How much nitro can the miss bud handle ?

[KG4]

I am running 20% now can it handle 30-40%

[haljmac]

I have seen a guy running 50% he just added one once castor 927 oil to one gallon of fuel. It seem to do just fine.

[haljmac]

Even though you will can some on speed, the higher the nitro contint the shorter engine life you may have. But the name of the game is to get out there and have a good time.

[KG4]

Thanks for the info.

[hydroracer]

i'm not sure what ProBoat's recommended limit for nitro content for the lil miss bud is, but i think it is 30%. if you use fuel with significantly higher nitro content, you MAY have to make some adjustments to the setup. this info may be a little technical for folks who are new to 2-stroke nitro motor theory, so i'll keep it easy. for instance, if the head clearance is set to run with a maximum of 30% nitro, the engine may detonate with higher nitro fuel like, say a 50% nitro mix. if this happens, it's very hard on the engine. in a nutshell, the engine piston, head button, and rod won't last to long if detonation is occuring. detonation is when fuel around the outside edge of the piston and head ignites before we want it to. if you run it like this for a while, you'll most likely destroy the piston and possibly the head button and conrod.

i'm fairly certain that motor could handle a quality boat fuel containing 50% nitro with the correct needle setting, head clearance, and PIPE LENGTH. you'll probably have to lengthen the tuned pipe by sliding it a little further from the engine a little bit to compensate the higher nitro.

if the piston shows evidence of detonation (you will see little pits or holes in the piston top and/or head button), you'll need to either raise the head button by using the appropriate brass head shims, or lower the nitro content of the fuel. otherwise, your engine will sooner than later commit a violent suicide.

if proboat's motor has a very conservative trapped compression ratio, you might get away with no head clearance changes at all!

does this make sense to ya? let us know any questions. later! :)

[TTKarl]

Can someone explain what exactly a tuned pipe does? What adjustments do what, etc. Basically the theory of it.

[hydroracer]

ok. here's a description short and sweet of a how a 2 stroke tuned pipe works.

picture a typical r/c boat pipe. it's a tube that gradually gets larger in diameter to a certain point then gets smaller in diameter ending in a small tube called a stinger that lets the exhaust gas out of the pipe. like 2 cones welded together. (don't picture an rc car pipe with the stinger exiting out the side for now, although they work exactly the same). ok? now, picture this process in slow motion--

when the piston is pushed down due to the fuel's explosion in the cylinder, it passes downwards past the exhaust port. the hot burnt exhaust gasses are released creating a positive pressure wave that travels down the first "expansion cone" of the pipe's chamber. as this pressure pulse travels down the expansion cone, it creates a negative pressure wave behind it that actually sucks the exhaust gas out of the cylinder as well as part of the new fresh air/fuel mixture that has been drawn through the carb into the cylinder for the next combustion cycle(there's more to induction than this, but I've shortened it for simplicity) this fresh air/fuel mixture is travelling though the crankcase and transfer ports into the cylinder immediately behind the previous cycle's burnt mixture. when the tuned pipe is working properly, this negative pressure behind the positive exhaust pulse will continue to pull the new fuel/air mixture right through the cylinder, out the exhaust port and right on into the beginning part of the tuned pipe. still with me? now, when that positive pulse hits the "convergent cone", which is the second back part of the pipe that reduces in diameter from the middle weld toward the pipe's small exit hole, a part of this positive exhaust pulse bounces directly back toward the engine's exhaust port. if timed just right, this reversed positive pulse will push the new air/fuel mixture that has escaped through the exhaust port back into the cylinder though the exhaust port for a supercharge effect. the cycle then repeats. timing that return pulse right is critical to get the power boost effect. the pulse timing is determined by the length of the tuned pipe.

there's a lot more to it then i've described here, but wheweee! i ain't no rocket scientist!!! LOL :D

these pulses move at around 1,100 mph!

hopefully this helps you understand the basics of how a 2 stroke tuned pipe works. this general description may not be 100% accurate, but it's pretty darn close :)

[haljmac]

to make it easy, run your boat, watch and listen to it, shorten the pipe length about 1/4" then run and listen again, do this until your boat is handleing like you want it to. A shorter pipe lenght will give you more rpms, and a longer pipe lenght will give you more horse power. Now combind this with hydroracer's reply and you should be able to get your boat dailed in and running at its best. With nitro boats it is a give and take relationship.
Hydroracer, do you do any of your own work to your engines to get anymore power from them?

