Is This Overkill ?

[c3racing0082]

Hello
I Was Wondering If A 30% Racing Blend Nitro Fuel Is To Much For My Stock HPI Nitro Star .15 In A RS4-3 . Over 20% Fuel ? I'm Tryin To Use Up Some Of My Last 10% Blue Thunder JUNK Fuel. I'm Straped On Funds Now So I can't Go Out And Buy A Faster Engine. So I Have To Deal With What I Got For Now!! Anyway Will 30% Nitro Give The HPI Nitro Star .15( @ a Whopping .56 hp)Better Performance Than That JUNK 10% Nitro.
Thank You.

 

[dougc]

well It might hurt it, have you regeared your car? that could make it go faster

 

[SkyMaxx]

You might find that the 20% variety works well with that particular engine. Most of these little two-strokers are designed for optimal running with a 20% nitro.

When you run 10% nitro you have to watch your tuning and make certain that you are running with a suitably rich setting to get the air to fuel mixture in the ball park. If you did not adjust your needles, then your JUNK fuel might not have actually been the problem. I am guessing by your profile, that you might already know this.

At any rate, the 30% will provide for an easier tune, but will require you to lean up the setting a bit to get into the sweet spot for the engine. Note, my comments with respect to rich and lean are relative to the factory pre-sets for the engine. The factory presets are made with 20% in most cases.

If you want a bit more zip from the engine, try re-gearing the drive train by adding a clutch bell with a larger tooth count and a spur gear with a smaller tooth count. This will take more rpms from the engine and get it to the wheels.

BUT would the fuel hurt the engine? Not particularly. You will want to take it easy for a tank or two before dropping the hammer. The engine (as crappy as it might be running) has been running on the 10% nitro and is used to the burn characteristics of that fuel. Changing the fuel to a higher nitro content changes the burn characteristics and allows the engine to get increased compression. This could cause small issues if you do not allow the engine to have a mini-break in with the new fuel.

 

[c3racing0082]

I'm using 10% blue thunder in a rs4-3 w/ 2spd. seems like it hates that fuel . i got to run it @ 280- 290 temp to even shift right .. if it's to rich it wont shift @ all or it shifts to late .. but when i run it hot it's great ( for .56hp ) that engine only has a HSN setting. i also have to keep the hammer down all the time. as soon as i slow down to turn it's boggy like it's rich again. then hammer down for a while it's fine . slow down bogs again. I've seen this in 1/8 buggies where they dont like to idle or slow down!

 

[SkyMaxx]

280-290 is actually a decent temperature for a .15. Some might say it is on the high side of right, but I have seen some .15s that run a lot hotter and live to tell about it.

I am not in any way, shape, or form trying to tell you to stick with the 10% nitro. If it isn't working out, then by all means move up to a different percentage. What I am trying to say is that you do not necessarily need to jump to 30% nitro. These engines are designed and built off a 20%nitro burn (in most cases) and that might be where you want to start.

If you have to keep the hammer down all the time, you might have an idle set issue. The bogging comes from remaining fuel flow into the engine after throttle release. You may want to consider some of the following issues that could be contributing factors to the problem:
1. Fuel filter: is it clean? Regularly?
2. Fuel tubing (both fuel feed and back pressure): Are they too long? Too short? I'm guessing a little on the too long side if you have to keep the hammer down for decent fuel flow.
3. Has the carb been cleaned recently?
4. Is the pipe the right one for the engine? Sometimes a pipe can suffocate an engine.

Just some food for thought.

 

[c3racing0082]

The Fuel Feed Is About Double The Lenght (more reserve i thought)and it does have the stock pipe on it.. although the exhaust outlet nub is broke off flush w/ the pipe!

 

[SkyMaxx]

The double length fuel feed does provide a reserve for those times when you end up on the lid, but it also requires increased pressure to push the fuel from the tank to the engine. Thus you are having to keep the hammer down to keep the engine running. That same reserve ends up causing the engine to bog as you let off the throttle because there is still enough pressure to push it to the tank, but now the air flow and rpms are not sufficient to do anything with the extra fuel coming in.

I'd suggest reducing the length of the fuel feed line.

The exhaust pipe is not really an issue unless the stinger is reduced in opening size. If it is simply ground down flush with the pipe itself, then you should be okay. If the exhaust opening has been reduced in size, this will cause excessive pressure down the back pressure line creating an artificially rich condition on the engine. The end result...too much fuel when you don't want it...

 

[c3racing0082]

Thank You SkyMaxx.
How short does the fuel feed need to be? and i will try 20% rather than30% fuel. any brands you recomend?
by the way do i need to get a motor saver air filt rather than the cheaply stock one .

 

[SkyMaxx]

No worries. We're here to help.

I would start by making the fuel feed line the same length as the back pressure line. On on-road cars (I'm mostly an off roader), I have seen various lengths of fuel tubing used. With a decent .15, you can run fuel tubing for fuel feed and back pressure in lengths of 6-9 inches. Without knowing what you currently have on there, I'd say make the fuel feed and back pressure the same length and start with the 6 inch variety. If you still have fuel issues, then lengthen them a little at a time, but do not exceed 9 inches each for the lines. I know this is counter to cost as starting with something shorter does not allow for adding to the fuel tube and would require you to buy more tubing. You could go the other way and just remove length until your performance settles down.

