Tune for 16% nitro with more compression

tuneboy

Member
Messages
13
Hello.
A recent EU law prohibits nitro fuel with more then 16% nitro. So I’m stuck to that. I removed one shim from the head to add compression (sticked to a 5 heat plug).

i have issues tuning. When it’s running very rich - that I can’t get it into 3rd gear, I’m running 120 degrees Celsius.

when it’s on good power I measured 170 degrees C!
So it’s either rich and slow and good temp - or running fine but way too hot.

also with the LSN. No matter how rich I tune it, even richer then factory, it’s not smoking on half throttle. Seems weirded. Is it suppose to smoke on half throttle?
 

ManMgn

Member
Messages
28
5 heat plug as in cold. u need a hotter plug. about ur lsn issue. how is the hsn tuned. most of these carb have a short lsn therefore the hsn control majority of the fuel flow. is it possible that ur hsn is too lean? and ur richening ur lsn to mask that?. do the pinch test to ascertain how rich ur lsn is. if u let the motor get to 338 degrees F again it will most likely fail. u don't want to exceed 270 F/ 132 C imo.
 
Last edited:

lokky

Well-Known Member
Messages
296
I read that changing gearing and pipe and header length may help when reducing nitro content to 16%, but don't ask me what type of pipe or header. Extract below.

I've spent a few years recently playing with 16% nitro in 1/8 onroad GT class (in case my friend who I help out with engine stuff decided to go to the IFMAR GT worlds). Here is what I've found;
Removing head shims and going to a hotter glow plug works OK for 16% to raise compression ratio for the higher percentage of methanol. However, it introduces another variable that is super important in a 2 stroke engine - the squish clearance. A tighter squish clearance can effect top end rpm and alter detonation point on the tune. If you really want to know why -look up MSV or Maximum Squish Velocity. The optimal MSV for nitro is different for methanol and different again for gasoline.
What also worked is maintaining the same squish clearance, but reducing the bowl volume of the combustion chamber. This requires a lathe if a lower volume head is not available. I'd dare say engine manufacturers will start making motors and heads to suit the lower nitro content over time.
I have found it most beneficial to also alter gearing and then test other pipes and headers when dropping down in nitro % from 25 to 16. That pipe that is killer on 25% may not be as fast on 16% at track XYZ as a pipe that wasn't so great on 25% and a gearing change.... Getting detonation, motor tune window is really hard to hit, or motor running way hotter? (30deg C+ more) Try a different pipe and header length. Nothing "bolt on" has a greater impact on power curve, rpm like finding the best pipe / pipe length.
 

ManMgn

Member
Messages
28
I read that changing gearing and pipe and header length may help when reducing nitro content to 16%, but don't ask me what type of pipe or header. Extract below.

I've spent a few years recently playing with 16% nitro in 1/8 onroad GT class (in case my friend who I help out with engine stuff decided to go to the IFMAR GT worlds). Here is what I've found;
Removing head shims and going to a hotter glow plug works OK for 16% to raise compression ratio for the higher percentage of methanol. However, it introduces another variable that is super important in a 2 stroke engine - the squish clearance. A tighter squish clearance can effect top end rpm and alter detonation point on the tune. If you really want to know why -look up MSV or Maximum Squish Velocity. The optimal MSV for nitro is different for methanol and different again for gasoline.
What also worked is maintaining the same squish clearance, but reducing the bowl volume of the combustion chamber. This requires a lathe if a lower volume head is not available. I'd dare say engine manufacturers will start making motors and heads to suit the lower nitro content over time.
I have found it most beneficial to also alter gearing and then test other pipes and headers when dropping down in nitro % from 25 to 16. That pipe that is killer on 25% may not be as fast on 16% at track XYZ as a pipe that wasn't so great on 25% and a gearing change.... Getting detonation, motor tune window is really hard to hit, or motor running way hotter? (30deg C+ more) Try a different pipe and header length. Nothing "bolt on" has a greater impact on power curve, rpm like finding the best pipe / pipe length.
couldnt have said it better :cool:
 

tuneboy

Member
Messages
13
5 heat plug as in cold. u need a hotter plug. about ur lsn issue. how is the hsn tuned. most of these carb have a short lsn therefore the hsn control majority of the fuel flow. is it possible that ur hsn is too lean? and ur richening ur lsn to mask that?. do the pinch test to ascertain how rich ur lsn is. if u let the motor get to 338 degrees F again it will most likely fail. u don't want to exceed 270 F/ 132 C imo.

Hi,
the HSN is tuned pretty rich. As i said, i started with that factory setup (all needles flush) and tuned the HSN first, until it runs fine. I only bash on sandpits, so i don't need to achieve the last bit of power. But it should run kinda ok without bogging. Also on WOT the engine is very smokey so it should be fine.

Is the engine supposed to smoke on half throttle? It seems like the LSN adjustment does not make any different.

Also: Where do you measure the temps? I have a temp run i just keep pressed so it will show me the max value and aim at the plug. On the cooling rips its much colder.
 

tuneboy

Member
Messages
13
yeah guys, i don’t know. I think the engine is done. So today i had the heatgun with me. I tuned it quite rich. Like half a turn lean from factory setting, and the engine was running okayis, but i got up to 128°C which is very hot. So i rich it 1/8 turn but then the car was bogging and wasn’t running „fluent“ so to say. But what could i do? The temps were too hot.

I think the engine is just done for it. I have some 25% nitro i will try but man, its been fruststrating. Ofc its not ideling at all so yeah..
 

ManMgn

Member
Messages
28
yeah guys, i don’t know. I think the engine is done. So today i had the heatgun with me. I tuned it quite rich. Like half a turn lean from factory setting, and the engine was running okayis, but i got up to 128°C which is very hot. So i rich it 1/8 turn but then the car was bogging and wasn’t running „fluent“ so to say. But what could i do? The temps were too hot.

I think the engine is just done for it. I have some 25% nitro i will try but man, its been fruststrating. Ofc its not ideling at all so yeah..
have u checked to make sure the tank is sealing meaning the o ring in the lid. air leaks will make the motor run hot. #2 check to make sure the exhaust gasket is good otherwise the motor will run hot as there is a leak within the back pressure system. #3 if the idle of the motor is too high the temps will not regulate. #4 upload clips so we can give u a better diagnosis.
 

Sparky

Well-Known Member
Messages
138
have u checked to make sure the tank is sealing meaning the o ring in the lid. air leaks will make the motor run hot. #2 check to make sure the exhaust gasket is good otherwise the motor will run hot as there is a leak within the back pressure system. #3 if the idle of the motor is too high the temps will not regulate. #4 upload clips so we can give u a better diagnosis.
If it’s running good don’t touch it,
Tuning by temp is to stop the novice user from completing cooking a nitro engine,
If there’s a trail of smoke from the pipe at wide open throttle and it’s performing
good, that’s all you can ask for,
I ditched the temp gun about 15 years ago and tune by sound and if the engines perfoing and running good,
Forget about the temp gun,
Also going to a medium plug will help you get a better tune on the 16%
 

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