[hydroracer]

yes i have modified the timing on a few engines for increased power. not radical timing changes though, as i've found that the engine is a lot less friendly and hard to dial in the needle setting.

if you want to get more power from an engine, the first thing to do is "blueprint" it. that just means taking it apart and reassembling it making sure the bearings are installed perfectly true, and checking the head clearance to make sure it's set right. they sometimes come from the factory with the clearance not set right for the fuel we run. higher nitro needs a higher head clearance, but if it's to high, you get less power. to low and you detonate. second, just "flowing" the case inside and knife-edging the conrod and "skirting" the piston can give you a lot of increased power. you can raise the exhaust timing a little to give you more rpm/horsepower with a loss of torque as the price to pay. raising the exhaust timing calls for a pipe length change as well. you can play with the induction and transfer timing, but if you go just a hair to far with any timing changes and it will perform worse than a stock engine. the guys who do mods well have done thousands of engines over years of recording data and they also have access to dynos to measure the performance after changes have been made. i'm sure they've messed up a lot of engines to get the right combination.

personally, if i want to modify an engine now, i send them out to a professional. like rod geraghty, andy brown, or john ackerman are the best. go to rcboat.com there's a ton of info there. there is also a program you can buy from there that i hear really helps with mods.

[TTKarl]

I see. I work on cadillac's for a living and like to think I know how to make a race car but it's just like a header for a car. Exhaust scavenging. Man I see all this stuff with cars I never knew people did it with rc motors :) Ok now you say timing. What controls the timing you have no cams or timing chains etc. like a 4 stroke.

[merctech]

ok tt picture this....
piston comes to TDC (top dead center), on its way down it is uncovering the exhaust port, your expanded gases go out ( this is one part of timing, expanding the exhaust port by removing material from the liner and block will raise port timing) on the other side of the liner you have your intake port, ( your incoming charge is pressurized by the piston's downward motion compressing the fuel and oil in the crankcase) this incoming charge also helps to force the exhaust gases out. (Hydro went over the exhaust side of a 2 stroke in another post.) when the piston reaches bottom dead center (BDC) it creates a vacuum in the crankcase drawing in your fresh mix of fuel and oil through a port in the crankshaft. (this is another aspect of timing, you can enlarge the intake port in the crank to allow more fuel into the crankcase, but if you do this you also have to enlarge the intake port on the block and liner to get more fuel into the engine) when the piston is on its way back up it is covering up the intake port first so that the engine can properly scavenge ( refer to hydro' explaination of scavinging) then the exhaust port closes and the engine compresses the fuel air mixture and the glow plug kicks it off. There you have the basis of a 2 stroke engine, r/c, outboards, motorcycles all basiclly the same. timing is in reference to the timing of when the ports open in relation to movement of the crankshaft.

[TTKarl]

Ok, I understand now so the crankcase is part of the intake creating the pressure for the intake charge. I was wondering how that worked. Ok since you guys seem to know what your talking about let me ask you guys a theoretical question. After you start the motor the glow plug becomes obsolite doesn't it? If you could remove the glow plug and basically fill the hole while the motor was running the compression would keep it running wouldn't it?

[merctech]

the glowplug is essential for the engine to run. it is like a diesel. the heat to the compression causes a reaction btwn. the platinum in the glow plug and heats it. since the engine is (even at idle) spinning faster then most car engines at full speed you can move fast enough to get the glow plug out. But you need the glow plug for all the parts to work well together. If you change the timing, pipe length, nitro content, needle settings, glow plug temp. range you must retune. All things work together to make a well tuned high performance engine.

[Ron Olson]

Back to the first question. I put some of my 50% into a tank of a Miss Bud and it really woke it up! two things to remember if and when you up the nitro percentage. One, use a fuel mixed for boat use and two, you have to richen the carb a little.

[hydroracer]

from what i understand, once running, the plug element continues to glow and creates the combustion after the battery is disconnected. the heat created by combustion continually heats the element and it doesn't have enough time to stop glowing before igniting the next charge.

although i must say, i've brought boats back in after a lean run and the element seems to be COMPLETELY destroyed and gone. just a hole in the plug where the element used to be. so there may be more to it than just having a glowing element there.

btw, after running, observing the plug element's color and condition is the single best way to check if your needle is set right. i pulled this description from another site to save time-

"How to "READ" your glow plug.
OS and Turbo glow plugs go gray sooner [easier] than McCoy plugs; this is not necessarily bad. Actually when A new plug wire just goes slightly gray after a 5 or 10 minute hard run it means your very close to an optimal horsepower tune, but be careful the next step is TOO LEAN!

My rule of thumb.
1** Wire and surrounding bottom of plug wet, with like new shiny wire = rich side of optimum power 85%
2** Wire and surrounding bottom of plug starting to dry and wire starting to gray = Very close to optimum power 95%
3** Wire and surrounding bottom of plug dry, wire totally gray but not distorted optimum power 100%
4** Wire and surrounding bottom of plug dry, wire distorted = slightly lean DANGER!
5** Wire and surrounding bottom of plug dry, wire broken and distorted or burnt up = extremely lean possible engine damage!

Note: You can only "Read" your plug in a nearly new state [Wire like new and shiny] A gray plug can still operate well. But after it has totally gone gray performance can start to fall off. To test just put in a new plug and if there is no difference in performance save the gray one or put it back in. If your engine does not feel or run right tray a new plug before making major tune change's

Good Luck
(information from Paris Racing)"

[TTKarl]

Thanks for all your help that answered my question.