I personally use Blue Thunder in the 20% variety. My recommendation is to get whatever your LHS has in mass. If they have a couple of fuels, look for O'Donnells, Blue Thunder, and others might provide some different suggestions. I like the smurf juice (as I refer to the blue stuff), and have not changed brands of fuel in over three years.

I would recommend getting the Motor Saver air filter. It will allow the engine to breath better and might help with the performance from a better air flow into the engine giving better fuel to air mixture reliability stand-point.

 

[parris001]

Not to bash a fellow R/Cer's choice of fuel, but I had a bad experience with 10% Blue Thunder in a .15 HPI FE. This engine was running awesome on 20% Eliminator and I gave it to a buddy and he installed it on his RS4 2, same model car I had it on. We retuned it for the new fuel and got it running and shifting good but it ran hot. We never could get it to run cool. We thought he might have a problem with his car, clutch, brake, or something binding. We ended up pouring in a tank of 20% Eliminator and tuning to it. Ran like a champ.

I have a buddy with a 2.5 on a TMaxx and his engine loves all of the Blue Thunder line.............. go figure

 

[c3racing0082]

No worries. We're here to help.

I would start by making the fuel feed line the same length as the back pressure line. On on-road cars (I'm mostly an off roader), I have seen various lengths of fuel tubing used. With a decent .15, you can run fuel tubing for fuel feed and back pressure in lengths of 6-9 inches. Without knowing what you currently have on there, I'd say make the fuel feed and back pressure the same length and start with the 6 inch variety. If you still have fuel issues, then lengthen them a little at a time, but do not exceed 9 inches each for the lines. I know this is counter to cost as starting with something shorter does not allow for adding to the fuel tube and would require you to buy more tubing. You could go the other way and just remove length until your performance settles down.

I personally use Blue Thunder in the 20% variety. My recommendation is to get whatever your LHS has in mass. If they have a couple of fuels, look for O'Donnells, Blue Thunder, and others might provide some different suggestions. I like the smurf juice (as I refer to the blue stuff), and have not changed brands of fuel in over three years.

I would recommend getting the Motor Saver air filter. It will allow the engine to breath better and might help with the performance from a better air flow into the engine giving better fuel to air mixture reliability stand-point.

As It Stands Now The Fuel Line Feed Is 7 inches The Back Pressure Line Is 4 inches.
Thanks Again For Your Help !

 

[SkyMaxx]

Glad to have helped.

Parris001, 10% nitro fuel burn hotter than the 20% and 30%. Why? It is creating a lean condition in the engine. This lean condition has the same affect as leaning out your needles. SO, it is no surprise to me that changing to 20% cooled the engine down.

In fact, most people find that upping the nitro percentage ends up giving a cooler running engine.

 

[c3racing0082]

No worries. We're here to help.

I would start by making the fuel feed line the same length as the back pressure line. On on-road cars (I'm mostly an off roader), I have seen various lengths of fuel tubing used. With a decent .15, you can run fuel tubing for fuel feed and back pressure in lengths of 6-9 inches. Without knowing what you currently have on there, I'd say make the fuel feed and back pressure the same length and start with the 6 inch variety. If you still have fuel issues, then lengthen them a little at a time, but do not exceed 9 inches each for the lines. I know this is counter to cost as starting with something shorter does not allow for adding to the fuel tube and would require you to buy more tubing. You could go the other way and just remove length until your performance settles down.

I personally use Blue Thunder in the 20% variety. My recommendation is to get whatever your LHS has in mass. If they have a couple of fuels, look for O'Donnells, Blue Thunder, and others might provide some different suggestions. I like the smurf juice (as I refer to the blue stuff), and have not changed brands of fuel in over three years.

I would recommend getting the Motor Saver air filter. It will allow the engine to breath better and might help with the performance from a better air flow into the engine giving better fuel to air mixture reliability stand-point.

Hey Sky Maxx. i made the both lines the same size... what a world of difference ! No more bottom end bog and i dont have to keep the Hammer down all the time. And the allaround performance has improved! i think now i will just upgrade to 20% Nitro !
Again Thanks A Bunch !

 

[SkyMaxx]

Glad to have helped out. Go out and burn some nitro for me...

 

[c3racing0082]

Glad to have helped out. Go out and burn some nitro for me...

I Did !! But Then The Engine Mounts Came Loose. And The Gear Mesh Of Course Got JACKED And Torched The 2 spd Spur Gears !

 

[SkyMaxx]

LOL...and the hobby continues its rampage...fix it, run it, break it, repeat.

 

[c3racing0082]

LOL...and the hobby continues its rampage...fix it, run it, break it, repeat.

LOL... What Would R/C Racing Be Without It !! 8 Bucks In Gears.. It's All Good !! :thumbsup: