the element will help burn the fuel you're trying to feed the engine. We cannot produce horsepower by taking fuel away; so find a way to burn the fuel you're trying to feed the engine

TJ Hammons said:

Increasing your nitro content will cool your operating temp, a hotter plug to offset this change may help. Something else to note, pulling the element will help burn the fuel you're trying to feed the engine. We cannot produce horsepower by taking fuel away; so find a way to burn the fuel you're trying to feed the engine

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I try to just cool with fuel and rarely run water to any of my engines. We just are always temp gun ready making a couple passes checking temps throwing it back out. We are getting pretty good even grabbing it off the side of the boat we run out of still running ,checking temp adjusting needle and tossing it back. I haven't tried the glow plug coil pull trick yet but Its on my list of things to try. Now that we have a better skyrc gps unit we will be able to see subtle changes easier.