nitro % vs head button capacity

[bob miller]

when using higher nitro what works better ...larger head button capacity or less head button capacity....thanks....bob

 

[tom galdys]

Bob, I'm not hijacking your thread, I just want to ask an additional question. In the high nitro thread, it was said depends on the head if higher nitro is better. Other than head capacity, what is the other consideration. Just adding to my sons post. Tom Galdys

 

[bob miller]

thanks dad.....

 

[Glenn Quarles]

The simple answer to the question is more nitro needs more compression.

In order to make nitro burn it needs to be highly compressed and heated up! Whenever you increase nitro you should also reduce head volume, reduce cooling, and richen the needle.

Feel free to give me a shout if you would like more details.

GQ

 

[bob miller]

glen , so if I reduce the head button volumn with my k/b outboard I may see a increase in power using 60 % nitro ,,,, bob .....thanks

 

[Glenn Quarles]

glen , so if I reduce the head button volumn with my k/b outboard I may see a increase in power using 60 % nitro ,,,, bob .....thanks

Hey Bob, I am not familiar with the head button on that motor...it may already be perfect for 60% and was too small for max performance with the lower nitro. I would say set the head clearance to .006" (NOTE: this should pretty much ALWAYS stay at .006" and you adjust the compression by changing the size of the bowl), pump in some 60% and see what happens! Remember to richen the needle and reduce the cooling. If you can't get the motor to clean out and run without leaning on the needle too much (it will blow plugs) then richen it back up and add more prop load. If you still can't get it to clean out, machine some off the squish band to reduce the bowl volume, set the head clearance back to .006" and run it again. Keep doing all that until it is awesome!!! You may want to get some extra head buttons to experiment with.

As you can tell it requires a lot of work sometimes, but will be worth it when you get it right!

Please remember you have to play with needle settings, head temp, head volume, and prop load all together to make it work!!!! You can't just change one thing and make it work with higher nitro!

GQ

 

[bob miller]

glen , thanks for the info.....bob

 

[anthony_marquart]

A question:

What are modern engines initially set up to run? say a NR 21 or AA45? would the initial design be made around a specific nitro content? This info could help us get the most out of a stock engine quickly..